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1 Departments of Pharmacology and Therapeutics and Physiology, Faculty of Medicine, Vancouver, British Columbia, Canada V6T 1Z3; and 2 Institute for Smooth Muscle Biology, Departments of Urology and Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461
Pressure-induced decreases in arterial diameter are accompanied by membrane depolarization and Ca2+ entry via voltage-gated Ca2+ channels. Recent evidence also suggests the involvement of Ca2+ sensitization of the contractile proteins. Both PKC and Rho kinase are candidate second messengers for the mediation of the sensitization process. We investigated the signaling pathways of pressure-induced decreases in rat cerebral artery diameter in vessels that were depolarized with a 60 mM potassium-physiological salt solution (KPSS). Arteries were mounted on a pressure myograph, and pressure-induced constrictions were recorded. In some experiments simultaneous changes in intracellular Ca2+ concentration ([Ca2+]i) were recorded by using fura 2 fluorescence photometry. Pressure increases induced constriction with significant changes in [Ca2+]i at high pressures (60-100 mmHg). The ratio of the change in diameter to change in [Ca2+]i was greater for pressure-induced constriction compared with constriction produced by depolarization with 60 mM KPSS, suggesting that in addition to increases in [Ca2+]i, enhanced myofilament Ca2+ sensitivity occurs during pressure-induced decreases in arterial diameter. Depolarizing the membrane with 60 mM KPSS increased [Ca2+]i via a Ca2+ influx pathway insensitive to PKC inhibition. Cerebral arteries were able to maintain their diameters in the continued presence of 60 mM KPSS. Pressure-induced constriction under these conditions was not associated with further increases in Ca2+ but was abolished by selective inhibitors of PLC, PKC, and Rho kinase. We report for the first time that in rat cerebral arteries, pressure-induced decreases in arterial diameter are not only due to increases in voltage-gated Ca2+ influx but also to accompanying increases in myofilament sensitivity to Ca2+ mediated by PKC/Rho kinase activation.
voltage-gated calcium ion channels; protein kinase C; Rho kinase; myogenic tone; calcium sensitization
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