STUDIES ON LIPIDS AND THE ACTIVITY OF NA,K-ATPASE IN LENS FIBER CELLS

Na,K-ATPase was studied in the two cell types that make up the lens of the eye. Membrane material was isolated from lens fibre cells, which make up the bulk of the lens cell mass, and also from lens epithelial cells, which are present only as a monolayer on the anterior lens surf ace. Judged by immunoblotting, greater amounts of Na,K-ATPase alpha(1) and beta(1) polypeptides were found in fibre cell membrane material t han in epithelial cell membrane material. However, the Na,K-ATPase act ivity in epithelial cell membrane material was 20 times that measured in fibre cell membrane material. In Rb-86 uptake experiments with inta ct lenses, ouabain-inhibitable Rb-86 uptake was observed for lens epit helium but not for lens fibres. These findings are consistent with a l ow Na,K-ATPase activity in lens fibre cells even though these cells ex press a considerable amount of Na,K-ATPase alpha(1) and beta(1) polype ptides. The lipid composition of lens fibre cell membranes causes them to be more ordered than epithelial cell membranes; this was confirmed by measurements of the infrared CH2 symmetric stretching band frequen cy. Because lipid composition can influence Na,K-ATPase activity, expe riments were conducted to determine whether the activity of Na,K-ATPas e alpha(1) beta(1) is inhibited by lens fibre lipid. However, no signi ficant difference in Na,K-ATPase activity was detected when Na,K-ATPas e alpha(1) beta(1) was purified from rabbit kidney and then reconstitu ted with lipid that had been isolated from either lens epithelium or l ens fibre cells. These studies indicate that lens fibre cells contain both Na,K-ATPase alpha(1) and beta(1) polypeptides but have low Na,K-A TPase activity. However, the results do not support the notion that th is is due to the lipid composition of lens fibre cell membranes.