On the mechanism of transport of proline in the ciliary body, optic nerve and choroid plexus

Abstract

An analysis of available data on proline transport in several tissues indicates that a single saturable active transport mechanism, together with a passive process, is not able to account for the data available. Introduction of a parallel transport mechanism which is not saturated below 50 mM, makes it possible to give a reasonably satisfactory account of the available data, from the three tissues, on (1) initial rate of uptake as a function of external concentration and (2) the uptake as a function of time. If the two transport mechanisms occur in two different types of cells, it is possible not only to account for the above two sets of data, but also to account reasonably well for the efflux data. While the model predicts more rapid efflux of tracer into a higher external concentration as found experimentally, an attempt was not made to account quantitatively for all four sets of experiments simultaneously.

For the three tissues, the root mean square of the relative error for the 24 data points available from the three different experiments, covering a range of values of concentration of 0.1 to 50 mM, a time range of 0.17 ao 240 minutes, are respectively 5.8, 13 and 9.6%.