Membrane charge moved at contraction thresholds in skeletal muscle fibres

The Journal of Physiology
P Horowicz, M F Schneider

Abstract

1. The current I(Q) due to membrane charge movement and the threshold pulse duration t(th) required to produce microscopically just-detectable contraction were determined for pulses to a variety of membrane potentials in tendon-terminated short segments of cut frog skeletal muscle fibres voltage-clamped using a single gap technique.2. The time course Q(t) of membrane charge movement was calculated as the running integral of I(Q). The threshold charge Q(th) moved by pulses which produced just-detectable contraction was estimated as Q(t(th)).3. Q(th) was constant for pulses to potentials ranging from about -45 mV, the rheobase potential for contraction, to about -15 mV, where t(th) was about 9 msec. The mean Q(th) from fourteen fibres was 11.5 nC/muF, when the holding potential was about -100 mV.4. Prepulses of 50 msec which were themselves sub-rheobase for producing contraction decreased the t(th) for an immediately following test pulse. The total threshold charge moved during the prepulse and during t(th) of the test pulse was equal to Q(th) for the test pulse without prepulse.5. Items 3 and 4 above indicate that t(th) is determined by the time required to move a set amount of intramembrane charge, independent of the kinetics o...Continue Reading

Citations

Jan 1, 1992·Progress in Biophysics and Molecular Biology·A F Dulhunty
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