scholarly journals Extracellular hypotonicity induces disturbance of sodium currents in rat ventricular myocytes

2009 ◽  
pp. 807-815 ◽  
Author(s):  
L Hu ◽  
J Ma ◽  
P Zhang ◽  
J Zheng
Keyword(s):  
Ventricular Myocytes ◽  
Ruthenium Red ◽  
Hypotonic Solution ◽  
Sodium Currents ◽  
Patch Clamp Technique ◽  
Rat Ventricular Myocytes ◽  
Whole Cell Patch Clamp ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Steady State Inactivation

Hypotonic solution alters ion channel activity, but little attention has been paid to voltage-dependent sodium channels. The aim of this study was to investigate the effects of hypotonic solution on transient sodium currents (INaT) and persistent sodium currents (INaP). We also explored whether the intracellular signal transduction systems participated in the hypotonic modifications of sodium currents. INaT and INaP were recorded by means of whole-cell patch-clamp technique in isolated rat ventricular myocytes. Our results revealed that hypotonic solution reduced INaT and simultaneously augmented INaP with the occurrence of interconversion between INaT and INaP. Hypotonic solution shifted steady-state inactivation to a more negative potential, prolonged the time of recovery from inactivation, and enhanced intermediate inactivation (IIM). Ruthenium red (RR, inhibitor of TRPV4), bisindolylmaleimide VI (BIM, inhibitor of PKC), Kn-93 (inhibitor of Ca/CaMKII) and BAPTA (Ca2+-chelator) inhibited the effects of hypotonic solution on INaT and INaP. Therefore we conclude that hypotonic solution inhibits INaT, enhances INaP and IIM with the effects being reversible. TRPV4 and intracellular Ca2+, PKC and Ca/CaMKII participate in the hypotonic modifications of sodium currents.

scholarly journals The calcium-independent transient outward potassium current in isolated ferret right ventricular myocytes. I. Basic characterization and kinetic analysis.

1993 ◽  
Vol 101 (4) ◽  
pp. 571-601 ◽  
Author(s):  
D L Campbell ◽  
R L Rasmusson ◽  
Y Qu ◽  
H C Strauss
Keyword(s):  
Steady State ◽  
Ventricular Myocytes ◽  
Nonlinear Least Squares ◽  
Patch Clamp Technique ◽  
Time Constants ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
K Current ◽  
Necessary And Sufficient

Enzymatically isolated myocytes from ferret right ventricles (12-16 wk, male) were studied using the whole cell patch clamp technique. The macroscopic properties of a transient outward K+ current I(to) were quantified. I(to) is selective for K+, with a PNa/PK of 0.082. Activation of I(to) is a voltage-dependent process, with both activation and inactivation being independent of Na+ or Ca2+ influx. Steady-state inactivation is well described by a single Boltzmann relationship (V1/2 = -13.5 mV; k = 5.6 mV). Substantial inactivation can occur during a subthreshold depolarization without any measurable macroscopic current. Both development of and recovery from inactivation are well described by single exponential processes. Ensemble averages of single I(to) channel currents recorded in cell-attached patches reproduce macroscopic I(to) and indicate that inactivation is complete at depolarized potentials. The overall inactivation/recovery time constant curve has a bell-shaped potential dependence that peaks between -10 and -20 mV, with time constants (22 degrees C) ranging from 23 ms (-90 mV) to 304 ms (-10 mV). Steady-state activation displays a sigmoidal dependence on membrane potential, with a net aggregate half-activation potential of +22.5 mV. Activation kinetics (0 to +70 mV, 22 degrees C) are rapid, with I(to) peaking in approximately 5-15 ms at +50 mV. Experiments conducted at reduced temperatures (12 degrees C) demonstrate that activation occurs with a time delay. A nonlinear least-squares analysis indicates that three closed kinetic states are necessary and sufficient to model activation. Derived time constants of activation (22 degrees C) ranged from 10 ms (+10 mV) to 2 ms (+70 mV). Within the framework of Hodgkin-Huxley formalism, Ito gating can be described using an a3i formulation.

