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...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.