Glucose transport and microvillus membrane physical properties along the crypt-villus axis of the rabbit.

Abstract

Both transport function and microvillus membrane physical properties evolve as the enterocyte matures and migrates up the crypt-villus axis. We isolated enriched fractions of villus tip, mid-villus, and crypt enterocytes from which microvillus membrane vesicles were prepared. Using this material we characterized the alterations that occur in microvillus membrane fluidity as the rabbit enterocyte matures and correlated these with kinetic studies of glucose transport. With increasing maturity the microvillus membrane becomes more rigid due to both an increase in the cholesterol/phospholipid ratio and alterations in individual phospholipid subclasses. Maximal rates of glucose transport were greatest in microvillus membrane vesicles prepared from mature cells. However, the glucose concentration producing half-maximal rates of transport (K.) was significantly lower in crypt microvillus membrane vesicles, suggesting that a distinct glucose transporter existed in crypt enterocytes. This distinction disappeared when differences between membrane lipid environments were removed. By fluidizing villus-tip microvillus membrane vesicles, in vitro, to levels seen in the crypt microvillus membrane, we observed a reduction in the K. of this transport system. These data suggest that the kinetic characteristics of the sodium-dependent glucose transporter are dependent upon its local membrane environment. (J. Clin. Invest. 1990Invest. . 85:1099Invest. -1107.) membrane fluidity -nutrient absorption -transport kinetics

Epidermal Growth Factor and Postnatal Development of Intestinal Transport and Membrane Structure

“…Controversy exists as to the existence of a second glucose transporter protein in the small intestine similar to that observed in renal brush border membranes (51). A number of investigators have argued for the presence of two distinct transporters based on kinetic evidence (52)(53)(54)(55)(56)(57), whereas others have claimed that differences in Km can be explained by either differences in membrane fluidity (30) or changes in cis-Na+ concentration and resultant conforlnational changes in the transporter (58). In the present study, no firm conclusions could be drawn concerning this matter.…”

“…Glucose uptake studies were carried out by a modification of Hopfer el al. 's (29) rapid filtration technique as previously described (30). Under the conditions used in these experiments, preliminary studies demonstrated that rates of glucose uptake were linear up to 10 s, the overshoot peaked at 30 s, and uptake reached equilibrium at 2 niin.…”

“…The term membrane fluidity is used in its (33). Total phospholipid content LK-5D TLC plates and developed as previously described (30).…”

“…Pentadecanoic acid was added as an internal standard and fatty acid methyl esters prepared by standard techniques (32). These were separated and quantitated using gas-lipid chromatography, also as previously described (30). Mucosal DNA ar7rl Protein Content and Na'K'ATPase Activity.…”

“…There is no simple relationship that exists between any specific phospholipid and transport function. Alterations in membrane fluidity have been shown to affect glucose transport (30,35), Na+K'-ATPase activity (48), and sodium uptake and water permeability (49). In the intestine, a proximal distal gradient exists in membrane lipid composition and fluidity, with the jejunum being more fluid than the ileum (50).…”