Gap junctions in rabbit corneal epithelium: limited permeability and inhibition by cAMP.
Rabbit corneas were mounted in Ussing chambers, and the apical membrane of the superficial cells (SCs) was permeabilized by exposure to digitonin in a Ca(2+)-free Ringer solution. This treatment resulted in the generation of large (60.7 +/- 13.2 microA/cm2, n = 25) Na(+)-dependent tear (T)-to-stroma (S) short-circuit currents (Isc). The Isc was abolished by ouabain and by 1.4 mM Ca2+ and was inhibited by heptanol, 18 alpha-glycyrrhetinic acid, and dieldrin, effects consistent with the notion that corneal transepithelial fluxes include translocations through gap junctions (GJs) before basolateral membrane transport. T-to-S Isc were also generated when T-side Na+ was replaced by K+, eliciting a T-to-S K+ flux via basolateral K+ channels and when, with either Na+ or K+ on the T side, channels were introduced at the apical membrane with amphotericin B. The Isc in all four conditions exhibited similar sensitivity to GJ inhibitors and were inhibited by adenosine 3',5'-cyclic monophosphate (cAMP) elevation. Fluorophotometry combined with SC permeabilization with digitonin demonstrated that the half-time for the SC to sub-SC movement of 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (mol wt 540) exceeded 3 h. These results indicate that junctional communications along the epithelial stratification axis are highly restricted and modulated by cAMP concentration.
Wolosin
J M
JM
Department of Ophthalmology, Mount Sinai School of Medicine, New York, New York 10029.
D000666:Amphotericin B / Q000494:pharmacology; D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects*; D003315:Cornea / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D000242:Cyclic AMP / Q000494:pharmacology*; D004072:Digitonin / Q000494:pharmacology; D004594:Electrophysiology; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D005452:Fluoresceins; D007365:Intercellular Junctions / Q000187:drug effects / Q000378:metabolism*; D007477:Ions; D011817:Rabbits
D005452:Fluoresceins; D007477:Ions; C057433:2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester; D000666:Amphotericin B; D000242:Cyclic AMP; D004072:Digitonin