L-type Calcium Channel Blocker Verapamil Research Articles

Role of L-type Ca2+ channels in the differential response to oxytocin of uteri from virgin and proven breeder rats

Introduction: The experience of pregnancy affects uterine function well beyond delivery. For instance, the likelihood of accelerated parturitions, spontaneous delivery, and risk of hemorrhage in future pregnancies is increased with parity. While epidemiological evidence for these phenomena is abundant, mechanistic explanations of these and other changes are still being investigated. We previously demonstrated that the response to oxytocin is more robust in the uteri of proven breeder rats and that T-type calcium channels, although slightly more expressed in proven breeder samples had a rather limited impact in this mechanism. Hypothesis: Here, we tested the hypothesis that voltage gated L-type calcium channels contribute more significantly than T-type calcium channels in the differential response to oxytocin in the myometrium from virgin (V) and proven breeder (PB) rats. Methods: V and PB non pregnant female 18-week-old rats were euthanized at proestrus. Uterine strips were suspended in a tissue bath containing Krebs solution (in mM, NaCl 117, KCl 4.7, NaHCO3 25, MgCl2 1.2, KH2PO4 1.2, CaCl2 2.5, glucose 11, pH= 7.4) at 37°C in 95% O2 and 5% CO2. Dose response curves to the L-type calcium channel blocker Verapamil (10E-8 to 10E-5 M) and dose responses to oxytocin in the presence of either 10 E-6 or 10E-5 Verapamil were recorded. Area under the curve, frequency, amplitude, and duration of contractions were measured. L-type channels expression was evaluated with qRT-PCR. T-tests and ANOVA two ways were used for statistical analysis. Results: Compared to control, both doses of Verapamil suppressed 100% of spontaneous and 50% of oxytocin-evoked contractility in V and PB samples. The maximal response to oxytocin was significantly stronger in PB than in V (p<0.001). Thus, blocking L-type Ca2+ channels does not alter the differential response to oxytocin observed in the absence of verapamil. The difference in Expression of the L-type calcium channel revealed a 2-fold increase in PB compared to V uteri. These findings closely align with oxytocin dose response data in the presence of the T-type calcium channels blocker Mibefradil and with the T-type channels expression. Conclusions: Neither L-type or T-type Ca2+ channels appear to be key players in the differential response to oxytocin of V and PB uteri. Instead, it is more likely that other elements of the intracellular calcium control are involved in this phenomenon. Acknowledgements: This study was supported by a Kenneth Suarez Fellowship to RP and an MWU intramural fund to MP. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Rapid antidepressant-like effects of muscarinic receptor antagonists require BDNF-dependent signaling in the ventrolateral periaqueductal gray.

Clinical reports reveal that scopolamine, an acetylcholine muscarinic receptor antagonist, exerts rapid antidepressant effects in depressed patients, but the mechanisms underlying the therapeutic effects have not been fully identified. The present study examines the cellular mechanisms by which scopolamine produces antidepressant-like effects through its action in the ventrolateral midbrain periaqueductal gray (vlPAG). We used a well-established mouse model of depression induced by chronic restraint stress (CRS) exposure for 14days. Behaviors were tested using the forced swim test (FST), tail suspension test (TST), female urine sniffing test (FUST), novelty-suppressed feeding test (NSFT), and locomotor activity (LMA). Synaptic transmission in the vlPAG was measured by whole-cell patch-clamp recordings. IntravlPAG microinjection was used to pharmacologically verify the signaling cascades of scopolamine in the vlPAG. The results demonstrated that intraperitoneal injection of scopolamine produced antidepressant-like effects in a dose-dependent manner without affecting locomotor activity. CRS elicited depression-like behaviors, whereas intraperitoneal injection of scopolamine alleviated CRS-induced depression-like behaviors. CRS diminished glutamatergic transmission in the vlPAG, while scopolamine reversed the above effects. Moreover, intravlPAG microinjection of the L-type voltage-dependent calcium channel (VDCC) blocker verapamil, tropomyosin-related kinase B (TrkB) receptor antagonist ANA-12, mammalian target of rapamycin complex 1 (mTORC1) inhibitor rapamycin, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA) antagonist CNQX prevented scopolamine-induced antidepressant-like effects. Scopolamine ameliorated CRS-elicited depression-like behavior required activation of VDCC, resulting in activity-dependent release of brain-derived neurotrophic factor (BDNF), engaging the TrkB receptor and downstream mTORC1 signalingin the vlPAG.

