Sodium ion transport of the ciliary body in vitro

Sodium ion influx and outflux were measured sinmltaneously, with two radioactive isotopes, in the cat ciliary body isolated in vitro. Measurements of membrane potential or short-circuit current were made concurrently with the isotope studies. In the non-short-circuited membrane, where the membrane electromotive force assisted sodium influx, the sodium ion current was two to three times larger than the estimated average short-circuit current, implying the coexistence of an anion transport. In the continuously short-circuited membrane, in tohich the membrane electromotive force was eliminated, a net sodium ion influx persisted and was approximately equal to the short-circuit current. Thus, the in vitro cat ciliary body membrane appears to function as a mixed sodium-anion pump in the non-short-circuited state, but mainly as a sodium ion pump ivhen short circuited.