KCl evokes contraction of airway smooth muscle via activation of RhoA and Rho-kinase.
Airway smooth muscle (ASM) cells express voltage-dependent Ca2+ channels, primarily of the L-subtype. These may play a role in excitation-contraction coupling of ASM, although other signaling pathways may also contribute: one of these includes Rho and its downstream effector molecule Rho-associated kinase (ROCK). Although voltage-dependent Ca2+ influx and Rho/ROCK signaling have traditionally been viewed as entirely separate pathways, recent evidence in vascular smooth muscle suggest differently. In this study, we monitored contractile activity (muscle baths) in bronchial and/or tracheal preparations from the pig, cow, and human, and further examined Rho and ROCK activities (Western blots and kinase assays) and cytosolic levels of Ca2+ (fluo 4-based fluorimetry) in porcine tracheal myocytes. KCl evoked substantial contractions that were suppressed in tracheal preparations by removal of external Ca2+ or using the selective L-type Ca2+ channel blocker nifedipine; porcine bronchial preparations were much less sensitive, and bovine bronchi were essentially unaffected by 1 microM nifedipine. Surprisingly, KCl-evoked contractions were also highly sensitive to two structurally different ROCK inhibitors: Y-27632 and HA-1077. Furthermore, the inhibitory effects of nifedipine and of the ROCK inhibitors were not additive. KCl also caused marked stimulation of Rho and ROCK activities, and both these changes were suppressed by nifedipine or by removal of external Ca2+. KCl-induced elevation of [Ca2+]i was not affected by Y-27632 but was reversed by NiCl2 or by BAPTA-AM. We conclude that KCl acts in part through stimulation of Rho and ROCK, possibly secondary to voltage-dependent Ca2+ influx.
Janssen
Luke J
LJ
Asthma Research Group, Firestone Institute for Respiratory Health, Saint Joseph's Hospital, Hamilton, Ontario, L8N 4A6, Canada. janssenl@mcmaster.ca
Tazzeo
Tracy
T
Zuo
Jianmin
J
Pertens
Evi
E
Keshavjee
Shaf
S
D000577:Amides / Q000494:pharmacology; D001980:Bronchi / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D020545:Respiratory Mucosa / Q000187:drug effects / Q000502:physiology*; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
D000577:Amides; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D011725:Pyridines; C108830:Y 27632; D011189:Potassium Chloride; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein; D002118:Calcium