Effects of anandamide on potassium channels in rat ventricular myocytes: a suppression of Ito and augmentation of KATP channels

2012 ◽  
Vol 302 (6) ◽  
pp. C924-C930 ◽  
Author(s):  
Qian Li ◽  
Hui-Jie Ma ◽  
Sheng-Li Song ◽  
Min Shi ◽  
Hui-Juan Ma ◽  
...  
Keyword(s):  
Steady State ◽  
Receptor Antagonist ◽  
Potassium Current ◽  
Ventricular Myocytes ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Inactivation Curve ◽  
Rat Ventricular Myocytes ◽  
Outward Potassium Current

Anandamide is an endocannabinoid that has antiarrhythmic effects through inhibition of L-type Ca2+ channels in cardiomyocytes. In this study, we investigated the electrophysiological effects of anandamide on K+ channels in rat ventricular myocytes. Whole cell patch-clamp technique was used to record K+ currents, including transient outward potassium current ( Ito), steady-state outward potassium current ( Iss), inward rectifier potassium current ( IK1), and ATP-sensitive potassium current ( IKATP) in isolated rat cardiac ventricular myocytes. Anandamide decreased Ito while increasing IKATP in a concentration-dependent manner but had no effect on Iss and IK1 in isolated ventricular myocytes. Furthermore, anandamide shifted steady-state inactivation curve of Ito to the left and shifted the recovery curve of Ito to the right. However, neither cannabinoid 1 (CB1) receptor antagonist AM251 nor CB2 receptor antagonist AM630 eliminated the inhibitory effect of anandamide on Ito. In addition, blockade of CB2 receptors, but not CB1 receptors, eliminated the augmentation effect of anandamide on IKATP. These data suggest that anandamide suppresses Ito through a non-CB1 and non-CB2 receptor-mediated pathway while augmenting IKATP through CB2 receptors in ventricular myocytes.

scholarly journals Effect of acidosis on transient outward potassium current in isolated rat ventricular myocytes

2000 ◽  
Vol 278 (1) ◽  
pp. H50-H59 ◽  
Author(s):  
J. T. Hulme ◽  
C. H. Orchard
Keyword(s):  
Potassium Current ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Solution Ph ◽  
Patch Clamp Technique ◽  
Inactivation Curve ◽  
Rat Ventricular Myocytes ◽  
Steady State Inactivation ◽  
Perforated Patch Clamp ◽  
Outward Potassium Current

The effect of acidosis on the transient outward K+ current ( Ito ) of rat ventricular myocytes has been investigated using the perforated patch-clamp technique. When the holding potential was −80 mV, depolarizing pulses to potentials positive to −20 mV activated Ito in subepicardial cells but activated little Ito in subendocardial cells. Exposure to an acid solution (pH 6.5) had no significant effect on Ito activated from this holding potential in either subepicardial or subendocardial cells. When the holding potential was −40 mV, acidosis significantly increased Ito at potentials positive to −20 mV in subepicardial cells but had little effect on Ito in subendocardial cells. The increase in Ito in subepicardial cells was inhibited by 10 mM 4-aminopyridine. In subepicardial cells, acidosis caused a +8.57-mV shift in the steady-state inactivation curve. It is concluded that in subepicardial rat ventricular myocytes acidosis increases the amplitude of Ito as a consequence of a depolarizing shift in the voltage dependence of inactivation.

Effect of Intravenous Anesthetics on Inward Rectifier Potassium Current in Rat and Human Ventricular Myocytes 

1997 ◽  
Vol 87 (2) ◽  
pp. 327-334 ◽  
Author(s):  
Cynthia A. Carnes ◽  
William Muir ◽  
David R. Van Wagoner
Keyword(s):  
Potassium Current ◽  
Ventricular Myocytes ◽  
Plasma Concentrations ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Pipette Solution ◽  
Rat Ventricular Myocytes ◽  
Ventricular Cells ◽  
Drug Concentrations

