Time Courses of Desensitization and Recovery From Adaptation in Mouse Rod Photoreceptors
Sensitivity and dynamic range are two important characteristics of sensory receptors in the nervous system that define the physiological role of these cells. Rod cells in the retina of a mouse have the ability to detect very dim lights by closing cyclic-gated nucleotide channels. This extreme sensitivity would be impractical if the dynamic range on these cells was limited. Adaptation is a process by which the sensitivity of the transduction cascade is adjusted so cells can function within broader ranges of stimuli. Electrical recordings of circulating currents have been used to show that in the presence of steady background light, rods are desensitized so that saturation doesn't occur, and they remain responsive to increments and decrements of illumination. Furthermore, changes in calcium concentration have been proposed to mediate modulations of various molecules within the transduction pathways. In this project, we investigated the time course of desensitization and recovery in adaptation using suction electrode recording. We were able to show, desensitization at various ranges of adapting light, as manifested by the fact that reduction in sensitivity acceleration of recovery is already present at 500 ms. We also demonstrated that in recovery from adaptation, sensitivity of the rod returns back to its dark-adapted levels within 2 seconds. The persistence of adaptation in the form of acceleration of recovery was present with extremely dim lights and the time constant of its recovery to dark-adapted levels was dependent on the intensity of the background light.