PERTUSSIS TOXIN PRETREATMENT ALTERS AGONIST BINDING TO GAMMA-ADRENOCEPTORS IN RABBIT VENTRICULAR MYOCARDIUM

The influence of pretreatment with pertussis toxin (PTX) on characteri stics of beta-adrenoceptor bindings was examined in myocardial ventric ular membranes prepared from rabbits which received an intravenous inj ection of PTX (10 mu g/kg) or its vehicle. The density and affinity of beta-adrenoceptors assessed by (-)-[I-125]iodocyanopindolol were not significantly altered by PTX pretreatment. However, a fraction of agon ist binding sites with high affinity significantly increased in PTX-pr etreated myocardial membranes. In the presence of 100 mu M 5'-guanylyl imidodiphosphate, all agonist binding sites were converted to low-aff inity sites in both control and PTX-pretreated membranes. The results suggest that G(i) might regulate negatively coupling of beta-adrenocep tors to G(5).