The bulbar-palpebral conjunctiva from albino rabbits was dissected as
a cylinder and cut longitudinally to convert it to a flat epithelium t
hat was mounted as a partition between Ussing-type chambers, exposing
0.38 cm(2) of cross-sectional area. The tissue was bathed with a modif
ied Tyrode's solution at 37 degrees C, pH 7.5. The tear-facing side (a
pical) 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 s
hort-circuit current (I-sc) was 14.4 +/- 1.3, mu A/cm(2). Sixty percen
t of the I-sc could be accounted for by a Na+-dependent, bumetanide-in
hibitable Cl- transport directed towards the apical side. The remainde
r of the I-sc reflected a Na+ absorptive process at the apical surface
that was amiloride resistant. Evidence was obtained that a likely con
tributor to this activity is an electrogenic Na+-glucose co-carrier. T
he Cl--dependent I-sc was stimulated by forskolin and epinephrine. Per
meabilization of the apical membrane with amphotericin B evinced a cur
rent carried by a basolateral Na+:K+ pump. An effect by heptanol sugge
sted that part of the I-sc traverses the epithelium via gap junctions.
Our results imply that transport processes at the conjunctiva could i
nfluence the composition of the tear film.