The Intestinal Brush Border Membrane in Diabetes

Abstract

A B S T R A C T Diabetes stimulates the functional activity of the intestinal brush border membrane with enhancement of both hydrolytic enzyme activity and membrane transport systems. To determine the mechanism of this effect, we studied the effects of streptozotocin diabetes on the metabolism of one membrane protein, sucrase-isomaltase, which increases its activity in diabetes. The protein was purified and an antiserum prepared. Sucrase-isomaltase from control and diabetic rats was immunologically identical as shown by Ouchterlony double-diffusion analysis of papainsolubilized mucosal proteins. The increase in sucrase enzyme activity in diabetic animals (31.0±1.4 U SEM 5 days after streptozotocin vs. 13.1±1.0 in controls) was the consequence of increased enzyme protein and not an alteration in catalytic efficiency as demonstrated by quantitative immunoprecipitin reactions.To account for increased sucrase-isomaltase protein in diabetes we studied papain-solubilized mucosal proteins labeled by injection of [14C]carbonate and[14C]leucine and analyzed incorporation into sucraseisomaltase protein (anti-serum precipitable) and total protein (trichloroacetic acid precipitable). We found that diabetes did not affect the decay of labeled total protein, but prolonged the decay of labeled sucraseisomaltase. t4 of sucrase-isomaltase was 4.4 h in control animals after [14C]carbonate injection and 8.8 and 10.2 h, respectively, 2 and 5 days after induction of streptozotocin diabetes. We obtained similar results in experiments with [14C]leucine with diabetes increasing t4 from 6 to 13.6 h. Diabetes did not appear to increase the rate of addition of sucrase-isomaltase to the brush border membrane, since it did not affect the 10-and 60-min incorporations of isotope into sucraseReceived for publication 11 January 1977 and in revised form 16 March 1977. isomaltase protein relative to incorporation into total protein and did not alter rate constants for synthesis calculated from the ti and the change in enzyme mass over time.Thus, enhanced sucrase activity in the diabetic animal is the consequence of an increase in sucraseisomaltase protein which develops because of a decrease in its rate of degradation. INTRODUCTIONInsulin deficiency stimulates the functional activity of the brush border membrane of the intestinal absorptive cell. For example, experimental diabetes has been reported to increase the enzymatic activity of many brush border hydrolases including the disaccharidases (1-4) and to stimulate a number of transport systems believed to reside in this membrane (5-10). Diabetes mellitus in man has also been associated with increased intestinal disaccharidase activity (11, 12) and enhanced glucose absorption (13), although negative studies in man have also been reported (14, 15) perhaps because of differing severity of the disease and effects of treatrnent. We have examined the effects of experimental diabetes on the metabolism of a representative brush border membrane enzyme, sucrase, to obtain some insight into the mechani...

Circadian Rhythm of Intestinal Sucrase Activity in Rats

“…Because degradation is essentially absent during these 6 h (t112 38 h), the value of 0.13 mg/h probably approximates the enzyme's true synthetic rate during that period. The value is quite similar to the synthetic rate of 0.11 mg/h found by us previously by analysis of enzyme mass and 24-h decay curves (7). Thus, the observed changes in sucrase-isomaltase protein appear to be compatible with the changes in degradation rates, and do not necessitate postulation of changing synthetic rates.…”

“…It is interesting that in two other experimental models of altered sucrase activity, diabetes and sucrose feeding (7,(36)(37)(38)(39), the mechanism also appears to be a change in the enzyme's degradation rate. Thus, the principal mleans of regulating sucrase-isomlaltase may be through changes in degradation.…”

“…Thus, the principal mleans of regulating sucrase-isomlaltase may be through changes in degradation. Time of Day (h) FIGURE 7 The relationship betwveen sucrase activity and half-life of the enzyme protein. Mean values for four animals ±SEM are given.…”

Suppressive effect of insulin on the synthesis of sucrase–isomaltase complex in small intestinal epithelial cells, and abnormal increase in the complex under diabetic conditions

“…In the small intestine this severe disease causes significant changes in the morphology and function of the mucosa [6][7][8]. In diabetic patients and animals, in particular in rats with streptozotocin-induced insulin-dependent diabetes mellitus (IDDM), abnormal increases in the activities of sucrase and isomaltase are observed in the small intestine [9,10]. Furthermore it has been reported that the postprandial metabolic profile is improved by the administration of an inhibitor of the sucrase and isomaltase in the experimental IDDM rats [11], suggesting that the abnormal increases in these enzyme activities exert a harmful influence on the metabolic imbalance under diabetic conditions.…”

Changes in brush-border enzyme activities of intestinal epithelial cells isolated from the villus-crypt axis during the early phase of alloxan diabetes in rats

“…The second segment from the pyrolus was everted and its enterocytes were isolated along the villus-crypt axis by the methods of Weiser s and Raul et al 9, except that the incubation times used were 10,3,4,5,6,7,8,9,10,15 and 20 min with shaking (100 oscillations per min). However, the site of these increased activities along the villuscrypt axis of diabetic animals has not been investigated.…”