The involvement of the sodium-potassium pump in postjunctional supersensitivity of the guinea-pig vas deferens as assessed by [3H]ouabain binding.
Previous evidence has suggested that postjunctional supersensitivity of the guinea-pig vas deferens results, in part, from partial depolarization of the cell membrane. The depolarization is believed to result from a reduction in the activity of the Na-K pump. Indeed, the Na, K+ -adenosine triphosphatase activity of subcellular fractions from supersensitive vas deferens is reduced. In order to determine whether the biochemical alteration seen in subcellular fractions correlate with Na-K pump sites in intact tissues, we have studied the binding of [3H] ouabain to intact vas deferens. [3H]ouabain binds to membrane sites which have the characteristics expected of Na+, K+ - adenosine triphosphatase. 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 a maximum number of binding sites (Bmax) of 558.7 +/- 15.6 fmol/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 to 7 days after these procedures, when supersensitivity was present, the Bmax was significantly reduced by 20 to 40%. The KD was not changed by any of the treatments. These data provide additional support for the concept that a reduction in the NaK pump sites contributes to postjunctional supersensitivity.
D000818:Animals; D001339:Autonomic Fibers, Preganglionic / Q000502:physiology; D001693:Biological Transport, Active; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009121:Muscle Denervation; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014649:Vas Deferens / Q000187:drug effects / Q000294:innervation / Q000378:metabolism
D010042:Ouabain; D012964:Sodium; D011188:Potassium