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Effect of overexpressed adenylyl cyclase VI on β 1 ‐ and β 2 ‐adrenoceptor responses in adult rat ventricular myocytes
Author(s) -
Stark Joalice C C,
Haydock Stephen F,
Foo Roger,
Brown Morris J,
Harding Sian E
Publication year - 2004
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0705976
Subject(s) - adenylyl cyclase , myocyte , medicine , endocrinology , chemistry , beta adrenoceptor , adrenergic receptor , receptor
Adenylyl cyclase VI (ACVI) is one of the most abundantly expressed β adrenergic receptor ( β AR)‐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 β 1 adrenergic receptor ( β 1 AR). 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. 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=6.60±0.98 vs 14.2±2.1 fmol cAMP/viable cell, n =4, P <0.05) and in the presence of 1 μ M isoprenaline or 10 μ M forskolin. ACVI myocytes had increased basal contraction (% shortening: GFP vs ACVI: 1.90±1.36 vs 3.91±2.29, P <0.0001) and decreased basal R50 (GFP vs ACVI: 62.6±24.2 ms ( n =50) vs 45.0±17.2 ms ( n =248), P <0.0001). ACVI myocyte responses were increased for forskolin ( E max : GFP=6.70±1.59 ( n =6); ACVI=9.06±0.69 ( n =14), P <0.01) but not isoprenaline. ACVI myocyte responses were increased ( E max : GFP vs ACVI=3.16±0.77 vs 5.10±0.60, P <0.0001) to xamoterol (a partial β 1 AR‐selective agonist) under β 2 AR blockade (+50 n M ICI 118, 551). AS decreased both control and ACVI‐stimulated xamoterol responses ( E max : AS=2.59±1.42, SAS=1.38±0.5). ACVI response was not mimicked by IBMX. Conversely, response through β 2 adrenergic receptor ( β 2 AR) was decreased in ACVI myocytes. In conclusion, ACVI overexpression constitutively increases myocyte contraction amplitudes by raising cAMP levels. Native ACVI did not contribute to basal cAMP production or contraction amplitude and only to a minor extent to the forskolin response. β 1 AR but not β 2 AR coupling was dependent on ACVI.British Journal of Pharmacology (2004) 143 , 465–476. doi: 10.1038/sj.bjp.0705976