Structural changes in intercellular junctions during keratinization of the stratum medium of the equine hoof wall.

Cells of the intertubular horn of the stratum medium of the equine hoof wall are joined by three types of junctions. Desmosomes and gap junctions were present in all strata. Septate-like junctions and an intercellular line were seen in the distal stratum spinosum subsequent to extrusion of the contents of membrane-coating granules. At a later stage of keratinization, non-membrane-bound acid phosphatase reaction product appeared to leak into the intercellular space except into areas occupied by septate-like junctions and the intercellular line. It is proposed that the formation of septate-like junctions and the intercellular line prior to leakage of acid phosphatase into the intercellular space created stable areas of intercellular adhesion between fully keratinized cells.