Chloride ion transport in the isolated ciliary body. II. Ion substitution experiments.

Unidirectional chloride ion jiuxes were measured in the cat ciliary body isolated as a living membrane in vitro. A statistically significant net chloride ion influx (nutrient to secretory) was demonstrated both in the presence of the spontaneous membrane potential and in short-circuited membranes. The isotopically measured net chloride ion influx exceeded the short-circuit current of the membrane, which implied the existence of a net transport of other ion(s). Comparison of the sodium and chloride partial conductances with the total membrane conductance also suggested the existence of other conductive ionic transport. The active transport of chloride ions explains the polarity of the membrane potential observed in vitro, in which the ciliary epithelial surface of the membrane is electronegative relative to its stromal (scleral) surface. The invitro active chloride ion transport also correlates well with the chemically demonstrated excess of chloride in the aqueous humor over that required for thermodynamic equilibrium with plasma. The chloride ion transport system is discussed in relation to its possible importance as a target system for the action of acetazolamide.