Selective changes in tyrosine transport by isolated choroid plexus exposed to inorganic lead

Abstract

Freshly excised cat brain tissues were preincubated for 15 min in artificial cerebrospinal fluid (CSF) only or in CSF plus lead nitrate (5 × 10 −6 m) and then incubated for an additional 5 min with varying concentrations of l-[ 3H]tyrosine. The time course (from 5 to 60 min) for the accumulation of l-[ 3H]tyrosine showed the highest uptake in the choroid plexus (CP); the mean steady-state distribution ratio at 60 min was close to 15. This value exceeded by twofold the uptake by the neural tissues. The relationship between V net and the medium l-[ 3H]tyrosine concentration was a rectangular hyperbola. The apparent K m value for all three tissues was similar, but the V max of the CP was more than three times that of the neural tissues. Addition of lead nitrate altered the kinetics of uptake of l-[ 3H]tyrosine by the CP; the V max was reduced by one-half, whereas the affinity of carrier for the amino acid was approximately tripled. There was no effect on the transport of l-[ 3H]tyrosine by caudate nucleus or hypothalamus.