Background Inhibition of the inward rectifying potassium current (I(K1)) may cause cardiac dysrhythmias by decreasing resting membrane potential or prolonging action potential. Methods The effects of thiopental, ketamine, and propofol on I(K1) conductance were evaluated in rat ventricular myocytes. The effect of thiopental on I(K1) conductance was also evaluated in human ventricular myocytes. Currents were recorded using the nystatin-perforated whole-cell patch-clamp technique (holding potential, -50 mV; test potentials, -140 to -40 mV). Pipette solution contained 130 mM KCl, 5 mM MgCl2, 5 mM HEPES, and 5 mM EGTA,pH 7.2. Bath solution (32 degrees C) contained 134 mM NaCI, 4 mM KCl, 1 mM MgCl2, 1 mM CaCl2, 0.3 mM CdCl2, 5 mM HEPES, and 5 mM d-glucose,pH 7.4. Drug concentrations examined encompassed the range of clinically relevant unbound plasma concentrations. Currents were normalized for cell capacitance. Conductance was calculated as current density/delta mV from -140 to -100 mV. Analysis of variance was used to test for changes in conductance as a function of drug concentration. Results Thiopental reduced I(K1) conductance in a concentration-dependent manner (P < 0.0001). Thiopental-induced changes in I(K1) conductance in rat ventricular myocytes were fit to an inhibitory E(max) model, with a median inhibitory concentration of 10.5 microM. The effect of thiopental on I(K1) conductance in human ventricular cells was comparable to that observed in rat ventricular myocytes. Neither ketamine nor propofol altered I(K1) conductance. Conclusions Thiopental reduces I(K1) conductance in a concentration-dependent manner at clinically relevant concentrations in both rat and human ventricular myocytes.

Propofol Inhibits Cardiac L-Type Calcium Current in Guinea Pig Ventricular Myocytes

1996 ◽  
Vol 84 (3) ◽  
pp. 626-635 ◽  
Author(s):  
Ching-Yue Yang ◽  
Chih-Shung Wong ◽  
Chuan-Cheng Yu ◽  
Hsiang-Ning Luk ◽  
Cheng-I Lin
Keyword(s):  
Steady State ◽  
Guinea Pig ◽  
Time Course ◽  
Single Channel ◽  
Ventricular Myocytes ◽  
Hill Coefficient ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Inactivation Curve ◽  
Whole Cell

Background Propofol may exert negative inotropic and chronotropic actions in the heart. Single-channel studies show that propofol affects the kinetics of opening and closing of cardiac L-type calcium channels (ICa(L)) without altering channel conductance. The aim of this study was to investigate the mechanisms of depressant effects of propofol on cardiac whole-cell ICa(L). Methods Single ventricular myocytes were freshly dissciated from guinea pig hearts using enzymatic isolation. One-suction electrode voltage-clamp technique (whole-cell mode) was used. LCa(L) was separated from other contaminated ionic currents. Propofol was applied in the commercial 10% Intralipid emulsion formula (Zeneca, UK). Results In isolated cardiomyocytes, propofol significantly inhibited whole-cell ICa(L) in a concentration-dependent manner (K D = 52.0 microM; Hill coefficient = 1.3). The solvent (Intralipid) did not affect ICa(L). Propofol decreased ICa(L) at all potentials tested along the voltage axis and reduced the slope conductance. The threshold potential for activation and the peak potential of the current-voltage relationship were not changed by propofol. The steady-state activation curves overlapped in the absence and the presence of 56 microM propofol. In contrast, the steady-state inactivation curve was shifted in the hyperpolarizing direction. The time course of the recovery from inactivation was delayed by 56 microM propofol. The blocking action on ICa(L) of propofol shows marked resting block and use-dependent block. Propofol caused more pronounced inhibition at a higher stimulation frequency. The effect of propofol on the inactivation process was even more clear on ICa(L). Conclusions The authors conclude tha propofol, at supratherapeutic concentrations, inhibits cardiac ICa(L). This inhibition is mainly due to a shift of inactivation curve and a reduction in slope conductance.

scholarly journals Inhibitory Effect of Cinobufagin on L-Type Ca2+Currents, Contractility, and Ca2+Homeostasis of Isolated Adult Rat Ventricular Myocytes

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Pinya Li ◽  
Qiongtao Song ◽  
Tao Liu ◽  
Zhonglin Wu ◽  
Xi Chu ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Inhibitory Effect ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Cell Contractility ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Time To Peak ◽  
Whole Cell Patch Clamp

