Increase In Maximal Response Research Articles

Torsional response of a bisymmetric structure induced by bending–torsion interaction in vertical members

AbstractThe biaxially symmetric column induces torsional moment owing to the bending–torsion interaction when the top of the column is given horizontal displacement in the two directions of the principal axes of the cross section and the rotation of the column ends around the axes is constrained. Hence, horizontal ground motions in two directions can cause non‐negligible torsional vibration in a high‐rise building owing to autoparametric resonance. To investigate this phenomenon, in this study, we focus on a single‐story structure with an aggregated column, which is a model for columns or core structures in tall buildings and is assumed to be an elastic Euler beam; subsequently we derive the equations of motion under horizontal ground motions in two directions. The resonance condition in the torsional direction is also investigated. Time‐series response analyses are performed for input ground motions of harmonic waves, white noise, acceleration records of prior earthquakes, and a long‐period design wave, and the relationship between the ratio of two translational natural frequencies and the increase in maximum responses is explained. The results demonstrate that the absolute acceleration response to the long‐period design wave could increase by more than 50% in the worst‐case scenario.

Dosimetry in magnetic fields with dedicated MR-compatible ionization chambers.

MR-integrated radiotherapy requires suitable dosimetry detectors to be used in magnetic fields. This study investigates the feasibility of using dedicated MR-compatible ionization chambers at MR-integrated radiotherapy devices. MR-compatible ionization chambers (Exradin A19MR, A1SLMR, A26MR, A28MR) were precisely modeled and their relative response in a 6MV treatment beam in the presence of a magnetic field was simulated using EGSnrc. Monte Carlo simulations were carried out with the magnetic field in three orientations: the magnetic field aligned perpendicular to the chamber and beam axis (transverse orientation), the magnetic field parallel to the chamber as well as parallel to the beam axis. Monte Carlo simulation results were validated with measurements using an electromagnet with magnetic field strength upto 1.1T with the chambers in transverse orientation. The measurements and simulation results were in good agreement, except for the A26MR ionization chamber in transverse orientation. The maximum increase in response of the ionization chambers observed was 8.6% for the transverse orientation. No appreciable change in chamber response due to the magnetic field was observed for the magnetic field parallel to the ionization chamber and parallel to the photon beam. Polarity and recombination correction factor were experimentally investigated in the transverse orientation. The polarity effect and recombination effect were not altered by a magnetic field. This study further investigates the response of the ionization chambers as a function of the chambers' rotation around their longitudinal axis. A variation in response was observed when the chamber was not rotationally symmetric, which was independent of the magnetic field.

RGS10 and RGS18 differentially limit platelet activation, promote platelet production, and prolong platelet survival

AbstractG protein–coupled receptors are critical mediators of platelet activation whose signaling can be modulated by members of the regulator of G protein signaling (RGS) family. The 2 most abundant RGS proteins in human and mouse platelets are RGS10 and RGS18. While each has been studied individually, critical questions remain about the overall impact of this mode of regulation in platelets. Here, we report that mice missing both proteins show reduced platelet survival and a 40% decrease in platelet count that can be partially reversed with aspirin and a P2Y12 antagonist. Their platelets have increased basal (TREM)-like transcript-1 expression, a leftward shift in the dose/response for a thrombin receptor–activating peptide, an increased maximum response to adenosine 5′-diphosphate and TxA2, and a greatly exaggerated response to penetrating injuries in vivo. Neither of the individual knockouts displays this constellation of findings. RGS10−/− platelets have an enhanced response to agonists in vitro, but platelet count and survival are normal. RGS18−/− mice have a 15% reduction in platelet count that is not affected by antiplatelet agents, nearly normal responses to platelet agonists, and normal platelet survival. Megakaryocyte number and ploidy are normal in all 3 mouse lines, but platelet recovery from severe acute thrombocytopenia is slower in RGS18−/− and RGS10−/−18−/− mice. Collectively, these results show that RGS10 and RGS18 have complementary roles in platelets. Removing both at the same time discloses the extent to which this regulatory mechanism normally controls platelet reactivity in vivo, modulates the hemostatic response to injury, promotes platelet production, and prolongs platelet survival.

