The dopamine precursorl-dihydroxyphenylalanine is transported by the amino acid transporters rBAT and LAT2 in renal cortex

Abstract

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.

Renal Albumin Excretion

“…14,15 Site of Action of Dopamine and DRD1 Polymorphism How might the DRD1 polymorphism influence the coupling of dopamine to albumin excretion? Dopamine may be synthesized locally within the kidney, 39 and then act at multiple sites, including the glomerulus and the proximal tubule. In the kidney, the DRD1 receptor is a major functional target of dopamine, although other subtypes are also active.…”

Intrarenal dopamine deficiency leads to hypertension and decreased longevity in mice

“…Circulating concentrations of dopamine are normally in the picomolar range, while dopamine levels in the kidney can reach high nanomolar concentrations (4). The dopamine precursor l-dihydroxyphenylalanine (l-DOPA) is taken up by the proximal tubule via multiple amino acid transporters, including rBat, LAT2, and ASCT2 (5,6), from the circulation or after filtration at the glomerulus and is then converted to dopamine by aromatic amino acid decarboxylase (AADC), which is also localized to the proximal tubule (7). There is evidence that intrarenal dopamine production is modulated by alterations in dietary salt intake (8,9).…”

Chronic regulation of the renal Na+/H+exchanger NHE3 by dopamine: translational and posttranslational mechanisms

“…DA is synthesized in the mammalian kidney and maintains Na ϩ homeostasis by altering renal Na ϩ transport as an autocrine/ paracrine natriuretic hormone (9,64). The precursor of dopamine, L-dihydroxyphenylalanine (L-DOPA), is taken up into the proximal tubule cell from the glomerular filtrate and plasma, and decarboxylated into DA via the aromatic amino acid decarboxylase in the proximal tubule cell (29,52,86,100,104,110). DA can be either degraded or transported out of the tubular cell to engage its receptor, which is coded by five different genes (dopamine receptors 1-5; DR 1-5 ) (63).…”