Beta-adrenergic receptor desensitization in the early stage of hereditary cardiomyopathy in hamsters.

The beta-adrenergic receptor (beta AR)/adenylyl cyclase signalling pathway was examined in cardiac membranes from cardiomyopathic Syrian hamsters. Three stages were examined during the progression of this hereditary cardiomyopathy (30 days old, prenecrotic phase; 60 days old, necrotic phase; and 120 days old, compensatory phase). Isoproterenol-stimulated adenylyl cyclase activity was decreased by 32 +/- 16% in 30-day-old cardiomyopathic hamsters, compared with age-matched controls. This was not accompanied by any change in the fluoride- or forskolin-stimulated activities, suggesting that the decrease reflects a perturbation of the receptor-mediated stimulation. Neither the density nor the subcellular distribution of the beta AR, as assessed by [125I]iodocyanopindolol binding assays, was affected in these animals. However, the agonist binding properties of the beta AR were significantly affected. Indeed, the effect of guanyl nucleotides on isoproterenol binding was decreased in 30-day-old cardiomyopathic hamsters. Given that guanyl nucleotide sensitivity is correlated with the ability of the beta AR to productively interact with Gs protein, these results suggest that the decreased beta-adrenergic-stimulated adenylyl cyclase activity results from a functional uncoupling of the beta AR with no change in receptor density. The desensitization of the beta-adrenergic-stimulated adenylyl cyclase was transient, since no change in isoproterenol-stimulated adenylyl cyclase was detected in 60- and 120-day-old hamsters, compared with age-matched controls. Similarly, the receptor number and distribution were not affected at those ages.(ABSTRACT TRUNCATED AT 250 WORDS)