Na⁺ and cl^- fluxes, and effects of pharmacological agents on the short-circuit Current of the isolated rabbit iris-ciliary body

Unidirectional Na⁺ and Cl^- fluxes were measured across the isolated rabbit iris-ciliary body under short-circuited conditions. Na⁺ fluxes were in the range of 9-13 μeq/hr.cm², and Cl^- fluxes varied between 7-12 μeq/hrμcm². A statistically significant net Na⁺ or Cl^- flux could not be found. Ouabain, 5×10^-5 M, did not change the Na⁺ or Cl^- flux in either direction despite a marked effect on the short-circuit current (SCC). There was a disagreement between the electrical conductance calculated from unidirectional fluxes and electrical measurements, suggesting the presence of electrically silent exchange mechanisms. Theophylline and isobutyl methylxanthine stimulated the SCC, whereas epinephrine, trifluormethazolamide and diisothiocyanostilbene disulfonic acid inhibited the SCC. Furosemide had a minor inhibitory effect, and the Ca²⁺ ionophore A23187 was without effect. Amphoterlcin B produced a substantial stimulation of the SCC from the aqueous side but an inhibition of the SCC from the blood side. This dual effect is consistent with the presence of Na⁺-K⁺ pumps in the basolateral membranes of both the pigmented and non-pigmented cell layers of the ciliary body.