A role for sodium in hypoxic but not in hypothermic injury to hepatocytes and LLC-PK1 cells

Background. Hypothermia is considered to be responsible for sodium influx d uring cold hypoxic incubation, However, we have previously shown that hypot hermia alone leads to a pronounced decrease in cellular sodium content when liver endothelial cells or hepatocytes are incubated under such conditions . In the research described here, we therefore studied the effects of hypot hermia and hypoxia, alone or combined, on cellular sodium homeostasis and a ssessed the role sodium plays in the pathogenesis of hypoxic and hypothermi c injury to cultured liver and kidney cells. Methods. Isolated hepatocytes and LLC-PK1 cells were incubated in Krebs-Hen seleit buffer or a sodium-free modification thereof under normoxic and hypo xic conditions at 4 degrees C as well as at 37 degrees C. Cytosolic sodium concentration was determined in isolated hepatocytes under both warm and co ld conditions using digital fluorescence microscopy and the Na+-sensitive d ye sodium-binding benzofuran isophthalate. Results. When hepatocytes were incubated under cold normoxic conditions the cellular sodium concentration decreased. However, it increased strongly un der hypoxic conditions at 4 degrees C and at 37 degrees C, When either hepa tocytes or LLC-PK1 cells were incubated under hypoxic conditions at 4 degre es C or 37 degrees C, sodium-free medium provided protection, In contrast, sodium-free medium did not alleviate the hypothermic injury observed when c ells were incubated under cold normoxia, Conclusions. The sodium influx observed during cold hypoxia is triggered by hypoxia and not by hypothermia, Sodium plays a prominent role in hypoxic i njury to cultured liver and kidney cells, although hypothermic injury of th ese cells is independent of sodium homeostasis.