Depolarization and Calcium Entry
In presenting this lecture on the occasion of the 80th birthday of Kenneth S. Cole, I am reminded of the fact that he and I (I always think of him as K. C.) have had many conversations about the subject of what is the proper external medium with which to bathe the squid axon. Conventionally, electrophysiologists use seawater but I am sure that they recognize that this is not necessarily an ultrafiltrate of squid blood. When we first started working on the movement of calcium across the membrane of the squid axon, this question of what was the proper external calcium concentration arose once again. Now, the analysis of both seawater and squid blood yields values of about 10 mM for calcium (Shoukimas, Adelman and Sege, 1977) but there are ample reasons for supposing that neither in squid blood nor in seawater does the activity of calcium approach the value of 10mM. This is so because in seawater there are large concentrations of sulfate, and CaS04 is a poorly dissociated substance, in addition to being rather insoluble. In blood, one has binding to a variety of proteins and one has a rather high concentration of sulfates, both organic and inorganic. It was for reasons such as these that Blaustein (1974) calculated that the activity of calcium ion (Ca++) was something like 4 m M around the squid axon.
KeywordsSodium Channel Potassium Channel Calcium Content Calcium Entry Squid Giant Axon
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