Antagonists of the TMEM16A calcium-activated chloride channel modulate airway smooth muscle tone and intracellular calcium.

ABSTRACT

BACKGROUND: Perioperative bronchospasm refractory to ß agonists continues to challenge anesthesiologists and intensivists. The TMEM16A calcium-activated chloride channel modulates airway smooth muscle (ASM) contraction. The authors hypothesized that TMEM16A antagonists would relax ASM contraction by modulating membrane potential and calcium flux. METHODS: Human ASM, guinea pig tracheal rings, or mouse peripheral airways were contracted with acetylcholine or leukotriene D4 and then treated with the TMEM16A antagonists benzbromarone, T16Ainh-A01, N-((4-methoxy)-2-naphthyl)-5-nitroanthranilic acid, or B25. In separate studies, guinea pig tracheal rings were contracted with acetylcholine and then exposed to increasing concentrations of isoproterenol (0.01 nM to 10 µM) ± benzbromarone. Plasma membrane potential and intracellular calcium concentrations were measured in human ASM cells. RESULTS: Benzbromarone was the most potent TMEM16A antagonist tested for relaxing an acetylcholine -induced contraction in guinea pig tracheal rings (n = 6). Further studies were carried out to investigate the clinical utility of benzbromarone. In human ASM, benzbromarone relaxed either an acetylcholine- or a leukotriene D4-induced contraction (n = 8). Benzbromarone was also effective in relaxing peripheral airways (n = 9) and potentiating relaxation by ß agonists (n = 5 to 10). In cellular mechanistic studies, benzbromarone hyperpolarized human ASM cells (n = 9 to 12) and attenuated intracellular calcium flux from both the plasma membrane and the sarcoplasmic reticulum (n = 6 to 12). CONCLUSION: TMEM16A antagonists work synergistically with ß agonists and through a novel pathway of interrupting ion flux at both the plasma membrane and sarcoplasmic reticulum to acutely relax human ASM.