Duramycin Increases Intracellular Calcium in Airway Epithelium

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Abstract
Duramycin increases short-circuit current (Isc) and net Cl- secretion in tracheal epithelium. We measured the intracellular free calcium ([Ca2+]i) response to duramycin using Indo-1 and bovine and canine tracheal cell suspensions, and the effect of an intracellular calcium chelator, BAPTA, and the protein kinase C inhibitor, staurosporine, on the Isc and [Ca2+]i response to duramycin. [Ca2+]i increased in a dose-dependent manner from basal levels of 34 +/- 5 to 949 +/- 136 nM at 5 x 10(-6) M duramycin. Both BAPTA (50 microM) and staurosporine (5-50 nM) pretreatment blunted the increase in Isc and net Cl- secretion produced by duramycin. BAPTA also blunted the rise in [Ca2+]i produced by duramycin (5 x 10(-6) M) in the presence of extracellular calcium (499 +/- 122 nM). In the absence of extracellular calcium, the duramycin-induced (5 x 10(-6) M) rise in [Ca2+]i was blunted from 949 +/- 136 nM (stimulation in the presence of Ca2+) to 621 +/- 122 nM, and was further decreased in the presence of BAPTA to 197 +/- 42 nM. In contrast, staurosporine (50 nM) pretreatment had no effect on the rise in [Ca2+]i produced by duramycin (basal 90 +/- 27 to 861 +/- 110 nM at 5 x 10(-6) M). Duramycin had no effect on [Ca2+]i in human neutrophils. These data demonstrate that duramycin releases calcium from intracellular stores and stimulates the influx of calcium in airway epithelial cells. These data also demonstrate that, in the presence of protein kinase C pathway blockade, an increase in intracellular free calcium is not sufficient for chloride secretion; thus, duramycin-stimulated chloride secretion may depend upon protein kinase C.