P-2u-purinoceptor regulation of chloride secretion in cultured human tracheal submucosal glands

We examined the purinergic regulation of chloride secretion and intracellular calcium ion concentration ([Ca2+](i)) in the cultured epithelial cells passaged from human tracheal submucosal glands. Adenosine, AMP, ADP, ATP, and UTP induced transient short-circuit current (I-sc) responses in a concentration-dependent fashion. The rank. order of peak I-sc responses at 10 mu M concentrations was UTP = ATP > ADP > AMP = adenosine. Diphenylamine-2-carboxylic acid (1 mM) and 4,4'-diisothiocyano-2,2'-stilbene disulfonate (0.5 mM), and quinidine (1 mM) inhibited I-sc responses induced by extracellular nucleotides. However, amiloride (10 mu M) was without effect. Theophylline (1 mM) did not alter ATP (10 mu M)-induced I-sc response. Increases in I-sc induced by ATP and UTP were significantly larger than those by alpha,beta-methylene ATP, beta,gamma-methylene ATP, or 2-methylthio ATP. Extracellular nucleotides caused increases in [Ca2+](i), and the rank order of [Ca2+](i) responses was same as that of I-sc responses. 1,2-Bis(2-aminophenoxy)ethane-N,N,N' ,N'-tetraacetic acid-acetoxymethyl ester (50 mu M) inhibited increases in I-sc and [Ca2+](i) induced by extracellular nucleotides. These results suggest that extracellular nucleotides induce chloride secretion across cultured human tracheal glands via a P-2u-purinoceptor, and this chloride secretion appears to be dependent on increases in [Ca2+](i) and activation of Ca-dependent K channels.