Characterization of L-type calcium channel activity in atrioventricular nodal myocytes from rats with streptozotocin-induced Diabetes mellitus

© 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society. Cardiovascular complications are common in patients with Diabetes mellitus (DM). In addition to changes in cardiac muscle inotropy, electrical abnormalities are also commonly observed in these patients. We have previously shown that spontaneous cellular electrical activity is altered in atrioventricular nodal (AVN) myocytes, isolated from the streptozotocin (STZ) rat model of type-1 DM. In this study, utilizing the same model, we have characterized the changes in L-type calcium channel activity in single AVN myocytes. Ionic currents were recorded from AVN myocytes isolated from the hearts of control rats and from those with STZ-induced diabetes. Patch-clamp recordings were used to assess the changes in cellular electrical activity in individual myocytes. Type-1 DM significantly altered the cellular characteristics of L-type calcium current. A reduction in peak ICaL density was observed, with no corresponding changes in the activation parameters of the current. L-type calcium channel current also exhibited faster time-dependent inactivation in AVN myocytes from diabetic rats. A negative shift in the voltage dependence of inactivation was also evident, and a slowing of restitution parameters. These findings demonstrate that experimentally induced type-1 DM significantly alters AVN L-type calcium channel cellular electrophysiology. These changes in ion channel activity may contribute to the abnormalities in cardiac electrical function that are associated with high mortality levels in patients with DM

Characterization of L-type calcium channel activity in atrioventricular nodal myocytes from rats with streptozotocin-induced Diabetes mellitus

© 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society. Cardiovascular complications are common in patients with Diabetes mellitus (DM). In addition to changes in cardiac muscle inotropy, electrical abnormalities are also commonly observed in these patients. We have previously shown that spontaneous cellular electrical activity is altered in atrioventricular nodal (AVN) myocytes, isolated from the streptozotocin (STZ) rat model of type-1 DM. In this study, utilizing the same model, we have characterized the changes in L-type calcium channel activity in single AVN myocytes. Ionic currents were recorded from AVN myocytes isolated from the hearts of control rats and from those with STZ-induced diabetes. Patch-clamp recordings were used to assess the changes in cellular electrical activity in individual myocytes. Type-1 DM significantly altered the cellular characteristics of L-type calcium current. A reduction in peak ICaL density was observed, with no corresponding changes in the activation parameters of the current. L-type calcium channel current also exhibited faster time-dependent inactivation in AVN myocytes from diabetic rats. A negative shift in the voltage dependence of inactivation was also evident, and a slowing of restitution parameters. These findings demonstrate that experimentally induced type-1 DM significantly alters AVN L-type calcium channel cellular electrophysiology. These changes in ion channel activity may contribute to the abnormalities in cardiac electrical function that are associated with high mortality levels in patients with DM

Capsaicin Inhibits Multiple Voltage-Gated Ion Channels in Rabbit Ventricular Cardiomyocytes in TRPV1-Independent Manner

Capsaicin is a naturally occurring alkaloid derived from chili pepper which is responsible for its hot, pungent taste. It exerts multiple pharmacological actions, including pain-relieving, anti-cancer, anti-inflammatory, anti-obesity, and antioxidant effects. Previous studies have shown that capsaicin significantly affects the contractility and automaticity of the heart and alters cardiovascular functions. In this study, the effects of capsaicin were investigated on voltage-gated ion currents in rabbit ventricular myocytes. Capsaicin inhibited rapidly activated (IKr) and slowly activated (IKs) K+ currents and transient outward (Ito) K+ current with IC50 values of 3.4 µM,14.7 µM, and 9.6 µM, respectively. In addition, capsaicin, at higher concentrations, suppressed voltage-gated Na+ and Ca2+ currents and inward rectifier IK1 current with IC50 values of 42.7 µM, 34.9 µM, and 38.8 µM, respectively. Capsaicin inhibitions of INa, IL-Ca, IKr, IKs, Ito, and IK1 were not reversed in the presence of capsazepine (3 µM), a TRPV1 antagonist. The inhibitory effects of capsaicin on these currents developed gradually, reaching steady-state levels within 3 to 6 min, and the recoveries were usually incomplete during washout. In concentration-inhibition curves, apparent Hill coefficients higher than unity suggested multiple interaction sites of capsaicin on these channels. Collectively, these findings indicate that capsaicin affects cardiac electrophysiology by acting on a diverse range of ion channels and suggest that caution should be exercised when capsaicin is administered to carriers of cardiac channelopathies or to individuals with arrhythmia-prone conditions, such as ischemic heart diseases

