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Vascular smooth muscle tone is regulated by changes in intracellular free Ca2+ concentration ([Ca2+]i) and myofilament Ca2+ sensitivity. These cellular mechanisms could serve as targets for anesthetic agents that alter vasomotor tone. This study tested the hypothesis that propofol increases myofilament Ca2+ sensitivity in pulmonary artery smooth muscle (PASM) via the protein kinase C (PKC) signaling pathway.Canine PASM strips were denuded of endothelium, loaded with fura-2/AM, and suspended in modified Krebs-Ringer's buffer at 37 degrees C for simultaneous measurement of isometric tension and [Ca2+]i.The KCl (30 mm) induced monotonic increases in [Ca2+]i and tension. Verapamil, an L-type Ca2+ channel blocker, attenuated KCl-induced increases in [Ca2+]i and tension to an equal extent. In contrast, propofol attenuated KCl-induced increases in [Ca2+]i to a greater extent than concomitant changes in tension and caused an upward shift in the peak tension-[Ca2+]i relation. Increasing extracellular Ca2+ in the presence of 30 mM KCl resulted in similar increases in [Ca2+]i in control and propofol-pretreated strips, whereas concomitant increases in tension were greater during propofol administration. The Ca2+ ionophore, ionomycin (0.1 microm), increased [Ca2+]i to approximately 50% of the value induced by 60 mm KCl. Under these conditions, propofol (10, 100 microm) caused increases in tension equivalent to 11 +/- 2 and 28 +/- 3% of the increases in tension in response to 60 mM KCl, whereas [Ca2+]i was slightly decreased. Similar effects were observed in response to the PKC activator, phorbol 12-myristate 13-acetate (PMA, 1 microm). Specific inhibition of PKC with bisindolylmaleimide I before ionomycin administration decreased the propofol- and PMA-induced increases in tension and abolished the propofol- and PMA-induced decreases in [Ca2+]i. Selective inhibition of Ca2+ -dependent PKC isoforms with Gö 6976 also attenuated propofol-induced increases in tension.These results suggest that propofol increases myofilament Ca2+ sensitivity in PASM, and this effect involves the PKC signaling pathway. |
