DOPA decarboxylase and potassium stimulation of ciliary activity was measured in the gill of Mytilus edulis. DOPA decarboxylase inhibitors (STH, and a-methyl-DOPA) decreased the decarboxylase activity in extracts of gill with subsequent enhancement of potassium stimulation of ciliary activity. Intramuscular injection of STH and a-methyl-DOPA caused a gradual decrease in the DOPA decarboxylase and green-fluorphore activities with an increase in lateral ciliary activity in response to potassium stimulation. Recovery was observed ten days after a single dose of a-methyl-DOPA. Intramuscular injection of 6-OH-DOPA caused a rapid decrease in the DOPA decarboyxlase and green-fluorophore activities with a rapid increase in lateral ciliary activity in response to potassium stimulation. However, there was a decrease in all three parameters to near zero activity within 10 days.
This study shows that potassium enhancement of lateral ciliary activity is correlated with and may depend on the amount of DOPA decarboxylase in the gill. A decrease in this enzyme results in a potentiation of the potassium effect on lateral ciliary activity.