Capsaicin Is a Negative Allosteric Modulator of the 5-HT3 Receptor

In this study, effects of capsaicin, an active ingredient of the capsicum plant, were investigated on human 5-hydroxytryptamine type 3 (5-HT3) receptors. Capsaicin reversibly inhibited serotonin (5-HT)-induced currents recorded by two-electrode voltage clamp method in Xenopus oocytes. The inhibition was time- and concentration-dependent with an IC50 = 62 μM. The effect of capsaicin was not altered in the presence of capsazepine, and by intracellular BAPTA injections or trans-membrane potential changes. In radio-ligand binding studies, capsaicin did not change the specific binding of the 5-HT3 antagonist [3H]GR65630, indicating that it is a noncompetitive inhibitor of 5-HT3 receptor. In HEK-293 cells, capsaicin inhibited 5-HT3 receptor induced aequorin luminescence with an IC50 of 54 µM and inhibition was not reversed by increasing concentrations of 5-HT. In conclusion, the results indicate that capsaicin acts as a negative allosteric modulator of human 5-HT3 receptors

Contraction and Intracellular Calcium Transport in Epicardial and Endocardial Ventricular Myocytes from Streptozotocin-Induced Diabetic Rat

Diabetes mellitus (DM) is a global health problem. According to the International Diabetes Federation, 424.9 million people suffered from DM in 2017 and this number is expected to rise to 628.6 million by 2045. Although diabetes can affect every organ in the body, cardiovascular disease is a major cause of death and disability in people with diabetes. Diabetic patients frequently suffer from systolic and diastolic dysfunction. Within the ventricles, the electromechanical properties of cardiac myocytes vary transmurally. The aim of this study was to investigate contraction and Ca2+ transport in epicardial (EPI) and endocardial (ENDO) myocytes from the left ventricle in the streptozotocin (STZ)-induced diabetic rat heart. Experiments were performed 5–6 months after STZ treatment. Ventricular myocytes were isolated by enzymic and mechanical dispersal techniques from EPI and ENDO regions of the left ventricle. Contraction and free intracellular Ca2+ concentration (Ca2+)i were measured by video edge detection and fl uorescence photometry techniques, respectively. Myocyte length and calculated surface area were smaller in EPI-STZ compared to EPI-CON. Time to peak (TPK) shortening was prolonged in EPI-STZ compared to EPI-CON and in ENDO-STZ compared to ENDO-CON myocytes. Time to half (THALF) relaxation of shortening was prolonged in EPI-STZ compared to EPI-CON. TPK Ca2+ transient was prolonged in EPI-STZ compared to EPI-CON, ENDO-STZ compared to ENDO-CON, ENDO-STZ compared to EPI-STZ and in ENDO-CON compared to EPI-CON myocytes. THALF decay of the Ca2+ transient was prolonged in ENDO-STZ compared to ENDO-CON. Fractional release of Ca2+ was increased in ENDO-STZ compared to ENDO-CON and in ENDO-STZ compared to EPI-STZ. Recovery of the Ca2+ transient was prolonged in ENDO-STZ compared to ENDO-CON. In conclusion, the kinetics of contraction and Ca2+ transient, fractional release of Ca2+ from the sarcoplasmic reticulum are altered to different extents in EPI and ENDO myocytes from STZ-induced diabetic rat

