Abstract
1. 1. The possible contribution of an electrogenie sodium pump to the resting membrane potential ( E m ) of smooth muscle of Mytilus has been investigated using glass microelectrodes. 2. 2. E m hyperpolarized by 12 mV in K +-free artificial sea water (ASW), repolarized to the original level upon returning to control ASW. E m was unchanged in ASW containing 10 −M ouabain or strophanthidin during the first 2 hr. 3. 3. Slight membrane depolarization (5–6 mV) occurred after prolonged soaking in K −-free or cardiac glycoside-containing ASW. 4. 4. After restoration to control ASW, the membrane transiently hyperpolarized. The hyperpolarization was blocked by 10 −4 M ouabain. 5. 5. The transient hyperpolarization was also demonstrated in the preparation exposed to isotonic NaCl-EGTA solution during soaking m K +-free ASW. 6. 6. The evidence suggested the existence of an electrogenic sodium extrusion mechanism; however, its activity in normal resting membrane seemed restricted.
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