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 neurotransmitter in the central nervous system (CNS), receptor or transporter molecules for L-DOPA have not been determined. In an attempt to identify a transporter 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 tested, rabbit intestinal epithelium poly A⁺ RNA gave the highest transport activity for L-[¹⁴C]DOPA in the oocytes. The uptake was approximately five times higher than that of water-injected oocytes, and was partially Na⁺-dependent. L-Tyrosine, L-phenylalanine, L-leucine and L-lysine inhibited this transport activity, whereas D-DOPA, dopamine, glutamate and L-DOPA cyclohexylester, 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-[¹⁴C]DOPA in the oocytes. On the other hand, an antisense cRNA of rabbit 4F2hc barely affected this L-[¹⁴C]DOPA uptake activity. rBAT was thus responsible for the L-[¹⁴C]DOPA uptake activity expressed in X. laevis oocytes injected with poly A⁺ RNA from rabbit intestinal epithelium. As rBAT is localized at the target regions of L-DOPA in the CNS, rBAT might be one of the components involved in L-DOPAergic neurotransmission. Copyright (C) 2000 Elsevier Science B.V.