The interactive effects of verapamil and CB1 cannabinoid receptor antagonist/inverse agonist, AM251 on passive avoidance learning and memory in rat.

There are reports regarding the effects of intracellular Ca2+ and synthesis and release of endocannabinoids. The secretion of endocannabinoids depends on the L-type calcium channel. The present study evaluated the involvement of the cannabinoid CB1 receptors in the effect of L-type calcium channel blocker verapamil on passive avoidance learning (PAL) in adult male rats. In this study, we examined the effects of an acute administration of the cannabinoid CB1 receptors antagonist/inverse agonist AM251 following a chronic administration of the Ca2+ channel blocker verapamil on PAL. Male Wistar rats were administered verapamil (10, 25 and 50 mg/kg) or saline intraperitoneally (i.p) daily for 13 days (n = 10/group). After this treatment period, a learning test (acquisition) was performed, and a retrieval test was performed the following day. The results indicated that chronic systemic administration of verapamil (in a dose-dependent manner) impaired memory acquisition and retrieval. Pre-training acute administration of a selective CB1 antagonist/inverse agonist, AM251 (5 mg/kg, i.p.) did not change memory acquisition and retrieval. Co-administration of the verapamil and AM251 significantly reversed verapamil-induced amnesia, suggesting a functional interaction between AM251 and verapamil. The results indicated the interactive effects of cannabinoid CB1 receptors and L-type calcium channel in passive avoidance learning and AM251 can counter the effects of verapamil on memory.

Relaxation Effect of Schisandra Chinensis Lignans on the Isolated Tracheal Smooth Muscle in Rats and Its Mechanism

Schisandra chinensis (S. chinensis) is one of the core drugs used for relieving cough and asthma in traditional Chinese medicine. However, there are few basic studies on the treatment of respiratory diseases with S. chinensis in modern pharmacology, and the material basis and mechanism of its antiasthmatic effect are still unclear. Lignans are the main active components of S. chinensis. The aim of this study was to observe the relaxation effect of S. chinensis lignans (SCL) on the tracheal smooth muscle of rats by in vitro tracheal perfusion experiments, and to explore the mechanism by preincubation with L-type calcium channel blocker verapamil, four potassium channel blockers glibenclamide, tetraethylamine, 4-aminopyridine and barium chloride (BaCl2), β-adrenoceptor blocker propranolol, nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME), and the cyclooxygenase inhibitor indomethacin, respectively. The results showed that SCL (0.25-1.75 mg/mL) reduced the contraction of isolated tracheal smooth muscle induced by acetylcholine, the preincubation with verapamil and glibenclamide could attenuate the relaxation effect, whereas propranolol, 4-aminopyridine, BaCl2, tetraethylamine, L-NAME, and indomethacin had no such effect. These results suggest that SCL has a significant relaxation effect on the isolated tracheal smooth muscle of rats, and the mechanism may be related to the inhibition of extracellular calcium influx and intracellular calcium release from the sarcoplasmic reticulum, as well as the activation of ATP-sensitive potassium channels. These findings may provide a pharmacological basis for the traditional use of S. chinensis to treat asthma.

158-OR: Calcium Channel Blockade Protects against Severe Hypoglycemia–Induced Fatal Cardiac Arrhythmias in Rats

It was hypothesized that in response to insulin-induced severe hypoglycemia, excess calcium influx into the heart causes fatal cardiac arrhythmias. To test if blocking the calcium channels would decrease fatal cardiac arrhythmias during severe hypoglycemia, L-type calcium channel blocker (Verapamil; 1 mg/kg, n = 25) or saline (n = 24) were infused into Sprague Dawley rats during a hyperinsulinemic (0.2 mU/kg/min) severe hypoglycemic (10-15 mg/dl) clamp for 3 hours with ECG. During severe hypoglycemia, verapamil completely prevented mortality compared to 21% mortality in controls (p < 0.05; Figure). Decreased mortality was associated with a 99% decrease in 2nd degree heart block (Figure) and prevention of 3rd degree heart block compared to saline (p < 0.05). Glucagon and epinephrine were similar between the groups suggesting verapamil does not affect hypoglycemic counterregulation. Consistent with the notion of calcium-mediated arrhythmias, separate experiments demonstrated that pharmacological blockade of ryanodine receptor-mediated calcium signaling also reduced heart block by 97% and prevented mortality due to hypoglycemia. In summary, blocking calcium channels protects against severe hypoglycemia-induced fatal cardiac arrhythmias. Blockade of cardiac calcium channels could be a potential approach to prevent arrhythmias in people with diabetes at risk for hypoglycemia. Disclosure C.M. Reno: None. Y. Huang: None. C.G. Christensen: None. M.B. Oxspring: None. J. Bayles: None. S.J. Fisher: None. Funding National Institutes of Health (5T32DK091317, R01NS070235); JDRF (3-APF-2017-407-A-N)

