Hexose transport in human adipocytes: Factors influencing the response to insulin and kinetics of methylglucose and glucose transport

Abstract

Summary. Optimal experimental conditions were defined for measuring the initial uptake rate of the non-metabolizable sugar analogue 3-O-methylglucose in non-stimulated and insulin-stimulated human adipocytes. The permeability of the adipocyte plasma membrane for tracer methylglucose (100 ~tmol/l) was 2.9 • 10 -7 cm • s -1 at 37~ and slightly lower at 20~ At 37~ and pH 7.4 insulin (5nmol/l) increased the permeability about twofold (range 1.5 to fivefold) with half maximal effect at about 100 pmol/1. At pH 7.0 the dose response curve for the insulin effect on the uptake rate of methylglucose was shifted about 2.5-fold to the right. The permeability to L-glucose due to simple diffusion was estimated as 3.0 • 10-~~ cm • s-1 suggesting that uptake of methylglucose occurs almost exclusively by facilitated diffusion. The Km for methylglucose equilibrium exchange in insulin stimulated cells was about 4.8mmol/1. The initial uptake of tracer methylglucose in insulin-stimulated cells was inhibited by unlabelled methylglucose and by D-glucose with inhibition constants of about 3.8 and 7.7 mmol/ 1, respectively. Uptake of tracer 2-deoxyglucose (50 ~tmol/l) in insulin-stimulated adipocytes was linear from 10 s to 5 min whereas the rate of uptake in the presence of 3 mmol/l of D-glucose was markedly decreased suggesting that deoxyglucose uptake after a few minutes is mainly limited by hexokinase in the presence of glucose.

Regional difference in insulin inhibition of non-esterified fatty acid release from human adipocytes: relation to insulin receptor phosphorylation and intracellular signalling through the insulin receptor substrate-1 pathway

“…A large rightwards shift in the position of the insulin dose-response curve for PI 3-kinase is apparent when compared with that of lipolysis. This finding is reminiscent of the difference in the dose-response curves between insulin action on glucose transport and insulin receptor binding, the latter being shifted to the right compared with the former in human fat cells [33]. This discrepancy between insulin receptor binding and downstream metabolic event could be due to ªspareº insulin receptors.…”

Marked Increase in Insulin Sensitivity of Human Fat Cells 1 Hour after Glucose Ingestion

“…For obvious reasons neither muscle nor liver can be used for the present type of experiments in man. Unfortunately, it is also not possible at present to study glucose transport in human fat cells in this respect, because the methods require a large amount of human fat (24). However, it is well recognized that the first step in insulin action is binding to cell surface receptors (25).…”

Historical perspectives in fat cell biology: the fat cell as a model for the investigation of hormonal and metabolic pathways

“…The method of isolation using collagenase presents some disadvantages because of poorly controlled contaminating protease activity in the collagenase batches. Modifications to the initial method to circumvent or limit the collagenase-related side effects were proposed (28,264). The monitoring of insulin-dependent effects (i.e., stimulation of glucose influx or metabolism) seemed to be a rapid, sensitive, and accurate means to validate the isolation technique and the potential side effects of inconsistent enzyme preparations.…”