DURAMYCIN INCREASES INTRACELLULAR CALCIUM IN AIRWAY EPITHELIUM

Duramycin increases short-circuit current (I(sc)) and net Cl- secretio n in tracheal epithelium. We measured the intracellular free calcium ( [Ca2+]i) response to duramycin using Indo-1 and bovine and canine trac heal cell suspensions, and the effect of an intracellular calcium chel ator, BAPTA, and the protein kinase C inhibitor, staurosporine, on the I(sc) 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 muM) and staurosporine (5-50 nM) pretreatment blunted the increase in I(sc) and net Cl- secretion produ ced by duramycin. BAPTA also blunted the rise in [Ca2+]i produced by d uramycin (5 x 10(-6) M) in the presence of extracellular calcium (499 +/- 122 nM). In the absence of extracellular calcium, the duramycin-in duced (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 furthe r decreased in the presence of BAPTA to 197 +/- 42 nM. In contrast, st aurosporine (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 da ta demonstrate that duramycin releases calcium from intracellular stor es and stimulates the influx of calcium in airway epithelial cells. Th ese data also demonstrate that, in the presence of protein kinase C pa thway blockade, an increase in intracellular free calcium is not suffi cient for chloride secretion; thus, duramycin-stimulated chloride secr etion may depend upon protein kinase C.