BACKGROUND: Activation of beta adrenoreceptors by catecholamines is an important mechanism for increasing the inotropic state of the heart. The objectives of the current study were to investigate the effects of propofol on beta-adrenoreceptor-mediated increases in cardiomyocyte intracellular Ca2+ concentration ([Ca2+]i), cell shortening, L-type Ca2+ current (ICa) and cyclic adenosine monophosphate (cAMP) accumulation. The authors also investigated the site of action of propofol in the beta-adrenoreceptor signaling pathway, as well as the role of protein kinase C (PKC), and tested the hypothesis that propofol would inhibit the beta-adrenoreceptor signaling pathway via a PKC-dependent mechanism. METHODS: Freshly isolated ventricular myocytes were obtained from adult rat and guinea pig hearts. Myocyte shortening (video edge detection) and [Ca2+]i (fura-2, 340/380 ratio) were monitored simultaneously in individual cells. Conventional whole cell patch clamp analysis was used to measure the ICa in individual myocytes. cAMP production was assessed in suspensions of myocytes using an enzyme immunoassay kit. RESULTS: Propofol (0.1-10 mum) had no effect on steady state [Ca2+]i, cell shortening, ICa, or cAMP production. In contrast, propofol caused dose-dependent decreases in isoproterenol-stimulated increases in [Ca2+]i, shortening, ICa, and cAMP. Forskolin-induced increases in [Ca2+]i, shortening, and cAMP production were not altered by propofol. PKC activation with phorbol myristate acetate attenuated isoproterenol-stimulated cAMP production. Inhibition of PKC with bisindolylmaleimide (broad range inhibitor) or Go 6976 (inhibitor of Ca2+-dependent PKC isoforms) abolished propofol-induced inhibition of isoproterenol-stimulated increases in [Ca2+]i, shortening, and cAMP production. CONCLUSIONS: Clinically relevant concentrations of propofol attenuate beta-adrenergic signal transduction in cardiac myocytes via inhibition of cAMP production. The inhibitory site of action of propofol is upstream of adenylyl cyclase and involves activation of PKC alpha.
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