Extremely low frequency electromagnetic fields promote mesenchymal stem cell migration by increasing intracellular Ca2+ and activating the FAK/Rho GTPases signaling pathways in vitro

BackgroundThe ability of mesenchymal stem cells (MSCs) to migrate to the desired tissues or lesions is crucial for stem cell-based regenerative medicine and tissue engineering. Optimal therapeutics for promoting MSC migration are expected to become an effective means for tissue regeneration. Electromagnetic fields (EMF), as a noninvasive therapy, can cause a lot of biological changes in MSCs. However, whether EMF can promote MSC migration has not yet been reported.MethodsWe evaluated the effects of EMF on cell migration in human bone marrow-derived MSCs. With the use of Helmholtz coils and an EMF stimulator, 7.5, 15, 30, 50, and 70 Hz/1 mT EMF was generated. Additionally, we employed the l-type calcium channel blocker verapamil and the focal adhesion kinase (FAK) inhibitor PF-573228 to investigate the role of intracellular calcium content, cell adhesion proteins, and the Rho GTPase protein family (RhoA, Rac1, and Cdc42) in EMF-mediated MSC migration. Cell adhesion proteins (FAK, talin, and vinculin) were detected by Western blot analysis. The Rho GTPase protein family activities were assessed by G-LISA, and F-actin levels, which reflect actin cytoskeletal organization, were detected using immunofluorescence.ResultsAll the 7.5, 15, 30, 50, and 70 Hz/1 mT EMF promoted MSC migration. EMF increased MSC migration in an intracellular calcium-dependent manner. Notably, EMF-enhanced migration was mediated by FAK activation, which was critical for the formation of focal contacts, as evidenced by increased talin and vinculin expression. Moreover, RhoA, Rac1, and Cdc42 were activated by FAK to increase cytoskeletal organization, thus promoting cell contraction.ConclusionsEMF promoted MSC migration by increasing intracellular calcium and activating the FAK/Rho GTPase signaling pathways. This study provides insights into the mechanisms of MSC migration and will enable the rational design of targeted therapies to improve MSC engraftment.

Effect of iron overload on electrophysiology of slow reaction autorhythmic cells of left ventricular outflow tract in guinea pigs

Objective: To investigate the electrophysiology effects and mechanism of iron overload on the slow response autorhythmic cells in the left ventricular outflow tract of guinea pigs. Methods: Standard microelectrode cell recording techniques were adopted to observe the electrophysiological effects of different concentrations of Fe2+ (100 μmol/L, 200 μmol/L) on the left ventricular outflow tract autorhythmic cells. Heart tissues were perfused with FeSO4 (200 μmol/L) combing with CaC12 (4.2 mmol/L), Verapamil, (1 μmol/L), and nickel chloride (200μmol/L) respectively to observe the influences of these contents on electrophysiology of FeSO4 (200 μmol/L) on the left ventricular outflow tract autorhythmic cells. Results: Fe2+ at both 100 μmol/L and 200 μmol/L could change the electrophysiological parameters of the slow response autorhythmic cells of the left ventricular outflow tract in a concentration-dependent manner resulting into decrease in Vmax, APA and MDP, slower RPF and VDD, and prolonged APD50 and APD90 (P all <0.05). Besides, perfusion of increased Ca2+ concentration could partially offset the electrophysiological effects of Fe2+ (200 μmol/L). The L-type calcium channel (LTCC) blocker Verapamil (1 μmol/L) could block the electrophysiological effects of Fe2+ (200 μmol/L). But the T-type calcium channel (TTCC) blocker nickel chloride (NiCl2, 200 μmol/L) could not block the electrophysiological effects of Fe2+ (200 μmol/L). Conclusions: Fe2+ can directly change the electrophysiological characteristics of the slow response autorhythmic cells of the left ventricular outflow tract probably through the L-type calcium channel.

