Electric current generated by squid giant axon sodium pump: external K and internal ADP effects.
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.
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology*; D001693:Biological Transport, Active / Q000187:drug effects; D049832:Decapodiformes; D004073:Digitoxigenin / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials; D011188:Potassium / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*
D004073:Digitoxigenin; D000244:Adenosine Diphosphate; D012964:Sodium; D011188:Potassium