Calcium regenerative potentials inMytilus edulis gill abfrontal ciliated epithelial cells

Abstract

The abfrontal cilia ofMytilus edulis gill become active when touched. The properties of the unique ciliated abfrontal cells have been determined electrophysiologically. 1. Mechanical stimulation of the abfrontal cells produces Ca++ dependent generator and regenerative potentials, strongly suggested through Ca++ removal or Cd++ substitution. 2. Sodium is not required for either motility or electrical activity in the abfrontal cells, but K+and possibly Cl− are involved in the repolarization, as indicated by TEA iontophoretic injections and Cl− free seawater substitution. EGTA iontophoretic injections produce long lasting depolarizations. A Ca++ deactivated Ca++ conductance or a Ca++ activated K+ conductance is implicated. 3. Both the activation of ciliary beat and the electrical events propagate in a decrementai manner; electron microscopy indicates extensive septate junctions but no obvious gap junctions. 4. Iontophoretic injection of EGTA, followed by mechanical stimulation, results in stepwise repolarization as one coupled cell after another repolarizes in accord with its relative degree of EGTA loading. 5. High external K+ depolarizes the abfrontal cells sufficiently that they will fire, but depolarization by current injection is ineffective since the current is apparently shunted through the low resistance cell bodies. Resistance measurements taken during the repolarization of regenerative potentials indicate little change compared to that of the resting resistance. These facts suggest that the excitable membrane is in the cilia. 6. Ca++ based regenerative potentials are the underlying basis for the activation of motility in these ciliated abfrontal cells.