Figure 2. Effect of stimulus strength on latency of regenerative potentials and changes in [Ca²⁺]_i evoked in a single bundle of antral circular muscle.

A, B and D, regenerative potentials (a) and the associated changes in [Ca²⁺]_i (b) triggered by passing depolarizing current pulses (c) through the second intracellular electrode. A, successive responses triggered by a threshold depolarizing current pulse. B, regenerative potentials triggered by a depolarizing current pulse of increased intensity. C, the relationship between current strength and mean latency of the increases in [Ca²⁺]_i. Each ▪ denotes the mean of latency of onset of [Ca²⁺]_i, the error bars represent ± 1 s.e.m (n = 10). Note that the latency shortens with increased strength and approaches a minimum value of about 1.1 s. The resting membrane potential was −61 mV. D, a regenerative potential of minimum latency with the time course of the associated change in [Ca²⁺]_i obtained by averaging 30 successive responses. Note that the onset of the increase in [Ca²⁺]_i lags behind the onset of applied depolarization by some 900 ms but corresponds with the start of the regenerative response. The resting membrane potential was −60 mV. The left hand voltage, calcium ratio, current and time calibration bars apply to the membrane potential, [Ca²⁺]_i and current traces shown in A and B. The right hand calibration bars apply to traces shown in D.