scholarly journals A time-dependent and voltage-sensitive K+ current in single cells from frog atrium.

1986 ◽  
Vol 88 (6) ◽  
pp. 739-755 ◽  
Author(s):  
M A Simmons ◽  
T Creazzo ◽  
H C Hartzell
Keyword(s):  
Single Cells ◽  
Quantitative Description ◽  
Reversal Potential ◽  
Outward Current ◽  
Time Dependent ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
K Current ◽  
And Shifts ◽  
Frog Atrium

A quantitative description of the time-dependent and voltage-sensitive outward currents in heart has been hampered by the complications inherent to the multicellular preparations previously used. We have used the whole-cell patch-clamp technique to record the delayed outward K+ current, IK, in single cells dissociated from frog atrium. Na+ currents were blocked with tetrodotoxin and Ca2+ currents with Mn2+ or Cd2+. After depolarizations from -50 mV to potentials positive to -30 mV, a time-dependent outward current was observed. This current has been characterized according to its steady state activation, kinetics, and ion transfer function. The current is well described as a single Hodgkin-Huxley conductance. The deactivation of the current is a single exponential. Activation of the current is sigmoid and is fitted well by raising the activation variable to the second power. The reversal potential of IK is near EK and shifts by 57 mV/10-fold change in [K+]o. This suggests that the current is carried selectively by K ions. The threshold for activation is near -30 mV. IK is maximally activated positive to +20 mV and shows no inactivation. The fully activated current-voltage relationship is linear between -110 and +50 mV. Neither Ba2+ (250 microM) nor Cd2+ (100 microM) affects IK.

Permeability of time-dependent K+ channel in guinea pig ventricular myocytes to Cs+, Na+, NH4+, and Rb+

1990 ◽  
Vol 259 (5) ◽  
pp. H1448-H1454 ◽  
Author(s):  
R. W. Hadley ◽  
J. R. Hume
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Outward Current ◽  
Time Dependent ◽  
K Channel ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Outward Currents

Currents through time-dependent K+ channels (also referred to as IK or the delayed rectifier) were studied with the whole cell patch-clamp technique in isolated guinea pig ventricular myocytes. IK measurements were restricted to the examination of deactivation tail currents. Substitution of various monovalent cations for external K+ produced shifts of the reversal potential of IK. These shifts were used to calculate permeability ratios relative to K+. The permeability sequence for the IK channels was K+ = Rb+ greater than NH4+ = Cs+ greater than Na+. Time-dependent outward currents were also examined when the myocytes were dialyzed with Cs+ instead of K+. A sizeable time-dependent outward current, quite similar to that seen with K+ dialysis, was demonstrated. This current was primarily carried by intracellular Cs+, as the reversal potential of the current shifted 46 mV per 10-fold change of external Cs+ concentration. The significance of Cs+ permeation through IK channels is discussed with respect to the common use of Cs+ in isolating other currents.

Ca2+-activated Cl− current in cultured myenteric neurons from murine proximal colon

2003 ◽  
Vol 284 (4) ◽  
pp. C839-C847 ◽  
Author(s):  
Sok Han Kang ◽  
Pieter Vanden Berghe ◽  
Terence K. Smith
Keyword(s):  
Membrane Potential ◽  
Channel Blocker ◽  
Reversal Potential ◽  
Outward Current ◽  
Proximal Colon ◽  
Time Dependent ◽  
Equilibrium Potential ◽  
Resting Membrane Potential ◽  
Myenteric Neurons ◽  
Whole Cell Patch Clamp

Whole cell patch-clamp recordings were made from cultured myenteric neurons taken from murine proximal colon. The micropipette contained Cs+ to remove K+ currents. Depolarization elicited a slowly activating time-dependent outward current ( I tdo), whereas repolarization was followed by a slowly deactivating tail current ( I tail). I tdo and I tail were present in ∼70% of neurons. We identified these currents as Cl− currents ( I Cl), because changing the transmembrane Cl− gradient altered the measured reversal potential ( E rev) of both I tdo and I tail with that for I tailshifted close to the calculated Cl− equilibrium potential ( E Cl). I Cl are Ca2+-activated Cl− current [ I Cl(Ca)] because they were Ca2+dependent. E Cl, which was measured from the E rev of I Cl(Ca) using a gramicidin perforated patch, was −33 mV. This value is more positive than the resting membrane potential (−56.3 ± 2.7 mV), suggesting myenteric neurons accumulate intracellular Cl−. ω-Conotoxin GIVA [0.3 μM; N-type Ca2+ channel blocker] and niflumic acid [10 μM; known I Cl(Ca) blocker], decreased the I Cl(Ca). In conclusion, these neurons have I Cl(Ca) that are activated by Ca2+entry through N-type Ca2+ channels. These currents likely regulate postspike frequency adaptation.

