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Journal of Experimental Biology 58,1-14 (1973)
Published by Company of Biologists 1973

The Effects of Sodium-Free Solutions on the Fast Action Potentials of Viviparus Contectus (Millet) (Gastropoda: Prosobranchia)

D. B. SATTELLE ¹

¹ A.R.C. Unit of Invertebrate Chemistry and Physiology, Department of Zoology, Cambridge

1. A 2 h exposure of connectives of Viviparus contectus to sodium-free Ringer, in which dextran maintains osmolarity, results in a decline in the conduction velocity of the fast axons to 50% of the value obtained in normal Ringer.

2. The changes in conduction velocity of the fast axons in response to the replacement in stages of the sodium salts of normal Ringer correspond to those exhibited by conventional excitable cells when tris is the substitute, but depart considerably from this behaviour when dextran is the substitute.

3. Experiments employing mannitol, sucrose, raffinose, inulin and dextran to replace the sodium salts of normal Ringer reveal that dextran alone of these non-electrolytes maintains fast action potentials in the absence of sodium.

4. Weight losses of connectives under sodium-free (isosmotic) conditions are greatest and are most rapidly achieved when dextran (of the range of non-electrolytes studied) replaces the sodium salts of normal Ringer. Adjusting to isotonic conditions (8 mM dextran) does not diminish the ability of this non-electrolyte to maintain fast action potentials.

5. During prolonged perfusion of connectives by tris Ringer brief(5 min) exposures to dextran Ringer at 15 min intervals rapidly restore fast action potentials. The decline of conduction velocity in these restored fibres closely follows the normal pattern of decline when function is maintained continuously in dextran Ringer.