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. 1981 Jan;310:97–115. doi: 10.1113/jphysiol.1981.sp013539

The tension-depolarization relationship of frog atrial trabeculae as determined by potassium contractures.

R A Chapman, J Tunstall
PMCID: PMC1274730  PMID: 6971932

Abstract

1. In the presence of extracellular Na ions K contractures evoked from isolated frog atrial trabeculae show an initial phasic and a subsequent tonic contractile response. 2. The phasic response shows a steep dependence on membrane potential, persists in Na-free fluid, but is blocked by Mn ions, D600 and tetracaine. It has an indirect dependence on the [Ca]0 and would seem to be associated with both the secondary inward current and the release of Ca2+ from intracellular stores. 3. The tonic component of the K contracture is unaffected by D600 or tetracaine, shows a shallow dependence on membrane potential but is absent in Na-free fluid. Its tension-depolarization curve is immediately affected by alteration of either the [Ca]0 or the [Na]0. The form of the tension-depolarization relationship and the effects of [Ca]0 and [Na]0 are consistent with the strength of the tonic tension being determined by a 3Na+ for 1Ca2+ exchange across the cell membrane. 4. The results agree well with those obtained previously with voltage-clamp experiments on the same tissue, and may also help with the interpretation of Ca-flux experiments.

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Selected References

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