Glucose depolarizes villous but not crypt cell apical membrane potential difference: a micropuncture study of crypt-villus heterogeneity in the rat

Abstract

Brush-border membrane potentials and fractional resistances have been recorded from enterocytes at different points along the crypt-villus axis of rat ileum in vitro. Microelectrode impalements were obtained under visual control and brush-border membrane potentials were higher in crypt than in villous cells (−57 ± 1.6 against −50 ± 1.6 mV referred to the mucosal side). Replacing mannitol with d-glucose in the mucosal perfusate resulted in a rise in transmural potential difference (0.5 ± 0.17 to 1.0 ± 0.21 mV ( n = 37)) and apical membrane potential was depolarized. This occurred consistently only in the upper two-thirds of the villus (−54 ± 1.7 to −47 ± 2.3 mV ( n = 17)) and not in crypt cells (−56 ± 2.6 to −57 ± 2.4 mV ( n = 10) or at the crypt-villus junction. The glucose-induced apical membrane depolarization in villous enterocytes was blocked by phlorizin, a competitive inhibitor of sodium-dependent glucose uptake (−50 ± 2.1 to −53 ± 2.8 mV ( n = 9) in the presence of phlorizin and glucose). Transmural resistance, R t, and fractional resistance, F R, were unaltered by glucose ( 61 ± 3.4 to 61 ± 3.5 Ω· cm 2 (n = 50) ) and (0.60 ± 0.06 to 0.57 ± 0.06 ( n = 17)). This micro-puncture technique provides dirct evidence for functional differentiation along the crypt-villus axis and indicates that active electrogenic accumulation of glucose is confined to villous epithelium.