Mehta D, Wang Z, Wu M F, Gunst S J
Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46202, USA.
Am J Physiol. 1998 Mar;274(3):C741-7. doi: 10.1152/ajpcell.1998.274.3.C741.
The tyrosine phosphorylation of paxillin increases in association with force development during tracheal smooth muscle contraction, suggesting that paxillin plays a role in the contractile activation of smooth muscle [Z. L. Wang, F. M. Pavalko, and S. J. Gunst. Am. J. Physiol. 271 (Cell Physiol. 40): C1594-C1602, 1996]. We compared the Ca2+ sensitivity of the tyrosine phosphorylation of paxillin and myosin light chain (MLC) phosphorylation in tracheal muscle and evaluated whether MLC phosphorylation is necessary to induce paxillin phosphorylation. Ca(2+)-depleted muscle strips were stimulated with 10(-7)-10(-4) M acetylcholine (ACh) in 0,0.05, 0.1, or 0.5 mM extracellular Ca2+. In the absence of extracellular Ca2+, 10(-4) M ACh induced a maximal increase in paxillin phosphorylation without increasing MLC phosphorylation or force. Increases in extracellular Ca2+ concentration did not further increase paxillin phosphorylation. However, during stimulation with 10(-6) M ACh, paxillin phosphorylation increased with increases in extracellular Ca2+ concentration. We conclude that the tyrosine phosphorylation of paxillin can be stimulated by signaling pathways that do not depend on Ca2+ mobilization and that the activation of contractile proteins is not required to elicit paxillin phosphorylation.
