Actin reorganization in airway smooth muscle cells involves G(q) and G(i-2) activation of Rho

Extracellular stimuli induce cytoskeleton reorganization (stress-fiber form ation) in cells and Ca2+ sensitization in intact smooth muscle preparations by activating signaling pathways that involve Rho proteins, a subfamily of the Ras superfamily of monomeric G proteins. In airway smooth muscle, the agonists responsible for cytoskeletal reorganization via actin polymerizati on are poorly understood. Carbachol-, lysophosphatidic acid (LPA)-, and end othelin-1-induced increases in filamentous actin staining are indicative of actin reorganization ( filamentous-to-globular actin ratios of 2.4 +/- 0.3 in control cells, 6.7 +/- 0.8 with carbachol, 7.2 +/- 0.8 with LPA, and 7. 4 +/- 0.9 with endothelin-1; P < 0.001; n = 14 experiments). Although the e ffect of all agonists was blocked by C3 exoenzyme (inactivator of Rho), onl y carbachol was blocked by pertussis toxin. Although carbachol-induced acti n reorganization was blocked in cells pretreated with antisense oligonucleo tides directed against G alpha(i-2) alone, LPA- and endothelin-1-induced ac tin reorganization were only blocked when both G alpha(i-2) and G(q)alpha w ere depleted. These data indicate that in human airway smooth muscle cells, carbachol induces actin reorganization via a G alpha(i-2) pathway, whereas LPA or endothelin-1 induce actin reorganization via either a G alpha(i-2) or a G(q)alpha pathway.