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

Abstract

Watts SW. Organic cation transporter 3 contributes to norepinephrine uptake into perivascular adipose tissue. Am J Physiol Heart Circ Physiol 309: H1904 -H1914, 2015. First published October 2, 2015; doi:10.1152/ajpheart.00308.2015.-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 M) in mesenteric PVAT was reduced by the NE transporter (NET) inhibitor nisoxetine (1 M, 73.68 Ϯ 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 M, 56.18 Ϯ 5.21%), and the NET inhibitor desipramine (10 M) with corticosterone (100 M, 61.18 Ϯ 6.82%). Aortic PVAT NE uptake was reduced by corticosterone (100 M, 53.01 Ϯ 10.96%). Confocal imaging of mesenteric PVAT stained with 4-[4-(dimethylamino)-styrl]-N-methylpyridinium iodide (ASP ϩ ), a fluorescent substrate of cationic transporters, detected ASP ϩ uptake into adipocytes. ASP ϩ (2 M) uptake was reduced by citalopram (100 nM, 66.68 Ϯ 6.43%), corticosterone (100 M, 43.49 Ϯ 10.17%), nisoxetine (100 nM, 84.12 Ϯ 4.24%), citalopram with corticosterone (100 nM and 100 M, respectively, 35.75 Ϯ 4.21%), and desipramine with corticosterone (10 and 100 M, respectively, 50.47 Ϯ 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. PERIVASCULAR ADIPOSE TISSUE (PVAT) closely envelops many blood vessels of the body (65). This relationship between PVAT and the blood vessel has earned PVAT its place as the fourth layer of the blood vessel, the "tunica adiposa" (14). Beyond providing structural support, PVAT has many roles in modulating blood vessel function (68). The release of vasoactive molecules from PVAT influences vascular function by altering the proliferation, migration, inflammation, and contraction of vascular smooth muscle (9, 20 -22, 24, 46, 68, 72). Interestingly, a releasable pool of catecholamines is present in PVAT (5, 67). Although both contractile and anticontractile substances can be released from PVAT (9,22,24,25,72), the presence of PVAT on blood vessels generally reduces vessel contraction in response to various agonists, including norepinephrine (NE) (64). Knowledge on how these mechanisms interact to influence the anticontractile properties of PVAT in NE-induced contraction is not complete (36).The anticontractile effect of PVAT is lost in obesity and hypertension, implicating PVAT as an integral lin...

New actions of an old friend: perivascular adipose tissue's adrenergic mechanisms

“…Since MAO‐A is located intracellularly, amines would have to enter the cell first before being metabolized. The authors demonstrated that NA uptake occurred through the extraneuronal transporter (now known as OCT3; Pizzinat et al, ), a finding further supported by functional studies showing that NA uptake in rat mesenteric resistance artery PVAT is also mediated by OCT3 (Ayala‐Lopez et al, ).…”

“…The uptake of NA has also been examined in IBAT where it was found to be mediated by NET (King et al, ). This is in contrast to mesenteric resistance artery PVAT, where the expression and activity of NET are low, and the transporter responsible for the uptake of NA is OCT3, present in adipocytes (Ayala‐Lopez et al, ). In IBAT, angiotensin II stimulates NA uptake, as demonstrated by the increase in [ 3 H]‐nisoxetine binding after an infusion of angiotensin II to rats (King et al, ).…”

“…NA uptake into thoracic aorta PVAT was sensitive to inhibition by the OCT3 inhibitor corticosterone. Immunohistochemistry and PCR have been used to demonstrate that OCT3 is abundant in PVAT adipocytes around the mesenteric resistance arteries and in aortic PVAT (Ayala‐Lopez et al, ). The gene for OCT3 ( Slc22a3 ) is highly expressed in adipose tissue but less so in the other tissues examined (Jacobsson et al, ).…”

3T3‐L1 cells and perivascular adipocytes are not equivalent in amine transporter expression

“…Using the 3T3‐L1 cells was a move to try to help us answer these questions. We isolated adipocytes from mesenteric PVAT and showed the presence of NE in these cells in ways we could not in the 3T3‐L1 cells . However, separation of adipocytes from PVAT is never perfect.…”

“…However, the similarities stop there. In rat mesenteric PVAT adipocytes, NE uptake was mainly attributed to OCT3 . The absence of mRNA for OCT3, as well as other plasma membrane transporters of NE—NET, SERT, DAT, and PMAT—suggests that NE is taken up by 3T3‐L1 adipocytes via another mechanism.…”