Large-conductance, calcium- and voltage-activated potassium (BK Ca) channels hyperpolarize coronary artery smooth muscle cells, causing vasorelaxation. Dopamine activates BKCa channels by stimulating D1-like receptor-mediated increases in cAMP in porcine coronary artery myocytes. There are two D1-like receptors (R), D 1R and D5R. We hypothesize that the specific D 1-like receptor involved in BKCa channel activation in human coronary artery smooth muscle cells (HCASMCs) is the D5R and that activation occurs via cAMP cross-activation of cGMP-dependent protein kinase (PKG), rather than cAMP-dependent protein kinase (PKA). The effects of D1-like receptor agonists and antagonists on BKCa channel opening in HCASMCs were examined in the presence and absence of PKG/PKA inhibition by cell-attached patch clamp. In the absence of commercially available ligands specific for D1R or D5R, D1R or D5R protein was down-regulated by transfecting HCASMCs with human D1R or D5R antisense oligonucleotides, respectively: cells transfected with scrambled oligonucleotides and nontransfected HCASMCs served as controls. The predominant ion channel conducting outward currents in nontransfected HCASMCs was identified as the large-conductance, calcium- and voltage-activated potassium (BKCa) channel, which was activated by D1-like receptor agonists despite PKA inhibition with (9R,10S,12S)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9, 12-epoxy-1H-diindolo[1,2,3-fg: 3',2',1'-kl]pyrrolo[3,4-i][1,6] benzodiazocine-10-carboxylic acid (KT 5720) (300 nM), but was abolished by inhibitingPKG with 9-methoxy-9-methoxycarbonyl-8-methyl-2, 3,9,10-tetrahydro-8, 11-epoxy-1H,8H,11H-2,7b-11a-triazadibenzo (a,g) cycloocta(cde)-trinden-1-one (KT 5823) (300 nM). D1-like receptor agonists activated BKCa channels in all transfected cells except those transfected with D5R antisense oligonucleotides. Thus, the dopamine (D1-like) receptor mediates activation of BKCa channels in HCASMCs by D5R, not D1R, and via PKG, not PKA. This is the first report of differential D1-like receptor regulation of vascular smooth muscle function in human cells.
Available at: http://works.bepress.com/richard_white/50/