Changes in protein phosphorylation in the eye of Aplysia associated with circadian rhythm regulation by serotonin

Serotonin (5-HT) shifts the phase of the circadian oscillator of the eye of Aplysia californica in a phase dependent manner. This indicates that 5-HT acts, either directly or through some intermediaries, on a component of the oscillator. Since our goal is to identify the components of the oscillator, we are following the pathway through which 5-HT has its effect on the rhythm. The effect of 5-HT on the rhythm has been shown to be mediated by an increase in intracellular cyclic adenosine-3',5'-monophosphate (cAMP). The most likely action of cAMP is to activate cAMP-dependent protein kinase. Therefore, we used two-dimensional polyacrylamide gel electrophoresis to investigate changes in 32P labelled phosphoproteins which occur with 5-HT and other treatments. Fourteen proteins showed increased incorporation of 32P when eyes were exposed to treatments of 5-HT from CT 06 to 12. Two proteins showed decreased incorporation. 8-bt-cAMP mimicked all but one of the increases and both decreases in incorporation produced by 5-HT. 8-bt-cAMP increased incorporation into three additional proteins and decreased incorporation into three others that were not affected by 5-HT. Incorporation into one protein was increased by 5-HT but decreased by 8-bt-cAMP. By comparison, light, which has little or no effect on the rhythm at this phase, only affected one protein. The protein increased by light was also increased by 5-HT. Tetradecanoic phorbol acetate (TPA), administered during CT 06-12, also had little effect on the rhythm at this phase. TPA increased incorporation into twenty proteins and decreased incorporation into three.(ABSTRACT TRUNCATED AT 250 WORDS)