Independent modulation by food supply of two distinct sodium-activated D-glucose transport systems in the guinea pig jejunal brush-border membrane.

Abstract

D-glucose transport across the intestinal brush-border membrane involves two transport systems designated here as systems 1 and 2. Kinetic properties for both D-glucose and methyl a-D-glucopyranoside transport were measured at 350C by using brush-border membrane vesicles prepared from either control, fasted (48 hr), or semistarved (10 days) animals. The results show the following: (i) The sugar influx rate by simple diffusion was identical under either altered condition. (ii) Semistarvation stimulated D-glucose uptake by system 2 (both its V__ and Km increased), whereas system 1 was untouched. (iii) Fasting increased the capacity of system 1 without affecting either Km of system 1 or V..: and Km of system 2. The effect of fasting on Vx,,,, of system 1 cannot be attributed to indirect effects from changes in ionic permeability because the kinetic difference between control and fasted animals persisted when the membrane potential was short-circuited with equilibrated K+ and valinomycin. This work provides further evidence for the existence of two distinct sodium-activated D-glucose transport systems in the intestinal brush-border membrane, which adapt independently to either semistarvation or fasting.D-glucose transport in the small intestine responds to a variety of pathophysiological conditions that include qualitative and quantitative modifications of the diet, small-bowel resection, and diabetes. Often, however, published results are contradictory. For instance, under apparently similar conditions total sugar absorption has been described as either increasing, decreasing, or exhibiting no change (for reviews, see refs. 1-3). No satisfactory explanation of these discrepancies thus far exists, but many variables that have escaped appropriate control may be involved. Furthermore, the procedures of analysis and data expression differ widely and complicate the situation (3-7).An additional source of confusion is the heterogeneity in intestinal transport. Although the suggestion that two Dglucose transport systems occur in the apical border of the intestine has existed since the work of Honegger and Semenza (for review, see ref. 8), D-glucose absorption is usually treated as involving a single homogeneous transport system, the D-glucose/Na+ cotransporter identified in the sixties (for reviews, see refs. 8-11). Consequently, work on intestinal adaptation has been concerned with overall transport function of the intestine, providing no answers to whether individual transport systems were being selectively affected. In this paper we describe experiments permitting such a diagnosis.We demonstrated recently that D-glucose transport across the intestinal brush-border membrane involves at least two distinct, sodium-activated transport agencies (12-14). Although we identified the first, system 1 (S-1), as being identical with the classical D-glucose/Na' cotransporter (12), the exact nature of system 2 (S-2) remains to be established.[In this paper we use our own classification (12-14); although two distinct D-glucos...

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.…”

Apical GLUT2

“…The lack of a species-specific antibody means that BBS2 has not been formally identified with GLUT2. Nevertheless, it is noteworthy that BBS2 is abolished by starvation (24) and increased in pig intestine by a glucose-rich diet (25). Although BBS2 showed some Na ϩ dependence, probably due to a contribution of SGLT1 to insertion, its other features are close to those of GLUT2.…”

“…Glucose transport in guinea pig and pig brush-border membrane vesicles comprises two systems (22,23); BBS1 is a high-affinity transporter identified with SGLT1, whereas the low affinity BBS2 is sensitive to cytochalasin B, a facilitative transport inhibitor, but not to ␣-methylglucoside, a highly specific SGLT1 substrate. The lack of a species-specific antibody means that BBS2 has not been formally identified with GLUT2.…”

Immunocytochemical Detection of GLUT2 at the Rat Intestinal Brush-border Membrane

“…However, two very recent studies in which trafficking and inactivation were controlled by the use of ice-cold conditions have shown that a GLUT2-mediated transport component can be readily detected in membrane vesicles in rat (Au et al 2002) and mice (Dr. E. Brot-Laroche, personal communication). Similarly, the cytochalasin B-sensitive glucose transport system BBS2 in guinea pig brush-border membrane vesicles (Brot-Laroche et al 1986,1988 and also in pig (Dr. E. Brot-Laroche, personal communication) seems likely to be GLUT2.…”