Kinetic control of signaling: role of RGS proteins and GRKs

G protein‐coupled receptors interact with the GDP‐bound heterotrimeric G‐protein, G protein‐coupled receptor kinases (GRKs), and arrestins through their cytosolic surface. Previous studies suggest that the interaction of GRKs and the heterotrimer with the receptor occur in the same space; therefore, there is likely steric hindrance allowing only one pathway to operate at a time. Supporting this claim, experimentally induced competition for the intracellular heterotrimeric G‐protein binding site results in a reduction in GRK and Gα function. We created a Gαs chimera, called sis, containing most of the helical domain of Gαi1. In initial studies, sis prevented GRK2, 4, 5, and 6‐mediated reductions in isoproterenol‐mediated cAMP accumulation. Therefore, we tested the hypothesis that sis disrupts GRK/arrestin function due to an alteration in the turnover of the sis protein. To exclude any background effects of endogenous Gαs, we used GnasE2−/E2− MEFs re‐expressing Gαs (control) or sis (experimental) as well as the β2‐adrenergic receptor. Experimentally, cAMP accumulation in the presence and absence of receptor and GRK inhibitors, receptor‐Gs kinetics, and receptor internalization were measured. The introduction of the Gαi1 helical domain into Gαs did not significantly affect the biochemistry of the chimeric sis protein; however, GRK function and cAMP production altered. GRK2 failed to attenuate isoproterenol‐mediated cAMP accumulation in sis‐expressing cells, but attenuated cAMP accumulation in Gs‐expressing cells. Accordingly, the rate of endocytosis decreased in sis‐expressing cells compared to Gαs‐expressing cells at 10 μM, but not 0.1 and 1 μM, isoproterenol (0.77 ± 0.10 versus 1.00 ± 0.14 min−1). The kinetics of 10 μM isoproterenol‐mediated cAMP production demonstrates that the rate of accumulation of cAMP is similar, yet sis‐expressing cells have an increase in maximal response, and the rate of degradation of cAMP fits two different models. Degradation of cAMP in Gαs‐expressing cells is fit to a classical first‐order equation with a rate constant of 0.068 ± 0.012 luminescence/min, whereas, in sis‐expressing cells, the degradation of cAMP fit a linear zero‐order model with a slope of −0.012 ± 0.0012 luminescence/min. As there is 10 μM of isoproterenol present, we hypothesized that the receptor is nearly always active, and sis has altered kinetics and GRK activity due to rapid cycling between the cyclase and receptor. To test this second hypothesis, exploratory experiments are being conducted to determine if the alterations observed can be explained through a chimerically‐derived interaction with RGS proteins. The collected preliminary data suggest that altered kinetics of signaling alter GRK function and receptor internalization, and consequently, RGS proteins may indirectly inhibit GRK function.Support or Funding InformationWesternU MSPS program funds and NIH grants DK073911 (MB), DK079307 (EKJ), and HL109002 (EKJ) supported this work.

Amendment in sensing response of Single Walled Carbon nanotube (SWCNT) towards ammonia gas with copper phthalocyanine functionalization

The sensing of composite of two p-type materials; Single Walled Carbon nanotube (SWCNT) and Copper Phthalocyanine (CuPc) towards ammonia gas is studied. Maximum increase in response of SWCNT after CuPc functionalization has been found to be ≈ 56% with 83% increase in saturation responses. The average crystallite size corresponding to characteristic CuPc has been decreased with SWCNT doping by 44% with negligible shift in its characteristic peak corresponding to β phase. The successive intercalation of CuPc and strong π-π stacking interaction with SWCNT has been confirmed in structural, surface and spectroscopic results of SWCNT doped CuPc.

