Regulation of Intracellular Calcium by Carbon Monoxide in Human Bronchial Epithelial Cells

Abstract

Background/Aims: Carbon monoxide (CO) is an important autocrine/paracrine messenger involved in a variety of physiological and pathological processes. This study aimed to investigate the regulatory role of CO released by CO-releasing molecule-2 (CORM-2) in a P2Y receptor-mediated calcium-signaling pathway in the human bronchial epithelial cell line, 16HBE14o-. Methods: Intracellular calcium ([Ca²⁺]_i) was measured by fura-2 microspectrofluorimetry. D-myo-inositol-1-phosphate (IP₁) levels and cGMP-dependent protein kinase activity (PKG) were also quantified. Results: The exogenous application of CORM-2 increased both intracellular Ca²⁺ and IP₁, which are inhibited by U73122, a phospholipase C (PLC) inhibitor. In contrast, the P2Y₂/P2Y₄ receptor-mediated intracellular Ca²⁺ release and influx induced by UTP were inhibited in the presence of CORM-2. However, CORM-2 did not affect the store-operated Ca²⁺ entry (SOCE) induced by thapsigargin (Tg). Moreover, the inhibitory effect of CORM-2 on UTP-induced calcium increase could be attenuated by a soluble guanylyl cyclase (sGC) inhibitor, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), or a Protein Kinase G (PKG) inhibitor, KT5823, suggesting the involvement of sGC/PKG signaling in this process. Conclusion: CORM-2 serves a dual role in modulating [Ca²⁺]_i in 16HBE14o- cells. Thus, CO released by CORM-2 may act as a regulator of calcium homeostasis in human airway epithelia. These findings help further elucidate the function of CO in many physiological and pathological conditions.