Involvement of rBAT in Na+-dependent and -independent transport of the neurotransmitter candidate L-DOPA in Xenopus laevis oocytes injected with rabbit small intestinal epithelium poly A(+) RNA

Although L-3,4-dihydroxyphenylalanine (L-DOPA) is claimed to be a neurotran smitter in the central nervous system (CNS), receptor or transporter molecu les for L-DOPA have not been determined. In an attempt to identify a transp orter for L-DOPA, we examined whether or not an active and high affinity L- DOPA transport system is expressed in Xenopus laevis oocytes injected with poly A(+) RNA prepared from several tissues. Among the poly A(+) RNAs teste d, rabbit intestinal epithelium poly A(+) RNA gave the highest transport ac tivity for L-[C-14]DOPA in the oocytes. The uptake was approximately five t imes higher than that of water-injected oocytes, and was partially Na+-depe ndent. L-Tyrosine, L-phenylalanine, L-leucine and L-lysine inhibited this t ransport activity, whereas D-DOPA, dopamine, glutamate and L-DOPA cyclohexy lester, an L-DOPA antagonist did not affect this transport. Coinjection of an antisense cRNA, as well as oligonucleotide complementary to rabbit rBAT (NBAT) cDNA almost completely inhibited the uptake of L-[C-14]DOPA in the o ocytes. On the other hand, an antisense cRNA of rabbit 4F2hc barely affecte d this L-[C-14]DOPA uptake activity. rBAT was thus responsible for the r-[C -14]DOPA uptake activity expressed in X. laevis oocytes injected with poly A(+) RNA from rabbit intestinal epithelium. As rBAT is localized at the tar get regions of L-DOPA in the CNS, rBAT might be one of the components invol ved in L-DOPAergic neurotransmission. (C) 2000 Elsevier Science B.V. All ri ghts reserved.