The Requirement of L-Type Voltage-Dependent Calcium Channel (L-VDCC) in the Rapid-Acting Antidepressant-Like Effects of Scopolamine in Mice

BackgroundPrevious studies have shown that a low dose of scopolamine produces rapid-acting antidepressant-like actions in rodents. Understanding the mechanisms underlying this effect and the dose-dependent variations of drug responses remains an important task. L-type voltage-dependent calcium channels were found to mediate rapid-acting antidepressant effects of certain medications (e.g., ketamine). Therefore, it is of great interest to determine the involvement of L-type voltage-dependent calcium channels in the action of scopolamine.MethodsHerein, we investigated the mechanisms underlying behavioral responses to various doses of scopolamine in mice to clarify the involvement of L-type voltage-dependent calcium channels in its modes of action. Open field test, novel object recognition test, and forced swimming test were performed on mice administered varied doses of scopolamine (0.025, 0.05, 0.1, 1, and 3 mg/kg, i.p.) alone or combined with L-type voltage-dependent calcium channel blocker verapamil (5 mg/kg, i.p.). Then, the changes in brain-derived neurotrophic factor and neuropeptide VGF (nonacronymic) levels in the hippocampus and prefrontal cortex of these mice were analyzed.ResultsLow doses of scopolamine (0.025 and 0.05 mg/kg) produced significant antidepressant-like effects in the forced swimming test, while higher doses (1 and 3 mg/kg) resulted in significant memory deficits and depressive-like behaviors. Moreover, the behavioral changes in responses to various doses may be related to the upregulation (0.025 and 0.05 mg/kg) and downregulation (1 and 3 mg/kg) of brain-derived neurotrophic factor and VGF in the hippocampus and prefrontal cortex in mice. We further found that the rapid-acting antidepressant-like effects and the upregulation on brain-derived neurotrophic factor and VGF produced by a low dose of scopolamine (0.025 mg/kg) were completely blocked by verapamil.ConclusionsThese results indicate that L-type voltage-dependent calcium channels are likely involved in the behavioral changes in response to various doses of scopolamine through the regulation of brain-derived neurotrophic factor and VGF levels.

The Role of Voltage‐Operated Calcium Channels in Astrocyte Reactivity

Reactive astrogliosis is a universal response of astrocytes to brain injuries and diseases as diverse as trauma, infection, neurodegeneration, and ischemia. Reactive astrocytes undergo dramatic morphological changes (Wilhelmsson et al., 2006), and various alterations in gene expression have been observed (Sofroniew, 2009). It has long been debated whether reactive astrocytes are harmful or beneficial. In the past few years, both types of properties have been observed. Previous studies have shown that the plasma membranes of astrocytes depolarize when treated with high levels of potassium and this in turn activates voltage‐operated calcium channels. What we are looking to find out more about is the role that these channels play in astrocyte reactivity. We hypothesize that incubating primary astrocyte cultures with high levels of potassium will cause astrocytes to become reactive and that blocking the voltage‐operated calcium channels of these cells will inhibit their ability to become reactive. Our experiments involved incubating cell cultures for three days with different levels of potassium and performing immunocytochemistry with GFAP and S100 antibodies to determine the amount of reactivity. We found that high levels of potassium caused the astrocytes to become reactive and through the use of L‐type voltage‐operated calcium channel blockers Verapamil and Nifedipine, we were able to conclude that these channels are necessary for reactivity under these conditions. In summary, our results suggest that voltage‐operated calcium channels may play a fundamental role in the induction of reactive astrocytes, and indicate that the inhibition of these calcium channels may be an effective way to prevent astrocyte activation.

Calcium channel blockade reduces mechanical strain-induced extracellular matrix gene response in lamina cribrosa cells

PurposeThis study examines the effect of the L-type calcium channel blocker verapamil on mechanical strain-induced extracellular matrix genes in optic nerve head lamina cribrosa (LC) cells.MethodsChanges in LC cell intracellular...

