Concentration-response Characteristics Research Articles

Tunable diode laser absorption spectroscopy for open-path monitoring gas markers in fire combustion products

This paper presents an open-path gas sensing technique based on tunable diode laser absorption spectroscopy (TDLAS) for simultaneously detecting multiple gas markers in fire combustion products for the purpose of early warning of fires. To demonstrate this detection method, a dual-gas sensing system was developed by combing calibration-free direct absorption spectroscopy (DAS) and a homemade three-mirror multi-pass optical system. A near-infrared (NIR) distributed feedback (DFB) diode laser emitting near 1579 nm was used as an excitation light source for simultaneously measuring dual-gas fingerprint absorption spectra of CO and CO2 in combustion products. Details of laser tuning characteristics, the cross-talk effect of CO and CO2 absorption spectra, and concentration response characteristics are initially investigated both theoretically and experimentally. Finally, various coal samples (anthracites) are used for evaluating the developed dual-gas sensor’s real-time response and combustion characteristics. The experimental results are in good agreement with the theoretical expectation, which proves its great potential for early diagnosis and warning research of fires and practical engineering applications.

Estragole: DNA adduct formation in primary rat hepatocytes and genotoxic potential in HepG2-CYP1A2 cells

Estragole is a natural constituent in herbs and spices and in products thereof such as essential oils or herbal teas. After cytochrome P450-catalyzed hydroxylation and subsequent sulfation, estragole acts as a genotoxic hepatocarcinogen forming DNA adducts in rodent liver. Because of the genotoxic mode of action and the widespread occurrence in food and phytomedicines a refined risk assessment for estragole is needed. We analyzed the time- and concentration-dependent levels of the DNA adducts N2-(isoestragole-3‘-yl)-2‘-desoxyguanosine (E3′N2dG) and N6-(isoestragole-3‘-yl)-desoxyadenosine (E3′N6dA), reported to be the major adducts formed in rat liver, in rat hepatocytes (pRH) in primary culture after incubation with estragole. DNA adduct levels were measured via UHPLC-ESI-MS/MS using stable isotope dilution analysis. Both adducts were formed in pRH and could already be quantified after an incubation time of 1 h (E3′N6dA at 10 μM, E3′N2dG at 1μM estragole). E3′N2dG, the main adduct at all incubation times and concentrations, could be detected at estragole concentrations < 0.1 μM after 24 h and < 0.5 μM after 48 h. Adduct levels were highest after 6 h and showed a downward trend at later time-points, possibly due to DNA repair and/or apoptosis. While the concentration-response characteristics of adduct formation were apparently linear over the whole concentration range, strong indication for marked hypo-linearity was obtained when the modeling was based on concentrations < 1 μM only. In the micronucleus assay no mutagenic potential of estragole was found in HepG2 cells whereas in HepG2-CYP1A2 cells 1 μM estragole led to a 3.2 fold and 300 μM to a 7.1 fold increase in micronuclei counts. Our findings suggest the existence of a ‘practical threshold’ dose for DNA adduct formation as an initiating key event of the carcinogenicity of estragole indicating that the default assumption of concentration-response-linearity is questionable, at least for the two major adducts studied here.

Concentration-dependent alterations in gene expression induced by cadmium in Solanum lycopersicum.

Cadmium (Cd) toxicity in agricultural soil has received significant attention because of its higher transformation in the food chain and toxicity to humans. The aim of the present study was to develop sensitive and specific biomarkers for Cd stress. Therefore, transcriptional analyses were performed to investigate concentration-response characteristics of Cd responsive genes identified from a Solanum lycopersicum microarray. The results showed that the lowest observable adverse effect concentrations (LOAECs) of Cd to S. lycopersicum were 1mg/kg for seed germination, 8mg/kg for root dry weight, 8mg/kg for root elongation, and 8mg/kg for root morphology. Furthermore, the genes were differentially expressed even at the lowest Cd concentrations (0.5mg/kg), indicating that the detection of Cd in soil at the molecular level is a highly sensitive method. Cd in soil was positively correlated with the expression of the F-box protein PP2-B15 (r=0.809, p<0.01) and zinc transporter 4 (r=0.643, p<0.01), indicating that these two genes could be selected as indicators of soil Cd contamination.

