Abstract
Cells from a parotid gland acinar cell line (PAR-C5) cells were investigated to compare the activity of the ecto-nucleotidase enzyme in those cells to those of native parotid gland acinar cells. The object of this study was to determine how useful the PAR-C5 cells are as a model for salivary gland ecto-nucleotidase function. Ecto-nucleotidase was defined as ATPase activity expressed on whole cells that is stimulated by Ca** and Mg** and resistant to the inhibitors, ouabain and vanadate. The enzyme was non-selective as to nucleotide substrate. Assays in the presence of 100 pM of each of the substrates gave the following relative activities (%) compared to that of 100 uM ATP; GTP (104.5±7.9), ITP (87.4±9.4), UTP (80.1±9.9), CTP (71.4+6.6), ADP (58.7+2.1), and p-nitrophenyl phosphate (14.0+2.4). Suramin and reactive blue-2 showed IC50 values of 19+1.3 pM and 17+0.4 pM respectively. The low IC50 values of inhibitors and activities in the presence of various substrates showed close similarity to our previously reported data for the native cells. Further studies showed that muscarinic receptor stimulation and inhibition had no effect on ecto-nucleotidase activity indicating that the enzyme was stable under a variety of cell activities. The results indicate that PAR-C5 cells maintain ecto-nucleotidase after immortalization and provide a valuable cell population for studying parotid ecto-nucleotidase.