Regulation of the Ca2+ dependence of smooth muscle contraction

Da Chun Tang, James T. Stull, Yasutaka Kubota, Kristine E. Kamm

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Cellular mechanisms for the regulation of Ca2+-dependent myosin light chain phosphorylation were investigated in bovine tracheal smooth muscle. Increases in the free intracellular Ca2+ concentration ([Ca2+]i), light chain phosphorylation, and force were proportional to carbachol concentration. KCaM, the concentration of Ca2+/calmodulin required for half-maximal activation of myosin light chain kinase, also increased proportionally, presumably due to Ca2+-dependent phosphorylation of the kinase. Isoproterenol treatment inhibited agonist-induced contraction by decreasing [Ca2+]i and thereby light chain phosphorylation. Depolarization by increasing concentrations of KCl also resulted in proportional increases in [Ca2+]i, KCaM, light chain phosphorylation, and force. However, the [Ca2+]i required to obtain a given value of either light chain phosphorylation or KCaM was greater in KCl-depolarized tissues compared to carbachol-treated tissues. In muscles contracted with KCl, isoproterenol treatment resulted in diminished light chain phosphorylation and force without alterations in [Ca2+]i- or KCaM. Thus, isoproterenol inhibition of KCl-induced contraction results from a cellular mechanism different from that found in agonist-induced contraction. In neither case does isoproterenol produce relaxation by altering the calmodulin activation properties of myosin light chain kinase.

Original languageEnglish (US)
Pages (from-to)11839-11845
Number of pages7
JournalJournal of Biological Chemistry
Issue number17
Publication statusPublished - Jun 15 1992


ASJC Scopus subject areas

  • Biochemistry

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