Effect of tetramethyl pyrazine on L-type calcium channel in rat ventricular myocytes

2001 ◽  
Vol 79 (7) ◽  
pp. 621-626 ◽  
Author(s):  
Lu-Yun Zou ◽  
Xue-Mei Hao ◽  
Guang-Qing Zhang ◽  
Mei Zhang ◽  
Ji-Hong Guo ◽  
...  
Keyword(s):  
Time Course ◽  
Ventricular Myocytes ◽  
Antagonistic Effect ◽  
Patch Clamp Technique ◽  
Inactivation Curve ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Whole Cell Patch Clamp ◽  
Steady State Inactivation ◽  
Ionic Mechanisms

To elucidate possible ionic mechanisms of antimyocardial ischemia and antiarrythmia of tetramethyl pyrazine (TP), we studied L-type Ca2+ currents (ICa.L) in adult rat ventricular myocytes using the whole-cell patch-clamp technique. The results showed: (i) under physiological conditions, 0.25 mmol/L TP decreased amplitude of ICa.L to 60.6% and this inhibition was increased with increasing concentration of TP. ID50 was 0.20 mmol/L. (ii) The Ca2+-antagonistic effect of TP was voltage-dependent. A marked negative shift of the steady-state inactivation curve was observed with long (10 s) conditioning prepulses, but not with short (350 ms) ones. (iii) The time course of inhibition during TP treatment was increased with an increase in drug concentration, and recovery from TP-induced inactivation of ICa.L was slower than in control cases. (iv) Tonic block and use-dependent block with TP treatment, which was induced by increasing the frequency of stimulation, occurred. We suggest that TP inhibits the ICa.L mainly by binding to inactivated Ca2+ channels. The high affinity of TP for the inactivated state of ICa.L may play an important role in developing therapies for pathological conditions.Key words: Tetramethyl pyrazine, L-type calcium current, rat ventricular myocytes.

Alpha 1b-adrenoceptor-mediated stimulation of Na-K pump current in adult rat ventricular myocytes

1993 ◽  
Vol 264 (4) ◽  
pp. H1315-H1318 ◽  
Author(s):  
A. P. Williamson ◽  
R. H. Kennedy ◽  
E. Seifen ◽  
J. P. Lindemann ◽  
J. R. Stimers
Keyword(s):  
Adrenergic Receptors ◽  
Ventricular Myocytes ◽  
Pump Current ◽  
Peak Effect ◽  
Patch Clamp Technique ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Whole Cell Patch Clamp ◽  
Dose Dependent ◽  
Stimulation Of

The purpose of this study was to determine if myocardial alpha 1a-and/or alpha 1b-adrenoceptors are involved in the increase in Na-K pump current (Ip) elicited by alpha 1-adrenergic agonists. Single rat ventricular myocytes were isolated by enzymatic disaggregation. The whole cell patch-clamp technique was used to examine dose-dependent effects of phenylephrine (PE) on holding current (Ih) and to determine whether observed actions were mediated via alpha 1a-or alpha 1b-adrenergic receptors. To minimize the contribution of transsar-colemmal currents other than Ip to Ih, membrane voltage was held constant -40 mV, and cells were maintained in a Ca-free perfusate containing 1 mM Ba and 0.1 mM Cd. All experiments were conducted in the presence of 3 microM nadolol. PE elicited dose-dependent increases in Ih, with a peak effect of 0.57 +/- 0.03 pA/pF observed at 30 microM. The response to PE was dose dependently inhibited by prazosin and chloroethylclonidine and was totally eliminated by 1 mM ouabain. When used at doses selective for the alpha 1a-subtype, WB4101 failed to significantly antagonize the action of PE. These data suggest that the observed alpha 1-adrenoceptor-mediated increase in Ih in isolated rat ventricular myocytes is the result of an increase in Ip effected via stimulation of alpha 1b-adrenergic receptors.

Divalent cations modulate the transient outward current in rat ventricular myocytes

1991 ◽  
Vol 261 (2) ◽  
pp. C310-C318 ◽  
Author(s):  
Z. S. Agus ◽  
I. D. Dukes ◽  
M. Morad
Keyword(s):  
Hippocampal Neurons ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Divalent Cations ◽  
Outward Current ◽  
Transient Outward Current ◽  
Patch Clamp Technique ◽  
Rat Ventricular Myocytes ◽  
Specific Effects ◽  
Whole Cell Patch Clamp

The modulation of the transient outward K+ current (Ito) by divalent cations was studied in enzymatically isolated rat ventricular myocytes with the whole cell patch-clamp technique. At holding potentials negative to -70 mV, 1 mM Cd2+ suppressed Ito, whereas, at potentials positive to -50 mV, the current was augmented. These effects were caused by shifts in the voltage dependence of both activation and inactivation of Ito toward more positive potentials. Cd2+ also slowed the activation kinetics of Ito by shifting the voltage dependence of its rate of activation, but the rate of inactivation was unaffected. Other divalent cations produced similar shifts but at markedly different concentrations. Thus, in the millimolar range, a rightward shift of approximately 20 mV was produced by 3 Co2+, 5 Ni2+, and 10 Ca2+, whereas 10 microM concentrations of Cu2+ and Zn2+ produced equivalent shifts. Similar effects were seen in hippocampal neurons with micromolar concentrations of Zn2+. Thus divalent cations have marked and specific effects on the kinetics and voltage dependence of Ito and may serve as a regulatory mechanism in its activation, particularly in cells with resting potentials positive to -60 mV.

