Morphology of isolated colonic crypts

The traditional paradigm of colonic fluid and electrolyte transport include s a spatial separation of absorptive and secretory processes to surface and crypt cells, respectively. Recent studies of isolated microperfused coloni c crypts revealed constitutive Na-dependent fluid absorption while secretio n is regulated by one or more neurohumoral agonists. One obvious reason for the difference found in microdissected crypts is their separation from the lamina propria milieu. While it has been shown that isolated crypts are de void of obvious lamina propria elements, including pericryptal fibroblasts, detailed morphologic information of the content of isolated crypts has bee n lacking. To characterize the morphology of the isolated crypt, we perform ed transmission electron microscopy (TEM) and immunofluorescence on microdi ssected and Ca2+ chelated crypts, Crypt cell type analysis was carried out separately on intact rat colon using light microscopy. TEM revealed a compl ete lack of either lamina propria cells or extracellular material in crypts isolated by either technique. TEM also revealed a subtle difference betwee n the two isolation methods, with intact basal membranes in microdissected crypts but focal disruption of basal membranes in Ca2+-chelated crypts. Imm unofluorescent stains for two basement membrane components (laminin and col lagen type IV) revealed the presence of adherent basement membrane only on microdissected crypts; evidence that the plane of separation differs in the se two preparations. Crypt cell type analysis on intact rat colon revealed an equal proportion of goblet cells in the right and left colon (approximat ely 50%) when measuring the middle 70% of the crypts - the area studied dur ing crypt microperfusion. This morphologic analysis will increase our under standing of the observed physiology of isolated colonic crypts, Copyright ( C) 2001 S. Karger AG, Basel.