Experimental analysis of alternative models of charge movement in frog skeletal muscle.

A series of pulse procedures was used to distinguish experimentally between a 'capacitative' (Schneider & Chandler, 1973) and a 'resistive' (Matthias, Levis & Eisenberg, 1980) model of 'charge movements' in skeletal muscle. A general condition describing the conservation of charge in a non-linear capacitor that was used as the basis for the experiments is derived in the Appendix. It was shown that earlier criteria concerning equality of 'on' and 'off' charge in response to large steps are insufficient to exclude resistive models. However, the capacitative, but not the resistive model successfully explained results bearing on charge conservation assessed through pulse procedures involving: (i) small, 10 mV voltage steps from a series of prepulse voltages, (ii) voltage steps to a fixed potential from a series of hyperpolarized voltages, (iii) pulse sequences incorporating a 'staircase' of voltage steps. It is concluded that the earlier use of 'on' and 'off' equality in response to large voltage steps is insufficient to exclude a resistive basis for the non-linear transient. However pulse procedures explicitly designed to distinguish the two models give results consistent with a capacitative model for the non-linear charge and at variance with a resistive one.