Slow delayed rectifier current and repolarization in canine cardiac Purkinje cells

2001 ◽  
Vol 280 (3) ◽  
pp. H1075-H1080 ◽  
Author(s):  
Wei Han ◽  
Zhiguo Wang ◽  
Stanley Nattel
Keyword(s):  
Purkinje Cells ◽  
Voltage Dependence ◽  
Delayed Rectifier ◽  
Adrenergic Stimulation ◽  
Early Afterdepolarizations ◽  
Voltage Range ◽  
Delayed Rectifier Current ◽  
Whole Cell Patch Clamp ◽  
Cardiac Purkinje Cells

Although cardiac Purkinje cells (PCs) are believed to be the source of early afterdepolarizations generating ventricular tachyarrhythmias in long Q-T syndromes (LQTS), the ionic determinants of PC repolarization are incompletely known. To evaluate the role of the slow delayed rectifier current ( I Ks) in PC repolarization, we studied PCs from canine ventricular false tendons with whole cell patch clamp (37°C). Typical I Ks voltage- and time-dependent properties were noted. Isoproterenol enhanced I Ks in a concentration-dependent fashion (EC50 ∼ 30 nM), negatively shifted I Ks activation voltage dependence, and accelerated I Ks activation. Block of I Ks with 293B did not alter PC action potential duration (APD) in the absence of isoproterenol; however, in the presence of isoproterenol, 293B significantly prolonged APD. We conclude that, without β-adrenergic stimulation, I Ks contributes little to PC repolarization; however, β-adrenergic stimulation increases the contribution of I Ks by increasing current amplitude, accelerating I Ks activation, and shifting activation voltage toward the PC plateau voltage range. I Ks may therefore provide an important “braking” function to limit PC APD prolongation in the presence of β-adrenergic stimulation.

Time-dependent changes in kinetics of Na+ current in single canine cardiac Purkinje cells

1992 ◽  
Vol 262 (4) ◽  
pp. H1197-H1207 ◽  
Author(s):  
D. A. Hanck ◽  
M. F. Sheets
Keyword(s):  
Purkinje Cells ◽  
Time Constant ◽  
Decay Time ◽  
Voltage Dependence ◽  
Na Channel ◽  
Time Constants ◽  
Voltage Range ◽  
Time To Peak ◽  
Cardiac Purkinje Cells ◽  
Voltage Dependent

The spontaneous hyperpolarizing shift in Na+ channel kinetics that occurs during a series of voltage-clamp recordings was characterized in single canine cardiac Purkinje cells at 10-13.5 degrees C. The change in the half-point of voltage-dependent availability, in the half-point of peak conductance, in the voltage dependence of deactivation and time to peak Na+ channel current (INa), and in the time constants of INa decay in response to step depolarizations were examined. The half points of availability and conductance shifted similarly, -0.41 +/- 0.13 and -0.47 +/- 0.19 mV/min, respectively (n = 14). These were directly correlated (slope 1.14 +/- 0.06, R2 = 0.81) with conductance shifting on average only -0.05 mV/min faster than availability. The deactivation time constant-voltage relationship shifted similarly to availability and conductance. Tail current decay time constants predicted the voltage dependence of the open to closed transition to be 0.9e-. Time to peak INa in response to step depolarizations changed e-fold for 25 mV but plateaued at positive potentials (531 microseconds, n = 22). INa decay was multiexponential between -40 and 80 mV. Decay time constants changed little as a function of voltage at positive potentials. The contribution of the second time constant to decay amplitude was 15-20% over the entire voltage range. Time to peak INa shifted in a curvilinear fashion, changing less late in an experiment. We conclude that the channel-voltage sensor responds to a changing fraction of the applied voltage during an experiment, producing similar rates of shift of voltage-dependent availability, conductance, and deactivation time constants.

scholarly journals Quantitative comparison of cardiac ventricular myocyte electrophysiology and response to drugs in human and nonhuman species

2012 ◽  
Vol 302 (5) ◽  
pp. H1023-H1030 ◽  
Author(s):  
Thomas O'Hara ◽  
Yoram Rudy
Keyword(s):  
Guinea Pig ◽  
Drug Response ◽  
Cellular Level ◽  
Quantitative Comparison ◽  
Rate Dependence ◽  
Delayed Rectifier ◽  
Adrenergic Stimulation ◽  
Early Afterdepolarizations ◽  
Rate Dependent ◽  
Delayed Rectifier Current

