Activation of neurosecretory cells enhances their synthesis of secretory protein.

We have asked whether neurosecretory cells respond to activation by selectively augmenting their synthesis of secretory protein, using the bag cells of Aplysia, which produce and secrete a peptide egg-laying hormone, ELH. Exposure of bag cell organs to 100 mM K+ for 4 h increased their incorporation of tritiated leucine into ELH precursors by about 25%, an effect which persisted for at least 8 h after the stimulus. Since the high potassium treatment had no effect on the rate of loss of label from previously-synthesized ELH proteins, we conclude that the enhanced labeling represents enhanced synthesis. Elevated external potassium did not enhance ELH synthesis in clusters of bag cell somata which had been surgically isolated from their neurites, suggesting that the augmentation of synthesis is not mediated by direct effects of the high potassium solution. Mediation by a secretion-linked process is indicated by the fact that low Ca2+/high Mg2+ media blocked the effect of high K+. Whether the regulatory signal involves receipt of presynaptic transmitter or hormone secretion remains to be determined.