Osmotic properties of the squid giant axon and their modifications.

Volume and morphological changes of the squid giant axons in response to hyper- and hypoosmotic media were examined. In hyperosmotic media, which were made by adding sucrose or sodium chloride to the artificial seawater, the axons behaved approximately as ideal osmometers. The fraction of the osmotically inactive volume was less than 0.05. In hypoosmotic media down to half the osmolality of the artificial seawater, intact squid axons did not show significant volume increases. However, following a combined treatment with hyaluronidase and collagenase, the volume of the squid axons increased in these hypoosmotic media. A wrinkled pattern appeared on the surface of the axons while they were in hyperosmotic media containing excess NaCl or KCl. Trypsin treatment prevented appearance of this surface pattern. Furthermore, no such patterns appeared in media which were made hyperosmotic by the addition of sucrose or sodium glutamate.