[3H]Forskolin binding to cardiac adenylate cyclase in guinea pigs chronically infused with isoproterenol

Lynne McMartin, Roger J. Summers

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Guinea pigs were infused with the β-adrenoceptor agonist isoproterenol (400 μg/kg/hr, 7 days) and cardiac adenylate cyclase was detected using [3H]forskolin. Two populations of [3H]forskolin binding sites were present in heart, the affinities (KD 2 nM and 280 nM) and densities (Bmax 9 and 900 fmol/mg protein) of which were unchanged by isoproterenol infusion compared with vehicle (l mM HCl). The autoradiographic localisation of [3H]forskolin binding was also unchanged. The G protein activators NaF 10 mM and 5′-guanylylimidodiphosphate (Gpp(NH)p) 10 μM increased [3H]forskolin binding in heart from vehicle-treated animals by 100% and 80% respectively. NaF-stimulated binding was unchanged in isoproterenol-treated animals, however, Gpp(NH)p-stimulated binding was reduced by 35% which may indicate an increased influence of Gi.

Original languageEnglish
Pages (from-to)1039-1049
Number of pages11
JournalLife Sciences
Issue number11
Publication statusPublished - 4 Aug 1995
Externally publishedYes


  • adenylate cyclase
  • isoproterenol
  • [H]forskolin

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