Immunocytochemical localization of the main intrinsic polypeptide (MIP) in ultrathin frozen sections of rat lens.

Abstract

The in situ distribution of the 26-kdalton main intrinsic polypeptide (MIP or MP 26), a putative gap junction protein in ocular lens fibers, was defined at the EM level using indirect immunoferritin labeling of ultrathin frozen sections of rat lens. MIP was found distributed throughout the plasma membrane of the lens fiber cells, with no apparent distinction between junctional and nonjunctional membrane. MIP was not detectable in the basal or lateral plasma membrane of the lens epithelial cell, including the interepithelial gap junctions; nor was MIP detectable in the plasma membrane or gap junctions of the hepatocyte. Previous reports have indicated that the protein composition of the lens fiber cell junction differs from that of the hepatocyte gap junction. The composition of the fiber cell junction and plasma membrane may also be immunocytochemically distinct from that of its progenitor, the lens epithelial cell.