K+ currents responsible for repolarization in mouse ventricle and their modulation by FK-506 and rapamycin

2000 ◽  
Vol 278 (3) ◽  
pp. H886-H897 ◽  
Author(s):  
W. H. DuBell ◽  
W. J. Lederer ◽  
T. B. Rogers
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Regulatory Proteins ◽  
Channel Blockers ◽  
Patch Clamp Technique ◽  
Fk 506 ◽  
Transient Component ◽  
Whole Cell Patch Clamp ◽  
Recovery From Inactivation ◽  
K Currents

Modulation of mouse ventricular action potentials and K+ currents was examined using the whole cell patch-clamp technique. The composite mouse ventricular K+ current (consisted of an outward transient followed by a slowly decaying sustained component. Use of the K+ channel blockers tetraethylammonium and 4-aminopyridine and a transgenic mouse model revealed three pharmacologically and kinetically distinct currents: I to, which contributed to the transient component; I K, which contributed to the sustained component; and a slowly activating current ( I slow), which contributed to both components. The immunosuppressant FK-506 increased action potential duration at 90% repolarization by 66.7% by decreasing the sustained component (−48% at +60 mV) and prolonging recovery from inactivation (by 26% at 200 ms) of the transient component. These effects were isolated to I K and I to, respectively. Rapamycin had strikingly similar effects on these currents. Both FK-506 and rapamycin are known to target the immunophilin FKBP12. Thus we conclude that FKBP12 modulates specific mouse K+ channels, and thus the mouse ventricular action potential, by interacting directly with K+ channel proteins or with other associated regulatory proteins.

Adenosine-induced changes in atrial action potential: contribution of Ca and K currents

1990 ◽  
Vol 258 (4) ◽  
pp. H1070-H1078 ◽  
Author(s):  
S. Visentin ◽  
S. N. Wu ◽  
L. Belardinelli
Keyword(s):  
Action Potential ◽  
Potassium Current ◽  
Potential Contribution ◽  
Strongly Correlated ◽  
Patch Clamp Technique ◽  
Relative Contribution ◽  
Whole Cell Patch Clamp ◽  
Maximum Decrease ◽  
Induced Changes ◽  
K Currents

In this study, we examined the relative contribution of the increase in acetylcholine-regulated potassium current (IK ACh) and decrease in calcium current (ICa) to the adenosine (Ado)-induced shortening of action potential duration (APD). In isolated guinea pig atrial myocytes, membrane potentials and currents were measured by the whole cell patch-clamp technique. ICa and IK ACh were individualized by blocking the K currents with Cs+ and ICa with Cd2+. The effects of Ado on membrane potential and currents were concentration dependent. Ado (10 microM) shortened APD at 0 mV and at 90% of repolarization (APD0,90) to 7 +/- 1 and 26 +/- 6 ms from control values of 23 +/- 3 and 89 +/- 6 ms, respectively. Concomitant with the changes in APD, Ado decreased ICa from -9.2 +/- 1.3 to -6.8 +/- 10 microA/microF (26% decrease) but increased IK ACh from +3.5 +/- 0.5 to +7.8 +/- 0.8 microA/microF (123% increase). When rundown of ICa was taken into account, the maximum decrease in ICa caused by Ado was 12%. The effect of Ado on ICa and IK ACh was not altered by treatment of the cells with either Cs+ or Cd2+. The shortening of ADP0,90 strongly correlated with the increase in IK ACh but minimally with the decrease in ICa. A 22% reduction in ICa caused by lowering extracellular Ca2+ concentration ([Ca2+]o) from 3.6 to 1.8 mM was associated with an 11 and 14% shortening of APD0 and APD90, respectively. In the same myocytes an 18% decrease in ICa by 10 microM Ado reduced APD0 and APD90 by 58 and 61%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of repetitive depolarization on sodium current in chick myocytes