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.

ATP-sensitive K+ channels mediate vasodilation produced by lemakalim in rabbit pulmonary artery

1993 ◽  
Vol 264 (6) ◽  
pp. H1907-H1915 ◽  
Author(s):  
L. H. Clapp ◽  
R. Davey ◽  
A. M. Gurney
Keyword(s):  
Pulmonary Artery ◽  
Single Cells ◽  
Outward Current ◽  
Atp Depletion ◽  
Clear Correlation ◽  
Patch Clamp Technique ◽  
Membrane Hyperpolarization ◽  
Rabbit Pulmonary Artery ◽  
K Channels ◽  
K Current

Tension recording and the patch-clamp technique were used to determine the mechanism underlying vasodilation produced by lemakalim in the rabbit pulmonary artery. Lemakalim produced relaxation of precontracted muscle strips that was inhibited by glibenclamide and tetrapentylammonium ions but not by 2 mM tetraethylammonium (TEA) ions. In single cells dialyzed with 1 mM ATP, lemakalim (10 microM) hyperpolarized cells by approximately 13 mV and activated a time-independent K+ current, averaging only 6.5 pA at -50 mV. Glibenclamide reversed both of these membrane effects of lemakalim but not the lemakalim-induced block of an outward current seen above -20 mV. ATP depletion hyperpolarized cells and selectively unmasked a background K+ current, which was sensitive to glibenclamide but not to TEA, with properties similar to the current activated by lemakalim during membrane hyperpolarization. Furthermore, when intracellular ATP concentrations were varied, a clear correlation was revealed between ATP levels and the magnitude of the depolarization or hyperpolarization seen with either glibenclamide or lemakalim, respectively. These results provide direct evidence that the background current is carried by ATP-sensitive K+ channels rather than by large-conductance Ca(2+)-activated K+ channels and that it underlies the hyperpolarization and relaxation to lemakalim.

scholarly journals The mammalian Na+/H+ antiporters NHE-1, NHE-2, and NHE-3 are electroneutral and voltage independent, but can couple to an H+ conductance.

1995 ◽  
Vol 106 (1) ◽  
pp. 85-111 ◽  
Author(s):  
N Demaurex ◽  
J Orlowski ◽  
G Brisseau ◽  
M Woodside ◽  
S Grinstein
Keyword(s):  
Cho Cells ◽  
Time Course ◽  
Chinese Hamster ◽  
Reversal Potential ◽  
Outward Current ◽  
Rt Pcr ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Transmembrane Currents ◽  
Cytosolic Acidification

