Calcium Influx in Internally Dialyzed Squid Giant Axons

I N T R O D U C T I O N Since the f inding that a fraction o f the Ca efflux in squid axons might be involved in a N a < o u p l e d exchange mechanism (Blaustein and Hodgkin , 1969) a great deal o f work has been devoted to analyze this particular unidirectional Ca f u x . Al though not all the features o f the Ca efflux have been firmly established, most o f the quantitative dependencies on Nao, Nat, Cao, Cat, E m, and ATPi are well documen ted in the literature (Baker et al., 1967, Baker, 1972; Baker and McNaughton , 1976; DiPolo, 1973, 1974, 1977; Mullins and Brinley, 1975; Blaustein and Russell, 1975; Blaustein, 1977). This picture is in contrast with our knowledge concerning Ca entry th rough the Na/Ca exchange mechanism. Al though it is known that Ca influx depends on variables such as Nao and Na~, (Baker et al., 1969), at present very little is known about the quantitative relationship between Nat, Ca~, ATPt, and Ca influx. The main purpose o f this paper is to examine the detailed propert ies o f the Ca influx into squid axons J. GEN. PHYSIOL. @ The Rockefeller University Press 9 0022-1295/79/01/0091-2~1.00 91 Volume 73 January 1979 91-115 on Jne 1, 2017 D ow nladed fom Published January 1, 1979