Gα13 regulates methacholine-induced contraction of bronchial smooth muscle via phosphorylation of MLC20

Reversible airway constriction is induced by an increase in airway smooth muscle contractility in response to methacholine likely as a bronchospastic stimulus. Despite the finding of G alpha(12) and G alpha(13) UP-regulation in airway hyperresponsive animals, their functional role of contraction in airway smooth muscle has not been directly explored. This study investigated the differential regulatory role of G alpha(12)/G alpha(13) 3 in methacholine-induced contraction of trachea and bronchus in G alpha(12) or G alpha(13) gene knockout mice after ovalbumin sensitization and challenges. Organ bath assays and videomicroscopy revealed that G alpha(13) deficiency delayed methacholine-induced contractile response of bronchiolar smooth muscle, but not that of tracheal smooth muscle. In primary bronchial smooth muscle cells, knockdown of G alpha(13) blocked methacholine-induced phosphorylation of 20 kDa regulatory light chain of myosin II (MLC20), a prerequisite step for the contractile initiation of actin and myosin. G alpha(13)-dependent MLC20 phosphorylation was confirmed in murine embryonic fibroblasts. After ovalbumin sensitization and challenges, wild type mice exhibited methacholine-induced bronchial contraction of lung tissue. Heterozygous absence of the G alpha(13) gene abrogated methacholine-induced contractions, whereas homozygous absence of the G alpha(12) gene failed to do so. Our findings indicate that G alpha(13), but not G alpha(12), specifically regulates cholinergic bronchial contraction in airway responsiveness via controlling phosphorylation of MLC20 by methacholine. (C) 2009 Elsevier Inc. All rights reserved.