Abstract
Diabetes was induced in rats by administration of streptozotocin. After 90-120 days, one group of chronic diabetic animals was treated with insulin for chronic diabetic animals was treated with insulin for 10 days. The lipid fluidity and composition of microvillus membranes prepared from ileal enterocytes of control, diabetic, and insulin-treated diabetic animals were determined. Lipid fluidity, as assessed by steady-state fluorescence polarization techniques using the probes 1,6-diphenyl-1,3,5-hexatriene, DL-2-(9-anthroyl)stearic acid and DL-12-(9-anthroyl)stearic acid, was decreased in membranes of diabetic animals compared to membranes of control and insulin-treated diabetic membranes. The differences in fluidity resulted from an increased cholesterol content and cholesterol/phospholipid molar ratio in membranes of diabetic animals. The activities of sucrase and alkaline phosphatase were also found to be higher in membranes of diabetic animals. Insulin treatment, however, failed to significantly influence the enzymatic activities of these membranes. These studies, therefore, demonstrate that alterations in the lipid fluidity, lipid composition, and certain enzymatic activities exist in microvillus membranes of enterocytes prepared from chronic streptozotocin-induced diabetic rats. Administration of insulin for 10 days to these animals restored membrane fluidity and lipid composition but not enzymatic activities to control membrane levels.
Highlights
From the Departmentof Medicine, Michael Reese Hospital and Medical Center, Pritzker School of Medicine, University of Chicago, Ch&ago,Illinois 60616
Administration of insulin for 10 days to these animals restored membranefluidity and branes (20).,the present studies were undertaken to determine: 1)whether alterations in thelipid fluidity and composition exist in microvillus membranes of enterocytes prepared from chronic streptozotocin-induced (90-120 days) diabetic rats; 2)whether administration of insulin for 10 days to diabetic animals could restore these parameters to control lipid composition but not enzymatic activities to con- levels; and 3) whether such alterations might play a role in trol membranelevels
Fluidity Studies-As shown in Table I, the lipid fluidity of have demonstrated that breakpoints detected by this method microvillus membranes of diabetic animals was significantly represent only the lower critical temperature of broad tranlower than control membranes, as assessed by steady-state sitions observed by differential scanning calorimetry in rat fluorescence polarization techniques using all three fluoro- enterocyte plasma membranes (22)
Summary
Anisotropy parameter; ro, maximal limiting anisotropy; r-, limiting hindered anisotropy; T.,correlation time; Tfm,ean lifetime of the excited state; F, total fluorescence; GLC, gas-liquid chromatography. Based on the present and prior studies (18-22) in our laboratory, it appears unlikely that alterations in thesmeembrane parameters are responsible for the functional abnormalities previously described in the intestine of chronic diabetic animals (7,8,11,12). These findings serve as thebasis for the present report. The fluidity of microvillus membranes prepared from diabetic animals treated with insulin for 10 days, ,was found to be similar to control values (Table I).
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