Comparative effects of external monovalent cations on sodium pump activity and ouabain inhibition rates in squid giant axon.

Abstract

SUMMARY1. A number of external monovalent cations were compared with regard to their effects on Na pump rate and the rate of ouabain inhibition of the pump in squid giant axon.2. External ions which stimulate active Na efflux (K, Rb, and Cs) were found to decrease the rate at which low concentrations of ouabain inhibit the pump, and those ions which inhibit the pump externally (Na and Li) to increase the rate of inhibition.3. In Na-and Li-containing solutions, pump rate appeared to be the major factor in determining the rate of ouabain inhibition regardless of whether K, Cs, or Rb was used to stimulate active Na efflux.4. When choline was substituted for external Na, ouabain inhibition rates were more than twice as rapid when Cs was used as the pump-stimulating cation than when K was activating the pump to a similar level.5. These results suggest that external monovalent cations modulate ouabain inhibition in squid axon at two classes of sites: pump activation sites, and also separate regulatory sites, whose occupation can significantly increase the rate of ouabain inhibition independent of pump turnover rate.

Phentolamine selectively affects the fast sodium component of sensory adaptation in an insect mechanoreceptor

“…The two components contribute approximately equally to the total increase in threshold current with depolarization, and this increase is responsible for the rapid adaptation of the tactile spine. The two components can also be separated using different drugs, the slow component being selectively reduced by Ouabain (French, 1989b j , which inhibits electrogenic sodium pumps (Hobbs, 1982), whereas the fast component is reduced by N-chlorosuccinimide (NCS) and chloramine-T (CT) (French, 1989a), which selectively affect sodium channel inactivation (Wang, 1984a). These findings indicate that rapid adaptation is caused by both an electrogenic sodium pump and sodium channel inactivation.…”

Coupling ratio of the Na-K pump in the lobster cardiac ganglion.

“…If this hypothesis is correct, then in Na-containing saline, the external face of the pump molecule must be loaded with 2 K before it can cycle, because of inhibition by external Na; in contrast, in the Na-free condition, the pump can cycle either loaded or partially loaded, because of the removal of Na inhibition . Hobbs (1982) recently suggested from ouabain inhibition studies that in Na-free media the pump could cycle in squid axon with less than its full complement of K ions . The pump coupling ratio in the absence of external Na would be somewhat K dependent and would vary from 3 :1 to 3 :2 with changes in external K concentration .…”