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.

Voltage-dependent stimulation of the Na+-K+ pump by insulin in rabbit cardiac myocytes

2000 ◽  
Vol 278 (3) ◽  
pp. C546-C553 ◽  
Author(s):  
Peter S. Hansen ◽  
Kerrie A. Buhagiar ◽  
David F. Gray ◽  
Helge H. Rasmussen
Keyword(s):  
Protein Phosphatase ◽  
Ventricular Myocytes ◽  
Pump Current ◽  
Phosphatidylinositol 3 Kinase ◽  
Patch Clamp Technique ◽  
Membrane Pump ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Phosphatase 2A

Insulin enhances Na+-K+ pump activity in various noncardiac tissues. We examined whether insulin exposure in vitro regulates Na+-K+ pump function in rabbit ventricular myocytes. Pump current ( I p) was measured using the whole-cell patch-clamp technique at test potentials ( V ms) from −100 to +60 mV. When the Na+ concentration in the patch pipette ([Na]pip) was 10 mM, insulin caused a V m-dependent increase in I p. The increase was ∼70% when V m was at near physiological diastolic potentials. This effect persisted after elimination of extracellular voltage-dependent steps and when K+ and K+-congeners were excluded from the patch pipettes. When [Na]pip was 80 mM, causing near-maximal pump stimulation, insulin had no effect, suggesting that it did not cause an increase in membrane pump density. Effects of tyrphostin A25, wortmannin, okadaic acid, or bisindolylmaleimide I in pipette solutions suggested that the insulin-induced increase in I p involved activation of tyrosine kinase, phosphatidylinositol 3-kinase, and protein phosphatase 1, whereas protein phosphatase 2A and protein kinase C were not involved.

Changes of action potential and L-type calcium channel current of Sprague–Dawley rat ventricular myocytes by different amlodipine isomers

2008 ◽  
Vol 86 (9) ◽  
pp. 620-625 ◽  
Author(s):  
Ru-xing Wang ◽  
Wen-ping Jiang
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Calcium Channel ◽  
Ventricular Myocytes ◽  
Channel Blockers ◽  
Sprague Dawley ◽  
Patch Clamp Technique ◽  
Rat Ventricular Myocytes ◽  
Channel Current ◽  
Steady State Inactivation

To investigate the effects of S- and R-amlodipine (Aml) on action potential (AP) and L-type calcium channel current (ICa-L), the whole-cell patch-clamp technique was used on rat ventricular myocytes to record AP, ICa-L, peak currents, steady-state activation currents, steady-state inactivation currents, and recovery currents from inactivation with S-Aml and R-Aml at various concentrations. Increasing concentrations of S-Aml gradually shortened AP durations (APDs). At concentrations of 0.1, 0.5, 1, 5, and 10 μmol/L, S-Aml blocked 1.5% ± 0.2%, 25.4% ± 5.3%, 65.2% ± 7.3%, 78.4% ± 8.1%, and 94.2% ± 5.0% of ICa-L, respectively (p < 0.05), and the half-inhibited concentration was 0.62 ± 0.12 µmol/L. Current–voltage curves were shifted upward; steady-state activation and inactivation curves were shifted to the left. At these concentrations of S-Aml, the half-activation voltages were –16.01 ± 1.65, –17.61 ± 1.60, –20.17 ± 1.46, –21.87 ± 1.69, and –24.09 ± 1.87 mV, respectively, and the slope factors were increased (p < 0.05). The half-inactivation voltages were –27.16 ± 4.48, –28.69 ± 4.52, –31.19 ± 4.17, –32.63 ± 4.34, and –35.16 ± 4.46 mV, respectively, and the slope factors were increased (p < 0.05). The recovery times from inactivation of S-Aml were prolonged (p < 0.05). In contrast, R-Aml had no effect on AP and ICa-L (p > 0.05) at the concentrations tested. Thus, only S-Aml has calcium channel blockade activity, whereas R-Aml has none of the pharmacologic actions associated with calcium channel blockers.

scholarly journals The calcium-independent transient outward potassium current in isolated ferret right ventricular myocytes. II. Closed state reverse use-dependent block by 4-aminopyridine.

