Stimulation of Na+/H+ exchange by insulin and phorbol ester during differentiation of 3T3-L1 cells. Relation to hexose uptake.
Acute exposure of 3T3-L1 undifferentiated fibroblasts to insulin or 4 beta-phorbol-12,13-dibutyrate (PDB) produced a moderate but significant stimulation of hexose transport (100% stimulation). In differentiated 3T3-L1 adipocytes, stimulation by insulin increased significantly (to 340%), while that by PDB remained at 130%. Total protein kinase C activity was 3-fold higher in 3T3-L1 fibroblast than adipocyte homogenates. PDB, but not insulin, induced migration of protein kinase C from the cytosol to the membrane, in both fibroblasts and adipocytes. Moreover, the hormone increased by 15% the protein kinase C activity of the cytosol. In 3T3-L1 fibroblasts, both insulin and PDB elicited a rapid (2 min lag) cytoplasmic alkalinization, measured with the fluorescent pH indicator bis-carboxyethyl carboxyfluorescein trapped in the cytoplasm. In 3T3-L1 adipocytes, PDB but not insulin elicited the cytoplasmic alkalinization. The alkalinization was prevented by amiloride or by replacing Na+ with either N-methylglucamine+ or K+. Stimulation of hexose transport by insulin or PDB was not affected by amiloride or Na+ substitution. It is concluded that: 1) Insulin and PDB have different effects on protein kinase C activity and subcellular distribution; 2) the responses of Na+/H+ exchange and hexose transport to insulin and PDB develop independently during differentiation of 3T3-L1 cells; 3) stimulation of Na+/H+ exchange and of hexose transport occur in parallel rather than in series in 3T3-L1 cells.
Klip
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Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
Ramlal
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Koivisto
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UM
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002273:Carcinogens / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D003837:Deoxy Sugars / Q000378:metabolism*; D003847:Deoxyglucose / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D015240:Phorbol 12,13-Dibutyrate; D010703:Phorbol Esters / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers
D002273:Carcinogens; D002352:Carrier Proteins; D003837:Deoxy Sugars; D007328:Insulin; D010703:Phorbol Esters; D017923:Sodium-Hydrogen Exchangers; D015240:Phorbol 12,13-Dibutyrate; D003847:Deoxyglucose; D011493:Protein Kinase C