The clinically approved drugs amiodarone, dronedarone and verapamil inhibit filovirus cell entry

ObjectivesFiloviruses such as Ebola virus and Marburg virus cause a severe haemorrhagic fever syndrome in humans for which there is no specific treatment. Since filoviruses use a complex route of cell entry that depends on numerous cellular factors, we hypothesized that there may be drugs already approved for human use for other indications that interfere with signal transduction or other cellular processes required for their entry and hence have anti-filoviral properties.MethodsWe used authentic filoviruses and lentiviral particles pseudotyped with filoviral glycoproteins to identify and characterize such compounds.ResultsWe discovered that amiodarone, a multi-ion channel inhibitor and adrenoceptor antagonist, is a potent inhibitor of filovirus cell entry at concentrations that are routinely reached in human serum during anti-arrhythmic therapy. A similar effect was observed with the amiodarone-related agent dronedarone and the L-type calcium channel blocker verapamil. Inhibition by amiodarone was concentration dependent and similarly affected pseudoviruses as well as authentic filoviruses. Inhibition of filovirus entry was observed with most but not all cell types tested and was accentuated by the pre-treatment of cells, indicating a host cell-directed mechanism of action. The New World arenavirus Guanarito was also inhibited by amiodarone while the Old World arenavirus Lassa and members of the Rhabdoviridae (vesicular stomatitis virus) and Bunyaviridae (Hantaan) families were largely resistant.ConclusionsThe ion channel blockers amiodarone, dronedarone and verapamil inhibit filoviral cell entry.

Effects of L-type Calcium Channel Antagonists Verapamil and Diltiazem on fKv1.4ΔN Currents in Xenopus oocytes.

The goal of this study was to determine the effects of the L-type calcium channel blockers verapamil and diltiazem on the currents of voltage-gated potassium channel (fKv1.4ΔN), an N-terminal-deleted mutant of the ferret Kv1.4 potassium channel. Measurements were made using a two electrode voltage clamp technique with channels expressed stably in Xenopus oocytes. The fKv1.4ΔN currents displayed slow inactivation, with a half-inactivation potential of -38.38 mV and slow recovery from inactivation (τ = 1.90 seconds at -90 mV). The fKv1.4ΔN currents exhibited state-dependent blockade by both drugs, and the inhibition was frequency-, voltage-, and concentration-dependent, consistent with open channel block. Verapamil and diltiazem blocked fKv1.4ΔN currents with 50% inhibitory concentration (IC50) values of 260.71 ± 18.50 μmol/L and 241.04 ± 23.06 μmol/L, respectively. Verapamil accelerated the C-type inactivation rate and slowed recovery of the fKv1.4Δ N channel, while shifting the steady activation curve to the right. Blockade of fKv1.4ΔN currents by diltiazem was similar to that of verapamil, but diltiazem accelerated the decay rate of inactivation of fKv1.4ΔN currents without modifying the kinetics of current activation. The present results suggest that verapamil and diltiazem accelerate the C-type inactivation and slow the recovery of the fKv1.4ΔN channel in the open state.

Contractile Activity Regulates Inducible Nitric Oxide Synthase Expression and NOiProduction in Cardiomyocytes via a FAK-Dependent Signaling Pathway

Intracellular nitric oxide (NOi) is a physiological regulator of excitation-contraction coupling, but is also involved in the development of cardiac dysfunction during hypertrophy and heart failure. To determine whether contractile activity regulates nitric oxide synthase (NOS) expression, spontaneously contracting, neonatal rat ventricular myocytes (NRVM) were treat with L-type calcium channel blockers (nifedipine and verapamil) or myosin II ATPase inhibitors (butanedione monoxime (BDM) and blebbistatin) to produce contractile arrest. Both types of inhibitors significantly reduced iNOS but not eNOS expression, and also reduced NOi production. Inhibiting contractile activity also reduced focal adhesion kinase (FAK) and AKT phosphorylation. Contraction-induced iNOS expression required FAK and phosphatidylinositol 3-kinase (PI(3)K), as both PF573228 and LY294002 (10 μM, 24 h) eliminated contraction-induced iNOS expression. Similarly, shRNAs specific for FAK (shFAK) caused FAK knockdown, reduced AKT phosphorylation at T308 and S473, and reduced iNOS expression. In contrast, shRNA-mediated knockdown of PYK2, the other member of the FAK-family of protein tyrosine kinases, had much less of an effect. Conversely, overexpression of a constitutively active form of FAK (CD2-FAK) or AKT (Myr-AKT) reversed the inhibitory effect of BDM on iNOS expression and NOi production. Thus, contraction-induced iNOS expression and NOi production in NRVM are mediated via a FAK-PI(3)K-AKT signaling pathway.

