THE ENTERIC SURFACE COAT ON CAT INTESTINAL MICROVILLI

TLDR

Enteric microvilli in cats, bats, and humans are coated with a conspicuous filamentous layer radiating from the outer dense leaflet of the plasma membrane, while in other species the coat is poorly developed or inconsistent yet traces remain on microvilli tips and sides. The component is revealed by ordinary electron microscopy sectioning when stained with uranyl acetate followed by lead staining. The coat, prominent on absorptive cells, is PAS positive, reacts with Alcian blue or Hale's colloidal iron, stains with low‑pH toluidine blue, resists washings or chemical treatments, but is lost during autolysis, indicating it is likely an integral part of the plasmalemma rather than an extraneous coat.

Abstract

The enteric microvilli of the cat, bat, and man are coated with a conspicuous layer composed of fine filaments radiating from the outer dense leaflet of the plasma membrane. This surface coat is prominent on the absorptive cells but is not so thick on the goblet and undifferentiated crypt cells. In other species the surface coat is poorly developed or inconsistent, but all intestinal microvilli have traces of such a coating over the tips and sides of the microvilli. Tissues prepared by the ordinary sectioning techniques for electron microscopy usually reveal this component when stained with uranyl acetate followed by lead staining. The surface coat is intensely periodic acid-Schiff (PAS) positive and reacts with Alcian blue or Hale's colloidal iron stain for acid mucopolysaccharide. It is also stained by toluidine blue at low pH. Repeated washings or incubation with various chemical agents have failed to remove or markedly alter the appearance of the coating, but extruded cells undergoing autolysis lose their surface coats. The stability, consistent presence, and intimate association of the mucopolysaccharide coat suggest that it may be an integral part of the plasmalemma rather than an "extraneous coat."