Dual effects of K ions upon the inactivation of the anomalous rectifier of the tunicate egg cell membrane

Ohmori, Harunori

doi:10.1007/bf01870582

Cited by 44 publications

(73 citation statements)

References 23 publications

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“…Furthermore inactivation upon large hyperpolarizations seems to be a regular finding for inward rectifiers of different preparations. Such inactivation in normal conditions has been shown for large hyperpolarizing steps in frog skeletal muscle by Almers (1972 a, b), in starfish eggs by Hagiwara, Miyazaki, Moody & Patlak (1978) and in tunicate eggs by Ohmori (1978Ohmori ( , 1980 and Fukushima (1981Fukushima ( , 1982. Since K depletion in a single-cell preparation is expected to be much reduced, the presence of a decay of the inward current for large hyperpolarizations could indicate that inactivation of the inward rectifier upon large hyperpolarizations can have a significant role in determining the current wave form in cardiac Purkinje cells.…”

Section: Single Cardiac Purkinje Cellsmentioning

confidence: 83%

Single cardiac Purkinje cells: general electrophysiology and voltage‐clamp analysis of the pace‐maker current.

Callewaert¹,

Carmeliet²,

Vereecke³

1984

The Journal of Physiology

113

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4. The upstroke of the action potential could be blocked by tetrodotoxin (TTX) in a dose-dependent manner. The rate of depolarization of the action potential was sensitive to changes in membrane potential; the resulting S-shaped curve showed a half-maximum potential of -65 mV and a steepness of 0'46 mV-1.5. The duration of the action potential was sensitive to external K concentrations, catecholamines and TTX in a way similar to intact Purkinje fibres.6. Both application of catecholamines and lowering the external K concentration induced spontaneous activity.7. The cells were used to study the ionic nature of the pace-maker current under voltage-clamp conditions using the two-micro-electrode technique. This pace-maker current was blocked in a voltage-dependent manner by 1 mM-Cs, and was not affected by 1 mM-Ba. The steady-state activation curve was shifted in the depolarizing direction by application of adrenaline.8. In contrast to voltage-clamp data obtained on the pace-maker current of intact Purkinje fibres, the pace-maker current in a single cell did not reverse near the presumed equilibrium potential for K ions; no reversal could be seen in the voltage range negative to -50 mV.9. These observations together with preliminary results on the Na and K depen-21-2 6. CALLEWAERT, E. CARMELIET AND J. VEREECKE dence of the pace-maker current are strong arguments in favour of the hypothesis that the pace-maker current in cardiac Purkinje fibres is an inward current carried by Na and K ions and activates upon hyperpolarization.

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Section: Single Cardiac Purkinje Cellsmentioning

confidence: 83%

Single cardiac Purkinje cells: general electrophysiology and voltage‐clamp analysis of the pace‐maker current.

Callewaert¹,

Carmeliet²,

Vereecke³

1984

The Journal of Physiology

113

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“…Analysis of single-channel activity in this preparation has shown that the presence of a channel blocker (i.e., Na +) is necessary to even see current fluctuations owing to channel closing (Ohmori, 1980). It has also been suggested that inactivation in skeletal muscle is at least partially due to a time-and voltage-dependent block of the inward current by extracellular Na § (Standen and Stanfield, 1979).…”

Section: Comparison Of Iki With Other Inward-rectifying K § Currentsmentioning

confidence: 95%

“…Although the mechanism is not understood, Ohmori (1980) suggested an Na + dependence for channel activation (as well as inactivation) because of the increase in apparent channel activity seen using fluctuation analysis. Fukushima (1982), however, suggested that extracellular Na + may facilitate single-channel conductance.…”

Section: Comparison Of Iki With Other Inward-rectifying K § Currentsmentioning

confidence: 99%

“…Inactivation of IKI in isolated ventricular myocytes was viewed as being the result of two INTRODUCTION Since Katz (1949) first discovered the property of anomalous rectification in skeletal muscle, it has been described in several different preparations. This anomalous or inward rectification has been studied extensively in starfish (Hagiwara and Takahashi, 1974;Hagiwara et al, 1976;Hagiwara and Yoshii, 1979) and tunicate (Miyazaki et al, 1974;Ohmori, 1978Ohmori, , 1980Fukusbima, 1982) egg cells as well as skeletal muscle preparations (Adrian et al, 1970;Almers, 1972a, b;Standen and Stanfield, 1979;Hestrin, 1981;Leech and Stanfield, 1981). Inward rectification is associated with the presence of a background K ion conductance that contributes to the maintenance of the resting membrane potential.…”

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confidence: 99%

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Characterization of the inward-rectifying potassium current in cat ventricular myocytes.