Cinobufagin (CBG), a major bioactive ingredient of the bufanolide steroid compounds of Chan Su, has been widely used to treat coronary heart disease. At present, the effect of CBG on the L-type Ca2+current (ICa-L) of ventricular myocytes remains undefined. The aim of the present study was to characterize the effect of CBG on intracellular Ca2+([Ca2+]i) handling and cell contractility in rat ventricular myocytes. CBG was investigated by determining its influence onICa-L, Ca2+transient, and contractility in rat ventricular myocytes using the whole-cell patch-clamp technique and video-based edge-detection and dual-excitation fluorescence photomultiplier systems. The dose of CBG (10−8 M) decreased the maximal inhibition of CBG by 47.93%. CBG reducedICa-Lin a concentration-dependent manner with an IC50of 4 × 10−10 M, upshifted the current-voltage curve ofICa-L, and shifted the activation and inactivation curves ofICa-Lleftward. Moreover, CBG diminished the amplitude of the cell shortening and Ca2+transients with a decrease in the time to peak (Tp) and the time to 50% of the baseline (Tr). CBG inhibited L-type Ca2+channels, and reduced[Ca2+]iand contractility in adult rat ventricular myocytes. These findings contribute to the understanding of the cardioprotective efficacy of CBG.

scholarly journals Aminophylline affects the cardiac rat inward rectifier potassium current in a dual way

EP Europace ◽  
2021 ◽  
Vol 23 (Supplement_3) ◽  
Author(s):  
NJD Ramalho ◽  
O Svecova ◽  
R Kula ◽  
M Simurdova ◽  
J Simurda ◽  
...  
Keyword(s):  
Steady State ◽  
Potassium Current ◽  
Ventricular Myocytes ◽  
Inward Rectifier ◽  
Public Institution ◽  
Patch Clamp Technique ◽  
Rat Ventricular Myocytes ◽  
Funding Sources ◽  
Inward Rectifier Potassium Current ◽  
Isolated Rat

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Ministry of Education, Youth and Sports of the Czech Republic Introduction Aminophylline, a bronchodilator used in clinical practice to treat namely severe astma attacks, often induces atrial fibrillation in patients. Modifications of the inward rectifier potassium current IK1 are known to play a role in the genesis of fibrillation. Purpose We aimed to investigate the effect of aminophylline at clinically-relevant concentrations between 3 and 100 µM on IK1 in isolated rat ventricular myocytes. Methods Experiments were performed by the whole cell patch clamp technique on enzymatically isolated rat right ventricular myocytes at room temperature. IK1 was measured as the current sensitive to 100 µM Ba2+. Results We observed a dual steady-state effect of aminophylline at most of the applied concentrations. Either inhibition or activation was apparent in individual cells during application of aminophylline at a given concentration. The smaller was magnitude of the control IK1, the more likely was activation of the current in the presence of aminophylline and vice versa (tested at 10 and 30 µM). The effect was voltage-independent and fully reversible during the subsequent wash-out. The mean aminophylline effect was inhibitory at all concentrations (10, 15, 4, and 23%-inhibition at -50 mV at 3, 10, 30, and 100 µM, respectively). Using a modified version of the population model of IK1 channels that we published before, the dual effect can be explained by interaction of aminophylline with two channel populations in a different way, the first one being inhibited and the second one being activated by the drug. Considering various fractions of these two channel populations in individual cells, varying effects observed in the measured cells can be simulated. Conclusions Aminophylline at clinically-relevant concentrations affects IK1 in rat ventricular myocytes in a dual way, showing both the steady-state activation and inhibition in various cells, even at the same concentration. It may be related to a different effect of the drug on various Kir2.x subunits forming the heterotetrameric IK1 channels present at the cell membrane of a single cell.

