A COMPARATIVE-STUDY ON THE SYNTHESIS OF THE NATRIURETIC HORMONE DOPAMINE IN OK AND LLC-PK1 CELLS

The V-max values (in nmol/mg protein/15 min) for AAAD in OK cells (0.9 4 +/- 0.08) were found to be significantly (P<0.01) lower than those o bserved in LLC-PK1 cells (4.37 +/- 0.08). However, in both cell lines decarboxylation reaction was a saturable process with similar K-m valu es (OK cells=1.1 mM (0.3, 1.8); LLC-PK1 cells=1.8 mM (1.6, 2.1)). Cont rariwise to OK cells, decarboxylation of L-DOPA to dopamine in LLC-PK1 cells followed a linear (7.6 +/- 0.1 pmol/mg protein/min) non-saturab le kinetics till 120 min of incubation. The formation of dopamine from increasing concentrations of L-DOPA (10 to 500 mu M) followed a non-l inear kinetics in both cell lines; the process of L-DOPA decarboxylati on was saturated at low concentrations of L-DOPA with an apparent K-m value of 11 mu M (0.2, 22.6) in OK cells and 27.4 mu M (11.1, 43.7) in LLC-PK1 cells. The formation of dopamine in LLC-PK1 cells (V-max = 20 97 +/- 113 pmol/mg protein/6 min) was 13.7-fold that occurred in OK ce lls (V-max = 153 +/- 10 pmol/mg protein/6 min). In conclusion, LLC-PK1 cells appear to be endowed with a greater ability to form dopamine fr om exogenous L-DOPA when compared to OK cells. (C) 1996 Academic Press Limited