Harvey

Eick

1988

The Journal of General Physiology

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Whole-cell membrane currents were measured in isolated cat ventricular myocytes using a suction-electrode voltage-clamp technique. An inward-rectifying current was identified that exhibited a time-dependent activation. The peak current appeared to have a linear voltage dependence at membrane potentials negative to the reversal potential. Inward current was sensitive to K channel blockers. In addition, varying the extracellular K § concentration caused changes in the reversal potential and slope conductance expected for a K § current. The voltage dependence of the chord conductance exhibited a sigmoidal relationship, increasing at more negative membrane potentials. Increasing the extraceUular K § concentration increased the maximal level of conductance and caused a shift in the relationship that was directly proportional to the change in reversal potential. Activation of the current followed a monoexponential time course, and the time constant of activation exhibited a monoexponential dependence on membrane potential. Increasing the extracellular K + concentration caused a shift of this relationship that was directly proportional to the change in reversal potential. Inactivation of inward current became evident at more negative potentials, resulting in a negative slope region of the steady state current-voltage relationship between --140 and --180 mV. Steady state inactivation exhibited a sigmoidal voltage dependence, and recovery from inactivation followed a monoexponential time course. Removing extracellular Na + caused a decrease in the slope of the steady state current-voltage relationship at potentials negative to --140 mV, as well as a decrease of the conductance of inward current. It was concluded that this current was IK~, the inward-rectifying K + current found in multicellular cardiac preparations. The K + and voltage sensitivity of IK1 activation resembled that found for the inward-rectifying K + currents in frog skeletal muscle and various egg cell preparations. Inactivation

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“…In the current-voltage relations given in this paper we have subtracted a linear element (leak), by extrapolating the currents obtained for depolarizations greater than 60 mV through the holding potential (c.f. Adrian & Freygang, 1962;Adrian, 1964;Standen & Stanfield, 1978, 1980 Membrane currents in 80 mM-TI Ringer Single-pulse experiments Fig. 1 A shows membrane potential and membrane current records from a fibre immersed in 80 mM-Tl Ringer, for a hyperpolarization of 140 mV from the holding potential.…”

Section: Methodsmentioning

confidence: 99%

The influence of the permeant ions thallous and potassium on inward rectification in frog skeletal muscle.

Ashcroft¹,

Stanfield²

1983

The Journal of Physiology

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SUMMARY1. A three-electrode voltage-clamp method was used to investigate the inactivation of Tl currents through the inward rectifier of frog sartorius muscle fibres, and the interaction between the permeant ions Tl+ and K+.2. In 80 mM-Tl Ringer inward currents inactivated on hyperpolarization along an exponential time course, with time constants that initially increased and then fell with increasing hyperpolarization.3. Because ofthe inactivation process steady-state conductances were smaller than instantaneous conductances at all potentials in Tl Ringer. The steady-state conductance increased to a maximum value at around -100 mV in 80 mM-Tl Ringer, and then fell with increasing hyperpolarization. In K Ringer the steady-state conductance was greater at all potentials than the instantaneous conductance because K currents activate (rather than inactivate) on hyperpolarization.4. Time constants of TI inactivation were the same when measured from the decay of current during a single pulse, or from the rate of recovery from inactivation using either a two-or a three-pulse method, indicating that inactivation obeys first-order kinetics.5. In 80 mM-Tl Ringer steady-state inactivation increased with increasing hyperpolarization, e-fold every 48 mV. This would be consistent with the site at which inactivation occurs experiencing 0.5 of the membrane voltage field.6. Tl+ was more permeant than K+ through the inward rectifier, the permeability ratio PT1+/PK+ being 1-66.7. In solutions containing both T1+ and K+ the membrane showed an anomalous mole-fraction dependence of conductance, the resting potential being more negative, and both instantaneous and steady-state conductances smaller than those recorded in solutions containing only Tl+ or only K+. 8. The reduction in the amplitude of the instantaneous conductance in Tl-K mixtures was voltage-dependent, the block being initially increased and then falling with increasing hyperpolarization.9. Inward currents also inactivated on hyperpolarization in T1-K mixtures. The time constants of inactivation, and the extent of inactivation which occurred, became less dependent on membrane potential in these solutions. * Present address: University Laboratory of Physiology, Parks Road, Oxford OX1 3PT.F. M. ASHCROFT AND P. R. STANFIELD 10. When K+ is the major permeant ion in solution, Tl+ has a blocking effect on the currents carried by K+, and the degree of block is voltage-dependent. Increasing [Tl]. increased the block at all potentials.11. The results of our experiments in solutions containing both Tl+ and K+ are discussed in terms of an interaction between these ions within the channel.

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Dual effects of K ions upon the inactivation of the anomalous rectifier of the tunicate egg cell membrane

Cited by 44 publications

References 23 publications

Single cardiac Purkinje cells: general electrophysiology and voltage‐clamp analysis of the pace‐maker current.

Single cardiac Purkinje cells: general electrophysiology and voltage‐clamp analysis of the pace‐maker current.

Characterization of the inward-rectifying potassium current in cat ventricular myocytes.

The influence of the permeant ions thallous and potassium on inward rectification in frog skeletal muscle.

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