Na+/H+ exchange in vertebrates is thought to be electroneutral and insensitive to the membrane voltage. This basic concept has been challenged by recent reports of antiport-associated currents in the turtle colon epithelium (Post and Dawson, 1992, 1994). To determine the electrogenicity of mammalian antiporters, we used the whole-cell patch clamp technique combined with microfluorimetric measurements of intracellular pH (pHi). In murine macrophages, which were found by RT-PCR to express the NHE-1 isoform of the antiporter, reverse (intracellular Na(+)-driven) Na+/H+ exchange caused a cytosolic acidification and activated an outward current, whereas forward (extracellular Na(+)-driven) exchange produced a cytosolic alkalinization and reduced a basal outward current. The currents mirrored the changes in pHi, were strictly dependent on the presence of a Na+ gradient and were reversibly blocked by amiloride. However, the currents were seemingly not carried by the Na+/H+ exchanger itself, but were instead due to a shift in the voltage dependence of a preexisting H+ conductance. This was supported by measurements of the reversal potential (Erev) of tail currents, which identified H+ (equivalents) as the charge carrier. During Na+/H+ exchange, Erev changed along with the measured changes in pHi (by 60-69 mV/pH). Moreover, the current and Na+/H+ exchange could be dissociated. Zn2+, which inhibits the H+ conductance, reversibly blocked the currents without altering Na+/H+ exchange. In Chinese hamster ovary (CHO) cells, which lack the H+ conductance, Na+/H+ exchange produced pHi changes that were not accompanied by transmembrane currents. Similar results were obtained in CHO cells transfected with either the NHE-1, NHE-2, or NHE-3 isoforms of the antiporter, indicating that exchange through these isoforms is electroneutral. In all the isoforms tested, the amplitude and time-course of the antiport-induced pHi changes were independent of the holding voltage. We conclude that mammalian NHE-1, NHE-2, and NHE-3 are electroneutral and voltage independent. In cells endowed with a pH-sensitive H+ conductance, such as macrophages, activation of Na(+)-H+ exchange can modulate a transmembrane H+ current. The currents reported in turtle colon might be due to a similar "cross-talk" between the antiporter and a H+ conductance.

Choline chloride activates time-dependent and time-independent K+ currents in dog atrial myocytes

1994 ◽  
Vol 266 (1) ◽  
pp. C42-C51 ◽  
Author(s):  
B. Fermini ◽  
S. Nattel
Keyword(s):  
Choline Chloride ◽  
Outward Current ◽  
Time Dependent ◽  
Equilibrium Potential ◽  
Delayed Rectifier ◽  
Atrial Myocytes ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
K Current ◽  
K Currents

Using the whole cell configuration of the patch-clamp technique, we studied the effect of isotonic replacement of bath sodium chloride (NaCl) by choline chloride (ChCl) in dog atrial myocytes. Our results show that ChCl triggered 1) activation of a time-independent background current, characterized by a shift of the holding current in the outward direction at potentials positive to the K+ equilibrium potential (EK), and 2) activation of a time- and voltage-dependent outward current, following depolarizing voltage steps positive to EK. Because the choline-induced current obtained by depolarizing steps exhibited properties similar to the delayed rectifier K+ current (IK), we named it IKCh. The amplitude of IKCh was determined by extracellular ChCl concentration, and this current was generally undetectable in the absence of ChCl. IKCh was not activated by acetylcholine (0.001-1.0 mM) or carbachol (10 microM) and could not be recorded in the absence of ChCl or when external NaCl was replaced by sucrose or tetramethylammonium chloride. IKCh was inhibited by atropine (0.01-1.0 microM) but not by the M1 antagonist pirenzepine (up to 10 microM). This current was carried mainly by K+ and was inhibited by CsCl (120 mM, in the pipette) or barium (1 mM, in the bath). We conclude that in dog atrial myocytes, ChCl activates a background conductance comparable to ACh-dependent K+ current, together with a time-dependent K+ current showing properties similar to IK.

scholarly journals Alteration of the transmembrane K+ gradient during development of delayed rectifier in isolated rat pulmonary arterial cells.

1994 ◽  
Vol 104 (2) ◽  
pp. 241-264 ◽  
Author(s):  
S V Smirnov ◽  
P I Aaronson
Keyword(s):  
Reversal Potential ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Tail Current ◽  
Whole Cell Patch Clamp ◽  
K Current ◽  
Pulmonary Arterial ◽  
External Face ◽  
Kinetics Of ◽  
Isolated Rat