Calcineurin-independent inhibition of KV1.3 by FK-506 (tacrolimus): a novel pharmacological property

2007 ◽  
Vol 292 (5) ◽  
pp. C1714-C1722 ◽  
Author(s):  
Hye Sook Ahn ◽  
Sung Eun Kim ◽  
Bok Hee Choi ◽  
Jin-Sung Choi ◽  
Myung-Jun Kim ◽  
...  
Keyword(s):  
Steady State ◽  
Chinese Hamster Ovary Cells ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Fk 506 ◽  
Inactivation Curve ◽  
Voltage Dependent ◽  
Dependent Inhibition ◽  
Steady State Inactivation

The interaction of FK-506 with KV1.3, stably expressed in Chinese hamster ovary cells, was investigated with the whole cell patch-clamp technique. FK-506 inhibited KV1.3 in a reversible, concentration-dependent manner with an IC50 of 5.6 μM. Rapamycin, another immunosuppressant, produced effects that were similar to those of FK-506 (IC50 = 6.7 μM). Other calcineurin inhibitors (cypermethrin or calcineurin autoinhibitory peptide) alone had no effect on the amplitude or kinetics of KV1.3. In addition, the inhibitory action of FK-506 continued, even after the inhibition of calcineurin activity. The inhibition produced by FK-506 was voltage dependent, increasing in the voltage range for channel activation. At potentials positive to 0 mV (where maximal conductance is reached), however, no voltage-dependent inhibition was found. FK-506 exhibited a strong use-dependent inhibition of KV1.3. FK-506 shifted the steady-state inactivation curves of KV1.3 in the hyperpolarizing direction in a concentration-dependent manner. The apparent dissociation constant for FK-506 to inhibit KV1.3 in the inactivated state was estimated from the concentration-dependent shift in the steady-state inactivation curve and was calculated to be 0.37 μM. Moreover, the rate of recovery from inactivation of KV1.3 was decreased. In inside-out patches, FK-506 not only reduced the current amplitude but also accelerated the rate of inactivation during depolarization. FK-506 also inhibited KV1.5 and KV4.3 in a concentration-dependent manner with IC50 of 4.6 and 53.9 μM, respectively. The present results indicate that FK-506 inhibits KV1.3 directly and that this effect is not mediated via the inhibition of the phosphatase activity of calcineurin.

scholarly journals Oxytocin Inhibits T-Type Calcium Current of Human Decidual Stromal Cells

2005 ◽  
Vol 90 (7) ◽  
pp. 4191-4197 ◽  
Author(s):  
Bo Liu ◽  
Stephen J. Hill ◽  
Raheela N. Khan
Keyword(s):  
Stromal Cells ◽  
Calcium Current ◽  
Elective Cesarean Section ◽  
Dependent Manner ◽  
Uterine Contractility ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Inactivation Curve ◽  
Decidual Cells ◽  
Elective Cesarean

Abstract Context: Little is known about the crosstalk between the decidua and myometrium in relation to human labor. The hormone oxytocin (OT) is considered to be a key mediator of uterine contractility during parturition, exerting some of its effects through calcium channels. Objective: The objective was to characterize the effect of OT on the T-type calcium channel in human decidual stromal cells before and after the onset of labor. Design: The nystatin-perforated patch-clamp technique was used to record inward T-type calcium current (ICa(T)) from acutely dispersed decidual stromal cells obtained from women at either elective cesarean section [CS (nonlabor)] or after normal spontaneous vaginal delivery [SVD (labor)]. Setting: These studies took place at the University of Nottingham Medical School. Results: I Ca(T) of both SVD and CS cells were blocked by nickel (IC50 of 5.6 μm) and cobalt chloride (1 mm) but unaffected by nifedipine (10 μm). OT (1 nm to 3.5 μm) inhibited ICa(T) of SVD cells in a concentration-dependent manner, with a maximal inhibition of 79.0% compared with 26.2% in decidual cells of the CS group. OT-evoked reduction of ICa(T) was prevented by preincubation with the OT antagonist L371,257 in the SVD but not CS group. OT, in a concentration-dependent manner, displaced the steady-state inactivation curve for ICa(T) to the left in the SVD group with no significant effect on curves of the CS group. Conclusion: Inhibition of ICa(T) by OT in decidual cells obtained during labor may signify important functional remodeling of uterine signaling during this period.