Biomarker discovery and gene expression responses in Lycopersicon esculentum root exposed to lead

Gene expression analysis has shown particular promise for the identification of molecular biomarkers that can be used for further evaluation of potential toxicity of chemicals present in agricultural soil. In the study, we focused on the development of molecular markers to detect Pb toxicity in agricultural soil. Using the results obtained from microarray analysis, twelve Pb-responsive genes were selected and tested in different Pb concentrations to examine their concentration–response characteristics using real-time quantitative polymerase chain reaction (RT-qPCR). All the Pb treatments set in our study could generally induce the differential expression of the 12 genes, while the lowest observable adverse effect concentration (LOAEC) of Pb for seed germination, root elongation, biomass and structural modification derived from 1,297, 177, 177, and 1,297mgPb/kg soil, respectively, suggesting that the transcriptional approach was more sensitive than the traditional end points of death, growth, and morphology for the evaluation of Pb toxicity. The relative expression of glycoalkaloid metabolism 1 (P=−0.790), ethylene-responsive transcription factor ERF017 (P=−0.686) and CASP-like protein 4C2 (P=−0.652) demonstrates a dose-dependent response with Pb content in roots, implying that the three genes can be used as sensitive bioindicators of Pb stress in Lycopersicon esculentum.

Odorant concentration differentiator for intermittent olfactory signals.

Animals need to discriminate differences in spatiotemporally distributed sensory signals in terms of quality as well as quantity for generating adaptive behavior. Olfactory signals characterized by odor identity and concentration are intermittently distributed in the environment. From these intervals of stimulation, animals process odorant concentration to localize partners or food sources. Although concentration-response characteristics in olfactory neurons have traditionally been investigated using single stimulus pulses, their behavior under intermittent stimulus regimens remains largely elusive. Using the silkmoth (Bombyx mori) pheromone processing system, a simple and behaviorally well-defined model for olfaction, we investigated the neuronal representation of odorant concentration upon intermittent stimulation in the naturally occurring range. To the first stimulus in a series, the responses of antennal lobe (AL) projection neurons (PNs) showed a concentration dependence as previously shown in many olfactory systems. However, PN response amplitudes dynamically changed upon exposure to intermittent stimuli of the same odorant concentration and settled to a constant, largely concentration-independent level. As a result, PN responses emphasized odorant concentration changes rather than encoding absolute concentration in pulse trains of stimuli. Olfactory receptor neurons did not contribute to this response transformation which was due to long-lasting inhibition affecting PNs in the AL. Simulations confirmed that inhibition also provides advantages when stimuli have naturalistic properties. The primary olfactory center thus functions as an odorant concentration differentiator to efficiently detect concentration changes, thereby improving odorant source orientation over a wide concentration range.

Postsynaptic odorant concentration dependent inhibition controls temporal properties of spike responses of projection neurons in the moth antennal lobe.

Although odorant concentration-response characteristics of olfactory neurons have been widely investigated in a variety of animal species, the effect of odorant concentration on neural processing at circuit level is still poorly understood. Using calcium imaging in the silkmoth (Bombyx mori) pheromone processing circuit of the antennal lobe (AL), we studied the effect of odorant concentration on second-order projection neuron (PN) responses. While PN calcium responses of dendrites showed monotonic increases with odorant concentration, calcium responses of somata showed decreased responses at higher odorant concentrations due to postsynaptic inhibition. Simultaneous calcium imaging and electrophysiology revealed that calcium responses of PN somata but not dendrites reflect spiking activity. Inhibition shortened spike response duration rather than decreasing peak instantaneous spike frequency (ISF). Local interneurons (LNs) that were specifically activated at high odorant concentrations at which PN responses were suppressed are the putative source of inhibition. Our results imply the existence of an intraglomerular mechanism that preserves time resolution in olfactory processing over a wide odorant concentration range.

