Insulin-stimulated cytosol alkalinization facilitates optimal activation of glucose transport in cardiomyocytes.
Abnormalities in intracellular pH regulation have been proposed to be important in type 2 diabetes and the associated cardiomyopathy and hypertension. We have therefore investigated the dependence of insulin-stimulated glucose transport on cytosolic pH in cardiomyocytes. Insulin treatment of cardiomyocytes resulted in a marked alkalinization of the cytoplasm as measured using carboxy-semi-napthorhodofluor-1. The alkalinizing effect of insulin was blocked by treatment with either cariporide (which inhibits the Na+/H+ exchanger) or by bafilomycin A1 (which inhibits H+-ATPase activity). After treatments with cariporide or bafilomycin A1, insulin stimulation of insulin receptor and insulin receptor substrate-1 phosphorylation and Akt activity were normal. In contrast, glucose transport activity and the levels of functional GLUT4 at the plasma membrane (detected using an exofacial photolabel) were reduced by approximately 50%. Immunocytochemical analysis revealed that insulin treatment caused a translocation of the GLUT4 from perinuclear structures and increased its co-localization with cell surface syntaxin 4. However, neither cariporide nor bafilomycin A1 treatment reduced the translocation of immunodetectable GLUT4 to the sarcolemma region of the cell. It is therefore hypothesized that insulin-stimulated cytosol alkalinization facilitates the final stages of translocation and incorporation of fully functional GLUT4 at the surface-limiting membrane.
Yang
Jing
J
Departments of Biology and Biochemistry and Pharmacy and Pharmacology, University of Bath, Bath BA2 7AY, United Kingdom.
Gillingham
Alison K
AK
Hodel
Alois
A
Koumanov
Francoise
F
Woodward
Brian
B
Holman
Geoffrey D
GD
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D006146:Guanidines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D018942:Macrolides; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors; D050765:Qa-SNARE Proteins; D051381:Rats; D017208:Rats, Wistar; D011972:Receptor, Insulin / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors; D013450:Sulfones / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D051275:Glucose Transporter Type 4; D006146:Guanidines; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D018942:Macrolides; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D050765:Qa-SNARE Proteins; C495694:Slc2a4 protein, rat; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C093373:cariporide; C040929:bafilomycin A1; D011972:Receptor, Insulin; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D006180:Proton-Translocating ATPases; D005947:Glucose