Light-induced changes in dye-treated lobster giant axons

Single giant axons from the lobster circumesophageal connective were studied using the sucrose gap voltage-clamp technique. The axon area in the gap was bathed in acridine orange for several minutes and then rinsed for several minutes. Subsequent illumination resulted in progressive prolongation of electrically stimulated action potentials to durations of 150 msec. The prolongation was accompanied by an increase in threshold. Currents in voltage clamp were altered such that transient current inactivation was greatly slowed. The turn on of transient current was somewhat slowed, the voltage at which peak transient current could be obtained was shifted to more positive internal potentials, and transient current at all potentials was decreased. Steady-state current was similarly affected. Low calcium following illumination partially counteracted some of the changes, but not the slowing of inactivation. Low calcium increased the duration of prolonged action potentials. Selective alteration of parameters in the Hodgkin-Huxley equations brought about a qualitative match between computations and data.