Abstract
The effect of subthreshold depolarization on mechanical threshold was investigated in tetrodotoxin-poisoned mammalian and amphibian skeletal muscle fibers using a two-microelectrode voltage-clamp technique. Mechanical threshold was determined with a 2-ms test pulse. The immediate effect of depolarization was inhibition of the mechanical system. The consequent increase in the test pulse threshold was linearly related to the size of the depolarization and there was, on the average, a 10% increase in threshold for a 10-mV depolarization in mammalian fibers. The duration of the inhibitory period was also related to the size of the depolarization. Inhibition was interrupted by the onset of activation (seen as a reduction in the test pulse threshold), and in rat soleus fibers this occurred within 100 ms with a 20-mV depolarization, inhibition decayed within 10 ms. The decay of activation after brief conditioning pulses was initially rapid (on the average, the test pulse threshold recovered to 80% of its control value within 1 ms) and then slow (full recovery took 100-500 ms). After long conditioning pulses, activation often decayed into a period of inhibition. When depolarization (of 20 mV or more) was maintained for several seconds, the fibers became inactivated. Rat extensor digitorum longus and sternomastoid fibers were strongly inactivated by depolarization to -40 mV and the test pulse to +40 mV did not cause contraction.
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- Adams D. J., Smith S. J., Thompson S. H. Ionic currents in molluscan soma. Annu Rev Neurosci. 1980;3:141–167. doi: 10.1146/annurev.ne.03.030180.001041. [DOI] [PubMed] [Google Scholar]
- 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., Chandler W. K., Rakowski R. F. Charge movement and mechanical repriming in skeletal muscle. J Physiol. 1976 Jan;254(2):361–388. doi: 10.1113/jphysiol.1976.sp011236. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Almers W., Best P. M. Effects of tetracaine on displacement currents and contraction of frog skeletal muscle. J Physiol. 1976 Nov;262(3):583–611. doi: 10.1113/jphysiol.1976.sp011611. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Caputo C., Fernandez de Bolaños P. Membrane potential, contractile activation and relaxation rates in voltage clamped short muscle fibres of the frog. J Physiol. 1979 Apr;289:175–189. doi: 10.1113/jphysiol.1979.sp012731. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Caputo C. The time course of potassium contractures of single muscle fibres. J Physiol. 1972 Jun;223(2):483–505. doi: 10.1113/jphysiol.1972.sp009859. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Chandler W. K., Rakowski R. F., Schneider M. F. Effects of glycerol treatment and maintained depolarization on charge movement in skeletal muscle. J Physiol. 1976 Jan;254(2):285–316. doi: 10.1113/jphysiol.1976.sp011233. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Costantin L. L. Contractile activation in frog skeletal muscle. J Gen Physiol. 1974 Jun;63(6):657–674. doi: 10.1085/jgp.63.6.657. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Dulhunty A. F. A refractory period after brief activation of mammalian skeletal muscle fibres. Neurosci Lett. 1979 Oct;14(2-3):223–228. doi: 10.1016/0304-3940(79)96152-4. [DOI] [PubMed] [Google Scholar]
- Dulhunty A. F. Distribution of potassium and chloride permeability over the surface and T-tubule membranes of mammalian skeletal muscle. J Membr Biol. 1979 Apr 9;45(3-4):293–310. doi: 10.1007/BF01869290. [DOI] [PubMed] [Google Scholar]
- Dulhunty A. F. Potassium contractures and mechanical activation in mammalian skeletal muscles. J Membr Biol. 1980 Dec 30;57(3):223–233. doi: 10.1007/BF01869590. [DOI] [PubMed] [Google Scholar]
- FEINSTEIN M. B. INHIBITION OF CAFFEINE RIGOR AND RADIOCALCIUM MOVEMENTS BY LOCAL ANESTHETICS IN FROG SARTORIUS MUSCLE. J Gen Physiol. 1963 Sep;47:151–172. doi: 10.1085/jgp.47.1.151. [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]
- Kovács L., Schneider M. F. Contractile activation by voltage clamp depolarization of cut skeletal muscle fibres. J Physiol. 1978 Apr;277:483–506. doi: 10.1113/jphysiol.1978.sp012286. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Palade P. T., Barchi R. L. Characteristics of the chloride conductance in muscle fibers of the rat diaphragm. J Gen Physiol. 1977 Mar;69(3):325–342. doi: 10.1085/jgp.69.3.325. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sanchez J. A., Stefani E. Inward calcium current in twitch muscle fibres of the frog. J Physiol. 1978 Oct;283:197–209. doi: 10.1113/jphysiol.1978.sp012496. [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]
- Valdiosera R., Clausen C., Eisenberg R. S. Impedance of frog skeletal muscle fibers in various solutions. J Gen Physiol. 1974 Apr;63(4):460–491. doi: 10.1085/jgp.63.4.460. [DOI] [PMC free article] [PubMed] [Google Scholar]