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Am J Physiol Cell Physiol 235: C63-C68, 1978;
0363-6143/78 $5.00
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AJP - Cell Physiology, Vol 235, Issue 1 63-C68, Copyright © 1978 by American Physiological Society

ARTICLES

Electric current generated by squid giant axon sodium pump: external K and internal ADP effects

R. F. Abercrombie and P. de Weer

The operation of the sodium pump of giant axons of the squid, Loligo pealei, has been studied simultaneously in two independent ways: 1) by measuring sodium efflux with 22Na, and 2) by calculating the transmembrane current generated by the pump from measurements of membrane resistance and digitalis-sensitive membrane potential. In normal, untreated axons, the effect of increasing the external potassium concentration on both sodium efflux and pump current is similar, which suggests that Na:K pump stoichiometry remains relatively constant in the range of 0-20 mM external K. The data are compatible with a 3:2 Na:K ratio. In axons whose intracellular ADP level has been elevated by injection of L-arginine, a large, electrically silent, cardiotonic steroid-sensitive sodium efflux takes place in the absence of external potassium; this suggests that pump-mediated Na:Na exchange is 1:1 or electroneutral. Finally, elevation of external potassium levels causes the appearance, in high-ADP axons, of electrogenic pumping, with little effect on sodium efflux; hence, in contrast to what is seen in normal (low-ADP) axons, the charge translocated, per sodium ion extruded, increases sharply with increasing extracellular potassium levels.


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J. A. Hernandez and E. Cristina
Modeling cell volume regulation in nonexcitable cells: the roles of the Na+ pump and of cotransport systems
Am J Physiol Cell Physiol, October 1, 1998; 275(4): C1067 - C1080.
[Abstract] [Full Text] [PDF]


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