THE INVOLVEMENT OF THE SODIUM-POTASSIUM PUMP IN POSTJUNCTIONAL SUPER-SENSITIVITY OF THE GUINEA-PIG VAS-DEFERENS AS ASSESSED BY [H-3]OUABAIN BINDING

  • 1 January 1981
    • journal article
    • research article
    • Vol. 219  (1) , 163-169
Abstract
Postjunctional supersensitivity of the guinea-pig vas deferens results partly from partial depolarization of the cell membrane. The depolarization results from a reduction in the activity of the Na-K pump. The Na, K+-ATP activity of subcellular fractions from supersensitive vas deferens is reduced. To determine whether the biochemical alterations seen in subcellular fractions correlate with Na-K pump sites in intact tissues, the binding of [3H] ouabain to intact vas deferens was studied. [3H]ouabain binds to membrane sites which have the characteristics expected of Na+, K+-ATP. Specific binding was saturable and reversible. Scatchard analysis of ouabain-binding in control tissues yielded a single class of binding sites with a dissociation constant (KD) of 156 .+-. 7 nM and maximum no. of binding sites (Bmax) of 558.7 .+-. 15.6 femtomol/mg wet wt. [3H]Ouabain binding was displaceable by several cardiac glycosides and aglycones, but not by steroid hormones or sodium vanadate. Alteration of concentrations of Na+ and K+ markedly affected ouabain binding, Denervation (with 6-hydroxydopamine), decentralization or reserpine treatment for 1 day, which do not produce supersensitivity, did not alter the Bmax, whereas 5-7 days after these procedures, when supersensitivity was present, the Bmax was significantly reduced by 20-40%. KD was not changed by any of the treatments. A reduction in the Na-K pump sites contributes to postjunctional supersensitivity.