Neurohumoral control of ionic pumping in molluscan muscle—II. evidence for an electrogenic sodium pump in radular protractor muscle of Busycon canaliculatum

Abstract

Abstract 1. A sucrose gap technique was used to study the effects of brief periods of superfusion with solutions in which the potassium content of artificial sea water was reduced or omitted. 2. Stepwise reduction in bath potassium had a complex effect, culminating in the response to potassium-free solution. This was composed of a rapid initial hyperpolarizing phase, overtaken by a slower depolarizing phase, which was accompanied by force. 3. Readmission of bath potassium induced a transient after-hyperpolarization. 4. There was a high degree of individual variability in RPM preparations from different animals. This was particularly evident in cases in which either the hyperpolarizing phase or the depolarizing phase predominated, in the response to zero-potassium, but the muscles from any one animal showed reproducible responses. 5. The RPM behaved as predicted on Nernst equation grounds, to the extent that initial hyperpolarization showed stepwise increases with stepwise reduction in [K + ] 0 , but as the steps approached zero-potassium there was a stepwise increase in the slower depolarizing response, suggesting reduction in electrogenic Na-K exchange. 6. In Na-free solution the depolarizing phase of the response to zero-K was abolished, leaving only an enhanced hyperpolarizing phase. 7. Abrupt chilling had a depolarizing effect. 8. There was only a slight increase in resistance during the action of zero K.