Proline transport by rabbit ciliary body-iris in vitro.

The rabbit ciliary body-iris preparation in vitro shows concentrative uptake of C-proline which is resistant to anoxia and to cyanide; inhibited by ouabain; and abolished in the absence of external sodium or by cold (0° C). It has a Q,o (27 to 37° C.) of 1.7. Uptake is decreased by preloading with unlabeled proline. Exchange diffusion of the accelerative type is demonstrable during efflux of >C-proline. Inhibitory effects of other neutral amino acids in this tissue differ from effects in rabbit choroid plexus and optic nerve. In the ciliary bodyiris preparation the neutral amino acids do not divide themselves into a high-affinity group, the imino acids, and a group with lesser affinity. Neither arginine nor aspartic acid inhibits the uptake of >C-proline. Saturable proline uptake is nearly completely inhibited by 50 mM N-methylalanine. Thus, proline is concentrated in the ciliary body-iris preparation by a mobile carrier system largely of the Ehrlich cell A type. Alanine uptake is only partly inhibited by N-methylalanine, and the residual saturable uptake is only partly sodium dependent. The ciliary body-iris preparation, therefore, transports alanine by three carrier systems like those described in the Ehrlich cell as the A, the ASC, and the L mediations. The functional role of these carrier systems is discussed.