The properties of the tail current associated with the delayed rectifier K+ current (IK) in isolated rat pulmonary artery smooth muscle cells were examined using the whole cell patch clamp technique. The tail currents observed upon repolarization to -60 mV after brief (e.g., 20 ms) or small (i.e. to potentials negative of 0 mV) depolarizations were outwardly directed, as expected given the calculated K+ reversal potential of -83 mV. The tail currents seen upon repolarization after longer (e.g., 500 ms) and larger (e.g., to +60 mV) depolarizations tended to be inwardly directed. Depolarizations of intermediate strength and/or duration were followed by biphasic tail currents, which were inwardly directed immediately upon repolarization, but changed direction and became outwardly directed before deactivation was complete. When cells were depolarized to +60 mV for 500 ms both IK and the subsequent inward tail current at -60 mV were similarly blocked by phencyclidine. Both IK and the inward tail current were also blocked by 4-aminopyridine. Application of progressively more depolarized 30 s preconditioning potentials inactivated IK, and reduced the inward tail current amplitude with a similar potential dependency. These results indicated that the inward tail current was mediated by IK. The reversal potential of the tail current became progressively more positive with longer depolarizations to +60 mV, shifting from -76.1 +/- 2.2 mV (n = 10) after a 20-ms step to -57.7 +/- 3.5 mV (n = 9) after a 500-ms step. Similar effects occurred when extracellular K+ and Na+ were replaced by choline. When extracellular K+ was raised to 50 mM, the tail current was always inwardly directed at -60 mV, but showed little change in amplitude as the duration of depolarization was increased. These observations are best explained if the dependencies of tail current direction and kinetics upon the duration of the preceding depolarization result from an accumulation of K+ at the external face of the membrane, possibly in membrane invaginations. A mathematical model which simulates the reversal potential shift and the biphasic kinetics of the tail current on this basis is presented.

Participation of fast-activating, voltage-dependent K currents in electrical slow waves of colonic circular muscle

1992 ◽  
Vol 263 (1) ◽  
pp. C226-C236 ◽  
Author(s):  
K. D. Thornbury ◽  
S. M. Ward ◽  
K. M. Sanders
Keyword(s):  
Smooth Muscles ◽  
Circular Muscle ◽  
Outward Current ◽  
Slow Waves ◽  
Plateau Phase ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
K Current ◽  
K Currents

The plateau phase of electrical slow waves in phasic gastrointestinal muscles is critical for excitation-contraction coupling. The plateau appears to depend upon a balance between inward Ca2+ current and outward K+ currents that is sustained for several seconds. Voltage-dependent, non-Ca(2+)-dependent K currents were studied in canine colonic circular muscle cells using the whole cell patch-clamp technique. At room temperature, depolarization activated a slow outward current that showed little inactivation during 500 ms. Increasing the temperature to 37 degrees C significantly increased the rate of activation of voltage-dependent outward current. The onset of the outward current overlapped the transient inward Ca2+ current, suggesting that this K current may act as a brake on the upstroke depolarization of electrical slow waves in intact muscles. Voltage-dependent outward current was sustained for the duration of test pulses. This current balanced the sustained inward current that was also activated at physiological test potentials. The outward current evoked by test pulses positive to -20 mV inactivated by at least 50% within 500 ms. Half inactivation occurred at -36 mV. Voltage-dependent K current was reduced by 4-aminopyridine (4-AP; 1-5 mM), but difference currents obtained by subtracting currents elicited from holding potentials of -45 mV from currents obtained from holding potentials of -100 mV were not affected by 4-AP (1 mM). Studies were also performed on intact muscles to test the effects of 4-AP on electrical slow waves. 4-AP increased the amplitude and rate of rise of the upstroke potential and increased the amplitude and prolonged the plateau phase of slow waves. These data suggest that a rapidly activating, inactivating, voltage-dependent K current participates in electrical slow waves of colonic circular smooth muscles.

scholarly journals The pacemaker current in cardiac Purkinje myocytes.

1995 ◽  
Vol 106 (3) ◽  
pp. 559-578 ◽  
Author(s):  
M Vassalle ◽  
H Yu ◽  
I S Cohen
Keyword(s):  
Reversal Potential ◽  
Time Dependent ◽  
Tyrode Solution ◽  
Voltage Range ◽  
Inward Current ◽  
Whole Cell Patch Clamp ◽  
Diastolic Depolarization ◽  
Cardiac Purkinje Fibers ◽  
K Current ◽  
K Depletion

