MEMBRANE DEPOLARIZATION IN NRK FIBROBLASTS BY BRADYKININ IS MEDIATED BY A CALCIUM-DEPENDENT CHLORIDE CONDUCTANCE

The effects of the phosphoinositide-mobilizing agonist bradykinin (BK) on membrane potential and intracellular calcium in monolayers of norm al rat kidney (NRK) fibroblasts were investigated. BK induced a rapid transient depolarization in these cells, which was mimicked by other p hosphoinositide-mobilizing factors such as prostaglandin F-2 alpha (PG F(2 alpha)), lysophosphatidic acid (LPA), platelet-derived growth fact or (PDGF-BB), and serum. Depolarization by BK was independent of extra cellular Ca2+ or Na+. It was shown using extracellular Cl- substitutio ns that the depolarization was caused by an increased Cl- conductance. Depolarization was inhibited by 5-nitro-2-3-phenylpropyl(amino)benzoi c acid (NPPB), niflumic acid, and flufenamic acid, inhibitors of calci um-dependent chloride channels. The depolarization provoked by BK coul d be mimicked by raising intracellular calcium with ionomycin or thaps igargin and could be blocked with geneticin, a blocker of phospholipas e C. When intracellular calcium was buffered by loading the cells with 1,2-bis(2-aminophenoxy)ethane-NNN'N'-tetra-acetic acid (BAPTA), depol arization was prevented. We conclude that in NRK fibroblasts extracell ular stimuli that increase intracellular calcium, depolarize the cells via the activation of a calcium-dependent chloride conductance. In ad dition to an increase in intracellular calcium, depolarization may be an important effector pathway in response to extracellular stimuli in fibroblasts. It is hypothesized that, in electrically coupled cells su ch as NRK fibroblasts, intercellular transmission of these depolarizat ions may represent a mechanism to coordinate uniform multicellular res ponses to Ca2+-mobilizing agonists. (C) 1997 Wiley-Liss, Inc.