Proposed mechanism for increased insulin-mediated glucose transport in adipose cells from young, obese Zucker rats. Large intracellular pool of glucose transporters.

M Guerre-Millo,M Lavau,J S Horne,L J Wardzala

doi:10.1016/s0021-9258(18)89537-0

Abstract

The mechanism for hyperresponsive insulin-mediated glucose transport in adipose cells from 30-day-old obese Zucker rats was examined. Glucose transport was assayed by measuring 3-O-methylglucose transport, and the concentration of glucose transporters was estimated by measuring specific D-glucose-inhibitable cytochalasin B binding. Insulin increased glucose transport activity by approximately 17 fmol/cell/min in cells from obese rats compared to 3 fmol/cell/min in lean littermates. Insulin increased the concentration of glucose transporters in the plasma membrane fraction by about 15 pmol/mg of membrane protein in both groups. The insulin-mediated decrease in the concentration of transporters in the low-density microsomal fraction was 30 pmol/mg of membrane protein for the obese rats compared to 15 pmol/mg of membrane protein for the lean controls. An estimated number of glucose transporters was calculated using membrane protein and enzyme recoveries for each group. Insulin increased the number of transporters in the plasma membrane by 3 X 10(6) sites/cell for the obese rats and only 0.6 X 10(6) sites/cell for the lean controls. In addition, insulin decreased the number of transporters/cell in the intracellular membrane pool by approximately 4 X 10(6) sites/cell for the obese rats and 0.9 X 10(6) sites/cells for the lean rats. The total number of transporters/cell was about 7 X 10(6) sites/cell for the obese animals and 1.6 X 10(6) sites/cell for the lean controls. In the basal state, more than 80% of these transporters were located in the intracellular pool for both the lean and obese rats. Thus, the marked hyperresponsive insulin-mediated glucose transport observed in adipose cells from 30-day-old obese Zucker rats may be the consequence of a marked increase in the number of glucose transporters in the intracellular pool.

Highlights

The number of glucose transporters/mg of membrane protein in the plasma membrane fraction was approximately 2-fold greater in the cells from the obese rats compared to the lean rats ( p 5 0.05)
The insulinmediated increase in the concentration of glucosetransporters in theplasma membrane fraction was similar in both groups (Fig. 2 A )
The numbers of glucose transporters/mg of membrane protein inthe low-density microsomal membranes prepared from the basal cells of the obese rats was increased by approximately 70% compared to the lean rats

Summary

MATERIALS AND METHODS

The basal state, more than 80% of these transporters were located in the intracellularpool for both the lean and obese rats. Bird Laboratory (Stowe, MA).Known lean heterozygous (Fa/fa) females and obese homozygous (fa/fa) males were mated. From this mating, 50%of the cells from 30-day-old obese Zucker rats may be the litter is expected to be obese (fa/fa) and 50% lean (Fa/fa). For each consequence of a marked increase in the number of study, approximately eight litters were selected with about 10 pups glucose transporters in the intracellulaprool. The pups were killed by cervical dislocation between 8 and 10 a.m. The marked hyperinsulinemia in vivo and marked insulin inguinal fat pads from approximately 40 lean and 40 obese rats (12), resistance both in vivo and in vitro in the adult Zucker rat and adipose cell size was determined microscopically (13).

Present address

RESULTS

Findings

DISCUSSION