Relation between alpha-methyl-D-glucoside influx and brush border surface area in enterocytes from chicken cecum and...

We have investigated the possible relation between the phloridzin-sensitive influx of alpha-methyl-D-glucoside (concentration 5 mmol/l) and the brush border surface area, in chicken isolated enterocytes. The intestinal regions studied were: jejunum and proximal cecum (both with high affinity sugar transport sites), medial cecum (with a low affinity transport system) and distal cecum (which lacks any transport ability). Cell apical surface measured by electron microscopy gave the following results; jejunal cells (0.41 micron 2) greater than proximal cecal cells (0.23 micron 2) greater than medial cecal cells (0.15 micron 2) = distal cecal cells (0.14 micron 2). This parameter is mainly determined by the length of microvilli. Sugar influx studies showed that the concentration of the substrate in cell water (in mmol/l) was jejunum (7.1) greater than proximal cecum (2.9) greater than medial cecum (1.7) greater than distal cecum (not different from zero). The decline in influx rate from proximal to distal cecum may be explained both by changes in surface and by the different carriers involved (different Km). Results of sugar concentration in the distal cecal cells do not correlate with the other segments studied since the substrate enters in these cells by a passive process. It is concluded that the degree of development of microvilli should be taken into account when estimating nutrient transport rates in different intestinal segments.