Transcriptomic Concentration-Response Evaluation of Valproic Acid, Cyproconazole, and Hexaconazole in the Neural Embryonic Stem Cell Test (ESTn)

Alternative developmental toxicity assays are urgently needed to reduce animal use in regulatory developmental toxicology. We previously designed an in vitro murine neural embryonic stem cell test (ESTn) as a model for neurodevelopmental toxicity testing (Theunissen et al., 2010). Toxicogenomic approaches have been suggested for incorporation into the ESTn to further increase predictivity and to provide mechanistic insights. Therefore, in this study, using a transcriptomic approach, we investigated the concentration-dependent effects of three known (neuro) developmental toxicants, two triazoles, cyproconazole (CYP) and hexaconazole (HEX), and the anticonvulsant valproic acid (VPA). Compound effects on gene expression during neural differentiation and corresponding regulated gene ontology (GO) terms were identified after 24 h of exposure in relation to morphological changes on day 11 of culture. Concentration-dependent responses on individual gene expression and on biological processes were determined for each compound, providing information on mechanism and concentration-response characteristics. All compounds caused enrichment of the embryonic development process. CYP and VPA but not HEX significantly enriched the neuron development process. Furthermore, specific responses for triazole compounds and VPA were observed within the GO-term sterol metabolic process. The incorporation of transcriptomics in the ESTn was shown to enable detection of effects, which precede morphological changes and provide a more sensitive measure of concentration-dependent effects as compared with classical morphological assessments. Furthermore, mechanistic insight can be instrumental in the extrapolation of effects in the ESTn to human hazard assessment.

Adsorption of CTAB on Zeolite A Detected by Surfactant Ion-selective Electrode

Abstract Adsorption of cationic surfactant, cetyltrimethylammonium bromide (CTAB) on zeolite A has been investigated using surfactant-selective electrode technique. The electrode consisted of a polyvinyl chloride (PVC) membrane based on neutral ion-pair carrier complex of cetyltrimethylammonium tetraphenylborate (CTA+TPB−). Adsorbance of CTAB on zeolite A was calculated from the potential and concentration response characteristics of the surfactant-selective electrode to get the surfactant adsorption isotherms. Adsorption isotherm of CTAB was S-shaped. The adsorbance was related to pH and electrolyte in the surfactant solutions.

Study of Adsorption of Sodium Dodecyl Sulfate on Alumina Using Surfactant Ion-selective Electrode

Abstract The adsorption of sodium dodecyl sulfate (SDS) on alumina was studied by using the surfactant ion-selective electrode. The adsorbance could be calculated from the potential and concentration response characteristics of surfactant ion-selective electrode to get surfactant adsorption isotherm. Further experiment results show that the adsorbance was greatly influenced by pH of the solution. It is demonstrated that surfactant ion-selective electrode could be utilized to measure surfactant concentrations in solution after adsorption equilibrium without solid-liquid separation.

(‐)Epicatechin stimulates ERK‐dependent cyclic AMP response element activity and up‐regulates GluR2 in cortical neurons

Emerging evidence suggests that the cellular actions of flavonoids relate not simply to their antioxidant potential but also to the modulation of protein kinase signalling pathways. We investigated in primary cortical neurons, the ability of the flavan-3-ol, (-)epicatechin, and its human metabolites at physiologically relevant concentrations, to stimulate phosphorylation of the transcription factor cAMP-response element binding protein (CREB), a regulator of neuronal viability and synaptic plasticity. (-)Epicatechin at 100-300 nmol/L stimulated a rapid, extracellular signal-regulated kinase (ERK)- and PI3K-dependent, increase in CREB phosphorylation. At micromolar concentrations, stimulation was no longer apparent and at the highest concentration tested (30 mumol/L) (-)epicatechin was inhibitory. (-)Epicatechin also stimulated ERK and Akt phosphorylation with similar bell-shaped concentration-response characteristics. The human metabolite 3'-O-methyl-(-)epicatechin was as effective as (-)epicatechin at stimulating ERK phosphorylation, but (-)epicatechin glucuronide was inactive. (-)Epicatechin and 3'-O-methyl-(-)epicatechin treatments (100 nmol/L) increased CRE-luciferase activity in cortical neurons in a partially ERK-dependent manner, suggesting the potential to increase CREB-mediated gene expression. mRNA levels of the glutamate receptor subunit GluR2 increased by 60%, measured 18 h after a 15 min exposure to (-)epicatechin and this translated into an increase in GluR2 protein. Thus, (-)epicatechin has the potential to increase CREB-regulated gene expression and increase GluR2 levels and thus modulate neurotransmission, plasticity and synaptogenesis.

