MEMBRANE CURRENT NOISE IN DARK-ADAPTED AND LIGHT-ADAPTED ISOLATED RETINAL RODS OF THE LARVAL TIGER SALAMANDER

1. Low-frequency light-sensitive membrane current noise in isolated ro d photoreceptors of the larval tiger salamander was recorded using suc tion electrodes, in the dark, and during light adaptation by backgroun ds or by bleaching visual pigment. 2. In background light, noise varia nce increases and then decreases. For rods desensitized to similar lev els by bleaching visual pigment, the noise variance either does not ch ange (weak adaptation) or decreases (with stronger adaptation). 3. The power spectral density of the current noise in dark-adapted rods show s a component with half-power cut-off frequency at about 0.1 Hz, attri buted to spontaneous single events and continuous noise from dark phos phodiesterase activity. A second component, with half-power cut-off fr equency at about 1 Hz, may be due to slow components in the light-sens itive channel gating. 4. The power spectral density of the noise in ba ckground light is dominated by noise generated by the background. Back ground light adapts at least the first component of the noise seen in dark-adapted cells. For cells desensitized by bleaching, light adaptat ion of both components of the dark-adapted noise is observed. 5. The r esults confirm that the low-frequency noise in dark-adapted cells aris es from the transduction mechanism of the rod, in that both components can be light adapted, and show that, for rods permanently desensitize d by bleaching, the desensitization is not due to the presence of acti ve visual pigment molecules similar to those produced by background li ght.