Cellular and Molecular Targets of Menthol Actions

Menthol belongs to monoterpene class of a structurally diverse group of phytochemicals found in plant-derived essential oils. Menthol is widely used in pharmaceuticals, confectionary, oral hygiene products, pesticides, cosmetics, and as a flavoring agent. In addition, menthol is known to have antioxidant, anti-inflammatory, and analgesic effects. Recently, there has been renewed awareness in comprehending the biological and pharmacological effects of menthol. TRP channels have been demonstrated to mediate the cooling actions ofmenthol. There has been new evidence demonstrating thatmenthol can significantly influence the functional characteristics of a number of different kinds of ligand and voltage-gated ion channels, indicating that at least some of the biological and pharmacological effects of menthol can be mediated by alterations in cellular excitability. In this article, we examine the results of earlier studies on the actions of menthol with voltage and ligand-gated ion channels

Contraction and Intracellular Calcium Transport in Epicardial and Endocardial Ventricular Myocytes from Streptozotocin-Induced Diabetic Rat

Introduction: Diabetes mellitus (DM) is a global health problem. According to the International Diabetes Federation, 424.9 million people suffered from DM in 2017 and this number is expected to rise to 628.6 million by 2045. Although diabetes can affect every organ in the body, cardiovascular disease is a major cause of death and disability in people with diabetes. Diabetic patients frequently suffer from systolic and diastolic dysfunction. Within the ventricles, the electromechanical properties of cardiac myocytes vary transmurally. Aims and Objectives: The aim of this study was to investigate contraction and Ca2+ transport in epicardial (EPI) and endocardial (ENDO) myocytes from the left ventricle in the streptozotocin (STZ) “ induced diabetic rat heart. Materials and Methods: Experiments were performed 5-6 months after STZ treatment. Ventricular myocytes were isolated by enzymic and mechanical dispersal techniques from EPI and ENDO regions of the left ventricle. Contraction and free intracellular Ca2+ concentration [Ca2+]i were measured by video edge detection and fluorescence photometry techniques, respectively. Results: Myocyte length and calculated surface area were smaller in EPI-STZ compared to EPI-CON. Time to peak (TPK) shortening was prolonged in EPI-STZ compared to EPI-CON and in ENDO-STZ compared to ENDO-CON myocytes. Time to half (THALF) relaxation of shortening was prolonged in EPI-STZ compared to EPI-CON. TPK Ca2+ transient was prolonged in EPI-STZ compared to EPI-CON, ENDO-STZ compared to ENDO-CON, ENDO-STZ compared to EPI-STZ and in ENDO-CON compared to EPI-CON myocytes. THALF decay of the Ca2+ transient was prolonged in ENDO-STZ compared to ENDO-CON. Fractional release of Ca2+ was increased in ENDO-STZ compared to ENDO-CON and in ENDO-STZ compared to EPI-STZ. Recovery of the Ca2+ transient was prolonged in ENDO-STZ compared to ENDO-CON. Conclusion: In conclusion the kinetics of contraction and Ca2+ transient and fractional release of Ca2+ from the sarcoplasmic reticulum are altered to different extents in EPI and ENDO myocytes from STZ-induced diabetic rat

Curcumin Potentiates the Function of Human α7-nicotinic Acetylcholine Receptors Expressed in SH-EP1 Cells

Effects of curcumin, a biologically active ingredient of turmeric, were tested on the Ca2+transients induced by the activation of α7 subunit of the human nicotinic acetylcholine (α7nACh) receptor expressed in SH-EP1 cells. Curcumin caused a significant potentiation of choline (1 mM)-induced Ca2+ transients with an EC50 value of 133 nM. The potentiating effect of curcumin was not observed in Ca2+ transients induced by high K+ (60 mM) containing solutions or activation of α4β2 nACh receptors and the extent of curcumin potentiation was not altered in the presence of Ca2+ channel antagonists nifedipine (1 μM), verapamil (1 μM), ω-conotoxin (1 μM), and bepridil (10 μM). Noticeably the effect of curcumin was not observed when curcumin and choline were co-applied without curcumin pre-incubation. The effect of curcumin on choline-induced Ca2+ transients was not reversed by pre-incubation with inhibitors of protein C, A, and CaM kinases. Metabolites of curcumin such as tetrahydrocurcumin, demethylcurcumin, and didemethylcurcumin also caused potentiation of choline-induced Ca2+ transients. Notably, specific binding of [125I]-bungarotoxin was not altered in the presence of curcumin. Collectively, our results indicate that curcumin allosterically potentiate the function of the α7-nACh receptor expressed in SH-EP1 cells

