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. 1973 Jun;231(2):209–232. doi: 10.1113/jphysiol.1973.sp010229

The ionic dependence of the strength and spontaneous relaxation of the potassium contracture induced in the heart of the frog Rana pipiens

R A Chapman
PMCID: PMC1350768  PMID: 4146462

Abstract

1. The tension generated by isolated frog atrial trabecules, during exposure to solutions containing a high potassium concentration, is not maintained but spontaneously relaxes. The final part of this relaxation can be fitted by a single exponential function.

2. The recovery of the tension generating mechanisms following the spontaneous relaxation of a potassium contracture depends on the preceding membrane potential and the time since the last contracture.

3. The rate of the exponential phase of the spontaneous relaxation is independent of the [K]o and hence the membrane potential, the [Ca]o; and when the [Ca]o/[Na]o2 ratio is maintained it is also independent of the [Na]o. This relaxation is not influenced by atropine or pronethalol.

4. When sodium is totally excluded from the bathing medium the rate of relaxation of a later potassium contracture is much increased. It is argued that this change is due to a fall in the intracellular sodium concentration.

5. The consequences of these results are discussed, and the hypothesis that is favoured would require that contraction is induced by a transient release of calcium into the sarcoplasm, probably triggered by a potential dependent, and probably also transient, influx of calcium through the cell membrane. Relaxation is supposed to occur when this activator-calcium is then removed by an intracellular relaxing system that resembles the sarcoplasmic reticulum of other muscles. What this intracellular structure might be, is also discussed.

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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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