Patch-clamp recording of charge movement, Ca2+ current, and Ca2+ transients in adult skeletal muscle fibers

Intramembrane charge movement (Q), Ca2+ conductance (G(m)) through the dihydropyridine-sensitive L-type Ca2+ channel (DHPR) and intracellular Ca2+ fluorescence (F) have been recorded simultaneously in flexor digitorum brevis muscle fibers of adult mice, using the whole-cell configuration of the patch-clamp technique. The voltage distribution of Q was fitted to a Boltzmann equation; the Q(max) V-1/2Q, and effective valence (z(Q)) values were 41 +/- 3.1 nC/mu F, -17.6 +/- 0.7 mV, and 2.0 +/- 0.12, respectively. V-1/2G and z(G) values were -0.3 +/- 0.06 mV and 5.6 +/- 0.34, respectively. Peak Ca2+ transients did not change significantly after 30 min of recording. F was fit to a Boltzmann equation, and the values for V-F1/2 and z(F) were 6.2 +/- 0.04 mV and 2.4, respectively. F was adequately fit to the fourth power of Q. These results demonstrate that the patch-clamp technique is appropriate for recording Q, G(m), and intracellular [Ca2+] simultaneously in mature skeletal muscle fibers and that the voltage distribution of the changes in intracellular Ca2+ can be predicted by a Hodgkin-Huxley model.