Catecholamine Production Along the Nephron
The present work proposes an extra neural site of catecholamine production along the nephron. LLC-PK1, MDCK, and mIMCD-3 (proximal and distal tubules and inner medullary collecting duct, respectively) presented the following amine concentrations in the cell homogenates: Norepinephrine = 275±34, 56±16 and 255±21; Epinephrine = 161±20, 83±17 and 53±7; and Dopamine = 63±15, 39±6 and 36±7 pg/mg cell protein (Means ± SEM), respectively. The culture medium showed Norepinephrine = 168±25, 22±3 and 135±8; Epinephrine = 32±6, 152±17 and 39±5; and Dopamine = 27±9, 241±34 and 26±5 pg/mg cell protein, respectively. The synthesis enzymes as tyrosine hydroxylase, dopa decarboxylase and dopamine β-hydroxylase were detected by Western blotting. Biopterin, the enzymatic cofactor of tyrosine hydroxylase, was quantified in the intracellular and medium of mIMCD-3 cells (17±4 and 24±3 nmol/mg cell protein, respectively) and in the medium of MDCK cells (19±4 nmol/mg cell protein). The data confirmed that the proximal tubule is an important source of dopa decarboxilase and Dopamine and epithelial cell along the nephron express the biochemical pathway for catecholamine production.