Effect of alkalosis adaptation on renal collecting duct cell growth.

RIVAROLA V; FLAMENCO P; GALIZIA L; FORD P; CAPURRO C

Montevideo, Uruguay

Congreso; International Conference of Biological Physics; 2007

International Union for Pure and Applied Biophysics

The mammalian collecting duct (CD) is critical for the final regulation of body acid-base balance. However, there are several pathologies which produce a chronic imbalance of this equilibrium. During these disorders CD cells must not only regulate transepithelial HCO3- transport but also maintain intracellular homeostasis. We have recently described that RCCD1 cells, a model of CD, can adapt to chronic, but not acute, extracellular alkalosis rising the abundance of Cl-/HCO3- exchanger isoform AE2. However, during this adaptation, even though cells are able to reestablish their steady-state pHi, external alkalosis is still present and transporters function are altered. Then, chronic alkalosis may affect many cellular functions. Our present goal was to determine whether chronic exposure to alkalosis distorts cellular growth. To evaluate this, RCCD1 cells monolayers were adapted to chronic alkalosis and then different growth parameters were measured. Cell proliferation was tested by counting cell number with a hemacytometer. Our results showed that after 48 h of alkalosis cell proliferation decreased (cell number: control = 80607 ± 7050 vs. alkali = 57233 ± 3823, p < 0.01, n=28). This reduction of cell number was accompanied with a 1.5 folds increase in cellular area (mm2: control= 559.5 ± 47.85 vs. alkali = 821.3 ± 50.09, p < 0.01, n=8). These results suggest that alkalosis may induce alterations of the cell cycle. We next investigate if the amount of cellular protein and DNA were altered. Our results showed that, after alkalotic conditioning, both protein and DNA cellular content increased respect to control (~ 35% and 75% respectively). Then protein/DNA ratio was not increased, indicating no cell hypertrophy. Altogether these results suggest that after chronic exposure to alkalotic conditions there is an alteration of cellular growth. The decreased cell number together with the increased cell area and DNA content suggest a possible `mitotic slippage´, a phenomenon in which cells exit mitosis without division, forming tetraploid cells.