Fatty acid cytotoxicity to bovine lens epithelial cells:: Investigations on cell viability, ecto-ATPase, Na+, K+-ATPase and intracellular sodium concentrations

Unsaturated non-esterified fatty acids have been shown to be cytotoxic in micromolar concentrations to bovine lens epithelial cells, in the following order: arachidonic acid > linoleic acid > oleic acid = Linolenic acid. As unsaturated free fatty acids are known to be Na+, K+-ATPase inhibitors, the aim of the study was to investigate whether or not the fatty acid cytotoxicity is correlated with effects on Na+, K+-ATPase activity and function in bovine lens epithelial cells. Furthermore, we also examined the effects of linoleic acid on an ecto-ATPase activity which could be demonstrated on the outside of primarily cultured bovine lens epithelial cells. It has already been shown that 10 mu mol l(-1) linoleic acid was cytotoxic but did not impair the ecto-ATPase activity of intact cells nor the Na+, K+-ATPase in enriched membrane fractions. Na+, K+-ATPase activity was slightly activated with 10 mu mol l(-1) linoleic acid and inhibited by about 50 % with 100 mu mol l(-1). Using the sodium-binding benzofuran isophthalate, measurements of intracellular sodium concentrations were carried out. In serum-starved bovine lens epithelial cells the basal [Na+](in) was clearly lower than 5 mmol l(-1). When the function of the Na+, K+-ATPase was interrupted by omitting K+-ions from the medium, [Na+](in) increased at a rate of 0.318 mmol l(-1) min(-1). Linoleic acid intensified that increase strongly in a concentration dependent manner. However, in K+-containing medium the linoleic acid-induced increase of [Na+](in), was completely prevented. Therefore, the high linoleioc acid cytotoxicity cannot be mediated by linoleic acid effects on Na+, K+-ATPase activity and function in bovine lens epithelial cells. (C) 2000 Academic Press.