Outward K+ current in epithelial cells isolated from intermediate portion of endolymphatic sac of guinea pigs

1996 ◽  
Vol 271 (5) ◽  
pp. C1765-C1773 ◽  
Author(s):  
D. Wu ◽  
N. Mori
Keyword(s):  
Epithelial Cells ◽  
Guinea Pigs ◽  
Outward Current ◽  
Endolymphatic Sac ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Tail Current ◽  
Voltage Dependent ◽  
Slope Factor ◽  
K Current

Ion currents in epithelial cells isolated from the intermediate portion of endolymphatic sac (ES) in guinea pigs were investigated with the use of the whole cell patch-clamp technique. Depolarizing voltage steps from a holding potential of -60 mV induced a time- and voltage-dependent outward current, which is comparable to that of delayed rectifying K+ currents. The average resting membrane potential in the current-clamp mode was -54.8 +/- 11 mV (n = 45), which was similar to the value of zero current potential (-55.6 +/- 0.8 mV, n = 32) obtained from current-voltage (I-V) relationships of outward currents in voltage-clamp mode. The I-V relationship of the tail current exhibited a reversal potential (Erev) of -78.1 +/- 0.9 mV (n = 19) in standard external solution. The Erev of the outward current was linearly related to the logarithm of extracellular K+ concentrations. The slope was 48 mV per 10-fold change in extracellular K+ concentrations. The time constants of K+ current activation, inactivation, and K+ tail current deactivation were voltage dependent. The steady-state activation and inactivation of K+ current exhibited a sigmoidal relationship to voltage. The 50% maximal activation voltage and slope factor were -21 and 11 mV (n = 8), respectively. The 50% maximal inactivation voltage and slope factor were -45 and 13 mV (n = 7), respectively. The K+ current was blocked by externally applied 1 mM 4-aminopyridine (4-AP), 5 mM Ba2+ and 20 mM tetraethylammonium chloride (TEA). The sensitivity of the current to 4-AP and Ba2+ was higher than that to TEA. Elimination of external Ca2+ and increase of internal Ca2+ failed to significantly change the current, suggesting that the K+ current may be Ca2+ independent. The results show that epithelial cells in the intermediate portion of the ES possess a delayed-rectifier K+ current, which may be involved in membrane stability or in the ion balance between the cytosol and the extracellular environment.

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.

Modulation of the delayed rectifier, IK, by cadmium in cat ventricular myocytes

1992 ◽  
Vol 262 (1) ◽  
pp. C75-C83 ◽  
Author(s):  
C. H. Follmer ◽  
N. J. Lodge ◽  
C. A. Cullinan ◽  
T. J. Colatsky
Keyword(s):  
Voltage Clamp ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Membrane Potentials ◽  
Delayed Rectifier ◽  
Voltage Range ◽  
Control Value ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Slope Factor

The effects of cadmium on the delayed outward potassium current (IK) were investigated in isolated cat ventricular myocytes using the single suction pipette voltage-clamp technique. IK activation was examined using peak tail currents elicited after 750-ms voltage-clamp steps to selected membrane potentials from a holding potential of -40 mV. In the presence of Cd2+ (0.2 mM), peak tail currents increased from a control value of 85 +/- 12 to 125 +/- 18 pA (n = 4). Activation curves constructed from the average peak tail-current measurements in all experiments showed that Cd2+ shifted the voltage dependence of activation to more positive potentials by 16.4 +/- 2.0 mV and increased the slope factor of the activation curve from 6.1 +/- 0.2 to 6.9 +/- 0.2 mV. In the absence of Cd2+, increases in holding potential from -30 to -70 mV had no effect on the magnitude of the peak tail currents, suggesting that the Cd(2+)-induced increase was not the result of a voltage-dependent increase in the number of available K+ channels at the holding potential. Slow voltage ramps from -70 to +70 mV revealed that Cd2+ increased the outward current at membrane potentials positive to +20 mV and shifted the voltage range in which IK inwardly rectified to more positive potentials. The fully activated current-voltage relationship was also shifted to more positive potentials by Cd2+. Cd2+ did not alter channel selectivity for K+.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous transient outward currents and delayed rectifier K+ current: effects of hypoxia

1998 ◽  
Vol 275 (1) ◽  
pp. L145-L154 ◽  
Author(s):  
C. Vandier ◽  
M. Delpech ◽  
P. Bonnet
Keyword(s):  
Steady State ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Outward Currents ◽  
K Current ◽  
The Mean ◽  
Patch Configuration ◽  
Spontaneous Transient Outward Currents ◽  
Dependent Mechanism