Calcium signaling in endocardial and epicardial ventricular myocytes from streptozotocin-induced diabetic rats

© 2020 The Authors. Journal of Diabetes Investigation published by Asian Association for the Study of Diabetes (AASD) and John Wiley & Sons Australia, Ltd Aims/Introduction: Abnormalities in Ca2+ signaling have a key role in hemodynamic dysfunction in diabetic heart. The purpose of this study was to explore the effects of streptozotocin (STZ)-induced diabetes on Ca2+ signaling in epicardial (EPI) and endocardial (ENDO) cells of the left ventricle after 5–6 months of STZ injection. Materials and Methods: Whole-cell patch clamp was used to measure the L-type Ca2+ channel (LTCC) and Na+/Ca2+ exchanger currents. Fluorescence photometry techniques were used to measure intracellular free Ca2+ concentration. Results: Although the LTCC current was not significantly altered, the amplitude of Ca2+ transients increased significantly in EPI-STZ and ENDO-STZ compared with controls. Time to peak LTCC current, time to peak Ca2+ transient, time to half decay of LTCC current and time to half decay of Ca2+ transients were not significantly changed in EPI-STZ and ENDO-STZ myocytes compared with controls. The Na+/Ca2+ exchanger current was significantly smaller in EPI-STZ and in ENDO-STZ compared with controls. Conclusions: STZ-induced diabetes resulted in an increase in amplitude of Ca2+ transients in EPI and ENDO myocytes that was independent of the LTCC current. Such an effect can be attributed, at least in part, to the dysfunction of the Na+/Ca2+ exchanger. Additional studies are warranted to improve our understanding of the regional impact of diabetes on Ca2+ signaling, which will facilitate the discovery of new targeted treatments for diabetic cardiomyopathy

Calcium signaling in endocardial and epicardial ventricular myocytes from streptozotocin‐induced diabetic rats

Aims/Introduction: Abnormalities in Ca2+ signaling have a key role in hemodynamic dysfunction in diabetic heart. The purpose of this study was to explore the effects of streptozotocin (STZ) - induced diabetes on Ca2+ signaling in epicardial (EPI) and endocardial (ENDO) cells of the left ventricle, after 5-6 months of STZ injection. Materials and Methods: Whole-cell patch clamp was used to measure L-type Ca2+ channel (LTCC) and Na+/Ca2+ exchanger (NCX) currents. Fluorescence photometry techniques were used to measure intracellular free Ca2+ concentration [Ca2+]i. Results: Although LTCC current was not significantly altered, the amplitude (AMP) of Ca2+ transients increased significantly in EPI-STZ and ENDO-STZ compared to controls. Time to peak (TPK) LTCC current, TPK Ca2+ transient, time to half (THALF) decay of LTCC current and THALF decay of Ca2+ transients were not significantly changed in EPI-STZ and ENDO-STZ myocytes compared to controls. NCX current was significantly smaller in EPI-STZ and in ENDO-STZ compared to controls. Conclusions: STZ-induced diabetes resulted in an increase in AMP of Ca2+ transients in EPI and ENDO myocyte that was independent of LTCC current. Such an effect can be attributed, at least in part, to the dysfunction of NCX. Additional studies are warranted to improve our understanding of the regional impact of diabetes on Ca2+ signaling, which will facilitate the discovery of new targeted treatments for diabetic cardiomyopathy