Abstract
1. Ca++ free/EGTA Ringer produces an abrupt change in the Retzius cell (RZ) membrane conductance resulting in a sustained depolarization: a plateau potential. 2. The long-lasting plateau potential is a consequence of Ca++ depletion and not a specific effect of EGTA. 3. The amplitude of this increased conductance plateau depends upon the external concentration of Na+. 4. Mn++ and La+++ completely block Ca++ depletion plateaus while Sr++ and Mg++ decrease plateau duration. Co++ has effects which are intermediate between these two cation groups. 5. We suggest that RZ membranes have a repolarizing potassium conductance which depends primarily upon Ca++ conductance and not membrane potential.
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