46 - Heparan sulfate proteoglycans regulate aortic response to vasoactive agents

The endothelial glycocalyx is known to regulate vascular function by sensing mechanical forces and by acting as a barrier to solute and protein transport. Its role on the regulation of vascular tone and blood pressure is incipient. Herein we sought to investigate if the genetic deletion of syndecan-1 (Sdc-1) and glypican-1 (Gpc-1) alters vascular reactivity. Male CD-1, C57BL/6, Sdc-1 knockout (Sdc-1-/-) and Gpc-1 knockout (Gpc-1-/-) mice were used. Vascular response to phenylephrine (PE, 1 nM to 0.1 µM), acetylcholine (Ach, 10 µM to 10 mM), angiotensin II (Ang II, 1 nM to 0.1 µM) was assessed in aortic rings with endothelium. The expression of p-eNOS Ser1177, eNOS, p-Akt Ser473, Akt, p-Cav-1 Tyr14 and Cav-1 were analyzed by immunoblotting. Aortic rings from Gpc-1-/- mice showed an increased maximum response to Ang II (0.21g) and preserved response to PE (0.30g) when compared to CD1 control (PE: 0.28g; Ang: 0.14g). Aortic rings from Sdc-1-/- mice showed an increased maximum response to PE (0.29g) and a decreased maximum response to Ang II (0.04g) when compared to C57BL/6 (PE: 0.13g; Ang: 0.08g). Both strains showed impaired endothelium-dependent relaxation and decreased eNOS and AKT activity. Only Sdc-1-/- showed decreased eNOS expression when compared to respective control. Gpc-1-/- showed increased p-Cav-1 Tyr14 and Cav-1 when compared to CD-1 mice. Sdc-1-/- mice had decreased p-Cav-1 Tyr14 and Cav-1 when compared to C57BL/6 mice. In addition, ROS were decreased in both Sdc-1-/- (4253.00 AU) and Gpc-1-/- (4993.20 AU) mice when compared to C57BL/6 (19166.40 AU) and CD-1 (15584.60 AU) controls. Deletion of heparan sulfate proteoglycans alter the vascular response to specific vasoactive agents by potentially redox-sensitive mechanisms. The endothelial glycocalyx may be a primary regulator of vascular tone.

Abstract 17603: Transgenic Overexpression of Alanine-glyoxylate Aminotransferase 2 in Mice Lowers Asymmetric Dimethylarginine and Improves Vasomotor Function

Background: ADMA (asymmetric dimethylarginine), an inhibitor of nitric oxide synthase, has been shown to be associated with the risk of cardiovascular diseases. There are two known pathways for ADMA catabolism: hydrolysis to citrulline by dimethylarginine dimethylaminohydrolases (DDAH) and transamination by alanine-glyoxylate aminotransferase 2 (AGXT2) with formation of asymmetric dimethylguanidino valeric acid (ADGV). In contrast to the first pathway, the second one is poorly characterized. The goal of our study was to test the hypothesis that transgenic overexpression of AGXT2 would lead to lowering of systemic levels of ADMA and improvement of vasomotor function. Results: We generated transgenic mice (TG) with ubiquitous overexpression of AGXT2 under control of the chicken beta actin (CAG) promoter. qPCR and Western Blot were used to confirm the ubiquitous expression of the transgene. We did not observe and developmental or phenotypic abnormalities in the TG animals. Biochemical data were generated using HPLC-MS/MS. AGXT2 TG mice had ADMA plasma levels decreased by 15% (p<0.05), whereas ADGV plasma levels were 6 times higher in comparison with wild-types (p<0.001). Lung and heart of TG animals exhibited 2 times lower tissue ADMA content in comparison with controls (p<0.05). Isolated aortic rings were used to estimate endothelium-dependent and -independent relaxation in response to acetylcholine (Ach) and sodium nitroprusside (SNP), respectively. Aortas from AGXT2 TG mice demonstrated an increase in maximal response to ACh (p<0.05). There was a similar relaxation in response to SNP in both groups. We did not observe any differences in mean arterial blood pressure measured by telemetry between the wild type and AGXT2 TG mice. Conclusion: In the current study we were able to demonstrate that upregulation of AGXT2 leads to lowering of ADMA levels and improvement in endothelial-dependent relaxation in vivo. AGXT2 thereby may be a potential drug target for long-term reduction of systemic ADMA levels in cardiovascular pathologies. This is especially important, because all the efforts to develop ADMA-lowering interventions by means of upregulation of DDAH have not been successful so far.

Cyclosporine-A, but not tacrolimus significantly increases reactivity of vascular smooth muscle cells.

Application of cyclosporine-A (CsA) or tacrolimus is associated with numerous side effects. One of the main reasons for restricting usage of CsA is hypertension. In tacrolimus treated subjects the frequency of these phenomena is significantly lower. The known molecular mechanism of action of tacrolimus and cyclosporine-A seems to be the same, thus we decided to compare modulatory effect of drugs on vascular smooth muscle contractility. Experiments were performed on isolated and perfused tail artery of Wistar rats. Contraction force was measured by increased degree of perfusion pressure with a constant flow rate. Concentration-response curves for agonist in the presence CsA were significantly shifted to the left with increase in maximal responses. This effect was due to increased calcium influx from extracellular calcium stores whereas there were no significant changes in calcium influx in the presence of tacrolimus; concentration-response curve was comparable to controls. Our results strongly support the idea that main difference between effects on smooth muscle contractility of calcineurin-dependent immunosuppressants: CsA and tacrolimus is related to the different level of extracellular calcium influx to the cytoplasm. The elucidation of these mechanisms may permit the identification of new therapeutic strategies against CsA-induced hypertension.

