Adreno-cholinergic modulation of junctional communications between the pigmented and nonpigmented layers of the ciliary body epithelium

Purpose. Cell-to-cell communications between the epithelial layers of the ciliary body may be critical for aqueous humor production. The aim of this study was to identify pharmacologic agents that affect this path. Methods. Whole New Zealand rabbit ciliary bodies were mounted in Ussing-type chambers with Ca⁺-free and Ca²⁺-rich Tyrode's in the nonpigmented (NPE; aqueous) and pigmented (PE; serosa) epithelial side hemichambers, respectively. The NPE or the PE were then permeabilized, either selectively to monovalent ions with amphotericin B or nonselectively to small solutes with digitonin. Resultant active transport activities were tracked as short circuit currents (I(sc)s). Results. Permeabilization of the NPE with either 10 μM amphotericin B or 10 μM digitonin led to an aqueous-to-serosa-positive I(sc). This I(sc) was inhibited by serosal-side ouabain and heptanol, indicating movement of Na⁺ from the permeabilized NPE to the PE by the interlayer junctional path, followed by PE-to-serosa active Na⁺ transport. Permeabilization of the PE with amphotericin B elicited an I(sc) in the opposite direction. This I(sc) was abolished by aqueous side ouabain and by heptanol, consistent with sequential PE to NPE Na⁺ translocation, followed by active, NPE-to-aqueous transport. Acetylcholine, epinephrine, norepinephrine, and the α₁-adrenergic agonist phenylephrine, but not brominidine, an α₂-adrenergic agonist, each caused an approximately 50% reduction of these currents. The inhibitions were fully dependent on serosal- side Ca²⁺ and were blocked by one calmodulin inhibitor, trifluoperazine, but not by another, calmidazolium. Conclusions. The above observations provide evidence that cholinergic or α₁-adrenergic activation of the PE causes Ca²⁺- dependent inhibition of the NPE-PE junctional path. A trifluoperazine-sensitive entity, which may be distinct from calmodulin, is involved in the inhibition.