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 μM 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 μM) was without effect. Theophylline (1 mM) did not alter ATP (10 μM)-induced I(sc) response. Increases in I(sc) induced by ATP and UTP were significantly larger than those by α,β-methylene ATP, β,α-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 μM) 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.