Cadmium inhibits glucose uptake in primary cultures of mouse cortical tubule cells.

We studied the effect of cadmium (Cd2+) on transport of alpha-methylglucoside in primary cultures of mouse kidney cortical tubule cells grown in defined medium. When cultured cells were exposed to Cd2+ concentrations from 0 to 6 microM for 24 h, uptake of alpha-methylglucoside was inhibited in a dose-dependent manner by up to 50%. By contrast, acute exposure of the cells to 7 microM Cd2+ for 60 min did not inhibit alpha-methylglucoside uptake. Increasing Cd2+ concentrations progressively decreased the Vmax of Na(+)-dependent glucose cotransport but not the Km for glucose. Cell ATP/ADP ratios of unexposed monolayers and of cells exposed to 4.5 microM Cd2+ for 24 h were 5.0 and 4.9, respectively (n = 3). Intracellular volume, lactate dehydrogenase activity, and cell Na+ and K+ concentrations were unaltered even after 24 h of exposure to 7 microM Cd2+. Untreated and Cd2+-treated monolayers preloaded with alpha-methylglucoside released the sugar analogue into the medium at nearly identical rates, indicating that Cd2+ did not alter cell permeability to glucose. Uptake of the amino acid analogue alpha-(methylamino)isobutyric acid was not affected by prior Cd2+ exposure. Whereas cell DNA content declined in Cd2(+)-exposed plates, both Na(+)-glucose and Na(+)-amino acid cotransport were enhanced at lower cell densities. Protein and DNA synthesis, estimated, respectively, by incorporation of [3H]leucine and [3H]thymidine into acid-insoluble material, were not significantly affected at 6 microM Cd2+. We conclude that after a lag time Cd2+ selectively inhibits renal Na(+)-dependent glucose transport despite an unchanged gradient for Na+ across the cell membrane.

Effect of pH on growth of mouse renal cortical tubule cells in primary culture.

We examined the effect of the medium pH on growth of primary cultures of mouse cortical tubule cells grown in defined medium. A significantly higher DNA content was observed within 24 h of lowering medium pH from 7.4 to 6.8 or 7.1 and persisted for the duration of the study. Further studies revealed that either medium acidification or insulin plus prostaglandin E1 nearly doubled uptake of [3H]thymidine in cells deprived of other growth factors for the previous 72-110 h. Moreover, the effects of insulin, prostaglandin E1, and medium acidification on [3H]thymidine uptake of quiescent cells were additive. An alkaline medium pH appeared to have a small but significant effect on cell hypertrophy, since cells exposed to pH 7.4 and 7.7 had a higher protein-to-DNA ratio than cells incubated at a lower pH. Cell pH of monolayers grown on glass slides determined from fluorescence of the carboxyfluorescein analogue 2',7'-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF) was linearly correlated with medium pH, and changes in medium pH resulted in changes in steady-state cell pH of a similar magnitude. Four hours after medium acidification, relative increases in cell Na+ and water content occurred, whereas medium alkalinization led to decreases in cell Na+ and water content. The increases in cell Na+ and cell water content at pH 6.8 could be inhibited by amiloride. We conclude that decreasing the cell pH can be a mitogenic stimulus for renal tubule cells. Medium acidification is accompanied by changes in cell Na+ transport, which may be mediated in part by altered Na+-H+ antiporter activity.