Intracellular Cl- fluxes play a novel role in Ca2+ handling in airway smooth muscle

• Published in: American journal of physiology. Lung cellular and molecular physiology 2006-06, Vol.290 (6), p.L1146-L1153
• Main Authors: Hirota, Simon, Trimble, Nancy, Pertens, Evi, Janssen, Luke J
• Format: Article
• Language: English
• Subjects: Acetylcholine - pharmacology; Angiogenesis Inhibitors - pharmacology; Animals; Calcium - physiology; Cattle; Chlorides - metabolism; In Vitro Techniques; Kinetics; Muscle Contraction - drug effects; Muscle Contraction - physiology; Muscle, Smooth - drug effects; Muscle, Smooth - physiology; Nifedipine - pharmacology; Niflumic Acid - pharmacology; Nitrobenzoates - pharmacology; Trachea - physiology
• ISSN: 1040-0605; 1522-1504
• DOI: 10.1152/ajplung.00393.2005

Asthma Research Group, Firestone Institute for Respiratory Health, St. Joseph's Healthcare; and Department of Medicine, McMaster University, Hamilton, Ontario, Canada Submitted 13 September 2005 ; accepted in final form 12 January 2006 Intracellular Ca 2+ is actively sequestered into the sarcoplasmic reticulum (SR), whereas the release of Ca 2+ from the SR can be triggered by activation of the inositol 1,4,5-trisphosphate and ryanodine receptors. Uptake and release of Ca 2+ across the SR membrane are electrogenic processes; accumulation of positive or negative charge across the SR membrane could electrostatically hinder the movement of Ca 2+ into or out of the SR, respectively. We hypothesized that the movement of intracellular Cl – (Cl ) across the SR membrane neutralizes the accumulation of charge that accompanies uptake and release of Ca 2+ . Thus inhibition of SR Cl – fluxes will reduce Ca 2+ sequestration and agonist-induced release. The Cl – channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB; 10 –4 M), previously shown to inhibit SR Cl – channels, significantly reduced the magnitude of successive acetylcholine-induced contractions of airway smooth muscle (ASM), suggesting a "run down" of sequestered Ca 2+ within the SR. Niflumic acid (10 –4 M), a structurally different Cl – channel blocker, had no such effect. Furthermore, NPPB significantly reduced caffeine-induced contraction and increases in intracellular Ca 2+ concentration ([Ca 2+ ] i ). Depletion of Cl , accomplished by bathing ASM strips in Cl – -free buffer, significantly reduced the magnitude of successive acetylcholine-induced contractions. In addition, Cl – depletion significantly reduced caffeine-induced increases in [Ca 2+ ] i . Together these data suggest a novel role for Cl fluxes in Ca 2+ handling in smooth muscle. Because the release of sequestered Ca 2+ is the predominate source of Ca 2+ for contraction of ASM, targeting Cl fluxes may prove useful in the control of ASM hyperresponsiveness associated with asthma. chloride; 5-nitro-2-(3-phenylpropylamino)benzoic acid; niflumic acid; calcium handling; excitation-contraction coupling Address for reprint requests and other correspondence: L. J. Janssen, L-314, St. Joseph's Healthcare, 50 Charlton Ave. East, Hamilton, Ontario, Canada L8N 4A6 (e-mail: janssenl{at}mcmaster.ca )