Abstract 373: Transgenic Overexpression of Alanine-glyoxylate Aminotransferase 2 Lowers Tissue Levels of Asymmetric Dimethylarginine and Improves Endothelial Function in Mouse Aortas

Introduction: Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase, which has been proposed to play a direct role in the pathogenesis of cardiovascular disease. There are two enzymatic pathways for degradation of ADMA: hydrolysis to citrulline by dimethylarginine dimethylaminohydrolase (DDAH) and transamination by alanine-glyoxylate aminotransferase 2 (AGXT2) with formation of asymmetric dimethylguanidino valeric acid (ADGV). The first pathway is well characterized, whereas the physiological role of AGXT2 is still poorly understood. The goal of our study was to test the hypothesis that transgenic overexpression of AGXT2 would lead to lowering of systemic levels of ADMA and improved vasomotor function. Methods and results: We generated transgenic mice (TG) with ubiquitous overexpression of AGXT2 under control of the chicken beta actin (CAG) promoter. Ubiquitous overexpression of the transgene was confirmed by qPCR and Western Blot. TG animals had normal weight and no observed developmental abnormalities. Biochemical data were generated using HPLC-MS/MS. ADMA plasma levels in AGXT2 TG animals were decreased by 15% (p<0.05), whereas ADGV levels were 6 times higher in TG animals in comparison with wild-types (p<0.001). Lung and heart of TG animals exhibited 2 times lower tissue ADMA content in comparison with controls (p<0.05). Isolated aortic rings were used to estimate endothelium-dependent and -independent relaxation in response to acetylcholine (Ach) and sodium nitroprusside (SNP), respectively. Aortas from AGXT2 TG mice demonstrated an increase in maximal response to ACh (p<0.05). There was a similar relaxation in response to SNP in both groups. Conclusions: Our findings show that upregulation of AGXT2 results in lower ADMA levels and improved endothelial-dependent relaxation in vivo. AGXT2 thereby may be a therapeutic target for long-term reduction of systemic ADMA levels and improvement of vascular function in vivo. This is especially important, because all the efforts to develop ADMA-lowering interventions by means of upregulation of DDAH have not been successful so far. Our data suggest that AGXT2 might be a promising drug target for cardiovascular pathologies associated with elevated ADMA levels.

Mechanisms of enhanced vasoconstriction in the mouse model of atherosclerosis: the beneficial effects of sildenafil.

Sildenafil ameliorates aortic relaxations in apolipoprotein E knockout (apoE) mice. Now, we tested the hypothesis that endothelial dysfunction (ED) in this model is characterized by contractile hyperresponsiveness to phenylephrine (PE) and that this abnormality may be repaired using sildenafil. The aortic rings were evaluated in apoE mice treated with sildenafil (apoE-sil, 40 mg/kg/day) and compared with apoE and wild-type (WT) mice administered with vehicle (veh). The apoE-veh mice exhibited an imbalance of nitric oxide and reactive oxygen species (NO/ROS) levels and an increased maximum response (Rmax, 20%) and sensitivity (7%) to PE, which were not modified by endothelial removal. Under the prostanoids blockade, vasocontraction was decreased more in apoE-veh (-37%) than in WT (-27%) and apoE-sil (-30%) mice. NADPH-oxidase blockade abolished the enhanced contractile responsiveness in apoE-veh (-33%), without effects in WT and apoE-sil groups. The atherosclerotic lesions and the imbalance of NO/ROS were reduced (40%) in apoE-sil mice. In conclusion, ED in apoE mice was characterized by decreased NO-bioavailability and contractile hyperresponsiveness, due to thromboxane and oxidative stress, and was normalized by sildenafil. The beneficial effects of this phosphodiesterase-5 inhibitor on ED and lipid deposition provide new insights for its use as adjuvant in the treatment of atherosclerosis.

Blockade of ventral midbrain NMDA receptors enhances brain stimulation reward: A preferential role for GluN2A subunits

Ventral midbrain (VM) neurons that project to limbic structures play a role in reward and incentive motivation. It has been suggested that a reward-related signal is transmitted when the firing rate of VM dopamine neurons shifts from a tonic to a phasic mode. Since glutamate is necessary for this transduction process, it is likely to play a role in reward signaling. This study was aimed at determining the effect of VM N-Methyl-D-Aspartate (NMDA) receptor blockade on reward induced by electrical brain stimulation.Experiments were performed on rats trained to self-administer an electrical stimulation in the medial posterior mesencephalon. Reward thresholds were measured with the curve-shift paradigm before and after bilateral VM injections of the following NMDA receptor antagonists: R-CPP, 3-(R-2-Carboxypiperazin-4-yl)-propyl-1 phosphonic acid, (0, 20.6, 41.2 and 82.5pmol/0.5μl/side), PPPA, (2R,4S)-4-(3-Phosphonopropyl)-2-piperidinecarboxylic acid, (0, 0.825 and 1.65nmol/0.5μl/side) orRo04-5595, 1-[2-(4-Chlorophenyl)ethyl]-1,2,3,4-tetrqahydro-6-methoxy-2-methyl-7-isoquinolinol hydrochloride (0, 0.825, 1.65nmol/0.5μl/side).R-CPP and PPPA produced a dose and time dependent decrease in reward threshold, an effect that was, at some doses and times after the injection, accompanied by an increase in maximum responses. These effects were not observed with Ro04-5595 over the range of doses tested. While previous studies suggest a role for glutamate in reward signaling, the present results show that VM glutamate exerts a tonic inhibition on the reward-relevant pathway. The selectivity of Ro04-5595 for NMDA receptors composed of GluN2B subunits and the higher affinity of R-CPP and PPPA for GluN2A suggest that the inhibition is mediated by receptors composed of GluN2A subunits.

Alterações vasculares em ratos obesos por dieta rica em gordura: papel da Via L-arginina/NO Endotelial

FUNDAMENTO: Mecanismos subjacentes a anormalidades vasculares na obesidade ainda não estão completamente esclarecidos. OBJETIVO: Foi avaliada a via do óxido nítrico/L-arginina na resposta vascular de ratos obesos por dieta rica em gordura, enfocando as células endoteliais e do músculo liso. MÉTODOS: Ratos com 30 dias de vida foram divididos em 2 grupos: controle (C) e obeso (OB, ratos sob dieta rica em gordura por 30 semanas). Após 30 semanas, foram registrados o peso corporal, índice de adiposidade, pressão arterial e perfis metabólicos e endócrinos dos animais. Foram obtidas curvas para noradrelanina na ausência e presença de inibidor de óxido nítrico sintase (L-NAME, 3x10-4M) em aorta torácica intacta e com desnudamento em ratos C e OB. RESULTADOS: As medidas de peso corporal, índice de adiposidade, leptina e insulina aumentaram nos ratos OB, enquanto a pressão arterial permaneceu inalterada. A obesidade também produziu tolerância à glicose e resistência à insulina. A reatividade à noradrenalina da aorta intacta foi similar em ratos C e OB. A presença de L-NAME produziu um aumento similar nas respostas máximas, mas um desvio maior à esquerda das respostas nas aortas intactas dos ratos C em relação aos ratos OB [EC50 (x10-7M): C = 1,84 (0,83-4,07), O = 2,49 (1,41-4,38); presença de L-NAME C = 0,02 (0,01-0,04)*, O = 0,21 (0,11-0,40)*†,*p < 0,05 vs controle respectivo,†p < 0,05 vs controle mais L-NAME, n = 6-7]. Nenhum dos protocolos alterou a reatividade à noradrenalina de aortas com desnudamento. CONCLUSÃO: A obesidade induzida por dieta rica em gordura promove alterações metabólicas e vasculares. A alteração vascular envolveu uma melhora da via endotelial L-arginina/NO provavelmente relacionada à hiperinsulinemia e hiperleptinemia induzidas por dieta. A maior resistência aos efeitos do L-NAME na aorta de ratos obesos diz respeito a menor vulnerabilidade de indivíduos obesos na presença de patologias associadas que causam danos à atividade do sistema NO.

Effects of coupled vertical stiffness-strength irregularity due to modified interstorey height

Structures may have vertical stiffness or strength irregularity for many reasons. In many practical cases, a change in storey stiffness, results a change in strength at the same storey. In this paper, the effect of a change in interstorey height is quantified. In order to do this, relationships between storey stiffness and strength resulting due to a modified interstorey height for a few common lateral force resisting systems was considered. It was applied to simple shear-type structures of 3, 5, 9 and 15 storeys, assumed to be located in Wellington. All structures were considered to have a constant mass at every floor level. Both regular and irregular structures were designed in accordance with the Equivalent Static method of the current New Zealand seismic design Standard, NZS 1170.5. Regular structures were designed to either (i) produce a constant target interstorey drift ratio at all the storeys simultaneously or (ii) to have uniform stiffness distribution over the height of the structure, with the target interstorey drift ratio at the first storey. An “interstorey height ratio” was defined as the ratio of modified to initial interstorey height, and applied separately at the first storey, mid-height storey and at the topmost storey by amounts between 0.5 and 3. The modified structures were then redesigned until the target interstorey drift ratio was achieved at the critical storey/storeys. Design structural ductility factors of 1, 2, 3, 4 and 6, and target (design) interstorey drift ratios ranging between 0.5% and 3%, were used in this study. Inelastic dynamic time-history analysis was carried out by subjecting these structures to code design level earthquake records, and the maximum interstorey drift ratio demands due to each record were used to compare the responses of regular and irregular structures.&#x0D; It was found that structural types in which only the storey stiffness was modified due to a change in the interstorey height produced the maximum increase in drift demands rather than structural forms with other stiffness-strength coupling cases. Shorter structures having an increased first storey height, and taller structures with an increased middle storey height generally produced greater interstorey drift demands than regular structures. For cases of increased storey stiffness due to decreased storey heights, the shorter structures with a decreased middle storey height resulted in higher median peak ISDR due to irregularity. A simple equation describing the maximum increase in response due to modifications to a storey height was developed. The equation was used along with the realistic correlations between storey stiffness and strength to obtain the governing code regularity limit.

Increased Cavernosal Relaxations in Sickle Cell Mice Priapism are Associated with Alterations in the NO-cGMP Signaling Pathway

Priapism is defined as prolonged and persistent penile erection, unassociated with sexual interest or stimulation, and is one of the many serious complications associated with sickle cell disease (SCD). The aim of this study was to evaluate the role of the NO-cGMP signaling pathway in priapism in Berkeley murine model of SCD (SS). SS mice and C57BL/6 mice (control) penile tissues were removed and the erectile tissue within the corpus cavernosum (CC) was surgically dissected free. The strips were mounted in 10 mL organ baths containing Krebs solution at 37 degrees C (95% O(2), 5% CO(2), pH 7.4), and vertically suspended between two metal hooks. Cumulative concentration-response curves were constructed for acetylcholine (ACh; endothelium-dependent responses), sodium nitroprusside (SNP; endothelium-independent relaxations) and BAY 41-2272 (a potent activator of NO-independent site of soluble guanylate cyclase) in CC precontracted with phenylephrine. Cavernosal responses induced by frequency-dependent electrical field stimulation (EFS) were also carried out to evaluate the nitrergic cavernosal relaxations. In SS mice, ACh-induced cavernosal relaxations were leftward shifted by 2.6-fold (P < 0.01) that was accompanied by increases in the maximal responses (78 +/- 5% and 60 +/- 3% in SS and C57B6/6J mice, respectively). Similarly, SNP- and BAY 41-2272-induced CC relaxations were leftward shifted by approximately 3.3- and 2.2-fold (P < 0.01) in SS mice, respectively. A significant increase in maximal responses to SNP and BAY 41-2272 in SS mice was also observed (113 +/- 6% and 124 +/- 5%, respectively) compared with C57B6/6J mice (83 +/- 4% and 99 +/- 2%, respectively). The EFS-induced cavernosal relaxations were also significantly higher SS mice. These results showed that SS mice exhibit amplified corpus carvenosum relaxation response mediated by NO-cGMP signaling pathway. Intervention in this signaling pathway may be a potential therapeutic target to treat SCD priapism.