Single smooth muscle cells of rabbit intrapulmonary artery were voltage clamped using the perforated-patch configuration of the patch-clamp technique. We observed spontaneous transient outward currents (STOCs) and a steady-state outward current. Because STOCs were tetraethylammonium sensitive and activated by Ca2+ influx, they were believed to represent activation of Ca2+-activated K+ channels. The steady-state outward current, which was sensitive to 4-aminopyridine, was the delayed rectifier K+ current. In cells voltage clamped at 0 mV, we found that STOCs were not randomly distributed in amplitude but were composed of multiples of 1.57 ± 0.56 pA/pF. The mean frequency of STOCs was 5.51 ± 3.49 Hz. Ryanodine (10 μM), caffeine (5 mM), thapsigargin (200 nM), and hypoxia [Formula: see text] = 10 mmHg) decreased STOCs. The effect of hypoxia on STOCs was partially reversible only if the experiment was conducted in the presence of thapsigargin. Hypoxia and thapsigargin decrease steady-state outward current. Thapsigargin and removal of external Ca2+abolished the effect of hypoxia, suggesting that hypoxia decreases steady-state outward current by a Ca2+-dependent mechanism.

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

1986 ◽  
Vol 88 (6) ◽  
pp. 777-798 ◽  
Author(s):  
J R Hume ◽  
W Giles ◽  
K Robinson ◽  
E F Shibata ◽  
R D Nathan ◽  
...  
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Outward Current ◽  
Cardiac Cells ◽  
Delayed Rectifier ◽  
Mechanical Dispersion ◽  
Atrial Cells ◽  
Voltage Dependent ◽  
K Current ◽  
Kinetics Of

Individual myocytes were isolated from bullfrog atrium by enzymatic and mechanical dispersion, and a one-microelectrode voltage clamp was used to record the slow outward K+ currents. In normal [K+]o (2.5 mM), the slow outward current tails reverse between -95 and -100 mV. This finding, and the observed 51-mV shift of Erev/10-fold change in [K+]o, strongly suggest that the "delayed rectifier" in bullfrog atrial cells is a K+ current. This current, IK, plays an important role in initiating repolarization, and it is distinct from the quasi-instantaneous, inwardly rectifying background current, IK. In atrial cells, IK does not exhibit inactivation, and very long depolarizing clamp steps (20 s) can be applied without producing extracellular K+ accumulation. The possibility of [K+]o accumulation contributing to these slow outward current changes was assessed by (a) comparing reversal potentials measured after short (2 s) and very long (15 s) activating prepulses, and (b) studying the kinetics of IK at various holding potentials and after systematically altering [K+]o. In the absence of [K+]o accumulation, the steady state activation curve (n infinity) and fully activated current-voltage (I-V) relation can be obtained directly. The threshold of the n infinity curve is near -50 mV, and it approaches a maximum at +20 mV; the half-activation point is approximately -16 mV. The fully activated I-V curve of IK is approximately linear in the range -40 to +30 mV. Semilog plots of the current tails show that each tail is a single-exponential function, which suggests that only one Hodgkin-Huxley conductance underlies this slow outward current. Quantitative analysis of the time course of onset of IK and of the corresponding envelope of tails demonstrate that the activation variable, n, must be raised to the second power to fit the sigmoid onset accurately. The voltage dependence of the kinetics of IK was studied by recording and curve-fitting activating and deactivating (tail) currents. The resulting 1/tau n curve is U-shaped and somewhat asymmetric; IK exhibits strong voltage dependence in the diastolic range of potentials. Changes in the [Ca2+]o in the superfusing Ringer's, and/or addition of La3+ to block the transmembrane Ca2+ current, show that the time course and magnitude of IK are not significantly modulated by transmembrane Ca2+ movements, i.e., by ICa. These experimentally measured voltage- and time-dependent descriptors of IK strongly suggest an important functional role for IK in atrial tissue: it initiates repolarization and can be an important determinant of rate-induced changes in action potential duration.

scholarly journals Voltage-dependent conductances in Limulus ventral photoreceptors.

