Pertussis toxin pretreatment alters agonist binding to beta-adrenoceptors in rabbit ventricular myocardium

The influence of pretreatment with pertussis toxin (PTX) on characteristics of beta-adrenoceptor bindings was examined in myocardial ventricular membranes prepared from rabbits which received an intravenous injection of PTX (10 micrograms/kg) or its vehicle. The density and affinity of beta-adrenoceptors assessed by (-)-[125I]iodocyanopindolol were not significantly altered by PTX pretreatment. However, a fraction of agonist binding sites with high affinity significantly increased in PTX-pretreated myocardial membranes. In the presence of 100 microM 5'-guanylyl imidodiphosphate, all agonist binding sites were converted to low-affinity sites in both control and PTX-pretreated membranes. The results suggest that Gi might regulate negatively coupling of beta-adrenoceptors to Gs.