Involvement of proteins in light resetting ocular circadian oscillators of Aplysia

Abstract

The effect of inhibitors of protein synthesis on the phase shifting action of light was investigated. Anisomycin and cycloheximide appeared to block advance phase shifts produced by light. This result suggested that light might phase shift by changing the synthesis of some proteins. Examining proteins separated by two-dimensional gel electrophoresis, we found that incorporation of amino acids into 11 proteins was changed during a 6-h light pulse. Nine of these 11 proteins were affected by light in a phase-dependent manner. Elevated extracellular potassium and 8-bromo-guanosine 3',5'-cyclic monophosphate (cGMP), two treatments that mimic effects of light on the rhythm, also changed amino acid incorporation into a number of proteins. All of the five proteins affected by 8-bromo-cGMP were also affected in the same manner by light. Three proteins were affected similarly by elevated potassium, light, and 8-bromo-cGMP. Exposure of eyes to label at different times after light treatment showed that the effects of light on some proteins were long lasting. In addition, some proteins were not affected during light but were affected only several hours after light. Some of the eye proteins affected by light were also altered by serotonin (5-HT), another phase-shifting agent. The proteins affected by light, elevated potassium, 8-bromo-cGMP, and 5-HT are candidates for components of the circadian system either as an element of the entrainment pathway or the oscillator mechanism.