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-adrenoreceptor-mediated PASM contraction
Center for Anesthesiology Research, Division of Anesthesiology and Critical Care Medicine, Cleveland Clinic Foundation, Cleveland, Ohio 44195
Our objectives were to
identify the relative contributions of intracellular free
Ca2+ concentration ([Ca2+]i) and
myofilament Ca2+ sensitivity in the pulmonary artery smooth
muscle (PASM) contractile response to the
-adrenoreceptor agonist
phenylephrine (PE) and to assess the role of PKC, tyrosine kinases
(TK), and Rho kinase (ROK) in that response. Our hypothesis was that
multiple signaling pathways are involved in the regulation of
[Ca2+]i, myofilament Ca2+
sensitization, and vasomotor tone in response to
-adrenoreceptor stimulation of PASM. Simultaneous measurement of
[Ca2+]i and isometric tension was performed
in isolated canine pulmonary arterial strips loaded with fura 2-AM.
PE-induced tension development was due to sarcolemmal Ca2+
influx, Ca2+ release from inositol
1,4,5-trisphosphate-dependent sarcoplasmic reticulum Ca2+
stores, and myofilament Ca2+ sensitization. Inhibition of
either PKC or TK partially attenuated the sarcolemmal Ca2+
influx component and the myofilament Ca2+ sensitizing
effect of PE. Combined inhibition of PKC and TK did not have an
additive attenuating effect on PE-induced Ca2+
sensitization. ROK inhibition slightly decreased
[Ca2+]i but completely inhibited myofilament
Ca2+ sensitization. These results indicate that PKC and TK
activation positively regulate sarcolemmal Ca2+ influx in
response to
-adrenoreceptor stimulation in PASM but have relatively
minor effects on myofilament Ca2+ sensitivity. ROK is the
predominant pathway mediating PE-induced myofilament Ca2+ sensitization.
intracellular calcium ion; myofilament calcium ion sensitivity; phenylephrine; vascular smooth muscle; pulmonary artery smooth muscle; protein kinase C
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