Functional uncoupling of muscarinic receptors from adenylate cyclase in rat cardiac membranes by the active component of islet-activating protein, pertussis toxin

H. Kurose, M. Ui

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53 Citations (Scopus)

Abstract

Direct effects of islet-activating protein (IAP), pertussis toxin, on membrane preparations from rat heart tissues were studied. The native IAP was without effect, but its A-protomer, an active subunit, was effective after reduction of disulfide bonds in the peptide chain; it catalyzed ADP-ribosylation of the membrane Mr=41,000 protein. Simultaneously, muscarinic receptor-mediated inhibition of adenylate cyclase was abolished. Carbachol, an agonist of muscarinic receptors, bound to membranes with the Hill coefficient smaller than unity. The affinity for the carbachol binding was lowered and the Hill coefficient was increased by guanylylimidodiphosphate (Gpp(NH)p), reflecting the muscarinic receptor coupling to the guanine nucleotide regulatory protein (N). Carbachol bound to the A-protomer-treated membranes with a lower affinity and a higher Hill coefficient and these kinetic values were not altered by Gpp(NH)p, indicating that treatment of membranes with the A-protomer of IAP uncoupled muscarinic receptors from N. This IAP-sensitive N is Ni involved in the cyclase inhibition. Neither β-adrenergic activation of adenylate cyclase nor β-agonist binding to membranes was affected by the A-protomer of IAP. Thus, N (Ns) coupled to β-receptors is not the site of its action. Although the affinity and the Hill coefficient for β-agonist binding was not affected by preactivated cholera toxin either, the effect of Gpp(NH)p to alter these kinetic parameters was much smaller in the cholera toxin-treated membranes than in non-treated membranes. Thus, cholera toxin modified β-receptor coupling to Ns in a manner quite different from IAP-induced modification of muscarinic receptor coupling to Ni.

Original languageEnglish
Pages (from-to)305-318
Number of pages14
JournalJournal of Cyclic Nucleotide and Protein Phosphorylation Research
Volume9
Issue number4-5
Publication statusPublished - Dec 1 1983
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biochemistry

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