Nonlinear relationship between V+max and h infinity in frog skeletal muscle.

The relationship between the maximum velocity of action potential upstroke (V+max) and steady-state Na+ channel inactivation (h infinity) was studied in frog skeletal muscle during repetitive discharges evoked in the presence of cevadine (1 mumol/l). Conventional microelectrodes and vaseline-gap voltage-clamp techniques were used. A severe degree of nonlinearity was found between (h infinity) and (V+max) especially when the Na+ conductance (gNa) was small. The observed nonlinearity could be explained as a property of the normal Na+ channel gating in skeletal muscle rather than that of cevadine-modified channels. Part of this work has been published in abstract form in Biophys. J. 57: 105A, 1990.