Permeability of the rat small intestinal epithelium along the villus-crypt axis: Effects of glucose transport

Abstract

Background and Aims: The aim of this study was to elucidate the permeability characteristics of the epithelium along the villus-crypt axis and investigate the effect of glucose transport on these characteristics along this axis. Methods: The disappearance rates of 14C-mannitol and 51Cr-EDTA or 3H-inulin were determined as clearance (Cl(x)) from a recirculating perfusion system of the jejunal lumen in anesthetized rats. Net fluid transport was varied over a large range by exchanging mannitol with glucose in the perfusate solution and by inhibition of nervously mediated secretory processes with hexa-methonium. The perfusion rate was 0.5 or 0.2 mL/min. Results: Cl(Man) enhanced significantly with increasing net fluid transport (secretion 8.50 ± 1.88, to absorption 16.72 ± 1.75 μL · min-1 · g-1) and with glucose perfusates. Cl(Cr-EDTA) was constant irrespective of net fluid transport and was reduced to insignificant values at a perfusion rate of 0.2 mL/min. Cl(ln) was not different from zero. Conclusions: The absorbing apical part of the villus contains small pores (radius, <6 Å) allowing passive transport via solvent drag of, e.g., monosaccharides, whereas the pores in the crypts are large (50-60 Å) and inaccessible to the luminal content. The basal part of the villus contains medium-sized pores (10-15 Å) through which no solvent drag occurs. Active glucose transport in the rat mainly increases the number of small pores accessible for passive transport, whereas the size of these pores seems to stay constant.