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. 1971 Dec;219(1):233–251. doi: 10.1113/jphysiol.1971.sp009659

Excitation—contraction coupling in amphioxus muscle cells

S Hagiwara, Maryanna P Henkart, Y Kidokoro
PMCID: PMC1331627  PMID: 5158596

Abstract

1. Excitation-contraction coupling was studied in myotomal muscles of amphioxus, Branchiostoma californiense.

2. The action potential of a muscle cell produces a twitch with a rise time of 30-40 msec at 11° C and its Q10 is about 2·2.

3. The twitch increases in amplitude with increasing external Ca concentration and is abolished in Ca-free saline (1 mM-EGTA and 55·7 mM-MgCl2); the twitch amplitude is suppressed by Co or La ions.

4. Caffeine at concentrations above 1 mM in the external saline causes a prolongation of the action potential and a contracture which lasts several minutes.

5. After exposure to caffeine the responsiveness of the muscle to subsequent applications of caffeine recovers in normal saline in 20-30 minutes but not in Ca-free saline.

6. The amplitude of the caffeine contracture is independent of the external Ca concentration and is unaltered after the twitch is eliminated in Ca-free saline.

7. After exposure to caffeine a full-sized twitch can be obtained before the responsiveness to caffeine shows any significant recovery.

8. It is concluded that the twitch is produced by the Ca influx resulting from the increased permeability of the muscle cell membrane to Ca during the action potential and that the Ca mobilized by caffeine is not necessary to the initiation of the twitch.

9. Electronmicroscopy shows the existence of sarcoplasmic reticulum.

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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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