Regulation of Rho/ROCK signaling in airway smooth muscle by membrane potential and [Ca2+]i

• Published in: American journal of physiology. Lung cellular and molecular physiology 2005-10, Vol.289 (4), p.L574-L582
• Main Authors: Liu, Caiqiong, Zuo, Jianmin, Pertens, Evi, Helli, Peter B, Janssen, Luke J
• Format: Article
• Language: English
• Subjects: Animals; Calcium - metabolism; Calcium Channels - drug effects; Calcium Channels - physiology; Cattle; Cells, Cultured; Intracellular Signaling Peptides and Proteins; Membrane Potentials - drug effects; Membrane Potentials - physiology; Muscle, Smooth - cytology; Muscle, Smooth - physiology; Potassium Chloride - pharmacology; Protein-Serine-Threonine Kinases - metabolism; rho-Associated Kinases; rhoA GTP-Binding Protein - metabolism; Signal Transduction - physiology; Trachea - cytology; Trachea - physiology
• ISSN: 1040-0605; 1522-1504
• DOI: 10.1152/ajplung.00134.2005

Asthma Research Group, Firestone Institute for Respiratory Health, St. Joseph's Hospital; and the Department of Medicine, McMaster University, Hamilton, Ontario, Canada Submitted 23 March 2005 ; accepted in final form 20 May 2005 Recently, we have shown that Rho and Rho-activated kinase (ROCK) may become activated by high-millimolar KCl, which had previously been widely assumed to act solely through opening of voltage-dependent Ca 2+ channels. In this study, we explored in more detail the relationship between membrane depolarization, Ca 2+ currents, and activation of Rho/ROCK in bovine tracheal smooth muscle. Ca 2+ currents began to activate at membrane voltages more positive than –40 mV and were maximally activated above 0 mV; at the same time, these underwent time- and voltage-dependent inactivation. Depolarizing intact tissues by KCl challenge evoked contractions that were blocked equally, and in a nonadditive fashion, by nifedipine or by the ROCK inhibitor Y-27632. Other agents that elevate intracellular calcium concentration ([Ca 2+ ] i ) by pathways independent of G protein-coupled receptors, namely the SERCA-pump inhibitor cyclopiazonic acid and the Ca 2+ ionophore A-23187, evoked contractions that were also largely reduced by Y-27632. KCl directly increased Rho and ROCK activities in a concentration-dependent fashion that paralleled closely the effect of KCl on tone and [Ca 2+ ] i , as well as the voltage-dependent Ca 2+ currents that were measured over the voltage ranges that are evoked by 0–120 mM KCl. Through the use of various pharmacological inhibitors, we ruled out roles for Ca 2+ /calmodulin-dependent CaM kinase II, protein kinase C, and protein kinase A in mediating the KCl-stimulated changes in tone and Rho/ROCK activities. In conclusion, Rho is activated by elevation of [Ca 2+ ] i (although the signal transduction pathway underlying this Ca 2+ dependence is still unclear) and possibly also by membrane depolarization per se. myosin light chain phosphatase; RhoA; Rho-activated kinase; voltage-dependent Ca 2+ channels Address for reprint requests and other correspondence: L. J. Janssen, L-314, St. Joseph's Hospital, 50 Charlton Ave. E., Hamilton, Ontario, Canada L8N 4A6 (e-mail: janssenl{at}mcmaster.ca )