1982 ◽  
Vol 79 (2) ◽  
pp. 187-209 ◽  
Author(s):  
J E Lisman ◽  
G L Fain ◽  
P M O'Day
Keyword(s):  
Outward Current ◽  
Delayed Rectifier ◽  
Molluscan Neurons ◽  
Inward Current ◽  
Transient Component ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
A Current

The voltage-dependent conductances of Limulus ventral photoreceptors have been investigated using a voltage-clamp technique. Depolarization in the dark induces inward and outward currents. The inward current is reduced by removing Na+ or Ca2+ and is abolished by removing both ions. These results suggest that both Na+ and Ca2+ carry voltage-dependent inward current. Inward current is insensitive to tetrodotoxin but is blocked by external Ni2+. The outward current has a large transient component that is followed by a smaller maintained component. Intracellular tetraethylammonium preferentially reduces the maintained component, and extracellular 4-amino pyridine preferentially reduces the transient component. Neither component is strongly affected by removal of extracellular Ca2+ or by intracellular injection of EGTA. It is concluded that the photoreceptors contain at least three separate voltage-dependent conductances: 1) a conductance giving rise to inward currents; 2) a delayed rectifier giving rise to maintained outward K+ current; and 3) a rapidly inactivating K+ conductance similar to the A current of molluscan neurons.

Characterization of macroscopic outward currents of canine colonic myocytes

1989 ◽  
Vol 257 (3) ◽  
pp. C461-C469 ◽  
Author(s):  
W. C. Cole ◽  
K. M. Sanders
Keyword(s):  
Outward Current ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Time Dependent ◽  
Delayed Rectifier ◽  
Delayed Rectifier Current ◽  
Outward Currents ◽  
Voltage Dependent ◽  
K Current ◽  
Time Courses

Outward currents of colonic smooth muscle cells were characterized by the whole cell voltage-clamp method. Four components of outward current were identified: a time-independent and three time-dependent components. The time-dependent current showed strong outward rectification positive to -25 mV and was blocked by tetraethylammonium. The time-dependent components were separated on the basis of their time courses, voltage dependence, and pharmacological sensitivities. They are as follows. 1) A Ca2+-activated K current sensitive to external Ca2+ and Ca2+ influx was blocked by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (0.1 X 10(-3) M) and nifedipine (1 X 10(-6) and was increased by elevated Ca2+ (8 X 10(-6) M) and BAY K 8644 (1 X 10(-6) M). 2) A "delayed rectifier" current was observed that decayed slowly with time and showed no voltage-dependent inactivation. 3) Spontaneous transient outward currents that were blocked by ryanodine (2 X 10(-6) M) were also recorded. The possible contributions of these currents to the electrical activity of colonic muscle cells in situ are discussed. Ca2+-activated K current may contribute a significant conductance to the repolarizing phase of electrical slow waves.

An outwardly rectifying K+ current active near resting potential in human retinal pigment epithelial cells

1995 ◽  
Vol 269 (1) ◽  
pp. C179-C187 ◽  
Author(s):  
B. A. Hughes ◽  
M. Takahira ◽  
Y. Segawa
Keyword(s):  
Retinal Pigment Epithelial ◽  
Retinal Pigment ◽  
Outward Current ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Rpe Cells ◽  
Pigment Epithelial ◽  
K Current

Currents in freshly dissociated adult human retinal pigment epithelial (RPE) cells were studied using the perforated patch-clamp technique. The zero-current potential (V0) averaged -48.9 +/- 7.7 mV (n = 50). Depolarizing voltage pulses from -70 mV evoked an outward current that activated with first-order kinetics and that did not inactivate during prolonged depolarizations. Repolarizing the membrane potential produced tail currents that reversed near the K+ equilibrium potential, indicating that the sustained outward current was carried mainly by K+. The outwardly rectifying K+ conductance (gK) had an activation threshold voltage near -60 mV and was half-maximal at -37 mV. Approximately 25% of gK was active at the average V0. The K+ current was nearly completely blocked by 2 mM Ba2+ but was relatively insensitive to 20 mM tetraethylammonium. The kinetics, voltage dependence, and blocker sensitivity of this current clearly distinguish it from delayed rectifier K+ currents previously identified in RPE cells. We conclude that the sustained outward K+ current may help establish the resting potential of the apical and/or basolateral membranes and may also participate in K+ transport across the RPE.

IK of rabbit ventricle is composed of two currents: evidence for IKs

1996 ◽  
Vol 271 (6) ◽  
pp. H2477-H2489 ◽  
Author(s):  
J. J. Salata ◽  
N. K. Jurkiewicz ◽  
B. Jow ◽  
K. Folander ◽  
P. J. Guinosso ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Rabbit Heart ◽  
Northern Analysis ◽  
Delayed Rectifier ◽  
Human Genes ◽  
Voltage Dependent ◽  
Slope Factor ◽  
K Current ◽  
A Subunit ◽  
K Concentration

