Potential mechanism of insulin resistance in ageing: impaired insulin-stimulated glucose transport due to a depletion of the intracellular pool of glucose transporters in Fischer rat adipocytes.
To examine the cellular mechanism responsible for impaired insulin action in ageing, we determined various in-vitro parameters involved in the pathogenesis of insulin resistance, i.e. basal and insulin-stimulated [14C]3-O-methylglucose transport (3OMG), 125I-labelled insulin binding, activation of insulin receptor kinase (IRKA) in intact cells, and number and subcellular distribution of glucose transporters in subcellular membrane fractions of adipocytes from 6- (FR-6) and 24- (FR-24) month-old Fischer rats. Ageing had no effect on basal 3OMG (12 +/- 4 vs 13 +/- 3 fmol/5 x 10(4) cells, means +/- S.E.M.); in contrast, in FR-24 rats insulin-stimulated 3OMG was markedly decreased by 43% when compared with that in FR-6 rats (158 +/- 14 vs 90 +/- 8 fmol/5 x 10(4) cells; P less than 0.01). Insulin binding to adipocytes from FR-6 rats was 2.40 +/- 0.38% compared with 2.28 +/- 0.47% in FR-24 (P not significant). Moreover, ageing had no significant effect on IRKA, as determined by insulin-stimulated (0, 1, 4 and 500 ng insulin/ml) 32P-incorporation into histone 2B. In subcellular membrane fractions, low density microsomes and plasma membranes, glucose transporter numbers were determined using [3H]cytochalasin B binding and immunodetection using an antiserum against the C-terminal peptide of the hepatoma-G2-glucose transporter. Cytochalasin B binding revealed that in the basal state the intracellular pool of glucose transporters was depleted in FR-24 by about 39% compared with low density microsomes from FR-6: (48.6 +/- 7.2 vs 29.8 +/- 5.5 pmol/mg membrane protein; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Matthaei
S
S
Department of Medicine, University-Hospital, Hamburg, Federal Republic of Germany.
Benecke
H
H
Klein
H H
HH
Hamann
A
A
Kreymann
G
G
Greten
H
H
D019325:3-O-Methylglucose; D000273:Adipose Tissue / Q000378:metabolism*; D000375:Aging / Q000378:metabolism*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D003571:Cytochalasin B / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology*; D008297:Male; D008757:Methylglucosides / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000032:analysis; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D011972:Receptor, Insulin / Q000032:analysis; D013347:Subcellular Fractions / Q000032:analysis
D001786:Blood Glucose; D007328:Insulin; D008757:Methylglucosides; D009004:Monosaccharide Transport Proteins; D019325:3-O-Methylglucose; D003571:Cytochalasin B; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin