ISSN:
0091-7419
Keywords:
Life Sciences
;
Molecular Cell Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Internal dialysis techniques have been used to examine the influence of external and internal cations on Ca efflux from ATP-depleted squid axons. The main observation is that Ca efflux is promoted by external Na and inhibited by internal Na. The Na0 -dependent Ca efflux appears to be a function of [Na]03, and is also affected by the membrane potential; a 25 mV depolarization may cause as much as an e-fold decrease in Ca efflux. These data are consistent with a counter-transport exchange of 3Na+-for-1Ca2+. A Ca0-dependent Ca efflux has also been observed; it is prominent in Na sea water or Le sea water, and is markedly diminished in choline sea water. This flux is consistent with the idea of a Ca-Ca exchange diffusion process. Taken together, the Na0 - and the Ca0 -dependent Ca effluxes fit a two-site model for carrier-mediated Ca transport; one site binds two Na+ or one Ca2+, while the second site can bind either one Na+ or one Li+. The data reported here suggest that both sites must be filled on the inward journey, but that only the Ca-binding site need be occupied on the outward journey of the carrier. A mechanism of this type could derive sufficient energy from the Na and voltage gradients to maintain a [Ca2+]0/[Ca2+]i concentration ratio of about 104 in the absence of ATP. The present experiments do not, however, rule out the possible participation of a metabolically driven Ca transport mechanism in vivo.
Additional Material:
14 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jss.400020505
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