Rabbit conjunctival epithelium transports fluid, and P2Y22 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 μA/cm2( n = 16). Four P2Y2 purinergic receptor agonists [UTP and the novel compounds INS365, INS306, and INS440 (Inspire Pharmaceuticals)] added apically (10 μM) resulted in temporary (∼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 μl · h−1 · cm−2 (range 2.1–15.3, n = 20). Fluid transport was stimulated by mucosal additions of 10 μM: 1) UTP, from 7.4 ± 2.3 to 10.7 ± 3.3 μl · h−1 · cm−2, n = 5; and 2) INS365, from 6.3 ± 1.0 to 9.8 ± 2.5 μl · h−1 · cm−2, n = 5. Fluid transport was abolished by 1 mM ouabain ( n = 5) and was drastically inhibited by 300 μM quinidine (from 6.4 ± 1.2 to 3.6 ± 1.0 μl · h−1 · cm−2, n = 4). We conclude that this epithelium secretes fluid actively and that P2Y2 agonists stimulate both Cl− and fluid secretions.