CHARACTERIZATION OF THE SYNTHESIS AND RELEASE OF DOPAMINE IN LLC-PK1 CELLS

The ability of a renal epithelial cell line of porcine origin (LLC-PK1 ) to synthesize dopamine (DA) from L-dopa and release DA into the cult ure media was studied. L-Dopa was rapidly taken up by LLC-PK1 cells an d converted to DA which was then released into the media. L-Dopa uptak e and conversion to DA was competitively inhibited by other aromatic a mino acids (Tyr and Phe). Studies were conducted to assess L-dopa upta ke, DA synthesis and DA release in LLC-PK1 cells in response to change s in the ionic composition of the Krebs-Ringer bicarbonate (KRB) buffe r media and to various drugs known to alter renal transport function. Sodium chloride addition to KRB media resulted in enhanced DA release into the media that was significantly attenuated by both quinine (1 mM ) and benzamil (0.1 mM). Other sodium salts (sodium acetate and sodium phosphate) also enhanced DA release from LLC-PK1 cells. Salts contain ing chloride (LiCl, NH4Cl, choline chloride) stimulated a greater effl ux of DA from LLC-PK1 cells than sodium salts at equimolar concentrati ons. Osmotic stimuli (sucrose, mannitol and dextran, 50-200 mM) also e licited increased DA release from LLC-PK1 cells into the media but not to the same extent as inorganic salts. DA release (secretion) from LL C-PK1 cells was strongly inhibited (25-50%) by drugs known to be subst rates for the renal cation transport system. These studies have charac terized extensively the factors that govern and regulate the synthesis of DA from L-dopa and the transport system responsible for the secret ion (release) of intracellular DA into the media.