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Journal of Experimental Biology 75,237-251 (1978)
Published by Company of Biologists 1978

Effects of Osmotic Stress on the Electrical Activities of the Giant Axon of a Marine Osmoconformer, Sabella Penicillus

A. D. CARLSON ¹, Y. PICHON ², and J. E. TREHERNE ³

¹ The Laboratory, Marine Biological Association, Citadel Hill, Plymouth, U.K.; Department of Cellular and Comparative Biology, State University of New York at Stony Brook, Stony Brook, N.Y. 11790, U.S.A.
² The Laboratory, Marine Biological Association, Citadel Hill, Plymouth, U.K.; Laboratoire de Neurobiologie Cellulaire, Centre Nationale de la Recherche Scientifique, 91190 Gif-sur-Yvette, France
³ The Laboratory, Marine Biological Association, Citadel Hill, Plymouth, U.K.; Department of Zoology, University of Cambridge U.K.

Reprint requests should be addressed to Dr Treherne.

The giant axons of the polychaete, Sabella penicillus, can withstand, in vitro, abrupt changes in osmotic and ionic concentration of the bathing medium in the range measured in the blood of this osmoconformer (543–1236 m-osmol) at different external salinities. Isosmotic dilution of the external ions (i.e. when osmotic concentration was maintained by sucrose) induced a modest hyperpolarization of the axonal membrane and a rapid decline in the overshoot of the action potential. In contrast, abrupt hyposmotic dilution resulted in a relatively slow and complex decline in overshoot in the absence of axonal hyperpolarization. A slow potassium depolarization and rate of decrease in overshoot in sodium-free conditions suggests that there is a reduced intercellular access to the axon surfaces following exposure to hyposmotic media. It is suggested that this restricted access could provide short-term protection from fluctuations in blood osmotic concentration.