Selective Enhancement of β-Adrenergic Receptor Signaling by Overexpression of Adenylyl Cyclase 6: Co-Localization of Receptor and Adenylyl Cyclase in Caveolae of Cardiac Myocytes

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We investigated the effect of adenovirally mediated overexpression of adenylyl cyclase type 6 (AC6), a major form of AC expressed in mammalian heart, on G protein-coupled receptor regulation of cAMP production in neonatal rat ventricular myocytes. Following gene transfer of AC6, isoproterenol- and forskolin- stimulated increases in cAMP were markedly enhanced, whereas basal levels of cAMP and responses to several other agonists that stimulate cAMP formation, e.g., prostaglandin E2 (PGE2), H2 agonist, glucagon, and A2 agonist were not increased. Studies to test whether the selective enhancement in b-adrenergic receptor (AR) response might result from inhibition of AC6 by Gai and Gbg indicated that pertussis toxinsensitive inhibition by the muscarinic cholinergic agonist carbachol was unaltered in myocytes overexpressing AC6. Pertussis toxin treatment failed to reveal an enhancement by AC6 overexpression of basal or PGE2-stimulated cAMP. Immunoblot analysis of membrane fractions indicated that b1-AR and AC6 are expressed in fractions enriched in caveolin-3 and morphologic caveolae. The data suggest that loss of Gi-mediated inhibition is not the mechanism for enhancement of b-ARstimulated cAMP formation and that key components of b-ARmediated activation of AC exist in caveolae of cardiac myocytes, providing a means by which b-AR response is selectively enhanced by increasing AC6 expression.


This article was originally published in Molecular Pharmacology, volume 57, in 2000.


American Society for Pharmacology and Experimental Therapeutics (ASPET)