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. 1978 Jan;274:193–216. doi: 10.1113/jphysiol.1978.sp012143

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

T F McDonald 1,*, W Trautwein 1
PMCID: PMC1282486  PMID: 624993

Abstract

1. The single sucrose gap method was used to control the membrane potential of cat ventricular fibres.

2. Following the early rapid events (capacitive, Na and slow inward (si) current spikes) the membrane current on depolarization contained three time-dependent components which appeared attributable to the inactivation of Isi and the activation of two outward currents labelled IK and Ix.

3. Tail currents were analysed with a view to confirming these conductance changes. At -60 mV the tail progressed from being predominantly inward in direction after short (30-50 msec) depolarizations to being predominantly outward after long (> 300 msec) depolarizations. Inward and outward components decayed exponentially with time constants independent of previous membrane history. The Q10s were about 3.

4. Experiments with D600 and variations of the driving force identified the inward tail component (τ ≈ 55 msec at -60 mV) as Isi. The major outward tail component (τ ≈ 300 msec) appears to be carried primarily by potassium. A second outward tail component (τ ≈ 3 sec) of much smaller amplitude than IK was observed after long depolarizations and is tentatively labelled Ix.

5. Membrane currents at 0 mV can be described as the sum of three exponential processes: Isi inactivation (τ ≈ 90 msec), IK activation (τ ≈ 370 msec) and Ix activation (τ ≈ 3 sec). Conductance measurements (envelops of Isi and IK tails) supported these time courses. Isi time constants increased from 50 msec at -40 mV to 120 msec at +40 mV. IK time constants increased from 400 msec at -40 to about 520 msec at -25 mV before declining to 300 msec at +40 mV.

6. Isi amplitudes measured visually (difference between peak Isi and current level after 200-500 msec) were compared with those measured graphically (semilog plots, subtraction of IK and Ix). As a consequence of the relative amplitudes and time courses of Isi and IK, the shapes of the Isi voltage relations were not markedly different: visual estimates at 200 msec were in agreement with graphic estimates, visual estimates at 300 or 500 msec exceeded these by 15-30% between -20 and +20 mV.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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