Voltage noise accompanying chemically-induced depolarization of insect photoreceptors

Abstract

Intracellular potentials are recorded from photoreceptors in a superfused preparation of the retina of a locust compound eye. Chloral hydrate and alkyl alcohols induce a rapid, superfusing reversible depolarization of these photoreceptors when dissolved in the saline. Analysis of voltage noise accompanying depolarization by chloral hydrate suggests that depolarizing ionic pathways are opened briefly and randomly in time in the photoreceptor membranes. This conclusion is supported by measurements of the cell resistance and of voltage noise amplitude as a function of membrane potential. Replacement of superfusate sodium by choline reversibly reduces the effects of chloral hydrate, suggesting that the ionic pathways opened are permeable by sodium. The voltage noise induced by chloral hydrate is compared to that during depolarization by steady illumination of the same cell. As the illumination intensity is increased, the amplitude and the shape of the power spectrum of light-induced voltage noise approach those of drug-induced noise at the same depolarization level. The possibility that these phenomena represent alterations in the mechanism of phototransduction is discussed.