Explanations for arrhythmia mechanisms at the cellular level are usually based on experiments in nonhuman myocytes. However, subtle electrophysiological differences between species may lead to different rhythmic or arrhythmic cellular behaviors and drug response given the nonlinear and highly interactive cellular system. Using detailed and quantitatively accurate mathematical models for human, dog, and guinea pig ventricular action potentials (APs), we simulated and compared cell electrophysiology mechanisms and response to drugs. Under basal conditions (absence of β-adrenergic stimulation), Na+/K+-ATPase changes secondary to Na+ accumulation determined AP rate dependence for human and dog but not for guinea pig where slow delayed rectifier current ( IKs) was the major rate-dependent current. AP prolongation with reduction of rapid delayed rectifier current ( IKr) and IKs (due to mutations or drugs) showed strong species dependence in simulations, as in experiments. For humans, AP prolongation was 80% following IKr block. It was 30% for dog and 20% for guinea pig. Under basal conditions, IKs block was of no consequence for human and dog, but for guinea pig, AP prolongation after IKs block was severe. However, with β-adrenergic stimulation, IKs played an important role in all species, particularly in AP shortening at fast rate. Quantitative comparison of AP repolarization, rate-dependence mechanisms, and drug response in human, dog, and guinea pig revealed major species differences (e.g., susceptibility to arrhythmogenic early afterdepolarizations). Extrapolation from animal to human electrophysiology and drug response requires great caution.

scholarly journals Mice With Monoallelic GNAO1 Loss Exhibit Reduced Inhibitory Synaptic Input To Cerebellar Purkinje Cells

2021 ◽  
Author(s):  
Huijie Feng ◽  
Yukun Yuan ◽  
Michael R Williams ◽  
Alex Roy ◽  
Jeffrey Leipprandt ◽  
...  
Keyword(s):  
Synaptic Transmission ◽  
Purkinje Cells ◽  
Gabab Receptor ◽  
Molecular Layer ◽  
Loss Of Function ◽  
Whole Cell Patch Clamp ◽  
The Difference ◽  
G Protein Alpha Subunit ◽  
Cerebellar Purkinje Cells

GNAO1 encodes Gαo, a heterotrimeric G protein alpha subunit in the Gi/o family. In this report, we used a Gnao1 mouse model G203R previously described as a gain-of-function Gnao1 mutant with movement abnormalities and enhanced seizure susceptibility. Here, we report an unexpected second mutation resulting in a loss-of-function Gαo protein and describe alterations in central synaptic transmission. Whole cell patch clamp recordings from Purkinje cells (PCs) in acute cerebellar slices from Gnao1 mutant mice showed significantly lower frequencies of spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs) compared to WT mice. There was no significant change in sEPSCs or mEPSCs. Whereas mIPSC frequency was reduced, mIPSC amplitudes were not affected, suggesting a presynaptic mechanism of action. A modest decrease in the number of molecular layer interneurons was insufficient to explain the magnitude of IPSC suppression. Paradoxically, Gi/o inhibitors (pertussis toxin), enhanced the mutant-suppressed mIPSC frequency and eliminated the difference between WT and Gnao1 mice. While GABAB receptor regulates mIPSCs, neither agonists nor antagonists of this receptor altered function in the mutant mouse PCs. This study is the first electrophysiological investigation of the role of Gi/o protein in cerebellar synaptic transmission using an animal model with a loss-of-function Gi/o protein.

Characterization and functional consequences of delayed rectifier current transient in ventricular repolarization

2000 ◽  
Vol 278 (3) ◽  
pp. H806-H817 ◽  
Author(s):  
Gary A. Gintant
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Inward Rectifier ◽  
Ventricular Repolarization ◽  
Delayed Rectifier ◽  
Voltage Range ◽  
Delayed Rectifier Current ◽  
Recovery From Inactivation ◽  
Voltage Dependent

Although inactivation of the rapidly activating delayed rectifier current ( I Kr) limits outward current on depolarization, the role of I Kr (and recovery from inactivation) during repolarization is uncertain. To characterize I Krduring ventricular repolarization (and compare with the inward rectifier current, I K1), voltage-clamp waveforms simulating the action potential were applied to canine ventricular, atrial, and Purkinje myocytes. In ventricular myocytes, I Kr was minimal at plateau potentials but transiently increased during repolarizing ramps. The I Kr transient was unaffected by repolarization rate and maximal after 150-ms depolarizations (+25 mV). Action potential clamps revealed the I Kr transient terminating the plateau. Although peak I Kr transient density was relatively uniform among myocytes, potentials characterizing the peak transients were widely dispersed. In contrast, peak inward rectifier current ( I K1) density during repolarization was dispersed, whereas potentials characterizing I K1 defined a narrower (more negative) voltage range. In summary, rapidly activating I Kr provides a delayed voltage-dependent (and functionally time-independent) outward transient during ventricular repolarization, consistent with rapid recovery from inactivation. The heterogeneous voltage dependence of I Kr provides a novel means for modulating the contribution of this current during repolarization.

