Rabbit conjunctival epithelium transports fluid, and P2Y2(2) receptor agonists stimulate Cl(-) and fluid secretion

Abstract

Rabbit conjunctival epithelium exhibits UTP-dependent Cl(-) secretion into the tears. We investigated whether fluid secretion also takes place. Short-circuit current (I(sc)) was 14.9 +/- 1.4 microA/cm(2) (n = 16). Four P2Y(2) purinergic receptor agonists [UTP and the novel compounds INS365, INS306, and INS440 (Inspire Pharmaceuticals)] added apically (10 microM) resulted in temporary (approximately 30 min) I(sc) increases (88%, 66%, 57%, and 28%, respectively; n = 4 each). Importantly, the conjunctiva transported fluid from serosa to mucosa at a rate of 6.5 +/- 0.7 microl x h(-1) x cm(-2) (range 2.1--15.3, n = 20). Fluid transport was stimulated by mucosal additions of 10 microM: 1) UTP, from 7.4 +/- 2.3 to 10.7 +/- 3.3 microl x h(-1) x cm(-2), n = 5; and 2) INS365, from 6.3 +/- 1.0 to 9.8 +/- 2.5 microl. h(-1) x cm(-2), n = 5. Fluid transport was abolished by 1 mM ouabain (n = 5) and was drastically inhibited by 300 microM quinidine (from 6.4 +/- 1.2 to 3.6 +/- 1.0 microl x h(-1) x cm(-2), n = 4). We conclude that this epithelium secretes fluid actively and that P2Y(2) agonists stimulate both Cl(-) and fluid secretions.