Permeability studies in neonatal rat lens epithelium.

Lanthanum nitrate (LN) and horseradish peroxidase (HRP) were used as tracers to study intercellular permeability as well as the existence and location of tight junctions and changes in them, if any, in the lens epithelium of Sprague Dawley rats. Thin sections of lenses taken from animals at birth and at three day intervals until the neonates were weaned at approximately 22 days were studied at the electron microscope level. At every age both tracers permeated the intercellular spaces of the anterior region epithelium and between the fiber cells of the equatorial region. The LN precipitates terminated near the apical part of the epithelium in the anterior polar region and were not seen at the epithelial-fiber interface or between fibers in this region. At the site of the tracer termination the intercellular space was found to be considerably constricted or completely sealed. The HRP precipitates, however, were present in these intercellular spaces and by using the HRP "washout" procedure could be washed out of the basolateral site of the intercellular spaces of the epithelium up to the point of constriction if a tight junction were present. The lens area occupied by epithelium with tight junctions was age related being very small in lenses from animals less than 24 hours old and becoming increasingly enlarged as the newborn aged. These findings further confirm the existence of a barrier in the form of tight junctions between epithelial cells in the central anterior region of the maturing rat lens. Moreover, our observations also provide information regarding the pattern of tight junction development and distribution during lens maturation.