Особенности цАМФ-зависимой регулировки каскада фототрансдукции в колбочках

Abstract

Retinal photoreceptor cells, rods and cones, are capable of light adaptation in a wide range of illuminations due to a set of regulatory mechanisms. Among them, the most studied are calcium feedbacks, and they may account approximately 50% of actual regulation of photosensitivity. There are other regulating mechanisms that contribute to adjusting photoreceptor reaction to light depending on the level of illumination, for example, regulation of phototransduction cascade under circadian cycle. During the phase of the circadian cycle, the level of cAMP increases and the sensitivity of rods also increases, which can be considered as an adaptive effect. In cone photoreceptors, operating under high light intensities and losing their contribution in the twilight, rise of photosensitivity may not have adaptive significance. In present study we investigated how the change in [cAMP]in affect the function of phototransduction cascade in carp cones. [cAMP]in in cones was elevated using adenylate cyclase activator forskolin. It has been shown that in cones, forskolin slows down both rising and declining phases of photoresponse. As a result, in cones, unlike rods, forskolin does not increase photosensitivity but causes nearly two-fold decrease of current. Thus, reaction of the cone phototransduction cascade to an increase in cAMP level is distinctly different from reaction of rod photoreceptors. For cones, this effect of [cAMP]in may also have an adaptive significance, not in the sense of increasing sensitivity, but for the purpose of reduction of metabolic load on cells that do not function in the dark phase.