ABSTRACT
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 current-voltage characteristics and by the adapting effect of the stimulus on the conductances arising from the PDA, the background light and the alcohol.
Subject(s)
Photoreceptor Cells, Invertebrate/physiology , Retinal Pigments/physiology , Thoracica/physiology , Vision, Ocular/physiology , Action Potentials/physiology , Animals , Membrane Potentials/physiologyABSTRACT
Several recent reports have shown that light absorption by metarhodopsin does not contribute to the excitation of invertebrate photoreceptors at low intensities. Where the pigment transition scheme is known, this result may be used to exclude some or most of the transitions and states of the pigment as sources of the coupling to excitation. The methodology of this approach is described and illustrated.