The delayed rectifier K+ current (IK) in rabbit heart has long been thought to consist of only a single, rapidly activating, dofetilide-sensitive current, IKr. However, we find that IK of rabbit ventricular myocytes actually consists of both rapid and slow components, IKr and IKs, respectively, that can be isolated pharmacologically. Thus, after complete blockade of IKr with dofetilide, the remaining current, IKs, is homogeneous as judged by an envelope of tails test. IKs activates and deactivates slowly, continues to activate during sustained depolarizations, has a half-activation potential of 7.0 +/- 0.8 mV and slope factor of 11.0 +/- 0.7 mV, reverses at -77.2 +/- 1.3 mV (extracellular K+ concentration = 4 mM), is increased by removing extracellular K+, and is enhanced by isoproterenol and stocked by azimilide. Northern analysis demonstrates that the minK (IsK) gene, which encodes a subunit of the channel that underlies the IKs current, is expressed in rabbit heart. Expression of the rabbit protein in Xenopus oocytes elicits a slowly activating, voltage-dependent current, IsK, similar to those expressed previously from mouse, rat, guinea pig, and human genes. The results demonstrate that IKs is present in rabbit ventricle and therefore contributes to cardiac repolarization in this species.

scholarly journals A whole-cell and single-channel study of the voltage-dependent outward potassium current in avian hepatocytes.

1988 ◽  
Vol 91 (2) ◽  
pp. 255-274 ◽  
Author(s):  
C Marchetti ◽  
R T Premont ◽  
A M Brown
Keyword(s):  
Single Channel ◽  
Reversal Potential ◽  
Outward Current ◽  
Single Type ◽  
K Channel ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
Single Channel Currents ◽  
K Currents

Voltage-dependent membrane currents were studied in dissociated hepatocytes from chick, using the patch-clamp technique. All cells had voltage-dependent outward K+ currents; in 10% of the cells, a fast, transient, tetrodotoxin-sensitive Na+ current was identified. None of the cells had voltage-dependent inward Ca2+ currents. The K+ current activated at a membrane potential of about -10 mV, had a sigmoidal time course, and did not inactivate in 500 ms. The maximum outward conductance was 6.6 +/- 2.4 nS in 18 cells. The reversal potential, estimated from tail current measurements, shifted by 50 mV per 10-fold increase in the external K+ concentration. The current traces were fitted by n2 kinetics with voltage-dependent time constants. Omitting Ca2+ from the external bath or buffering the internal Ca2+ with EGTA did not alter the outward current, which shows that Ca2+-activated K+ currents were not present. 1-5 mM 4-aminopyridine, 0.5-2 mM BaCl2, and 0.1-1 mM CdCl2 reversibly inhibited the current. The block caused by Ba was voltage dependent. Single-channel currents were recorded in cell-attached and outside-out patches. The mean unitary conductance was 7 pS, and the channels displayed bursting kinetics. Thus, avian hepatocytes have a single type of K+ channel belonging to the delayed rectifier class of K+ channels.

A slowly inactivating K+ current in retinal ganglion cells from postnatal rat

1992 ◽  
Vol 8 (2) ◽  
pp. 171-176 ◽  
Author(s):  
Nikolaus J. Sucher ◽  
Stuart A. Lipton
Keyword(s):  
Retinal Ganglion Cells ◽  
Ganglion Cells ◽  
Outward Current ◽  
Retinal Ganglion ◽  
Patch Clamp Technique ◽  
External Application ◽  
Lower Vertebrates ◽  
Voltage Dependent ◽  
K Current

AbstractThe whole-cell configuration of the patch-clamp technique was used to study voltage-gated K+ conductances in retinal ganglion cells from postnatal rat. Retinal ganglion cells were fluorescently labeled in situ, dissociated from the retina, and maintained in culture. With physiological solutions in the bath and the pipette, depolarizing voltage steps from physiological holding potentials activated Na+-(INa), Ca2+ (ICa), and K+ -currents studied previously in retinal ganglion cells. Here we report on a slowly decaying K+ current, not heretofore reported in rat. With 4-AP, TEA, and Co2+ in the bath, to block IA, IK, and IK(Ca), respectively, a slowly decaying outward current was activated from —80 mV by steps positive to —40 mV. This current was present in 92% of all ganglion cells tested (n = 83). It activated within 10 ms and inactivated with a voltage-independent time constant of about 70 ms at 35°C. Inactivation was voltage-dependent, half-maximal at —55 mV, and almost complete at 0 mV. The current was blocked by internal Cs+ and TEA, or by external application of 1 mM Ba2+, but not by 3 mM extracellular Co2+. The biophysical and pharmacological properties of this current are distinctly different from those of slowly inactivating K+ currents studied in other rat neurons. It was very similar, however, to a slowly inactivating K+ current previously reported in ganglion cells of tiger salamander retina. This last finding indicates conservation of a defined K+ channel type in functionally related cells in both lower vertebrates and mammals.

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