Adaptation of glucose transport across rat enterocyte basolateral membrane in response to altered dietary carbohydrate intake.

Abstract

1. The effect of changes in the carbohydrate content of the diet on D‐glucose transport across the basolateral membrane of rat enterocytes has been compared with alterations in transport across the brush‐border membrane. 2. Measurement of carrier‐mediated D‐glucose uptake across the jejunal brush border from animals fed a low‐ or high‐carbohydrate diet showed a change in the maximal rate of transport by 7 days which was maintained for 14 days. The low‐carbohydrate diet produced a progressive decline in uptake whereas the high‐carbohydrate diet increased the transport. There was no alteration in the apparent affinity constant as a result of the dietary manipulations and no discernible trend for changes in the passive permeability to glucose. 3. Transport of D‐glucose across the basolateral membrane was also affected by the dietary composition. After 7 days the maximal transport rate was greater in the animals fed the high‐carbohydrate diet. However, while this increase was maintained for 14 days, uptake into vesicles prepared after 2 weeks on the low‐carbohydrate diet showed a return to control levels. 4. A detailed analysis of the time course of these responses showed the effect on basolateral membrane transport to be inducible within 3 days of switching from the low‐ to the high‐carbohydrate diet and could be reversed within a similar period. 5. Kinetic studies using purified basolateral membrane vesicles confirmed that the change in transport was the result of an increase in the maximal transport rate. Analysis of cytochalasin B binding to these membranes showed a parallel change in the number of glucose‐inhibitable binding sites. 6. The component of the diet responsible for these changes was further investigated by replacing the glucose in the high‐carbohydrate food with galactose, fructose, mannose or 3‐O‐methylglucose. Only glucose and fructose produced any significant change in the transport across the basolateral membrane. 7. It is concluded that in response to changes in the carbohydrate content of the diet there are alterations in the capacity for glucose transport across the basolateral membrane of the enterocyte as well as in the brush‐border membrane. The change in transport across the basolateral membrane is best explained by an increase in the number of glucose carriers in this membrane.

Active transport of 3-O-methyl-glucose by the small intestine in chronically catheterized rats.

“…The results of this study are in conflict with those studies of intestinal glucose absorption that claimed that passive absorption begins to exceed active transport at luminal concentration of glucose as low as 35-60 mM (1)(2)(3)(4). These studies used methods in which the intestine had been acutely manipulated surgically either in vivo or in vitro.…”

“…In contrast, most previous studies of intestinal glucose absorption using techniques such as perfusion of an isolate intestinal loop or everted sleeves measured the rate of disappearance of glucose from the lumen or mucosal surface (2,(4)(5)(6)(7)(8)(12)(13)(14). Because 30MG is not metabolized or accumulated by the intestine, the rate of appearance of 30MG into the portal vein is equal to the rate of disappearance from the intestinal lumen (9).…”

“…Some of these studies claim that passive absorption of glucose by the intestine begins to exceed active transport at luminal glucose concentrations as low as 35-60 mM (1)(2)(3)(4). The primary in vivo method for studying intestinal glucose transport has been the measurement of the rate of disappearance of glucose from the perfusate of a luminally perfused isolated loop of intestine in an anesthetized, acutely laparotomized animal (2,(5)(6)(7)(8).…”

“…In some studies, the intestinal vasculature is also perfused (9)(10)(11). In vitro methods for studying intestinal glucose transport include everted sleeves of intestinal tissue (4,(12)(13)(14), isolation of membrane vesicles (15)(16)(17)(18), and cell cultures (19).…”

Mechanism and rate of glucose absorption differ between an Australian honeyeater (Meliphagidae) and a lorikeet (Loriidae)

“…Lower affinity for glucose transporters may result in lower uptake rates of 3-OMG relative to D-glucose. Furthermore, because 3-OMG apparently does not stimulate the recruitment of the GLUT2 transporter to the apical membrane (Cheeseman and Harley, 1991), the mediated component may be underestimated in studies using only 3-OMG. However, we think this explanation is unlikely in the present study because birds were fed on a sucrose maintenance diet (hydrolysed to D-glucose and fructose in the intestine) immediately before and after gavage with 3-OMG.…”