CHARGE CONSERVATION IN INTACT FROG SKELETAL-MUSCLE FIBERS IN GLUCONATE-CONTAINING SOLUTIONS

1. The conservation of intramembrane charge was investigated in intact voltage-clamped frog skeletal muscle fibres under conditions that min imized time-dependent ionic currents and so facilitated precise determ ination of capacitative charge. 2. Prolonged (q(gamma)) transients wer e demonstrated in 3,4-diaminopyridine and tetraethylammonium gluconate -containing low [Ca2+] solutions in response to 125 ms pulses that exp lored the voltage range -90 to -20 mV. The tetracaine-sensitive, q(gam ma), component then accounted for a significant proportion (over 50 %) of available charge. 3. Both delayed 'on' q(gamma) currents and 'off' current tails decayed to steady direct current (DC) baselines without significant residual ionic current slopes in the chosen extracellular solutions. This suggested that the current transients represented cap acitative decays. It was also compatible with the precise determinatio n of effective charge by integration. 4. The advent of 'on' q(gamma) c urrent was accompanied by increased 'off' charge. Thus, charge was con served through all 'on' and 'off' steps and through test voltages that extended from the threshold appearance of q(gamma) as a slow transien t to its full merger with the earlier q(beta) decay at stronger depola rizations. 5. Charge conservation persisted through a wide range of 'o n' pulse durations between 60 and 370 ms and was therefore independent of the interval following the q(gamma) decay. 6. The quantity of q(ga mma) charge remained a monotonic single-valued function of test voltag e, whether this potential was reached directly from the -90 mV holding potential or following: a prepulse to -10 mV. 7. These findings sugge st that the q(gamma) charge movement represents the electrical signatu re of an intramembrane entity whose transitions are primarily driven b y, and therefore conserved with, the steady-state potential.