Coupling of the canine renal parathyroid hormone receptor to adenylate cyclase: modulation by guanyl nucleotides and N-ethylmaleimide.

Abstract

Guanyl nucleotides greatly enhance PTH stimulation of renal adenylate cyclase activity. As part of an investigation of the mechanism of this potentiation, we evaluated the effect of guanosine triphosphate (GTP) and a GTP analog, guanylimidodiphosphate [Gpp(NH)p] on the specific binding of l25I-labeled bovine (b) PTH-(l–34) to canine renal cortical plasma membranes. Dissociation of [l25I]bPTH-(l–34) from receptors was slow (t½ 200 min) in the absence of added guanyl nucleotide, whereas in the presence of GTP or Gpp(NH)p (100 μM), dissociation was rapid (t½ 1 min). The increase in dissociation rate prompted by Gpp(NH)p was reflected in a 3- to 4-fold decrease in PTH receptor affinity, from 5 nM to 17 nM. In contrast to the slow dissociation rate of the l25I-labeled agonists [Nle8,Nle18,Tyr34]bPTH-(l–34)amide and bPTH(l–34), the dissociation rate of the l25I-labeled antagonist analog of PTH [Nle8,Nle18,Tyr34]bPTH-(3–34)amide was rapid (t½ 2 min). Moreover, binding of the labeled PTH antagonist analog was not...