It is generally assumed that in cardiac Purkinje fibers the hyperpolarization activated inward current i(f) underlies the pacemaker potential. Because some findings are at odds with this interpretation, we used the whole cell patch clamp method to study the currents in the voltage range of diastolic depolarization in single canine Purkinje myocytes, a preparation where many confounding limitations can be avoided. In Tyrode solution ([K+]o = 5.4 mM), hyperpolarizing steps from Vh = -50 mV resulted in a time-dependent inwardly increasing current in the voltage range of diastolic depolarization. This time-dependent current (iKdd) appeared around -60 mV and reversed near EK. Small superimposed hyperpolarizing steps (5 mV) applied during the voltage clamp step showed that the slope conductance decreases during the development of this time-dependent current. Decreasing [K+]o from 5.4 to 2.7 mM shifted the reversal potential to a more negative value, near the corresponding EK. Increasing [K+]o to 10.8 mM almost abolished iKdd. Cs+ (2 mM) markedly reduced or blocked the time-dependent current at potentials positive and negative to EK. Ba2+ (4 mM) abolished the time-dependent current in its usual range of potentials and unmasked another time-dependent current (presumably i(f)) with a threshold of approximately -90 mV (> 20 mV negative to that of the time-dependent current in Tyrode solution). During more negative steps, i(f) increased in size and did not reverse. During i(f) the slope conductance measured with small (8-10 mV) superimposed clamp steps increased. High [K+]o (10.8 mM) markedly increased and Cs+ (2 mM) blocked i(f). We conclude that: (a) in the absence of Ba2+, a time-dependent current does reverse near EK and its reversal is unrelated to K+ depletion; (b) the slope conductance of that time-dependent current decreases in the absence of K+ depletion at potentials positive to EK where inactivation of iK1 is unlikely to occur. (c) Ba2+ blocks this time-dependent current and unmasks another time-dependent current (i(f)) with a more negative (> 20 mV) threshold and no reversal at more negative values; (d) Cs+ blocks both time-dependent currents recorded in the absence and presence of Ba2+. The data suggest that in the diastolic range of potentials in Purkinje myocytes there is a voltage- and time-dependent K+ current (iKdd) that can be separated from the hyperpolarization-activated inward current i(f).

BICUCULLINE/BACLOFEN-INSENSITIVE GABA RESPONSE IN CRUSTACEAN NEURONES IN CULTURE

1994 ◽  
Vol 191 (1) ◽  
pp. 167-193
Author(s):  
C Jackel ◽  
W Krenz ◽  
F Nagy
Keyword(s):  
Reversal Potential ◽  
Membrane Conductance ◽  
Gamma Aminobutyric Acid ◽  
Action Potential Firing ◽  
Patch Clamp Technique ◽  
Conformationally Restricted ◽  
Whole Cell Patch Clamp ◽  
Gabac Receptor ◽  
Potential Firing ◽  
Sr 95531

Neurones were dissociated from thoracic ganglia of embryonic and adult lobsters and kept in primary culture. When gamma-aminobutyric acid (GABA) was applied by pressure ejection, depolarizing or hyperpolarizing responses were produced, depending on the membrane potential. They were accompanied by an increase in membrane conductance. When they were present, action potential firing was inhibited. The pharmacological profile and ionic mechanism of GABA-evoked current were investigated under voltage-clamp with the whole-cell patch-clamp technique. The reversal potential of GABA-evoked current depended on the intracellular and extracellular Cl- concentration but not on extracellular Na+ and K+. Blockade of Ca2+ channels by Mn2+ was also without effect. The GABA-evoked current was mimicked by application of the GABAA agonists muscimol and isoguvacine with an order of potency muscimol>GABA>isoguvacine. cis-4-aminocrotonic acid (CACA), a folded and conformationally restricted GABA analogue, supposed to be diagnostic for the vertebrate GABAC receptor, also induced a bicuculline-resistant chloride current, although with a potency about 10 times lower than that of GABA. The GABA-evoked current was largely blocked by picrotoxin, but was insensitive to the GABAA antagonists bicuculline, bicuculline methiodide and SR 95531 at concentrations of up to 100 µmol l-1. Diazepam and phenobarbital did not exert modulatory effects. The GABAB antagonist phaclophen did not affect the GABA-induced current, while the GABAB agonists baclophen and 3-aminopropylphosphonic acid (3-APA) never evoked any response. Our results suggest that lobster thoracic neurones in culture express a chloride-conducting GABA-receptor channel which conforms to neither the GABAA nor the GABAB types of vertebrates but shows a pharmacology close to that of the novel GABAC receptor described in the vertebrate retina.

Sign in / Sign up

Export Citation Format

Share Document