Inotropic effects of prokinetic agents with 5-HT4 receptor agonist actions on human isolated myocardial trabeculae

AimsBesides acting as gastrointestinal prokinetic agents, 5-hydroxytryptamine4 (5-HT4) receptor agonists can induce positive inotropism in human isolated atrium, but not in ventricles. We pharmacologically evaluated the gastroprokinetic 5-HT4 receptor agonists tegaserod, prucalopride, R199715, cisapride, the cisapride metabolite norcisapride, and the 5-HT3 receptor agonist MKC773 on human isolated myocardial trabeculae, and compared their effects with those induced by 5-HT and 5-methoxytryptamine (5-MeOT). Main methodsAtrial and ventricular trabeculae were paced and changes in contractile force were studied in the absence or presence of the 5-HT4 receptor antagonist GR113808. Partial agonism was assessed using 5-HT4 receptor agonists as antagonists against 5-HT. To test the contribution of L-type calcium channels, the inotropic responses to 5-HT and 5-MeOT were studied in the absence or presence of verapamil. Key findingsLike 5-HT and 5-MeOT, cisapride and tegaserod, but not prucalopride, R19971 and MKC­733, induced concentration-dependent positive inotropic responses on atrial trabeculae, which were abolished by GR113808. The L-type calcium channel blocker verapamil attenuated inotropic responses to 5-HT and 5-MeOT. None of the agonists affected the contraction of left ventricular trabeculae. Concentration response curves to 5-HT were shifted to the right in the presence of prucalopride, cisapride, tegaserod and R199715, but not MKC-773. SignificanceWe conclude that (i) inotropic responses to 5-HT and 5-MeOT seem to depend on L-type calcium channels, (ii) tegaserod and cisapride behave as partial 5-HT4 receptor agonists, while prucalopride, norcisapride and MKC-733 cause no significant effects on human atrial trabeculae, (iii) R199715 seems to behave as a 5-HT4 receptor antagonist.

Angiotensin II mediates cell survival through upregulation and activation of the serum and glucocorticoid inducible kinase 1

The serum- and glucocorticoid-inducible kinase 1 (SGK1) is known to regulate a wide variety of cellular processes, including renal sodium retention and cell survival. Angiotensin II (Ang II) is one of the many signaling molecules capable of regulating SGK1 expression, and is also known to impact cell survival. Here, we examined the role of SGK1 in Ang II-mediated cell survival. We hypothesized that Ang II protects cells from apoptosis by upregulating and activating SGK1. To test this, we examined the effects of Ang II stimulation on SGK1 expression and downstream signaling. We also examined the effects of Ang II treatment and siRNA-mediated SGK1 knockdown on apoptosis after serum starvation. We found that after 2h of Ang II treatment, SGK1 mRNA expression was increased approximately 2-fold. This induction was sensitive to reductions in intracellular calcium levels after pretreatment with BAPTA-AM, but insensitive to the L-type calcium channel blocker verapamil. SGK1 induction was also sensitive to the tyrosine kinase inhibitor genistein. Ang II treatment also caused a rapid increase in the level of phosphorylation of SGK1 at Ser422 and Thr256, and Ser422 phosphorylation was rapamycin-sensitive. We found that Ang II treatment was protective against serum starvation-induced apoptosis, and this protective effect was significantly blunted when SGK1 was silenced via siRNA. Lastly, Ang II induced FOXO3A phosphorylation in an SGK1-dependent manner, thereby reducing the pro-apoptotic actions of FOXO3A. Overall, these results indicate that Ang II upregulates and activates SGK1, leading to increased cell survival via multiple, non-redundant mechanisms.