Modelling a Spontaneously Reported Side Effect by Use of a Markov Mixed-Effects Model

To present a method for analyzing side-effect data where change in severity is spontaneously reported during the experiment. A clinical study in 12 healthy volunteers aimed to investigate the concentration-response characteristics of a CNS-specific side-effect was conducted. After an open session where the subjects experienced the side-effect and where the individual pharmacokinetic parameters were evaluated they were randomized to a sequence of three different infusion rates of the drug in a double-blinded crossover way. The infusion rates were individualized to achieve the same target concentration in all subjects and different drug input rates were selected to mimic absorption profiles from different formulations. The occurrence of the specific side-effect and any subsequent change in severity was self-reported by the subjects. Severity was recorded as 0 = no side-effect, 1 = mild side-effect and 2 = moderate or severe side-effect. The side-effect data were analyzed using a mixed-effects model for ordered categorical data with and without Markov elements. The former model estimated the probability of having a certain side-effect score conditioned on the preceding observation and drug exposure. The observed numbers of transitions between scores were from 0 -> 1: 24, from 0- > 2: 11, from 1 - >, 2: 23, from 2- > 1: 1, from 2- > 0: 32 and from 1 - >0: 2. The side-effect model consisted of an effect-compartment model with a tolerance compartment. The predictive performance of the Markov model was investigated by a posterior predictive check (PPC), where 100 datasets were simulated from the final model. Average number of the different transitions from the PPC was from 0 - > 1: 26, from 0 - > 2: 11, from 1 - > 2: 25, from 2 - >1: 1, from 2 - >0: 35 and from 1 - > 0: 1. A similar PPC for the model without Markov elements was at considerable disparity with the data. This approach of incorporating Markov elements in an analysis of spontaneously reported categorical side-effect data could adequately predict the observed side-effect time course and could be considered in analyses of categorical data where dependence between observations is an issue.

Assessment of agonist- and cell-mediated responses in airway microsections by computerized videomicrometry

The objective of this investigation was to develop a method for real-time measurement of changes in luminal area in microexplants of airways during pharmacological and physiological interventions. After guinea pigs were killed, tracheal rings (1- to 2-mm thick) were excised and placed in 300-microliters chambers. The area of the airway lumen was calculated as pixel number with the use of computerized videomicrometry. In 29 epithelium-intact airways, 10(-3) M acetylcholine (ACh) caused decrease in luminal area of 38.1 +/- 2.80% (P < 0.001 vs. 10(-9) M). Spontaneous tone also was demonstrated in 34 preparations from 4 guinea pigs; decrease in area of 17.0 +/- 1.45% after 60-min incubation in buffer alone was blocked completely by 10(-5) M indomethacin (P = 0.01). Luminal narrowing caused by < or = 10(-6) M ACh was reversed completely by 10(-6) M albuterol (P = 0.002). Addition of 100,000 activated human eosinophils caused 24.7 +/- 4.41% decrease in luminal area vs. 7.24 +/- 5.51% for nonactivated cells (P = 0.048). We demonstrate a real-time method for the assessment of auxotonic changes in airway caliber that utilizes microsections of explanted airways and permits the use of extremely small numbers of isolated cells to achieve physiological activation. Concentration-response characteristics and spontaneous tone are similar to those of large chamber preparations, and narrowing is reversed by beta 2-adrenoceptor activation.

Acute Effects of Ozone on Heart Rate and Body Temperature in the Unanesthetized, Unrestrained Rat Maintained at Different Ambient Temperatures

AbstractThe present studies were conducted to investigate the concentration-response characteristics of acute ozone (O3) exposure on the cardiovascular and thermoregulatory function of the unanesthetized, unrestrained rat, and to examine the modulating effects produced by changes in ambient temperature (T a) on the induced toxic response. For all studies, groups of male Fischer 344 rats (n - 4-6/group) were implanted with radiotelemetry transmitters and allowed to recover overnight. The transmitters permitted continuous monitoring of electrocardiogram (ECG) and body core temperature (T co); heart rate (HR) was derived from the ECG signal. Frequency of breathing (f) was obtained in selected experiments using a barometric plethysmograph. All animals were monitored according to the following protocol: control (filtered air, 0.25 hr); exposure (O3, 2 hr); recovery (filtered air, 3–18 hr). For the concentration-response experiments, O3 concentration was varied from 0.25 to 1.0 ppm and all exposures were conduc...