1991 ◽  
Vol 260 (6) ◽  
pp. H1810-H1818
Author(s):  
M. R. Gold ◽  
G. R. Strichartz
Keyword(s):  
Time Course ◽  
Sodium Current ◽  
Complete Recovery ◽  
Acute Effects ◽  
Na Current ◽  
Patch Clamp Technique ◽  
Membrane Hyperpolarization ◽  
Atrial Cells ◽  
Whole Cell Patch Clamp ◽  
Recovery From Inactivation

Acute effects of repetitive depolarization on the inward Na+ current (INa) of cultured embryonic chick atrial cells were studied using the whole cell patch-clamp technique. Stimulation rates of 1 Hz or greater produced a progressive decrement of peak INa. With depolarizations to 0 mV of 150-ms duration, applied at 2 Hz from a holding potential of -100 mV, the steady-state decrement was approximately 20%. The magnitude of this effect increased with stimulation frequency and with test potential depolarization and decreased with membrane hyperpolarization. Analysis of INa kinetics revealed that reactivation was sufficiently slow to preclude complete recovery from inactivation with interpulse intervals less than 1,000 ms. Moreover, reactivation accelerated markedly with membrane hyperpolarization, in parallel with the response to repetitive stimulation. The multiexponential time course of recovery of peak INa from repetitive depolarization was similar to that observed after single stimuli; however, there was a shift toward a greater proportion of current recovering with the slower of two time constants. It is concluded that incomplete recovery from inactivation is responsible for the decrement in INa observed with short interpulse intervals.

Effects of estrogen on action potential and membrane currents in guinea pig ventricular myocytes

1999 ◽  
Vol 277 (2) ◽  
pp. H826-H833 ◽  
Author(s):  
Seiko Tanabe ◽  
Toshio Hata ◽  
Masayasu Hiraoka
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Action Potentials ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Membrane Currents ◽  
Patch Clamp Technique ◽  
17Β Estradiol ◽  
Electrophysiological Effects ◽  
Ionic Basis

To explore a possible ionic basis for the prolonged Q-T interval in women compared with that in men, we investigated the electrophysiological effects of estrogen in isolated guinea pig ventricular myocytes. Action potentials and membrane currents were recorded using the whole cell configuration of the patch-clamp technique. Application of 17β-estradiol (10–30 μM) significantly prolonged the action potential duration (APD) at 20% (APD20) and 90% repolarization (APD90) at stimulation rates of 0.1–2.0 Hz. In the presence of 30 μM 17β-estradiol, APD20 and APD90 at 0.1 Hz were prolonged by 46.2 ± 17.1 and 63.4 ± 11.7% of the control ( n = 5), respectively. In the presence of 30 μM 17β-estradiol the peak inward Ca2+ current ( I CaL) was decreased to 80.1 ± 2.5% of the control ( n = 4) without a shift in its voltage dependence. Application of 30 μM 17β-estradiol decreased the rapidly activating component of the delayed outward K+ current ( I Kr) to 63.4 ± 8% and the slowly activating component ( I Ks) to 65.8 ± 8.7% with respect to the control; the inward rectifier K+ current was barely affected. The results suggest that 17β-estradiol prolonged APD mainly by inhibiting the I Kcomponents I Krand I Ks.

Ca2+ Currents in Central Insect Neurons: Electrophysiological and Pharmacological Properties

1997 ◽  
Vol 77 (1) ◽  
pp. 186-199 ◽  
Author(s):  
Dieter Wicher ◽  
Heinz Penzlin
Keyword(s):  
Periplaneta Americana ◽  
Low Voltage ◽  
Fast Time ◽  
Channel Blockers ◽  
Pharmacological Properties ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Blocking Effects ◽  
Dum Neurons ◽  
Maximal Peak

