ISSN:
1432-2013
Keywords:
GLUT-4 (glucose transporter)
;
Ca2+ effects
;
Insulin signal tansduction
;
Cardiomyocytes (permeabilized)
;
2,3-Butanedionemonoxime
;
GTP[γS]
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract In cardiomyocytes glucose transport is activated not only by insulin but also by contractile activity that causes translocation of the glucose transporter, GLUT-4, from intracellular vesicles to the plasma membrane. The latter effect may possibly be mediated by intracellular Ca2+, as suggested by previous studies. To investigate the role of Ca2+, we permeabilized neonatal rat myocytes with α-toxin and incubated them for 1 h either at a pCa (i.e.−log10 [Ca2+]) of 8 (control) or at a pCa of 5 in the presence of adenosine 5′-triphosphate (ATP). Translocation of GLUT-4 was then monitored by a novel immunoprecipitation method using a peptide antibody directed against an exofacial (extracellular) loop of GLUT-4 (residues 58–80). Incorporation of GLUT-4 into the plasmalemma was stimulated 1.8-fold by 10 μM Ca2+ and 1.7-fold by insulin (as in the case of intact cells). The insulin effect was Ca2+ independent, i.e. it was identical in the absence and presence of Ca2+ (10 μM). Guanosine 5′-O-(3-thiotriphosphate) (GTP[γS]), which was inactive in intact cells, also caused translocation of GLUT-4 in permeabilized cardiomyocytes. Thus, incorporation of GLUT-4 into the plasma membrane was enhanced 2.5-fold by 200 μM GTP[γS] in the virtual absence of Ca2+ (pCa 8) and even 3.5-fold at 10 μM free Ca2+. We conclude that an increase in intracellular Ca2+ concentration increases GLUT-4 translocation of (permeabilized) cardiomyocytes to a similar extent as do insulin and GTP[γS] in the absence of Ca2+, but that the effects of Ca2+ and GTP[γS] may be additive.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00373907
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