Membrane currents in cat myocardium: separation of inward and outward components

McDonald, Terence F.; Trautwein, W.

doi:10.1113/jphysiol.1978.sp012143

Cited by 119 publications

(49 citation statements)

References 32 publications

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“…2 and 3). Peak values of the slow inward current were measured by the method developed by McDonald & Trautwein (1978) and were plotted against the membrane potential of the test pulses. In altering pH0, the most striking change in the I-V curve for the slow inward current is that the slow current increased with alkalinization of the perfusing solution (Fig.…”

Section: Voltage-clamp Experimentsmentioning

confidence: 99%

On the mechanism by which changes in extracellular pH affect the electrical activity of the rabbit sino‐atrial node.

Satoh¹,

Seyama²

1986

The Journal of Physiology

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SUMMARY1. The effect of altering the extracellular pH (pHO) on the electrical activity of the isolated rabbit sino-atrial (s.a.) node was studied using the two-micro-electrode voltage-clamp technique.2. Alkalinization of the perfusate increased the maximum rate of rise and amplitude of the nodal action potential, and also the frequency of spontaneous beating of the s.a. node; acidification produced opposite effects.3. A change in the extracellular pH from a value of 6-5 to 8'5 caused increases of the maximal conductance for both the slow inward current and the steady-state outward current systems without affecting the gating processes of the channels.4. H+ could modify the electrical activity of s.a. nodal cells, not through altering the membrane surface potential but through the protonation of the ionic channels themselves. From the titration curves, the apparent pKa values for the slow inward current and the steady-state outward current were estimated to be 6-4 and 60, respectively.

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Section: Voltage-clamp Experimentsmentioning

confidence: 99%

On the mechanism by which changes in extracellular pH affect the electrical activity of the rabbit sino‐atrial node.

Satoh¹,

Seyama²

1986

The Journal of Physiology

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“…Well described examples include cardiac (Beeler & Reuter, 1970;Reuter, 1978;McDonald & Trautwein, 1978) As another possibility, a decline in Ica under maintained depolarization could result from Ca2+ depletion in restricted extracellular spaces. Such spaces exist in most preparations where ICa has so far been studied.…”

Section: Introductionmentioning

confidence: 99%

Calcium depletion in frog muscle tubules: the decline of calcium current under maintained depolarization.

Almers¹,

Fink²,

Palade³

1981

The Journal of Physiology

255

160

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SUMMARY1. Ca2+ currents in frog skeletal muscle fibres were studied with a voltage-clamp technique. Under membrane depolarization maintained for several seconds, Ca2+ current was found to decline with time constants of 0-2-2 see when LCa2+]o = 10 mM.2. Ca2+ currents are diminished by nifedipine, D-600, tetracaine and Ni2+.3. When peak current is diminished by making the membrane potential positive, by block with drugs or by substituting the relatively less permeant Mn2+ for Ca2+, then the rate ofdecline is diminished also. When peak current is increased by recording at relatively negative membrane potentials or by substituting for Ca2+ the more permeant ions Ba2+ or Sr2+, then the rate of decline is increased in proportion. Evidently, the size of the current determines the rate of decline.4. Decline of current is greatly slowed in isotonic Ca2+ saline or when the [Ca2+]o is buffered by the organic anion malate. These findings indicate that the decline of current arises from Ca2+ depletion in an extracellular compartment, most probably the transverse tubules. On this basis, an analysis of Ca2+ current decline and recovery leads to the following conclusions.5. Ca2+ current flows almost entirely across the membranes of the transverse tubules.6. After allowing for the tortuosity of the tubular network, the apparent diffusion coefficient for Ca2+ in the transverse tubules is about 2-6 x 10-6 cm2/sec, three times less than the diffusion coefficient for K+ in the transverse tubules and about three times less than the diffusion coefficient for Ca2+ in free solution.7. The transverse tubule lumen does not appear to have a large Ca2+-buffering capacity in the millimolar range. At [Ca2+]j = 10 mM, the tubule lumen binds less than 0-6 dissociable Ca2+ ions for every free ion.

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“…An inward-rectifying K + current (IKj) has also been described in cardiac ventricular tissue, but it is considered to be an instantaneous current that is not associated with any time dependence (Beeler and Reuter, 1977;McDonald and Trautwein, 1978;Cleeman and Morad, 1979). This may be due to the technical difficulties associated with detecting IK~.…”

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confidence: 99%

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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Membrane currents in cat myocardium: separation of inward and outward components

Cited by 119 publications

References 32 publications

On the mechanism by which changes in extracellular pH affect the electrical activity of the rabbit sino‐atrial node.

On the mechanism by which changes in extracellular pH affect the electrical activity of the rabbit sino‐atrial node.

Calcium depletion in frog muscle tubules: the decline of calcium current under maintained depolarization.

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

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