EFFECT OF HEPTANOL ON THE SHORT-CIRCUIT CURRENTS OF CORNEA AND CILIARY BODY DEMONSTRATES RATE-LIMITING ROLE OF HETEROCELLULAR GAP-JUNCTIONSIN ACTIVE CILIARY BODY TRANSPORT

Rabbit ciliary body and cornea were mounted in Ussing-type chambers in Tyrode's under voltage clamp and the effects of heptanol, a gap junct ion inhibitor, on the short circuit current generated by each of the r espective epithelia were determined. Studies were carried out either i n control conditions or following amphotericin B permeabilization of e ither the basolateral membrane of the nonpigmented epithelium of the c iliary body or the apical membrane of the corneal epithelium, respecti vely. Previous studies have shown that, following these permeabilizati ons, short circuit currents are established, reflecting aqueous (or te ar) -to-serosa Na+ fluxes, and that Na+ translocation through gap junc tions connecting the individual layers of these tissues constitutes th e major rate limiting step. Heptanol inhibited most of the short circu it current of the amphotericin B-modified ciliary body and cornea and of the unmodified ciliary body epithelium (control). In all these case s, the apparent IC50, was about 0.8 M. In the unmodified corneal epith elium, where ion translocation across the apical membrane constitutes the main rate limiting step for active secretion, 0.4 or 0.8 mM heptan ol induced short circuit current increases; partial inhibition was obs erved only at high concentrations known to cause maximal inhibition of junctional permeability. Heptanol also enhanced the volume regulatory decrease of cultured human NPE cells, a process dependent on cell swe lling-induced stimulation of Cl- and K+ permeabilities. Combined with our previous results demonstrating the lack of heptanol effects on oth er epithelial functions, these data suggest that the effect of heptano l on the active ciliary body transepithelial transport is primarily du e to inhibition of the nonpigmented-pigmented junctional path and that this path is a potential site of rate limitation for the secretory pr ocess. (C) 1997 Academic Press Limited.