1993 ◽  
Vol 101 (4) ◽  
pp. 603-626 ◽  
Author(s):  
D L Campbell ◽  
Y Qu ◽  
R L Rasmusson ◽  
H C Strauss
Keyword(s):  
Steady State ◽  
Right Ventricular ◽  
Ventricular Myocytes ◽  
Patch Clamp Technique ◽  
Time Constants ◽  
Closed State ◽  
Whole Cell Patch Clamp ◽  
Dependent Behavior ◽  
Steady State Inactivation ◽  
K Current

Block of the calcium-independent transient outward K+ current, I(to), by 4-aminopyridine (4-AP) was studied in ferret right ventricular myocytes using the whole cell patch clamp technique. 4-AP reduces I(to) through a closed state blocking mechanism displaying "reverse use-dependent" behavior that was inferred from: (a) development of tonic block at hyperpolarized potentials; (b) inhibition of development of tonic block at depolarized potentials; (c) appearance of "crossover phenomena" in which the peak current is delayed in the presence of 4-AP at depolarized potentials; (d) relief of block at depolarized potentials which is concentration dependent and parallels steady-state inactivation for low 4-AP concentrations (V1/2 approximately -10 mV in 0.1 mM 4-AP) and steady-state activation at higher concentrations (V1/2 = +7 mV in 1 mM 4-AP, +15 mV in 10 mM 4-AP); and (e) reassociation of 4-AP at hyperpolarized potentials. No evidence for interaction of 4-AP with either the open or inactivated state of the I(to) channel was obtained from measurements of kinetics of recovery and deactivation in the presence of 0.5-1.0 mM 4-AP. At hyperpolarized potentials (-30 to -90 mV) 10 mM 4-AP associates slowly (time constants ranging from approximately 800 to 1,300 ms) with the closed states of the channel (apparent Kd approximately 0.2 mM). From -90 to -20 mV the affinity of the I(to) channel for 4-AP appears to be voltage insensitive; however, at depolarized potentials (+20 to +100 mV) 4-AP dissociates with time constants ranging from approximately 350 to 150 ms. Consequently, the properties of 4-AP binding to the I(to) channel undergo a transition in the range of potentials over which channel activation and inactivation occurs (-30 to +20 mV). We propose a closed state model of I(to) channel gating and 4-AP binding kinetics, in which 4-AP binds to three closed states. In this model 4-AP has a progressively lower affinity as the channel approaches the open state, but has no intrinsic voltage dependence of binding.

Channels involved in transient currents unmasked by removal of extracellular calcium in cardiac cells

2002 ◽  
Vol 282 (5) ◽  
pp. H1879-H1888 ◽  
Author(s):  
Regina Macianskiene ◽  
Francesco Moccia ◽  
Karin R. Sipido ◽  
Willem Flameng ◽  
Kanigula Mubagwa
Keyword(s):  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Monovalent Cation ◽  
Cardiac Cells ◽  
Time Dependent ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
High Concentrations ◽  
Low Sensitivity

In cardiac cells that lack macroscopic transient outward K+ currents ( I to), the removal of extracellular Ca2+ can unmask “ I to-like” currents. With the use of pig ventricular myocytes and the whole cell patch-clamp technique, we examined the possibility that cation efflux via L-type Ca2+channels underlies these currents. Removal of extracellular Ca2+ and extracellular Mg2+ induced time-independent currents at all potentials and time-dependent currents at potentials greater than −50 mV. Either K+ or Cs+ could carry the time-dependent currents, with reversal potential of +8 mV with internal K+ and +34 mV with Cs+. Activation and inactivation were voltage dependent [Boltzmann distributions with potential of half-maximal value ( V 1/2) = −24 mV and slope = −9 mV for activation; V 1/2 = −58 mV and slope = 13 mV for inactivation]. The time-dependent currents were resistant to 4-aminopyridine and to DIDS but blocked by nifedipine at high concentrations (IC50 = 2 μM) as well as by verapamil and diltiazem. They could be increased by BAY K-8644 or by isoproterenol. We conclude that the I to-like currents are due to monovalent cation flow through L-type Ca2+ channels, which in pig myocytes show low sensitivity to nifedipine.

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.

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