Targeted deletion or selective pharmacological inhibition of α2C-adrenoceptors in mice results in increased brain tissue levels of dopamine and its precursor L-3,4-dihydroxyphenylalanine (L-DOPA), without significant changes in L-DOPA synthesis. L-DOPA uptake is considered the rate-limiting step in dopamine synthesis in the kidney. Since α2C-adrenoceptors may influence the transport of L-DOPA, we investigated the effect of α2C-adrenoceptor activation on L-DOPA uptake in a kidney cell line [Opossum Kidney (OK)]. L-DOPA and dopamine kidney tissue levels in α2C-adrenoceptor knockout (KO) mice and of mice treated with the selective α2C-adrenoceptor antagonist JP-1302 were also evaluated. The α2-adrenoceptor agonist medetomidine (0.1-1000 nM) produced a concentration dependent decrease in L-DOPA uptake in OK cells (IC50: 2.5±0.5 nM; Emax in: 28±5% of inhibition). This effect was abolished by pre-incubation with JP-1302 (300 nM). Furthermore the effect of medetomidine (100 nM) was abolished by pre-incubation with U0126 (10 μM) a mitogen-activated protein kinase kinase (MEK) 1/2 inhibitor. Kidney tissue levels of L-DOPA were significantly higher in α2C-adrenoceptor KO mice compared to wild type [WT: 58±2; α2CKO: 81±15* pmol.(g tissue)-1, *P<0.05] and in mice treated with JP-1302 [3 µmol.(Kg b.w.)-1] compared to control [CT: 62±2; JP-1302: 75±1* pmol.(g tissue)-1, *P<0.05], both without significant changes in dopamine kidney tissue levels. However mice treated with JP-1302 on a high salt (HS) diet presented significantly higher dopamine levels in kidney and urine compared to control animals on a HS diet. In conclusion, in a kidney cell line α2C-adrenoceptor activation inhibits L-DOPA uptake and in mice deletion or blockade of α2C-adrenoceptors increases L-DOPA kidney tissue levels.
- OK cells
- knockout mice
- Copyright © 2011, American Journal of Physiology - Renal Physiology