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

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Abstract
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. CGRP (50 nm) activated an inward current at −60 mV in symmetrical 140 mm K+ that was blocked by glibenclamide (10 μm), an inhibitor of ATP‐sensitive potassium (KATP) channels. CGRP‐induced currents were larger in cells dialysed with 0.1 mm ATP than with 3.0 mm ATP. Forskolin (10 μm) activated a glibenclamide‐sensitive current, as did intracellular dialysis with cAMP (100 μm). 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. CGRP‐induced currents were reduced by the PKA inhibitors adenosine 3′,5′‐cyclic monophosphorothioate, RP‐isomer, triethylammonium salt (Rp‐cAMPS; 100 μm) and N‐[2‐((p‐bromocinnamyl)amino)ethyl]‐5‐isoquinolinesulphonamide dihydrochloride (H‐89; 1 μm), and abolished by inclusion of a PKA inhibitor peptide in the pipette solution. The β‐adrenergic agonist isoprenaline (10 μm) also activated a glibenclamide‐sensitive K+ current. CGRP‐induced currents were unaffected by the inhibitor of cGMP‐dependent protein kinase (PKG) KT5823 (1 μm). Sodium nitroprusside (10 μm) 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). Our findings suggest that CGRP activates coronary KATP channels through a pathway that involves adenylyl cyclase and PKA, but not PKG.