Wicher, Dieter, and Heinz Penzlin. Ca2+ currents in central insect neurons: electrophysiological and pharmacological properties. J. Neurophysiol. 77: 186–199, 1997. Ca2+ currents in dorsal unpaired median (DUM) neurons isolated from the fifth abdominal ganglion of the cockroach Periplaneta americana were investigated with the whole cell patch-clamp technique. On the basis of kinetic and pharmacological properties, two different Ca2+ currents were separated in these cells: mid/low-voltage-activated (M-LVA) currents and high-voltage-activated (HVA) currents. M-LVA currents had an activation threshold of −50 mV and reached maximal peak values at −10 mV. They were sensitive to depolarized holding potentials and decayed very rapidly. The decay was largely Ca2+ dependent. M-LVA currents were effectively blocked by Cd2+ median inhibiting concentration (IC50 = 9 μM), but they also had a remarkable sensitivity to Ni2+ (IC50 = 19 μM). M-LVA currents were insensitive to vertebrate LVA channel blockers like flunarizine and amiloride. The currents were, however, potently blocked by ω-conotoxin MVIIC (1 μM) and ω-agatoxin IVA (50 nM). The blocking effects of ω-toxins developed fast (time constant τ = 15 s) and were fully reversible after wash. HVA currents activated positive to −30 mV and showed maximal peak currents at +10 mV. They were resistant to depolarized holding potentials up to −50 mV and decayed in a less pronounced manner than M-LVA currents. HVA currents were potently blocked by Cd2+ (IC50 = 5 μM) but less affected by Ni2+ (IC50 = 40 μM). These currents were reduced by phenylalkylamines like verapamil (10 μM) and benzothiazepines like diltiazem (10 μM), but they were insensitive to dihydropyridines like nifedipine (10 μM) and BAY K 8644 (10 μM). Furthermore, HVA currents were sensitive to ω-conotoxin GVIA (1 μM). The toxin-induced reduction of currents appeared slowly (τ ∼ 120 s) and the recovery after wash was incomplete in most cases. The dihydropyridine insensitivity of the phenylalkylamine-sensitive HVA currents is a property the cockroach DUM cells share with other invertebrate neurons. Compared with Ca2+ currents in vertebrates, the DUM neuron currents differ considerably from the presently known types. Although there are some similarities concerning kinetics, the pharmacological profile of the cockroach Ca2+ currents especially is very different from profiles already described for vertebrate currents.

scholarly journals Contribution of L-type Ca2+current to electrical activity in sinoatrial nodal myocytes of rabbits

1999 ◽  
Vol 276 (3) ◽  
pp. H1064-H1077 ◽  
Author(s):  
E. Etienne Verheijck ◽  
Antoni C. G. van Ginneken ◽  
Ronald Wilders ◽  
Lennart N. Bouman
Keyword(s):  
Action Potential ◽  
Calcium Current ◽  
Sodium Current ◽  
Delayed Rectifier ◽  
Current Clamp ◽  
Patch Clamp Technique ◽  
Inward Current ◽  
Delayed Rectifier Current ◽  
Diastolic Depolarization ◽  
Recovery From Inactivation

The role of L-type calcium current ( I Ca,L) in impulse generation was studied in single sinoatrial nodal myocytes of the rabbit, with the use of the amphotericin-perforated patch-clamp technique. Nifedipine, at a concentration of 5 μM, was used to block I Ca,L. At this concentration, nifedipine selectively blocked I Ca,L for 81% without affecting the T-type calcium current ( I Ca,T), the fast sodium current, the delayed rectifier current ( I K), and the hyperpolarization-activated inward current. Furthermore, we did not observe the sustained inward current. The selective action of nifedipine on I Ca,L enabled us to determine the activation threshold of I Ca,L, which was around −60 mV. As nifedipine (5 μM) abolished spontaneous activity, we used a combined voltage- and current-clamp protocol to study the effects of I Ca,L blockade on repolarization and diastolic depolarization. This protocol mimics the action potential such that the repolarization and subsequent diastolic depolarization are studied in current-clamp conditions. Nifedipine significantly decreased action potential duration at 50% repolarization and reduced diastolic depolarization rate over the entire diastole. Evidence was found that recovery from inactivation of I Ca,L occurs during repolarization, which makes I Ca,L available already early in diastole. We conclude that I Ca,L contributes significantly to the net inward current during diastole and can modulate the entire diastolic depolarization.