A comparison of the biological activities of authentic rat GRF(1–43)OH with the analogue rat GRF(1–29)NH2

The purpose of this study was to characterize the biological activity of the synthetic rat growth hormone releasing factor analogue rGRF(1-29)NH2 and to compare its action on growth hormone (GH) release to that of authentic rGRF(1-43)OH. We first compared the concentration-response characteristics of the two peptides in static incubation, and then examined the reversibility and repeatability of the GH response in a perifusion system. Authentic rGRF(1-43)OH was significantly more potent in static incubation (EC50 = 3 x 10(-11) M) than the analogue (5 x 10(-11) M), whereas the reverse held true in perifusion. The shapes of the GH responses were similar for both peptides in the perifusion system. However, while the GH response to authentic rGRF was repeatable, the prior administration of rGRF(1-29)NH2 significantly reduced (greater than 50%) the GH response to the subsequent administration of either rGRF(1-29)NH2 or rGRF(1-43)OH. Thus authentic rGRF and the synthetic fragment may have different actions at the level of the GRF receptor or at a postreceptor (second messenger) step.

Angiotensin II does not contract bovine retinal resistance arteries in vitro

The effect of angiotensin II was studied in vitro on ring segments of bovine retinal resistance arteries (i.d. 126–271 μm) and posterior ciliary arteries (i.d. 207–1153 μm). Although the retinal resistance arteries were responsive to 5-hydroxytryptamine, prostaglandin F 2α, and changes in extracellular K +-concentration, they did not, in contrast to the posterior ciliary arteries, contract to cumulative or single doses of angiotensin II. In the latter arteries, angiotensin II induced a small concentration dependent contraction, 5% of maximal 125 m m K +-induced response, with a pD 2-value of 9·3. The single addition of 10 −6 m angiotensin II increased the maximal vessel response of the posterior ciliary arteries three times to angiotensin II. Tachyphylaxis was pronounced in the posterior ciliary arteries, in which the response to angiotensin II could not be repeated. Indomethacin (10 −5 m), methylene blue (3 × 10 −6 m), or removal of endothelium did not make the retinal resistance arteries responsive to angiotensin II. Retinal arteries precontracted with 30 m m potassium did not respond to angiotensin II. Angiotensin II did not potentiate the 5-hydroxytryptamine- and noradrenaline concentration-response characteristics of both retinal resistance and posterior ciliary arteries. Although angiotensin II-receptors have been detected in bovine retinal vascular smooth muscle using radioligand-binding technique, the present results suggest that these receptors are non-functional in respect to regulation of retinal resistance artery tone.

Novel tool for the study of cholecystokinin-stimulated pancreatic enzyme secretion.

The molecular events that mediate cholecystokinin (CCK)-stimulated pancreatic secretion are not well defined because of the complex receptor-binding and concentration-response characteristics of this hormone. Functional models of receptor occupancy initiating the cascade leading to secretion have been complicated by the inhibition of secretion effected by supramaximal concentrations of CCK. Recent report of a CCK analogue that does not exhibit supramaximal inhibition led us to synthesize a similar analogue that could also be radiolabeled for studies of receptor binding and affinity labeling, and for studies of second messenger activity. This probe, D-Tyr-Gly-[(Nle28,31)CCK-26-32]-phenethyl ester, was a fully efficacious secretagogue with no supramaximal inhibition, and, unlike native hormone, bound to a single class of sites present on both acini and membranes. Occupation of this site correlated well with stimulation of secretion. Evidence that this was indeed a CCK-binding site were the abilities of CCK and the antagonist L-364, 718 to inhibit binding of this analogue. Affinity labeling confirmed the identity of the site mediating secretory stimulation as a Mr = 85,000-95,000 protein. Whereas the nonhydrolyzable guanosine triphosphate analogue, 5'-guanylyl-imidodiphosphate, was a potent inhibitor of CCK binding, it had no effect on binding of this secretagogue, suggesting that a novel cascade not involving a guanine nucleotide-binding protein mediates CCK stimulation of pancreatic secretion.

