17 KINETICS OF HUMAN SMALL INTESTINAL BRUSH BORDER MEMBRANE D-GLUCOSE TRANSPORT: JEUNUM AND ILEUM COMPARED

Translocation of glucose across the small intestinal brush border membrane is of fundamental physiological and clinical importance, yet little is known about the kinetics of this transport process in man. Using a recently developed miniaturised technique employing human brush border membrane vesicle (BBMV), we have studied the initial 3 sec uptake of glucose by BBMV under Na+ gradient (out:100mM; in:0) and non-Na+ gradient (out and in:0) conditions, over a range of substrate concentrations (extra-vesicular glucose:0-3.2mM). BBMV were derived from small (150-175 mg), full thickness specimens of jejunum (n=8) or ileum (n=12), obtained from children undergoing elective intestinal resection. Eadie-Hofstee transformation of the data showed that in the jejunum, glucose was transported by 3 different mechanisms: (i) a diffusional process and/or a low affinity, Na+-independant carrier (ii) a high affinity, low capacity, Na+-dependant saturable system (approximately Km 0.3mM; Vtaax 13nmol/mg/min). (iii) a Na+-dependant diffusional process and/or a very low affinity, high capacity saturable carrier. In contrast, it was not possible to consistently demonstrate saturable glucose uptake by ileal BBMV. These data provide a basis for an explanation of the heterogeneity seen in glucose-galactose malabsorption, and suggest that in the ileum, transcellular glucose transport may be relatively unimportant.