THE INFLUX OF ISOLEUCINE INTO THE CEREBRAL HEMISPHERES AND CEREBELLUM: CARRIER-MEDIATED TRANSPORT AND DIFFUSION

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Abstract
The influx of L-isoleucine from the blood into the cerebral hemispheres and the cerebellum of the living rat was studied. When various raised levels of L-isoleucine were maintained in the circulation, influx did not increase in proportion to the raised blood levels, which showed that a carrier-mediated transport was being saturated. The values for influx could not be explained precisely by Michaelis-Menten kinetics. The divergence of the observed values for influx, from those which were obtained by the application of Michaelis-Menten kinetics, could be explained if part of the influx was due to a small, non-saturable component. This minor component of influx may be due to diffusion or to a 2nd carrier-mediated transport system that is not readily saturated.