Regulation of NO-dependent acetylcholine relaxation by K+ channels and the Na+-K+ ATPase pump in porcine internal mammary artery.

This study was designed to determine whether K+ channels play a role in nitric oxide (NO)-dependent acetylcholine relaxation in porcine internal mammary artery (IMA). IMA segments were isolated and mounted in organ baths to record isometric tension. Acetylcholine-elicited vasodilation was abolished by muscarinic receptor blockade with atropine (10(-6)M). Incubation with indomethacin (3 x 10(-6)M), superoxide dismutase (150 U/ml) and bosentan (10(-5)M) did not modify the acetylcholine response ruling out the participation of cyclooxygenase-derivates, reactive oxygen species or endothelin. The relaxation response to acetylcholine was strongly diminished by NO synthase- or soluble guanylyl cyclase-inhibition using L-NOArg (10(-4)M) or ODQ (3 x 10(-6)M), respectively. The vasodilation induced by acetylcholine and a NO donor (NaNO(2)) was reduced when rings were contracted with an enriched K+ solution (30 mM), by voltage-dependent K+ (K(v)) channel blockade with 4-amynopiridine (4-AP; 10(-4)M), by Ca(2+)-activated K+ (K(Ca)) channel blockade with tetraethylammonium (TEA; 10(-3)M), and by apamin (5 x 10(-7)M) plus charybdotoxin (ChTx; 10(-7)M) but not when these were added alone. In contrast, large conductance K(Ca) (BK(Ca)), ATP-sensitive K+ (K(ATP)) and inwardly rectifying K+ (K(ir)) channel blockade with iberiotoxin (IbTx; 10(-7)M), glibenclamide (10(-6)M) and BaCl(2) (3 x 10(-5)M), respectively, did not alter the concentration-response curves to acetylcholine and NaNO(2). Na+-K+ ATPase pump inhibition with ouabain (10(-5)M) practically abolished acetylcholine and NaNO(2) relaxations. Our findings suggest that acetylcholine-induced relaxation is largely mediated through the NO-cGMP pathway, involving apamin plus ChTx-sensitive K+ and K(v) channels, and Na+-K+-ATPase pump activation. Copyright (c) 2010 Elsevier B.V. All rights reserved.