Involvement of Calcium/Camodulin-Dependent Kinase II in the Regulation of Vascular Tone in Porcine Coronary Arteries

Abstract

Objectives: Inhibition of calcium/calmodulin-dependent kinase II (CaMKII) has been shown to reduce vascular contraction and relaxation. The present study examined the role of CaMKII in the different signaling pathways involved in the regulation of vascular tone. Methods: Isolated porcine coronary arteries were incubated in organ chamber for the measurement of isometric tension. They were contracted with cumulative additions of contracting agents, potassium chloride and the thromboxane A2 analogue, U46619, or contracted with U46619 (30 nM) followed by cumulative additions of different relaxing agents, in the presence or absence of the CaMKII inhibitor, KN-93. Results: Inhibition of CaMKII by KN-93 (30 μM) significantly inhibited contractions to potassium chloride (10-70 mM) and U46619 (0.1 nM-1 μM) in porcine coronary arteries without endothelium. While endotheliumdependent nitric oxide (NO)-mediated relaxations to bradykinin (0.1 nM- 1 μM) were significantly inhibited by KN-93, endothelium-dependent hyperpolarization (EDH)-mediated relaxations were not affected. On the other hand, KN-93 inhibited endothelium-independent relaxations to levcromakalim (adenosine triphosphate-sensitive potassium channel opener; 0.1 nM-100 μM), but not those to sodium nitroprusside (NO donor; 0.1 nM- 100 μM). Conclusions: Our data suggested that CaMKII in both the endothelium and smooth muscle of porcine coronary arteries plays a role in the regulation of vascular tone. In the smooth muscle, CaMKII contributes to contraction likely via mechanisms downstream of increases in intracellular calcium concentration. It is also involved in the activation of adenosine triphosphatesensitive potassium channels leading to vascular relaxation. In the endothelium, CaMKII appears to play a role in the release of NO, but not the induction of EDH, for relaxation. (This study was supported by the Small Project Funding of the University of Hong Kong Research Grant).