Characterization of ep prostanoid receptor subtypes in primary cultures of bovine ciliary epithelial cells by immunofluorescent microscopy and functional studies.

PURPOSE: To determine the expression and functional coupling of EP prostanoid receptor subtypes to second messenger pathways in bovine ciliary epithelium.

METHODS

Primary cultures of bovine ciliary epithelial (BCE) cells were established and maintained in culture up to four passages. EP receptor protein expression was examined by indirect immunofluorescence microscopy with subtype selective antibodies in both tissue sections and primary cultures of BCE cells. Messenger RNA expression was determined using reverse transcription and polymerase chain reaction. The effects of prostanoid agonists on total inositol phosphate accumulation and cAMP formation were used to assess functional activity.

RESULTS

Positive immunoreactivity was obtained in both frozen thin-sections and primary cultures of bovine ciliary process to the prostanoid EP(1 ), EP(2), EP(3) and EP(4) receptor subtypes. Reverse transcription followed by the polymerase chain reaction yielded products corresponding to each of the prostanoid EP subtypes which was confirmed by restriction enzyme analysis. PGE(2) dose-dependently stimulated the accumulation of total inositol phosphates in cultured cells with an EC( 50) value of 100 nM. PGE(2), forskolin and isoproterenol produced dose-dependent increases in cAMP formation with EC(50) values of 100, 300 and 200 nM, respectively. Isoproterenol-stimulated cAMP formation was attenuated by the EP(3) receptor agonist sulprostone in cultured BCE cells. The inhibition elicited by sulprostone was reversed in cells pretreated with pertussis toxin.

CONCLUSIONS

This study demonstrates the presence of functional prostanoid EP receptor subtypes in the bovine ciliary epithelium. EP(1) and EP(4) receptor subtypes were found primarily in the NPE cells, whereas, EP(2) receptor subtype immunofluorescence was detected in the PE cells. EP(3) receptor subtype labeling was observed in both the NPE and the PE cells. PGE(2) produces opposing effects on adenylyl cyclase through EP(2)/EP(4) and EP(3) receptor activation. The predominant effect of PGE(2) is on the adenylyl cyclase stimulatory receptors (EP(2)/EP(4)).