The dopamine precursor L-dihydroxyphenylalanine is transported by the amino acid transporters rBAT and LAT2 in renal cortex.
The intrarenal autocrine-paracrine dopamine (DA) system is critical for Na(+) homeostasis. l-Dihydroxyphenylalanine (l-DOPA) uptake from the glomerular filtrate and plasma provides the substrate for DA generation by the renal proximal tubule. The transporter(s) responsible for proximal tubule l-DOPA uptake has not been characterized. Renal cortical poly-A(+) RNA injected into Xenopus laevis oocytes induced l-DOPA uptake in a time- and dose-dependent fashion with biphasic K(m)s in the millimolar and micromolar range and independent of inward Na(+), K(+), or H(+) gradients, suggesting the presence of low- and high-affinity l-DOPA carriers. Complementary RNA from two amino acid transporters yielded l-DOPA uptake significantly above water-injected controls the rBAT/b(0,+)AT dimer (rBAT) and the LAT2/4F2 dimer (LAT2). In contradistinction to renal cortical poly-A(+), l-DOPA kinetics of rBAT and LAT2 showed classic Michaelis-Menton kinetics with K(m)s in the micromolar and millimolar range, respectively. Sequence-specific antisense oligonucleotides to rBAT or LAT2 (AS) caused inhibition of rBAT and LAT2 cRNA-induced l-DOPA transport and cortical poly-A(+)-induced arginine and phenylalanine transport. However, the same ASs only partially blocked poly-A(+)-induced l-DOPA transport. In cultured kidney cells, silencing inhibitory RNA (siRNA) to rBAT significantly inhibited l-DOPA uptake. We conclude that rBAT and LAT2 can mediate apical and basolateral l-DOPA uptake into the proximal tubule, respectively. Additional l-DOPA transport mechanisms exist in the renal cortex that remain to be identified.
Quiñones
Henry
H
Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390-8856, USA. henry.quinones@utsouthwestern.edu
Collazo
Roberto
R
Moe
Orson W
OW
D027182:Amino Acid Transport System y+ / Q000494:pharmacology*; D026923:Amino Acid Transport Systems, Basic; D000596:Amino Acids / Q000493:pharmacokinetics*; D000818:Animals; D002352:Carrier Proteins / Q000494:pharmacology*; D018929:Cell Culture Techniques; D015259:Dopamine Agents / Q000493:pharmacokinetics*; D004305:Dose-Response Relationship, Drug; D005260:Female; D027301:Fusion Regulatory Protein 1, Light Chains / Q000494:pharmacology*; D007672:Kidney Cortex / Q000502:physiology*; D007980:Levodopa / Q000493:pharmacokinetics*; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D009865:Oocytes / Q000502:physiology; D012313:RNA; D034622:RNA Interference; D051381:Rats; D014982:Xenopus laevis / Q000502:physiology
D027182:Amino Acid Transport System y+; D026923:Amino Acid Transport Systems, Basic; D000596:Amino Acids; D002352:Carrier Proteins; D015259:Dopamine Agents; D027301:Fusion Regulatory Protein 1, Light Chains; D008562:Membrane Glycoproteins; C486582:Slc7a8 protein, rat; D007980:Levodopa; D012313:RNA