Bkca potassium channels and sympathetic transmission in the pulmonary artery from pulmonary hypertensive rats

Pulmonary hypertension (PH) is a chronic disabling disease that affects the pulmonary vasculature. In this study, we have examined the effect of blocking potassium channels on sympathetic neurotransmission in the pulmonary artery and how this is influenced by PH.The right ventricular pressure was 30.4±3.5 mmHg and 52.8±5.4 mmHg in control and hypertensive rats respectively. These values were significantly different from each other indicating pulmonary hypertension. Electrical stimulation of the pulmonary artery produced frequency‐dependent contractions with LogES50 values of 1.13±0.18 and 0.44±0.26 in control hypertensive rats, respectively. There was no significant difference in the maximum response between the groups. TEA (1 mM), a BKca channel blocker, produced a nonsignificant increase in maximum response in control rat but produced a significant shift of the frequency‐response curve to the left reducing the LogES50 value from 1.13±0.18 to 0.37±0.32 (n=5). In hypertensive rats TEA (1 mM) shifted the frequency‐response curve to the left and significantly increased the maximum response. It was concluded that BKCA channels modulated adrenergic transmission in the rat pulmonary artery and this was not affected by pulmonary hypertension.

Increased sympathetic venoconstriction and reactivity to norepinephrine in mesenteric veins in anesthetized DOCA-salt hypertensive rats

Increased sympathetic nervous activity (SNA) elevates venomotor tone in deoxycorticosterone acetate (DOCA)-salt hypertension. We studied the mechanisms by which the SNA increases venomotor tone in DOCA-salt hypertension by making in situ intracellular recordings of venous smooth muscle cell (VSMC) membrane potential (E(m)) and measurement of outside diameter (OD) in mesenteric veins (MV) and mesenteric arteries (MA) of anesthetized rats. We also studied norepinephrine (NE)- and endothelin-1 (ET-1)-induced increases in MA or MV perfusion pressure (PP) in vitro. E(m) in DOCA-salt MV was depolarized compared with sham MV. Prazosin hyperpolarized VSMC E(m) in DOCA-salt but not in sham MV. NE concentration-response curves (CRCs) for OD decreases in MV from DOCA-salt rats were left-shifted with an increased maximum response (E(max)) compared with sham MV. NE CRCs for OD decreases in MA were right-shifted with reduced E(max) in DOCA-salt compared with sham rats. ET-1 CRCs were similar in DOCA-salt and sham MV but were right-shifted with reduced E(max) in DOCA-salt MA. NE CRCs for MAPP increases were left-shifted without a change in E(max) in DOCA-salt rats. NE did not change MVPP. MAPP and MVPP for ET-1 CRCs were similar in sham and DOCA-salt rats, but E(max) for MAPP was reduced in DOCA-salt rats. Hematoxylin staining revealed hypertrophy in DOCA-salt MA but not in MV. We conclude that there is increased reactivity to NE released from the sympathetic nervous system in DOCA-salt MV that causes VSMC depolarization and increased venomotor tone. In DOCA-salt rats, in vivo ET-1 reactivity is maintained in MV, but reduced in MA.

α 2-Adrenoceptor subsensitivity in mesenteric vascular bed of cholestatic rats: The role of nitric oxide and endogenous opioids

Cholestasis is associated with vascular changes and in previous studies decreased response of visceral vessels of cholestatic animals to phenylephrine and acetylcholine has been shown. In the present study, the response of mesenteric vascular bed of cholestatic rats to clonidine (an α 2-adrenoceptor agonist) was investigated and we also examined the role of endogenous opioids and nitric oxide (NO). Seven-day ligation of bile duct was used as the model to study cholestasis. Six groups of rats, each of which divided into two subgroups (bile duct-ligated and sham-operated), were examined. Three groups of animals were chronically treated with either normal saline, naltrexone (an opioid receptor antagonist, 20 mg/kg/day, s.c.) or aminoguanidine (a selective inducible nitric oxide synthase inhibitor, 150 mg/kg/day, s.c.) for 7 days. After 7 days the response of the mesenteric vascular bed to subsequent doses of clonidine was studied. In other two groups, 7 days after the operation, the response of the mesenteric vascular bed to clonidine in the presence of either yuhimbine, an α 2-adrenoceptor antagonist, or N(ω)-nitro- l-arginine methyl ester ( l-NAME), a non-selective nitric oxide synthase inhibitor, was studied. In the last group, vasodilation response to sodium nitroprusside (an endothelium-independent vasorelaxant) was evaluated. Clonidine caused vasodilation in a dose-dependent manner by acting on endothelial α 2-adrenoceptors since its effect was antagonized by yohimbine, and this vasodilation was through the l-arginine pathway since there was no response in the presence of l-NAME in the perfusate. Compared to sham-operated rats, there was a significant right shift in the clonidine concentration curves of cholestatic animals. Maximum response in cholestatic rats was significantly lower comparing to the sham group ( P < 0.01) and the dose of clonidine that causes 50% of maximum response (ED 50) was significantly higher in cholestatic rats ( P < 0.05). Vasodilation response to sodium nitroprusside was the same in cholestatic and sham-operated rats. Seven-day treatment with aminoguanidine recovered the effect of cholestasis. Seven-day treatment with naltrexone caused an increase in maximum response ( P < 0.01) and a decrease in ED 50 ( P < 0.05) in cholestatic rats, while this treatment in sham-operated rats caused a decrease in the maximum response ( P < 0.01) and an increase in ED 50 ( P < 0.05). This study showed that cholestasis is associated with decreased responsiveness of mesenteric vascular bed to clonidine and the cholestasis-associated NO overproduction and increased level of endogenous opioids may contribute to this process.

