AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 1 256-R262, Copyright © 1990 by American Physiological Society
Involvement of proteins in light resetting ocular circadian oscillators of Aplysia
U. Raju, S. J. Yeung and A. Eskin
Department of Biochemical and Biophysical Sciences, University of Houston, Texas 77204-5500.
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.