Delayed rectification in single cells isolated from guinea pig sinoatrial node

1992 ◽  
Vol 262 (3) ◽  
pp. H921-H925 ◽  
Author(s):  
J. M. Anumonwo ◽  
L. C. Freeman ◽  
W. M. Kwok ◽  
R. S. Kass
Keyword(s):  
Guinea Pig ◽  
Sinoatrial Node ◽  
Single Cells ◽  
Equilibrium Potential ◽  
Delayed Rectifier ◽  
Experimental Conditions ◽  
Whole Cell ◽  
Voltage Range ◽  
Whole Cell Patch Clamp ◽  
Delayed Rectification

We have studied delayed rectifier K+ currents (IK) in cells isolated from the sinoatrial node (SAN) region of the guinea pig. Using whole cell patch-clamp procedures, we measured the voltage dependence of IK activation and IK kinetics and the IK equilibrium potential in 4.8 mM extracellular K concentration solutions. Experiments were designed to contrast properties of guinea pig SAN IK with those of IK recorded from SAN cells of the rabbit. We find that guinea pig SAN IK differs from IK recorded from single rabbit SAN cells in its activation threshold, and in the absence of inactivation of whole cell currents recorded over a wide voltage range. These results, along with the relative insensitivity of guinea pig SAN IK to E-4031 and lanthanum, suggest that under our experimental conditions, a strongly rectifying IK component (IK,r) is not the major component of delayed rectification in the guinea pig SAN, as it appears to be in SAN cells of the rabbit.

Properties of voltage-gated Ca2+ channels in rabbit ventricular myocytes expressing Ca2+ channel α1E cDNA

2001 ◽  
Vol 280 (1) ◽  
pp. C175-C182 ◽  
Author(s):  
Michihiro Tateyama ◽  
Shuqin Zong ◽  
Tsutomu Tanabe ◽  
Rikuo Ochi
Keyword(s):  
Cardiac Myocytes ◽  
Fluorescent Protein ◽  
Ventricular Myocytes ◽  
Foreign Gene ◽  
Adrenergic Stimulation ◽  
Patch Clamp Technique ◽  
Voltage Range ◽  
Whole Cell Patch Clamp ◽  
Green Fluorescent ◽  
Ca2 Channels

Using the whole-cell patch-clamp technique, we have studied the properties of α1ECa2+ channel transfected in cardiac myocytes. We have also investigated the effect of foreign gene expression on the intrinsic L-type current ( I Ca,L). Expression of green fluorescent protein significantly decreased the I Ca,L. By contrast, expression of α1E with β2b and α2/δ significantly increased the total Ca2+ current, and in these cells a Ca2+ antagonist, PN-200-110 (PN), only partially blocked the current. The remaining PN-resistant current was abolished by the application of a low concentration of Ni2+and was little affected by changing the charge carrier from Ca2+ to Ba2+ or by β-adrenergic stimulation. On the basis of its voltage range for activation, this channel was classified as a high-voltage activated channel. Thus the expression of α1E did not generate T-like current in cardiac myocytes. On the other hand, expression of α1E decreased I Ca,L and slowed the I Ca,L inactivation. This inactivation slowing was attenuated by the β2b coexpression, suggesting that the α1E may slow the inactivation of I Ca,L by scrambling with α1C for intrinsic auxiliary β.

Direct block of cloned hKv1.5 channel by cytochalasins, actin-disrupting agents

2005 ◽  
Vol 289 (2) ◽  
pp. C425-C436 ◽  
Author(s):  
Bok Hee Choi ◽  
Jung-Ah Park ◽  
Kyung-Ryoul Kim ◽  
Ggot-Im Lee ◽  
Yong-Tae Lee ◽  
...  
Keyword(s):  
Actin Filament ◽  
Cytochalasin B ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Independent Manner ◽  
Concentration Dependent Manner ◽  
Voltage Range ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent

The action of cytochalasins, actin-disrupting agents on human Kv1.5 channel (hKv1.5) stably expressed in Ltk− cells was investigated using the whole cell patch-clamp technique. Cytochalasin B inhibited hKv1.5 currents rapidly and reversibly at +60 mV in a concentration-dependent manner with an IC50 of 4.2 μM. Cytochalasin A, which has a structure very similar to cytochalasin B, inhibited hKv1.5 (IC50 of 1.4 μM at +60 mV). Pretreatment with other actin filament disruptors cytochalasin D and cytochalasin J, and an actin filament stabilizing agent phalloidin had no effect on the cytochalasin B-induced inhibition of hKv1.5 currents. Cytochalasin B accelerated the decay rate of inactivation for the hKv1.5 currents. Cytochalasin B-induced inhibition of the hKv1.5 channels was voltage dependent with a steep increase over the voltage range of the channel's opening. However, the inhibition exhibited voltage independence over the voltage range in which channels are fully activated. Cytochalasin B produced no significant effect on the steady-state activation or inactivation curves. The rate constants for association and dissociation of cytochalasin B were 3.7 μM/s and 7.5 s−1, respectively. Cytochalasin B produced a use-dependent inhibition of hKv1.5 current that was consistent with the slow recovery from inactivation in the presence of the drug. Cytochalasin B (10 μM) also inhibited an ultrarapid delayed rectifier K+ current ( IK,ur) in human atrial myocytes. These results indicate that cytochalasin B primarily blocks activated hKv1.5 channels and endogenous IK,ur in a cytoskeleton-independent manner as an open-channel blocker.

Properties of potassium currents in Purkinje cells of failing human hearts

2002 ◽  
Vol 283 (6) ◽  
pp. H2495-H2503 ◽  
Author(s):  
Wei Han ◽  
Liming Zhang ◽  
Gernot Schram ◽  
Stanley Nattel
Keyword(s):  
Purkinje Cells ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Ionic Currents ◽  
Time Dependent ◽  
Transient Outward Current ◽  
Whole Cell Patch Clamp ◽  
Cardiac Purkinje Fibers ◽  
Cardiac Purkinje Cells ◽  
Hyperpolarization Activated Current

Cardiac Purkinje fibers play an important role in cardiac arrhythmias, but no information is available about ionic currents in human cardiac Purkinje cells (PCs). PCs and midmyocardial ventricular myocytes (VMs) were isolated from explanted human hearts. K+ currents were evaluated at 37°C with whole cell patch clamp. PCs had clear inward rectifier K+current ( I K1), with a density not significantly different from VMs between −110 and −20 mV. A Cs+-sensitive, time-dependent hyperpolarization-activated current was measurable negative to −60 mV. Transient outward current ( I to) density was smaller, but end pulse sustained current ( I sus) was larger, in PCs vs. VMs. I to recovery was substantially slower in PCs, leading to strong frequency dependence. Unlike VM I to, which was unaffected by 10 mM tetraethylammonium, Purkinje I to was strongly inhibited by tetraethylammonium, and Purkinje I to was 10-fold more sensitive to 4-aminopyridine than VM. PC I sus was also reduced strongly by 10 mM tetraethylammonium. In conclusion, human PCs demonstrate a prominent I K1, a time-dependent hyperpolarization-activated current, and an I towith pharmacological sensitivity and recovery kinetics different from those in the atrium or ventricle and compatible with a different molecular basis.

scholarly journals Kinetic analysis of single sodium channels from canine cardiac Purkinje cells.

1990 ◽  
Vol 95 (3) ◽  
pp. 411-437 ◽  
Author(s):  
B E Scanley ◽  
D A Hanck ◽  
T Chay ◽  
H A Fozzard
Keyword(s):  
Maximum Likelihood ◽  
Kinetic Parameters ◽  
Purkinje Cells ◽  
Voltage Dependence ◽  
Neuroblastoma Cells ◽  
Likelihood Method ◽  
Pituitary Cells ◽  
Cardiac Purkinje Cells ◽  
Channel Open Time ◽  
Near Threshold

Single sodium channel events were recorded from cell-attached patches on single canine cardiac Purkinje cells at 10-13 degrees C. Data from four patches containing two to four channels and one patch with one channel were selected for quantitative analysis. The channels showed prominent reopening behavior at voltages near threshold, and the number of reopenings declined steeply with depolarization. Mean channel open time was a biphasic function of voltage with the maximum value (1-1.5 ms) occurring between -50 and -40 mV and lower values at more and at less hyperpolarized levels. Inactivation without opening was also prominent near threshold, and this occurrence also declined with depolarization. The waiting time distributions and the probability of being open showed voltage and time dependence as expected from whole-cell current studies. The results were analyzed in terms of a five-state Markovian kinetic model using both histogram analysis and a maximum likelihood method to estimate kinetic parameters. The kinetic parameters of the model fits were similar to those of GH3 pituitary cells (Horn, R., and C. A. Vandenberg. 1984. Journal of General Physiology. 84:505-534) and N1E115 neuroblastoma cells (Aldrich, R. W., and C. F. Stevens. Journal of Neuroscience. 7:418-431). Both histogram and maximum likelihood analysis implied that much of the voltage dependence of cardiac Na current is in its activation behavior, with inactivation showing modest voltage dependence.

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