Charged Amino Acids of the N-terminal Domain Are Involved in Coupling Binding and Gating in α7 Nicotinic Receptors

Binding of agonists to nicotinic acetylcholine receptors generates a sequence of conformational changes resulting in channel opening. Previously, we have shown that the aspartate residue Asp-266 at the M2-M3 linker of the alpha7 nicotinic receptor is involved in connecting binding and gating. High resolution structural data suggest that this region could interact with the so-called loops 2 and 7 of the extracellular N-terminal region. In this case, certain charged amino acids present in these loops could integrate together with Asp-266 and other amino acids, a mechanism involved in channel activation. To test this hypothesis, all charged residues in these loops, Asp-42, Asp-44, Glu-45, Lys-46, Asp-128, Arg-130, and Asp-135, were substituted with other amino acids, and expression levels and electrophysiological responses of mutant receptors were determined. Mutants at positions Glu-45, Lys-46, and Asp-135 exhibited poor or null functional responses to different nicotinic agonists regardless of significant membrane expression, whereas D128A showed a gain of function effect. Because the double reverse charge mutant K46D/D266K did not restore receptor function, a gating mechanism controlled by the pairwise electrostatic interaction between these residues is not likely. Rather, a network of interactions formed by residues Lys-46, Asp-128, Asp-135, Asp-266, and possibly others appears to link agonist binding to channel gating.

Infrared antennas coupled to lithographic Fresnel zone plate lenses

Several designs for Fresnel zone plate lenses (FZPLs) to be used in conjunction with antenna-coupled infrared detectors have been fabricated and tested. The designs comprise square and circular FZPLs with different numbers of Fresnel zones working in transmissive or reflective modes designed to focus infrared energy on a square-spiral antenna connected to a microbolometer. A 163x maximum increase in response was obtained from a 15-zone circular FZPL in the transmissive mode. Sensor measurements of normalized detectivity D* resulted in a 2.67x increase with FZPLs compared with measurements made of square-spiral antennas without FZPLs. The experimental results are discussed and compared with values obtained from theoretical calculations.

The impact of subchronic lead poisoning on the vascular effect of nitric oxide in rats

Lead-induced arterial hypertension is suggested to have resulted mainly from a reduction in nitric oxide (NO) bioactivity in vessel walls. The aim of this study was to evaluate the impact of poisoning by lead in so-called hypertensive doses on the basal and stimulated released NO effect in the rat mesenteric bed. Male Buffalo rats were given lead in a dose of 50 or 100 ppm in drinking water for three months. The isolated mesenteric bed preconstricted by norepinephrine (0.5 μg/ml) was used to determine the changes in vascular resistance induced by N-ω-nitro- l-arginine injected in increasing doses from 1.0 to 200.0 μg or by acetylcholine administered in doses from 0.05 × 10 −10 to 5.0 × 10 −10 mol. These changes were measured as an increase or decrease in perfusion pressure in the constant flow system. In comparison with controls rats given 50 ppm of lead, an increase in maximal response to N-ω-nitro- l-arginine ( P < 0.01) and acetylcholine ( P < 0.05) and a shift to the left of the dose–response curve for acetylcholine were demonstrated. Vascular responses in rats, who were given 100 ppm of lead, were similar to those observed in the control group. It is concluded that lead induces NO-mediated changes of vascular tone and vascular reactivity only in the small range of doses known as hypertensive.