I A in Kenyon Cells of the Mushroom Body of Honeybees Resembles Shaker Currents: Kinetics, Modulation by K+, and Simulation

1999 ◽  
Vol 81 (4) ◽  
pp. 1749-1759 ◽  
Author(s):  
Corinna Pelz ◽  
Johannes Jander ◽  
Hendrik Rosenboom ◽  
Martin Hammer ◽  
Randolf Menzel
Keyword(s):  
Action Potential ◽  
Time Constant ◽  
Mushroom Body ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Time Constants ◽  
Voltage Gated ◽  
Kenyon Cells ◽  
Recovery From Inactivation ◽  
A Current

I A in Kenyon cells of the mushroom body of honeybees resembles shaker currents: kinetics, modulation by K+, and simulation. Cultured Kenyon cells from the mushroom body of the honeybee, Apis mellifera, show a voltage-gated, fast transient K+ current that is sensitive to 4-aminopyridine, an A current. The kinetic properties of this A current and its modulation by extracellular K+ ions were investigated in vitro with the whole cell patch-clamp technique. The A current was isolated from other voltage-gated currents either pharmacologically or with suitable voltage-clamp protocols. Hodgkin- and Huxley-style mathematical equations were used for the description of this current and for the simulation of action potentials in a Kenyon cell model. Activation and inactivation of the A current are fast and voltage dependent with time constants of 0.4 ± 0.1 ms (means ± SE) at +45 mV and 3.0 ± 1.6 ms at +45 mV, respectively. The pronounced voltage dependence of the inactivation kinetics indicates that at least a part of this current of the honeybee Kenyon cells is a shaker-like current. Deactivation and recovery from inactivation also show voltage dependency. The time constant of deactivation has a value of 0.4 ± 0.1 ms at −75 mV. Recovery from inactivation needs a double-exponential function to be fitted adequately; the resulting time constants are 18 ± 3.1 ms for the fast and 745 ± 107 ms for the slow process at −75 mV. Half-maximal activation of the A current occurs at −0.7 ± 2.9 mV, and half-maximal inactivation occurs at −54.7 ± 2.4 mV. An increase in the extracellular K+concentration increases the conductance and accelerates the recovery from inactivation of the A current, affecting the slow but not the fast time constant. With respect to these modulations the current under investigation resembles some of the shaker-like currents. The data of the A current were incorporated into a reduced computational model of the voltage-gated currents of Kenyon cells. In addition, the model contained a delayed rectifier K+ current, a Na+current, and a leakage current. The model is able to generate an action potential on current injection. The model predicts that the A current causes repolarization of the action potential but not a delay in the initiation of the action potential. It further predicts that the activation of the delayed rectifier K+ current is too slow to contribute markedly to repolarization during a single action potential. Because of its fast activation, the A current reduces the amplitude of the net depolarizing current and thus reduces the peak amplitude and the duration of the action potential.

Changes in ventricular repolarization during acidosis and low-flow ischemia

1998 ◽  
Vol 275 (2) ◽  
pp. H551-H561 ◽  
Author(s):  
Hugh W. L. Bethell ◽  
Jamie I. Vandenberg ◽  
Gerry A. Smith ◽  
Andrew A. Grace
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Respiratory Acidosis ◽  
Control Flow ◽  
Low Flow ◽  
Channel Blockers ◽  
Monophasic Action Potentials ◽  
Ferret Heart ◽  
Action Potential Repolarization ◽  
Intact Heart

