Effect of overexpressed adenylyl cyclase VI on b1- and b2- adrenoceptor responses in adult rat ventricular myocytes

1 Adenylyl cyclase VI (ACVI) is one of the most abundantly expressed b adrenergic receptor (bAR)-coupled cyclases responsible for cyclic AMP (cAMP) production within the mammalian myocardium. We investigated the role of ACVI in the regulation of cardiomyocyte contractility and whether it is functionally coupled with b1 adrenergic receptor (b1AR). 2 Recombinant adenoviruses were generated for ACVI and for antisense to ACVI (AS). Adult rat ventricular myocytes were transfected with ACVI virus, AS or both (SAS). Adenovirus for green fluorescent protein (GFP) served as control. Myocyte contraction amplitudes ( % shortening) and relaxation times (R50) were analysed. ACVI function was determined using cAMP assays. 3 ACVI-transfected cells demonstrated a strong 139 kDa ACVI protein band compared to controls. ACVI myocytes had higher steady-state intracellular cAMP levels than GFP myocytes when unstimulated (GFP vs ACVI 6.6070.98 vs 14.272.1 fmol cAMP/viable cell, n 4, Po0.05) and in the presence of 1mM isoprenaline or 10 mM forskolin. 4 ACVI myocytes had increased basal contraction ( % shortening: GFP vs ACVI: 1.9071.36 vs 3.9172.29, Po0.0001) and decreased basal R50 (GFP vs ACVI: 62.6724.2ms (n 50) vs 45.0717.2ms (n 248), Po0.0001). ACVI myocyte responses were increased for forskolin (Emax