Effects of extracellular ATP on ion transport and [Ca2+](i) in Mongolian gerbil middle ear epithelium

The present study investigates the effects of ATP on ion transport and Ca2+ mobilization in primary cultures of gerbil middle ear epithelium. Extracellular ATP and other nucleotides elicited a transient increase in short-circuit current (I-sc) in a dose-dependent manner. The rank order of potency in I-sc responses corresponded with the sequence of the P-2u purinergic gic receptor when applied to the mucosal or the basolateral side. Extracellular ATP induced a rise in the intracellular Ca2+ concentration ([Ca2+](i)) in a dose-dependent manner. A similar rank order of potency in the ATP-induced increases in [Ca2+](i) was observed. The time courses of the [Ca2+](i) responses induced by ATP closely paralleled those of the I-sc responses. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid acetoxymethyl ester greatly reduced the increase in the I-sc and [Ca2+](i) responses to ATP. Diphenylamine-2-carboxylate, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, quinidine, and Ba2+ significantly blocked the ATP-stimulated I-sc. Glibenclamide had no effect on the ATP-stimulated I-sc. These results are consistent with the hypothesis that extracellular ATP and other nucleotides induce Cl- secretion across the apical membrane in cultured gerbil middle ear epithelium by activation of the apical Cl- channels via multiple modes of regulation.