In-vitro recording of adult zebrafish heart electrocardiogram — A platform for pharmacological testing

Background Recently zebrafish has become a powerful vertebrate model system for cardiac arrhythmia and another advantage is that the heart could be rapidly excised for in-vitro electrophysiological recording. Methods We made direct in-vitro recordings of adult zebrafish heart ECG using the microelectrode and tested the effects of various drugs on zebrafish heart ECG. Results The QT interval change in the ECG was verified by optically mapped action potential duration (APD). The mean in-vitro heart rate (HR) of the adult zebrafish was 118 ± 22 beats/min. The mean QT interval was 312 ± 36 ms and mean HR corrected QT interval (QTc) 439 ± 39 ms. The mean optically mapped APD was 308 ± 30 ms, which was close to the QT interval in ECG (p = 0.815). We found that sympathomimetic drug isoproterenol increased HR, whereas L-type calcium channel blocker verapamil decreased HR. Sodium channel blocker quinidine and L-type calcium channel activator BayK8644 prolonged QTc interval in a dose-dependent manner (515 ± 24 ms and 519 ± 27 ms, respectively, both p < 0.01). The APD was also prolonged accordingly. Both rapidly and slowly activating delayed rectifier potassium channel (IKr and IKs) blockers E4031 and chromanol 293B, respectively, also prolonged QTc interval in a dose-dependent manner (523 ± 25 ms and 529 ± 27 ms, respectively, both p < 0.01). Quinidine, E4031 and chromanol 293B also decreased HR. Conclusions Direct in-vitro recording of adult zebrafish heart is an efficient platform for test of drugs which exert electrophysiological effects on cardiomyocytes, and perturbation of ionic channels that are responsible for human long QT syndrome also modulates QT interval in adult zebrafish heart.

Regulation of Spinal Substance P Release by Intrathecal Calcium Channel Blockade

The authors investigated the role of different voltage-sensitive calcium channels expressed at presynaptic afferent terminals in substance P release and on nociceptive behavior evoked by intraplantar formalin by examining the effects of intrathecally delivered N- (ziconotide), T- (mibefradil), and L-type voltage-sensitive calcium channel blockers (diltiazem and verapamil). Rats received intrathecal pretreatment with saline or doses of morphine, ziconotide, mibefradil, diltiazem, or verapamil. The effect of these injections upon flinching evoked by intraplantar formalin (5%, 50 μl) was quantified. To assess substance P release, the incidence of neurokinin-1 receptor internalization in the ipsilateral and contralateral lamina I was determined in immunofluorescent-stained tissues. Intrathecal morphine (20 μg), ziconotide (0.3, 0.6, and 1 μg), mibefradil (100 μg, but not 50 μg), diltiazem (500 μg, but not 300 μg), and verapamil (200 μg, but not 50 and 100 μg) reduced paw flinching in phase 2 compared with vehicle control (P < 0.05), with no effect on phase 1. Ziconotide (0.3, 0.6, and 1 μg) and morphine (20 μg) significantly inhibited neurokinin-1 receptor internalization (P < 0.05), but mibefradil, diltiazem, and verapamil at the highest doses had no effect. These results emphasize the role in vivo of N-type but not T- and L-type voltage-sensitive calcium channel blockers in mediating the stimulus-evoked substance P release from small primary afferents and suggest that T- and L-type voltage-sensitive calcium channel blockers exert antihyperalgesic effects by an action on other populations of afferents or mechanisms involving postsynaptic excitability.

In-vitro Recording of Adult Zebrafish Heart Electrocardiogram—A Platform for Pharmacological Testing

Background: Recently zebrafish has become a powerful vertebrate model system for cardiac arrhythmia and another advantage is that the heart could be rapidly excised for in-vitro electrophysiological recording. Methods: We made direct in-vitro recordings of adult zebrafish heart ECG using the microelectrode array and tested the effects of various drugs on zebrafish heart ECG. Results: The QT interval change in the ECG was verified by optically mapped action potential duration (APD). The mean optically mapped APD was 308±30 ms, which was close to the QT interval in ECG (p=0.815). We found that sympathomimetic drug isoproterenol increased HR, whereas L-type calcium channel blocker verapamil decreased HR. Sodium channel blocker quinidine and L-type calcium channel activator BayK8644 prolonged QTc interval in a dose-dependent manner (515±24 ms and 519±27 ms, respectively, both p<0.01). The APD was also prolonged accordingly. Both rapidly and slowly activating delayed rectifier potassium channel (IKr and IKs) blockers E4031 and Chromanol 293B, respectively, also prolonged QTc interval in a dose-dependent manner (523±25 ms and 529±27 ms, respectively, both p<0.01). Quinidine, E4031 and Chromanol 293B also decreased HR. Conclusions: Direct in-vitro recording of adult zebrafish heart is an efficient platform for test of drugs which exert electrophysiological effects on cardiomyocytes, and perturbation of ionic channels that are responsible for human long QT syndrome also modulates QT interval in adult zebrafish heart.

