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ANESTHETIC PHARMACOLOGY

The Mechanisms of Propofol-Mediated Hyperpolarization of In Situ Rat Mesenteric Vascular Smooth Muscle

Tamotsu Nagakawa, MD^*, Mitsuaki Yamazaki, MD^*, Noboru Hatakeyama, MD^*, and Thomas A. Stekiel, MD

*Department of Anesthesiology, Toyama Medical and Pharmaceutical University, Toyama, Japan, and the Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, Wisconsin

Address correspondence and reprint requests to Mitsuaki Yamazaki, MD, Department of Anesthesiology, Toyama Medical and Pharmaceutical University, Toyama, 930–0194, Japan. Address e-mail to myama@ ms.toyama-mpu.ac.jp.

Previously, we reported that propofol hyperpolarizes vascular smooth muscle (VSM) cells of small arteries and veins. The current study was designed to determine whether propofol-mediated hyperpolarization is the result of specific effects on potassium channels known to exist in VSM and on steps in the intracellular nitric oxide (NO), cyclic guanosine monophosphate (cGMP), and cyclic adenosine monophosphate (cAMP) second messenger pathways. VSM transmembrane potentials (E_m) were measured in situ in sympathetically denervated, small mesenteric arteries and veins of Sprague-Dawley rats. Effects of propofol on VSM E_m were determined before and during superfusion with specific inhibitors of VSM calcium-activated (K_Ca), adenosine triphosphate-sensitive (K_ATP), voltage-dependent (K_v), and inward rectifying (K_IR) potassium channels and with endogenous mediators of vasodilation. Propofol significantly hyperpolarized VSM in small mesenteric vessels. This hyperpolarization was abolished on inhibition of K_Ca and K_ATP channel activity and on inhibition of NO and cGMP (but not cAMP). Assuming a close inverse correlation between the magnitude of VSM E_m and contractile force, these results suggest that propofol induces hyperpolarization and relaxation in denervated, small mesenteric vessels by activation of K_Ca and K_ATP channels. Such channel activation may be mediated by activation of NO and cGMP, but not cAMP, second messenger pathways.

IMPLICATIONS: The results of this study indicate that propofol-mediated hyperpolarization in vascular smooth muscle can be attributed to the activation of calcium-activated, adenosine triphosphate-sensitive potassium channels, the nitric oxide, and cyclic guanosine monophosphate pathways.

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