Synaptic stimulation alters protein phosphorylation in vivo in a single Aplysia neuron

Protein phosphorylation was examined in the identified Aplysia neuron R15, in vivo, after the intracellular injection of [gamma-(32)P]ATP. Two-dimensional gel electrophoretic analysis indicates that at least 70 proteins are phosphorylated within R15 during a 50-min labeling period. Application of serotonin (5HT) results in an increase in K(+) conductance in R15 and a concomitant change in the phosphorylation pattern: there are increases or decreases in the phosphorylation of some proteins, and at least five phosphoproteins appear that are not observed in control cells. Dopamine causes a decrease in voltage-dependent inward conductance in R15 and also alters the phosphorylation pattern: several of the phosphorylation changes are similar to those produced by 5HT, while others are unique to dopamine. Stimulation of the branchial nerve leading to the abdominal ganglion results in a long-lasting synaptic hyperpolarization of R15. The conductance changes underlying this response include an increase in K(+) conductance (identical to that produced by 5HT) together with a decrease in voltage-dependent inward conductance (identical to that produced by dopamine). The phosphorylation changes induced in R15 by branchial nerve stimulation resemble a combination of the changes induced by 5HT and dopamine. The results demonstrate that synaptic stimulation can modulate the phosphorylation of specific proteins in a single identified postsynaptic neuron and are consistent with the hypothesis that protein phosphorylation can regulate the regulate the activity of neuronal ion channels.