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 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'-tetraacetic 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.