Attenuation of anterior pituitary phosphoinositide phosphorylase activity by the D2 dopamine receptor.

We have examined the influences of dopamine and the D2 receptor agonist bromocriptine on phosphoinositide metabolism in primary cultures of rat anterior pituitary cells, monitoring changes in the levels of phosphatidylinositol (PtdIns), phosphatidylinositol-4-phosphate [PtdIns(4)P], and phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2]. Basal incorporation of [3H]inositol ([3H]Ins) into phosphoinositides was progressive, and radioisotopic equilibrium was attained in all three species within 48 h. The inclusion of dopamine or bromocriptine in the incubation medium promoted concentration-dependent reductions in the rate, but not the magnitude, of phosphoinositide radiolabeling. The onset of this effect was rapid; inhibition of [3H]Ins incorporation by dopamine (500 nM) and bromocriptine (100 nM) could be detected within 2 h. This treatment also produced a comparable reduction in the incorporation of [32P]orthophosphate into PtdIns(4,5)P2. In extended time-course studies, bromocriptine dramatically retarded the radiolabeling of PtdIns(4)P and PtdIns(4,5)P2, and apparent equilibria in these species were attained only after 96 h. We also assessed the ability of dopamine to modify the concentration-response characteristics of [3H]Ins-labeled inositol phosphate ([3H]InsPx) production by TRH, angiotensin II (AII), neurotensin (NTS), bombesin (BBS), and vasoactive intestinal polypeptide (VIP). Neither dopamine nor bromocriptine altered the rate or magnitude of TRH-, AII-, NTS-, or BBS-related InsPx generation. VIP was completely ineffective in stimulating InsPx generation. PRL release was significantly reduced in all dopamine-treated groups. That the InsPx concentration-response relationships for each of these peptides remained unimpaired by exposure to dopamine or bromocriptine extends our previous observation that the phosphoinositide-specific phospholipase-C is insensitive to dopaminergic tone. Consistent with our earlier findings, these data indicate that activation of the D2 dopamine receptor attenuates the activity of mechanisms associated with the serial phosphorylations of PtdIns and PtdIns(4)P, reactions that give rise to PtdIns(4)P and PtdIns(4,5)P2, respectively. It is our conclusion that dopamine, in addition to its other actions, attenuates the phosphorylation, rather than the hydrolysis, of anterior pituitary phosphoinositide. This attenuation appears to be mediated by an inhibitory coupling of the D2 receptor with the phosphoryltransferase activities that catalyze PtdIns(4)P and PtdIns(4,5)P2 formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Biphasic dose-response relationship for effects of toluene inhalation on locomotor activity

To investigate the effects of inhalation of toluene on spontaneous locomotor activity, rats were exposed to graded concentrations of toluene and locomotor activity was measured continuously before, during and after exposure. This study used a randomized, cross-over, graded-dose experimental design, with sham-exposure as the control. The locomotor activity pattern during toluene exposure depended upon the toluene concentration in the air. At the lowest effective concentration (50000 ppm) locomotor activity increased monophasically during exposure, and decreased monophasically during recovery. At higher concentrations (10, 000–15, 00 ppm) locomotor activity initially increased in a concentration-dependent manner. With continued exposure to the higher concentrations, locomotor activity decreased and eventually ceased at the highest concentration. Recovery from exposure to high concentrations of toluene was also biphasic. These results demonstrate that the behavioral responses to extremely high concentrations of toluene are characterized by biphasic actions as demonstrated both by analysis of concentration-response and time-action characteristics. Exposure to concentrations of toluene similar to those used in this study occurs during organic solvent abuse and glue sniffing in humans.

