ACTIVE SODIUM AND CHLORIDE TRANSPORT ACROSS THE ISOLATED RABBIT CONJUNCTIVA

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 cm(2) of cross-sectional area. The tissue was bathed with a modified Tyrode's solution at 37 degrees 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 K Omega . cm(2) and the short-circuit current (I-sc) was 14.4 +/- 1.3, mu A/cm(2). Sixty percent of the I-sc could be accounted for by a Na+-dependent, bumetanide-inhibitable Cl- transport directed towards the apical side. The remainder of the I-sc 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 electrogenic Na+-glucose co-carrier. The Cl--dependent I-sc 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 I-sc traverses the epithelium via gap junctions. Our results imply that transport processes at the conjunctiva could influence the composition of the tear film.