ATP-induced mucin release from cultured airway goblet cells involves, in part, activation of protein kinase C.

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Abstract
Extracellular nucleotides stimulate mucin release by binding to the P-2u receptor coupled to phospholipase C via G proteins (Be J. Pharmacol. 103:1053-1056, 1991; Am. J. Respir. Cell Mel. Biol. 8:121-125, 1993). In the present study, we intended to investigate pathways downstream to the phospholipase C activation which is responsible for adenosine triphosphate (ATP)-induced mucin release in hamster tracheal epithelial cells in primary culture. We have found that: (1) Ca2+ ionophores (A23187 and ionomycin) did not affect mucin release even at 1 mu M; (2) thapsigargin (10 mu M), either alone or in combination with ATP (20 mu M), did not enhance mucin release over its respective control group; (3) pretreatment of hamster tracheal surface epithelial (HTSE) cells with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) (50 mu M) did not inhibit ATP-induced mucin release; (4) 4 beta-phorbol 12 alpha-myristate 13-acetate (PMA, 1 mu M) stimulated mucin release and its effect was completely blocked by protein kinase C inhibitors such as sphingosine (10 mu M) and calphostin C (0.1 mu M), whereas ATP-induced mucin release was blocked, only in part, by these inhibitors; (5) desensitization of protein kinase C by pretreatment with PMA inhibited the PMA-induced mucin release completely, however, ATP-induced mucin release was inhibited only partially. We conclude that mucin release by ATP does not require an increase in the intracellular Ca2+ level but involves the activation of protein kinase C. The results also suggest the presence of another mechanism separate from the phospholipase C-protein kinase C pathway for the ATP-induced mucin release.

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