ATP-sensitive K+ channel activation by calcitonin gene-related peptide and protein kinase A in pig coronary arterial smooth muscle

1. We used patch clamp to study whole-cell K+ currents activated by calcitonin gene-related peptide (CGRP) in smooth muscle cells freshly dissociated from pig coronary arteries. 2. CGRP (50 nM) activated an inward current at -60 mV in symmetrical 140 mM K+ that was blocked by glibenclamide (10 mu M), an inhibitor of ATP-sensitive potassium (K-ATP) channels. CGRP-induced currents were larger in cells dialysed with 0.1 mM ATP than with 3.0 mM ATP. 3. Forskolin (10 mu M) activated a glibenclamide-sensitive current, as did intracellular dialysis with cAMP (100 mu M). The catalytic subunit of cAMP-dependent protein kinase (protein kinase A, PKA), added to the pipette solution, activated equivalent currents in five out of twelve cells. 4. CGRP-induced currents were reduced by the PKA inhibitors adenosine 3',5'-cyclic monophosphorothioate, R-p-isomer, triethylammonium salt (Rp-cAMPS; 100 mu M) and N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulphonamide dihydrochloride (H-89; 1 mu M), and abolished by inclusion of a PKA inhibitor peptide in the pipette solution. 5. The beta-adrenergic agonist isoprenaline (10 mu M) also activated a glibenclamide-sensitive K+ current. 6. CGRP-induced currents were unaffected by the inhibitor of cGMP-dependent protein kinase (PKG) KT5823 (1 mu M). Sodium nitroprusside (10 mu M) did not activate a glibenclamide-sensitive current in cells held at -60 mV, but did activate an outward current at +60 mV that was abolished by KT5823, or by 100 nM iberiotoxin (an inhibitor of BKCa channels). 7. Our findings suggest that CGRP activates coronary K-ATP channels through a pathway that involves adendylyl cyclase and PKA, but not PKG.