C-JunNH2-Terminal Kinase Contributes to Dexmedetomidine-Induced Contraction in Isolated Rat Aortic Smooth Muscle

PurposeDexmedetomidine, a full agonist of α2B-adrenoceptors, is used for analgesia and sedation in the intensive care units. Dexmedetomidine produces an initial transient hypertension due to the activation of post-junctional α2B-adrenoceptors on vascular smooth muscle cells (SMCs). The aims of this in vitro study were to identify mitogen-activated protein kinase (MAPK) isoforms that are primarily involved in full, α2B-adrenoceptor agonist, dexmedetomidine-induced contraction of isolated rat aortic SMCs.Materials and MethodsRat thoracic aortic rings without endothelium were isolated and suspended for isometric tension recording. Cumulative dexmedetomidine (10-9 to 10-6 M) dose-response curves were generated in the presence or absence of extracellular signal-regulated kinase (ERK) inhibitor PD 98059, p38 MAPK inhibitor SB 203580, c-Jun NH2-terminal kinase (JNK) inhibitor SP 600125, L-type calcium channel blocker (verapamil and nifedipine), and α2-adrenoceptor inhibitor atipamezole. Dexmedetomidine-induced phosphorylation of ERK, JNK, and p38 MAPK in rat aortic SMCs was detected using Western blotting.ResultsSP 600125 (10-6 to 10-5 M) attenuated dexmedetomidine-evoked contraction in a concentration-dependent manner, whereas PD 98059 had no effect on dexmedetomidine-induced contraction. SB 203580 (10-5 M) attenuated dexmedetomidine-induced contraction. Dexmedetomidine-evoked contractions were both abolished by atipamezole and attenuated by verapamil and nifedipine. Dexmedetomidine induced phosphorylation of JNK and p38 MAPK in rat aortic SMCs, but did not induce phosphorylation of ERK.ConclusionDexmedetomidine-induced contraction involves a JNK- and p38 MAPK-mediated pathway downstream of α2-adrenoceptor stimulation in rat aortic SMCs. In addition, dexmedetomidine-induced contractions are primarily dependent on calcium influx via L-type calcium channels.

L-type voltage-gated calcium channel blockade with isradipine as a therapeutic strategy for Alzheimer's disease

There is strong evidence that intracellular calcium dysregulation plays an important pathological role in Alzheimer's disease, and specifically that beta amyloid may induce increases in intracellular calcium and lead to neuronal cell dysfunction and death. Here we investigated the feasibility of modifying Alzheimer's pathology with the L-type voltage-gated calcium channel blockers verapamil, diltiazem, isradipine and nimodipine. All four compounds protected MC65 neuroblastoma cells from amyloid beta protein precursor C-terminal fragment (APP CTF)-induced neurotoxicity. Isradipine was the most potent blocker, preventing APP CTF neurotoxicity at nanomolar concentrations. Intracellular beta amyloid expression was associated with increased expression of Cav 1.2 calcium channels and increased intracellular calcium influx from the extracellular space. Despite the cytoprotection afforded by calcium channel blockers, amyloid beta oligomer formation was not suppressed. The mechanism of cell death in MC65 cells is appeared to be caspase-3 independent. With the goal of determining if there is sufficient experimental support to move forward with animal trials of isradipine, we determined its bioavailability in the triple transgenic mouse model of AD. Subcutaneous implantation of carrier-bound isradipine (3 μg/g/day) for 60 days resulted in nanomolar concentrations in both the plasma and brain. Taken together, our in vitro results support the theory that calcium blockers exert protective effects downstream of the effects of beta amyloid. Isradipine's neuroprotective effect at concentrations that are clinically relevant and achievable in vitro and in vivo suggests that this particular calcium blocking agent may have therapeutic value in the treatment of Alzheimer's disease.