Increased numbers of ion channels promoted by an intracellular second messenger

The anomalous rectifier potassium current in Aplysia neurons was examined to determine the immediate cause of an increase in conductance induced by serotonin and mediated by adenosine 3',5'-monophosphate. Voltage-dependent cesium ion block and steady-state current power spectral density were measured under voltage clamp before and after application of serotonin. The amplitude of the anomalous rectifier conductance was increased by adding serotonin, but the shapes of the conductance-voltage curve and the power spectrum were not altered. Calculation of the number of functional channels and of the single-channel conductance from the power spectra indicates that the serotonin-induced increase in conductance resulted from an increase in the number of functional channels, while the single-channel conductance and the open-channel probability were unchanged.