Reconstitution of MIP26 from single human lenses into artificial membranes. I. Differences in pH sensitivity of cataractous vs. normal human lens fiber cell proteins.

Reconstitution of the lens fiber cell protein known as MIP26 into liposomes composed of heterologous phospholipids was achieved; this protein renders the liposomes permeable to low molecular weight compounds. MIP26 from either bovine or human lenses was capable of forming channels in artificial membranes. The assay technique was sufficiently sensitive to allow reconstitution of MIP26 from single human lenses, enabling us to examine the function of channels from either cataractous or age-matched normal lenses. Decreases in pH can cause these channels to close, analogous to the hypothesized channel closing in the in vivo situation. The pH optimum of reconstituted channels in liposomes containing MIP26 from bovine lenses or normal human lenses is very sharp; but is substantially broadened if the liposomes contain MIP26 from cataractous human lenses. This latter result suggests a functional alteration in human lens membranes which is correlated with the development of human senile cataract.