Active sodium and chloride transport across the isolated rabbit conjunctiva

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Abstract
The bulbar-palpebral conjunctiva from albino rabbits was dissected as a cylinder and cut longitudinally to convert it to a flat epithelium that was mounted as a partition between Ussing-type chambers, exposing 0.38 cm2 of cross-sectional area. The tissue was bathed with a modified Tyrode's solution at 37d`C, pH 7.5. The tear-facing side (apical) was 14.6 ± 1.5 mV negative relative to the basolateral side. Transepithelial resistance was 1.23 ± 0.01 KΩ. cm2 and the short-circuit current (Isc) was 14.4 ± 1.3, μA/cm2. Sixty percent of the Isc could be accounted for by a Na+-dependent, bumetanide-inhibitable Cl− transport directed towards the apical side. The remainder of the lsc reflected a Na+ absorptive process at the apical surface that was amiloride resistant. Evidence was obtained that a likely contributor to this activity is an elec-trogenic Na+-glucose co-carrier. The Cl− -dependent Isc was stimulated by forskolin and epinephrine. Permeabilization of the apical membrane with amphotericin B evinced a current carried by a basolateral Na+:K+ pump. An effect by heptanol suggested that part of the Isc traverses the epithelium via gap junctions. Our results imply that transport processes at the conjunctiva could influence the composition of the tear film.