Abstract
Contractile activation was studied in frog single muscle fibers treated with tetrodotoxin to block action potentials. The membrane potential in a short segment of the fiber was controlled with a two-electrode voltage clamp, and the contractile response of superficial myofibrils in this segment was observed microscopically. The strength-duration relation for contractile activation was similar to that reported by Adrian, Chandler, and Hodgkin (1969); at 3.9°C, the contraction threshold was –44 mV for long depolarizing pulses (100-ms) and increased to +64 mV for 2-ms depolarizations. Hyperpolarizing postpulses shifted the threshold for 2-ms pulses to more positive values, and a similar, but smaller, effect was produced by hyperpolarizing prepulses. The decay of excitability following subthreshold pulses showed two apparently distinct components; at 3.9°C, excitability fell to 50% of its initial value within 4 ms, while the subsequent decline of excitability proceeded with a half-time of about 20 ms.
Full Text
The Full Text of this article is available as a PDF (984.6 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Adrian R. H., Chandler W. K., Hodgkin A. L. The kinetics of mechanical activation in frog muscle. J Physiol. 1969 Sep;204(1):207–230. doi: 10.1113/jphysiol.1969.sp008909. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Adrian R. H., Costantin L. L., Peachey L. D. Radial spread of contraction in frog muscle fibres. J Physiol. 1969 Sep;204(1):231–257. doi: 10.1113/jphysiol.1969.sp008910. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Adrian R. H., Peachey L. D. Reconstruction of the action potential of frog sartorius muscle. J Physiol. 1973 Nov;235(1):103–131. doi: 10.1113/jphysiol.1973.sp010380. [DOI] [PMC free article] [PubMed] [Google Scholar]
- BIANCHI C. P., SHANES A. M. Calcium influx in skeletal muscle at rest, during activity, and during potassium contracture. J Gen Physiol. 1959 Mar 20;42(4):803–815. doi: 10.1085/jgp.42.4.803. [DOI] [PMC free article] [PubMed] [Google Scholar]
- COLE K. S., MOORE J. W. Potassium ion current in the squid giant axon: dynamic characteristic. Biophys J. 1960 Sep;1:1–14. doi: 10.1016/s0006-3495(60)86871-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Costantin L. L., Taylor S. R. Graded activation in frog muscle fibers. J Gen Physiol. 1973 Apr;61(4):424–443. doi: 10.1085/jgp.61.4.424. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Costantin L. L. The effect o f calcium on contraction and conductance thresholds in frog skeletal muscle. J Physiol. 1968 Mar;195(1):119–132. doi: 10.1113/jphysiol.1968.sp008450. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Costantin L. L. The role of sodium current in the radial spread of contraction in frog muscle fibers. J Gen Physiol. 1970 Jun;55(6):703–715. doi: 10.1085/jgp.55.6.703. [DOI] [PMC free article] [PubMed] [Google Scholar]
- González-Serratos H. Inward spread of activation in vertebrate muscle fibres. J Physiol. 1971 Feb;212(3):777–799. doi: 10.1113/jphysiol.1971.sp009356. [DOI] [PMC free article] [PubMed] [Google Scholar]
- HODGKIN A. L., HOROWICZ P. Potassium contractures in single muscle fibres. J Physiol. 1960 Sep;153:386–403. doi: 10.1113/jphysiol.1960.sp006541. [DOI] [PMC free article] [PubMed] [Google Scholar]
- HUXLEY A. F., TAYLOR R. E. Local activation of striated muscle fibres. J Physiol. 1958 Dec 30;144(3):426–441. doi: 10.1113/jphysiol.1958.sp006111. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schneider M. F., Chandler W. K. Voltage dependent charge movement of skeletal muscle: a possible step in excitation-contraction coupling. Nature. 1973 Mar 23;242(5395):244–246. doi: 10.1038/242244a0. [DOI] [PubMed] [Google Scholar]