Organic cation transporter 3 contributes to norepinephrine uptake into perivascular adipose tissue

Perivascular adipose tissue (PVAT) reduces vasoconstriction to norepinephrine (NE). A mechanism by which PVAT could function to reduce vascular contraction is by decreasing the amount of NE to which the vessel is exposed. PVATs from male Sprague-Dawley rats were used to test the hypothesis that PVAT has a NE uptake mechanism. NE was detected by HPLC in mesenteric PVAT and isolated adipocytes. Uptake of NE (10 mu M) in mesenteric PVAT was reduced by the NE transporter (NET) inhibitor nisoxetine (1 mu M, 73.68 +/- 7.62%, all values reported as percentages of vehicle), the 5-hydroxytryptamine transporter (SERT) inhibitor citalopram (100 nM) with the organic cation transporter 3 (OCT3) inhibitor corticosterone (100 mu M, 56.18 +/- 5.21%), and the NET inhibitor desipramine (10 mu M) with corticosterone (100 mu M, 61.18 +/- 6.82%). Aortic PVAT NE uptake was reduced by corticosterone (100 mu M, 53.01 +/- 10.96%). Confocal imaging of mesenteric PVAT stained with 4-[4-(dimethylamino)-styrl]-N-methylpyridinium iodide (ASP), a fluorescent substrate of cationic transporters, detected ASP(+) uptake into adipocytes. ASP(+) (2 mu M) uptake was reduced by citalopram (100 nM, 66.68 +/- 6.43%), corticosterone (100 mu M, 43.49 +/- 10.17%), nisoxetine (100 nM, 84.12 +/- 4.24%), citalopram with corticosterone (100 nM and 100 mu M, respectively, 35.75 +/- 4.21%), and desipramine with corticosterone (10 and 100 mu M, respectively, 50.47 +/- 5.78%). NET protein was not detected in mesenteric PVAT adipocytes. Expression of Slc22a3 (OCT3 gene) mRNA and protein in PVAT adipocytes was detected by RT-PCR and immunocytochemistry, respectively. These end points support the presence of a transporter-mediated NE uptake system within PVAT with a potential mediator being OCT3.