Myocardial ischemia, primarily a metabolic insult, is also defined by altered cardiac mechanical and electrical activity. We have investigated the metabolic contributions to the electrophysiological changes during low-flow ischemia (7.5% of the control flow) using31P NMR spectroscopy to monitor metabolic parameters, suction electrodes to study epicardial monophasic action potentials, and 86Rb as a tracer for K+-equivalent efflux during low-flow ischemia in the Langendorff-perfused ferret heart. Shortening of the action potential duration at 90% repolarization (APD90) was most marked between 1 and 5 min after induction of ischemia, at which time it shortened from 261 ± 4 to 213 ± 8 ms. The period of marked APD90 shortening was accompanied by a fivefold increase in the rate of86Rb efflux, both of which were inhibited by the ATP-sensitive K+(KATP)-channel blockers glibenclamide and 5-hydroxydecanoate (5-HD), as well as by a significant fall in intracellular pH (pHi) from 7.14 ± 0.02 to 6.83 ± 0.03 but no change in intracellular ATP concentration ([ATP]i). We therefore investigated whether a fall in pHi could be the metabolic change responsible for modulating cardiac KATP channel activity in the intact heart during ischemia. Both metabolic (30 mM lactate added to extracellular solution) and respiratory ([Formula: see text] increased to 15%) acidosis caused an initial lengthening of APD90 to 112 ± 1.5 and 113 ± 0.9%, respectively, followed by shortening during continued acidosis to 106 ± 1.2 and 106 ± 1.4%, respectively. The shortening of APD90 during continued acidosis was inhibited by glibenclamide, consistent with acidosis causing activation of KATP channels at normal [ATP]i. The similar responses to metabolic (induced by adding either l- or d-lactate) and respiratory acidosis suggest that lactate has no independent metabolic effect on action potential repolarization.

Regulation of whole cell currents by cytosolic cAMP, Ca2+, and Cl- in rat fetal distal lung epithelium

1995 ◽  
Vol 269 (1) ◽  
pp. C156-C162 ◽  
Author(s):  
T. Nakahari ◽  
Y. Marunaka
Keyword(s):  
Lung Epithelium ◽  
Cellular Mechanisms ◽  
Patch Clamp Technique ◽  
Pipette Solution ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Lung Epithelial ◽  
Distal Lung ◽  
Adrenergic Receptor Agonist ◽  
K Currents

The whole cell patch-clamp technique was used to study ionic conductances in fetal distal lung epithelial (FDLE) cells. In unstimulated FDLE cells, K+ conductances were detected in lowered intracellular Cl- concentration ([Cl-]i, < or = 50 mM). The whole cell currents of FDLE cells were increased by elevation of intracellular Ca2+ concentration ([Ca2+]i) or intracellular adenosine 3',5'-cyclic monophosphate (cAMP) concentration ([cAMP]i). The elevation of [Ca2+]i activated the K+ currents. The amiloride-blockable whole cell currents were activated by [cAMP]i of 1 mM with [Cl-]i of 20 mM and were more frequently detected in the pipette solution without ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) than with it (0.5 mM). When the [Cl-]i was fixed at 50 or 145 mM, however, the increase in these currents was not detected even with cAMP and without EGTA. The amiloride-blockable currents were detected in both the Na+ and K+ pipette solutions. Thus the increase in amiloride-blockable whole cell currents was due to the activation of nonselective cation channels. In FDLE cells treated with terbutaline, which is a beta 2-adrenergic receptor agonist, or forskolin, these currents were detected in the pipette solution containing 20 mM Cl- but were suppressed with time when the pipette solution contained 50 or 145 mM Cl-. It seems likely that maintenance of [Cl-]i at the lowered level is an important requirement for the FDLE cells to activate the amiloride-blockable whole cell currents. It is proposed that cellular mechanisms, such as cell shrinkage, exist to reduce the [Cl-]i in response to cAMP.

scholarly journals Propagation of Action Potentials From the Soma to Individual Dendrite of Cultured Rat Amacrine Cells Is Regulated by Local GABA Input

