Biophysical Journal 61: 1109-1116 (1992)
© 1992 the Biophysical Society

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Charge movement and SR calcium release in frog skeletal muscle can be related by a Hodgkin-Huxley model with four gating particles.

Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.

ABSTRACT

Charge movement currents (IQ) and calcium transients (delta[Ca2+]) were measured simultaneously in frog skeletal muscle fibers, voltage clamped in a double vaseline gap chamber, using Antipyrylazo III as the calcium indicator. The rate of release of calcium from the SR (Rrel) was calculated from the calcium transients using the removal model of Melzer, W., E. Rios, and M. F. Schneider (1987. Biophys. J. 51:849-863.). IQ and delta [Ca2+] were calculated for 100 ms depolarizing test pulses to membrane potentials from -30 to +20 mV. To eliminate an inactivating component of Rrel, each test pulse was preceded by a large, fixed prepulse to +20 mV. The resulting Rrel records, which represent the noninactivating component of Rrel, were compared with integral of IQdt.(Q), the total charge that moves. The voltage dependence of the steady state Rrel was steeper then that of Q and shifted to the right. During depolarization, the Rrel waveform was similar to that of Q but was delayed by several ms, while, during repolarization, Rrel preceded Q. All of these results could be explained with a Hodgkin-Huxley type model for E-C coupling in which four voltage sensors in the t-tubule membrane which give rise to IQ must all be in their activating positions for the calcium release channel in the SR membrane to open.(ABSTRACT TRUNCATED AT 250 WORDS)

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