Regulation of ocular mucin secretion by P2Y2 nucleotide receptors in rabbit and human conjunctiva

The effects of adenine analogues on secretion of high molecular weight, mucin-like glycoproteins (mucins) by conjunctival goblet cells were investigated using isolated rabbit and human conjunctiva. Mucin secretion was assayed using a quantitative dot-blot assay of Helix pomatia agglutinin-horseradish peroxidase binding to mucins absorbed, to nitrocellulose filters. In rabbit conjunctiva, exogenous ATP (10(-7)-10(-3) M) induced a concentration-dependent, four-fold increase in mucin secretion that reached a plateau 15 min after drug addition. The rank order of potency of agonists was UTP greater than or equal to ATP gamma S > ATP > ITP > ADP much greater than AMP. Adenosine, alpha,beta-methylene-ATP and beta,gamma-methylene-ATP were ineffective in stimulating mucin release. The response to ATP was unmodified by the putative P-2 purinergic antagonists suramin or reactive blue (5 x 10(-5) M). In human conjunctiva, ATP and UTP were nearly equipotent in stimulating mucin secretion with an EC50 congruent to 5 x 10(-6) M.. These findings demonstrate that rabbit and human conjunctival cells contain functional P2Y(2) (formerly designated as P-2U) nucleotide receptors that govern mucin secretion. These receptors may provide useful pharmacological targets for therapeutic modulation of tear film mucins in dry-eye disorders and/or corneal wound healing. (C) 1998 Academic Press.