Effects of extracellular ATP on ICa, [Ca2+]i, and contraction in isolated ferret ventricular myocytes

1993 ◽  
Vol 264 (3) ◽  
pp. C702-C708 ◽  
Author(s):  
Y. Qu ◽  
H. M. Himmel ◽  
D. L. Campbell ◽  
H. C. Strauss
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Ventricular Myocardium ◽  
Inhibitory Effect ◽  
Extracellular Atp ◽  
Maximal Effect ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
The Right

The effects of extracellular ATP on the voltage-activated "L-type" Ca current (ICa), action potential, resting and transient intracellular Ca2+ levels, and cell contraction were examined in enzymatically isolated myocytes from the right ventricles of ferrets. With the use of the whole cell patch-clamp technique, extracellular ATP (10(-7) to 10(-3) M) inhibited ICa in a time- and concentration-dependent manner. ATP decreased the peak amplitude of ICa without altering the residual current at the end of 500-ms clamp steps. The concentration-response relationship for ATP inhibition of ICa was well described by a conventional Michaelis-Menten relationship with a half-maximal inhibitory concentration of 1 microM and a maximal effect of 50%. Consistent with its inhibitory effect on ICa, ATP hyperpolarized the plateau phase and shortened the action potential duration. In fura-2-loaded myocytes, extracellular ATP did not change the resting myoplasmic Ca2+ levels; however, when current was elicited under voltage-clamp conditions, ATP both decreased the myoplasmic intracellular Ca2+ transient and inhibited the degree of cell shortening. Our results suggest that ATP could be a genuine and potent extracellular modulator of cardiac function in ferret ventricular myocardium.

Effects of Mg2+ on Ca2+ waves and Ca2+ transients of rat ventricular myocytes

1996 ◽  
Vol 270 (3) ◽  
pp. H907-H914 ◽  
Author(s):  
H. Terada ◽  
H. Hayashi ◽  
N. Noda ◽  
H. Satoh ◽  
H. Katoh ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Channel Blocker ◽  
Ventricular Myocytes ◽  
Inhibitory Effect ◽  
Antiarrhythmic Action ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Triggered Activity ◽  
Rat Ventricular Myocytes ◽  
High Concentrations

It has been shown that the occurrence of the transient inward current, which is responsible for triggered activity, was often associated with propagating regions of increased intracellular Ca2+ concentration ([Ca2+]i), i.e., the “Ca2+ wave.” To investigate the mechanism of antiarrhythmic action of Mg2+, we have studied effects of high concentrations of Mg2+ on Ca2+ waves in isolated rat ventricular myocytes. [Ca2+]i was estimated using the Ca(2+)-indicating probe indo 1. Ca2+ waves in myocytes, stimulated at 0.2 Hz, were induced by perfusion of isoproterenol (10(-7) M). High Mg2+ concentration suppressed Ca2+ waves in a concentration-dependent manner (36% at 4 mM, 70% at 8 mM, and 82% at 12 mM). The Ca2+ channel blocker verapamil also suppressed Ca2+ waves in a similar way. In contrast with marked depression of Ca2+ transients by verapamil, Ca2+ transients were not affected by high Mg2+ concentration (8 mM). High Mg2+ concentration also reduced frequencies of Ca2+ waves in the absence of electrical stimulation, whereas verapamil failed to reduce frequencies of Ca2+ waves. Reduction in frequency of Ca2+ waves by high Mg2+ concentration was associated with slowing of propagation velocity of Ca2+ waves. To examine whether suppressive effects of high Mg2+ concentration on Ca2+ waves were related to an increase in intracellular Mg2+ concentration ([Mg2+]i), the effect of high-Mg2+ solution on [Mg2+]i was examined in myocytes loaded with mag-fura 2. An increase in extracellular Mg2+ concentration from 1 to 12 mM increased [Mg2+]i from 1.06 +/- 0.16 to 1.87 +/- 0.22 mM (P < 0.01) in 30 min. To examine the effect of high Mg2+ concentration on amount of releasable Ca2+ in the sarcoplasmic reticulum, the effect of high Mg2+ concentration on the Ca2+ transient induced by a rapid application of caffeine was examined. High-Mg2+ solution increased the peak of the caffeine-induced Ca2+ transient. These results suggest that the inhibitory effect of Mg2+ on Ca2+ waves was not due to inhibition of the sarcolemmal Ca2+ channel but could be due to a decreased propensity for the sarcoplasmic reticulum to divest itself of excess Ca2+.

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