Calcium-activated potassium channel family in coronary artery bypass grafts.

Abstract

We examined the expression, distribution, and contribution to vasodilatation of the calcium-activated potassium (K_Ca) channel family in the commonly used coronary artery bypass graft internal thoracic artery (ITA) and saphenous vein (SV) to understand the role of large conductance K_Ca (BK_Ca), intermediate-conductance K_Ca (IK_Ca), and small-conductance K_Ca (SK_Ca) channel subtypes in graft dilating properties determined by endothelium-smooth muscle interaction that is essential to the postoperative performance of the graft. Real-time polymerase chain reaction and western blot were employed to detect the messenger RNA and protein level of K_Ca channel subtypes. Distribution of K_Ca channel subtypes was examined by immunohistochemistry. K_Ca subtype-mediated vasorelaxation was studied using wire myography. Both ITA and SV express all K_Ca channel subtypes with each subtype distributed in both endothelium and smooth muscle. ITA and SV do not differ in the overall expression level of each K_Ca channel subtype, corresponding to comparable relaxant responses to respective subtype activators. In ITA, BK_Ca is more abundantly expressed in smooth muscle than in endothelium, whereas SK_Ca exhibits more abundance in the endothelium. In comparison, SV shows even distribution of K_Ca channel subtypes in the 2 layers. The BK_Ca subtype in the K_Ca family plays a significant role in vasodilatation of ITA, whereas its contribution in SV is quite limited. K_Ca family is abundantly expressed in ITA and SV. There are differences between these 2 grafts in the abundance of K_Ca channel subtypes in the endothelium and the smooth muscle. The significance of the BK_Ca subtype in vasodilatation of ITA may suggest the potential of development of BK_Ca modulators for the prevention and treatment of ITA spasm during/after coronary artery bypass graft surgery.