Active sodium and chloride transport across the isolated rabbit conjunctiva

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 (I_sc) was 14.4 ± 1.3, μA/cm². 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 l_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 elec-trogenic 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.

Key Words:

• cotransport
• membrane permeability
• tear film
• conjunctiva
• rabbit
• sodium transport
• chloride transport