Properties of the on-transient of the intracellular response in the barnacle photoreceptor

We have studied the on-transient of the receptor potential of the barnacle photoreceptor. Its amplitude has previously been shown to depend on light intensity and state of light-dark adaptation. We have examined its dependence on 1) the presence of a prolonged depolarizing afterpotential (PDA), 2) a background light, 3) added alcohol, or 4) decreased K⁺ concentration in the bath. We find that the relative on-transient amplitude tends to increase initially with increasing depolarization arising from 1)-4) and then to decrease again at higher depolarization. This behavior is qualitatively explainable by the cell's currentvoltage characteristics and by the adapting effect of the stimulus on the conductances arising from the PDA, the background light and the alcohol.