Mitochondrial monoamine oxidase‐A‐mediated hydrogen peroxide generation enhances 5‐hydroxytryptamine‐induced contraction of rat basilar artery

BACKGROUND AND PURPOSE We evaluated the role(s) of monoamine oxidase (MAO)‐mediated H2O2 generation on 5‐hydroxytryptamine (5‐HT)‐induced tension development of isolated basilar artery of spontaneously hypertensive rats (SHR) and normotensive Wistar‐Kyoto (WKY) rats. EXPERIMENTAL APPROACH Basilar artery (endothelium‐denuded) was isolated for tension measurement and Western blots. Enzymically dissociated single myocytes from basilar arteries were used for patch‐clamp electrophysiological and confocal microscopic studies. KEY RESULTS Under resting tension, 5‐HT elicited a concentration‐dependent tension development with a greater sensitivity (with unchanged maximum tension development) in SHR compared with WKY (EC50: 28.4 ± 4.1 nM vs. 98.2 ± 9.4 nM). The exaggerated component of 5‐HT‐induced tension development in SHR was eradicated by polyethylene glycol‐catalase, clorgyline and citalopram whereas exogenously applied H2O2 enhanced the 5‐HT‐elicited tension development in WKY. A greater protein expression of MAO‐A was detected in basilar arteries from SHR than in those from WKY. In single myocytes and the entire basilar artery, 5‐HT generated (clorgyline‐sensitive) a greater amount of H2O2 in SHR compared with WKY. Whole‐cell iberiotoxin‐sensitive Ca2+‐activated K+ (BKCa) amplitude measured in myocytes of SHR was approximately threefold greater than that in WKY (at +60 mV: 7.61 ± 0.89 pA·pF−1 vs. 2.61 ± 0.66 pA·pF−1). In SHR myocytes, 5‐HT caused a greater inhibition (clorgyline‐, polyethylene glycol‐catalase‐ and reduced glutathione‐sensitive) of BKCa amplitude than in those from WKY. CONCLUSIONS AND IMPLICATIONS 5‐HT caused an increased generation of mitochondrial H2O2 via MAO‐A‐mediated 5‐HT metabolism, which caused a greater inhibition of BKCa gating in basilar artery myocytes, leading to exaggerated basilar artery tension development in SHR.