Effects of bepridil on the electrophysiologic properties of isolated canine and rabbit myocardial fibers

Bepridil hydrochloride is a relatively new calcium antagonist which appears to have a complex pharmacologic profile, but its concentration-response characteristics with respect to its electrophysiologic properties of varying concentrations (0.1 to 10.0 μg/ml) of the drug were therefore determined in rabbit and canine myocardial fiber preparations in vitro by standard microelectrode techniques. The following were measured: sinus cycle length (SCL), action potential amplitude (APA), maximum diastolic potential (MDP), threshold potential (TP), slope of phase 4 depolarization, action potential duration (APD), and dV dt max of phase 0 depolarization (V max) in rabbit sinoatrial (SA) node. Also measured were APA, membrane resting potential (MRP), V max, APD at 50% and 90% repolarization (APD 50 and APD 90), and effective refractory period (ERP) in rabbit atria and canine Purkinje fibers and ventricular muscle. At the lowest concentrations bepridil selectively prolonged SCL by reducing the slope of phase 4 and decreased APA and MDP in a concentration-dependent manner in the sinus node. At higher concentrations, bepridil exerted additional effects in producing concentration-dependent decreases in APA and V max in rabbit atria and in canine Purkinje fibers and ventricular muscle. During superfusion with 1.0 μg/ml bepridil, V max fell by 22.2% ( p < 0.05) in Purkinje fibers and by 11.8% (NS) in ventricular muscle; at 10.0 μg/ml, V max fell by 46.5% ( p < 0.01), respectively. The depression of V max was frequency dependent. There was a differential effect of bepridil on repolarization in Purkinje fibers as compared to that in ventricular muscle. The APD 50 and APD 90 in Purkinje fibers were shortened, respectively, by 29.6% ( p < 0.05) and 5.5% (NS) at 1.0 μg/ml, and by 45.0% ( p < 0.01) and 14.1% ( p < 0.05) at 10.0 μg/ml. By contrast, in ventricular muscle, they were lengthened by 17.1% (NS) and 16.7% ( p < 0.05) at 1.0 μg/ml, and by 37.9% ( p < 0.05) and 33.7% ( p < 0.01) at 10.0 μg/ml. Slow-response potentials induced by high K + (20 mM) and isoproterenol (2 × 10 −6M) were suppressed by bepridil (0.1 μg/ml) but reversed by high Ca 2+ concentrations (7.2mM). Automatic firing induced by isoproterenol (1 × 10 −6M) in Purkinje fibers was slowed by bepridil (0.01 μg/ml) by both the depression of phase 4 depolarization and the elevation of the threshold potential. The data indicate that bepridil has a relative selectivity of inhibitory action for the slow channel with a significant depressant effect on the fast sodium inward current at higher concentrations. Bepridil differs from most fast-channel inhibitors in exerting a differential effect on repolarization in Purkinje fibers vs ventricular muscle.

Effect of felodipine, a new dihydropyridine vasodilator, on contractile responses to potassium, noradrenaline, and calcium in mesenteric resistance vessels of the rat.

The effect of felodipine [4-(2,3-dichloro-phenyl)-1,4-dihydro-2,6-dimethyl-3-ethoxycarbonyl-5- methoxycarbonylpyridine on the contractile responses of mesenteric resistance vessels denervated in vitro was investigated. Sustained contractions of this vessel type were totally dependent on extracellular calcium. Felodipine (10-(15)-10-(9)M) had a concentration-dependent inhibitory action on contraction induced by maximal potassium (125 mM) and noradrenaline (10-(5)M) stimulation. Felodipine was more potent and more selective than D600 and nifedipine. Potassium and noradrenaline concentration-response characteristics were insurmountably antagonized by felodipine, the potassium sensitivity of vessels being unaffected while noradrenaline sensitivity was decreased. In calcium-depleted vessels, felodipine in all concentrations tested produced insurmountable antagonism of the potassium-activated calcium concentration-response characteristics, whereas the antagonism in low concentrations (10-(15)-10-(11)M) was surmountable in noradrenaline-activated vessels. Felodipine 10-(9) M blocked the response of potassium-activated vessels almost completely, whereas approximately 50% of the response of noradrenaline-activated vessels persisted. The results of this investigation indicate that the effect of felodipine may be caused primarily by selective inhibiton of responses evoked by membrane depolarization.