2002 ◽  
Vol 87 (6) ◽  
pp. 2858-2866 ◽  
Author(s):  
Yoshitake Yamada ◽  
Amane Koizumi ◽  
Eisuke Iwasaki ◽  
Shu-Ichi Watanabe ◽  
Akimichi Kaneko
Keyword(s):  
Patch Clamp ◽  
Action Potential ◽  
Lateral Inhibition ◽  
Action Potentials ◽  
Amacrine Cell ◽  
Amacrine Cells ◽  
Inner Plexiform Layer ◽  
Whole Cell ◽  
Cell Patch Clamp ◽  
Whole Cell Patch Clamp

Retinal amacrine cells are interneurons that make lateral and vertical connections in the inner plexiform layer of the retina. Amacrine cells do not possess a long axon, and this morphological feature is the origin of their naming. Their dendrites function as both presynaptic and postsynaptic sites. Half of all amacrine cells are GABAergic inhibitory neurons that mediate lateral inhibition, and their light-evoked response consists of graded voltage changes and regenerative action potentials. There is evidence that the amount of neurotransmitter release from presynaptic sites is increased by spike propagation into the dendrite. Thus understanding of how action potentials propagate in dendrites is important to elucidating the extent and strength of lateral inhibition. In the present study, we used the dual whole cell patch-clamp technique on the soma and the dendrite of cultured rat amacrine cells and directly demonstrated that the action potentials propagate into the dendrites. The action potential in the dendrite was TTX sensitive and was affected by the local membrane potential of the dendrite. Propagation of the action potential was suppressed by local application of GABA to the dendrite. Dual dendrite whole cell patch-clamp recordings showed that GABA suppresses the propagation of action potentials in one dendrite of an amacrine cell, while the action potentials propagate in the other dendrites. It is likely that the action potentials in the dendrites are susceptible to various external factors resulting in the nonuniform propagation of the action potential from the soma of an amacrine cell.

Interaction of Intravenous Anesthetics with Human Neuronal Potassium Currents in Relation to Clinical Concentrations 

1999 ◽  
Vol 91 (6) ◽  
pp. 1853-1853 ◽  
Author(s):  
Patrick Friederich ◽  
Bernd W. Urban
Keyword(s):  
Clinical Effects ◽  
Cellular Functions ◽  
Response Curves ◽  
Patch Clamp Technique ◽  
Maximal Inhibition ◽  
Intravenous Anesthetics ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Ic50 Values ◽  
K Currents

Background Neuronal voltage-dependent potassium (K) currents are crucial for various cellular functions, such as the integration of temporal information in the central nervous system. Data for the effects of intravenous anesthetics on human neuronal K currents are limited. It was the authors' aim to evaluate the concentration-related effects of three opioids (fentanyl, alfentanil, sufentanil) and seven nonopioids (thiopental, pentobarbital, methohexital, propofol, ketamine, midazolam, droperidol) used in clinical anesthesia on neuronal voltage-dependent K currents of human origin. Method K currents were measured in SH-SY5Y cells using the whole cell patch-clamp technique. Currents were elicited by step depolarization from a holding potential of -80 to -50 mV through +90 mV, and their steady state amplitudes were determined. Results All drugs inhibited the K currents in a concentration-dependent and reversible manner. Because time dependence of inhibition differed among the drugs, effects were measured after 54-64 ms of the test pulse. The IC50 values (concentration of half-maximal inhibition) for current suppression ranged from 7 microM for sufentanil to 2 mM for pentobarbital. Suppression of the K currents by the opioids occurred at 10-fold lower IC50 values (concentration of half-maximal inhibition) than that by the barbiturates. As estimated from the concentration-response curves, K-current suppression at clinical concentrations would be less than 0.1% for the opioids and approximately 3% for the other drugs. Conclusions Effects of intravenous anesthetics on voltage-dependent K currents occur at clinical concentrations. The IC50 values for current inhibition of the nonopioid anesthetics correlated with these concentrations (r = 0.95). The results suggest that anesthetic drug action on voltage-dependent K currents may contribute to clinical effects or side effects of intravenous anesthetics.

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