title: Charge inactivation in the membrane of intact frog striated muscle fibers.
abstract: 1. Charge movements were compared in normally polarized and depolarized intact frog muscle fibres under voltage clamp. 2. The membrane capacitance was linear through positive control steps made consistently from a holding voltage of -10 mV, in agreement with earlier reports from cut fibres. 3. A shift in holding voltage from -90 to -10 mV reduced both the absolute amount and the voltage dependence of charge movement elicited by voltage steps imposed from a fixed conditioning voltage of -180 mV. The charge transferred by steps from -180 to -20 mV was 43.8 +/- 1.14 nC/microF in fully polarized fibres and 21.7 +/- 1.49 nC/microF in the same depolarized fibres (means +/- S.E. of the mean; four fibres). 4. Charge movement in response to steps from -90 to -20 mV increased from 10.4 +/- 1.60 nC/microF to 28.4 +/- 2.42 nC/microF (five fibres) within 30s of changing the holding voltage from -10 to -90 mV. 5. The same fibres also showed significant charge movement between voltages of -180 and -90 mV. However, shifts in holding voltage did not significantly alter the maximum value of this charge, around 10-11 nC/microF. 6. Membrane capacitance as measured by small steps to a voltage of -90 mV remained constant despite holding potential changes, or lidocaine (10 mM) treatment. 7. The same results were obtained whether the above procedures were applied to fibres exposed to normal extracellular [Ca2+], or in Ca(2+)-free media. In both cases tubular cable corrections did not affect the results. 8. These findings suggest independent charge I and charge II systems in which inactivation of charge I is not associated with its interconversion into charge II.
authors.affiliation: Physiological Laboratory, Cambridge.
authors.forename: C L
authors.initials: CL
authors.lastname: Huang
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D004594:Electrophysiology; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009132:Muscles / Q000502:physiology*; D011896:Rana temporaria