Dehydroascorbic acid uptake by coronary artery smooth muscle: effect of intracellular acidification.
Dehydroascorbic acid (DHAA) enters cells via Na(+)-independent glucose transporters (GLUT) and is converted to ascorbate. However, we found that Na(+) removal inhibited [(14)C]DHAA uptake by smooth-muscle cells cultured from pig coronary artery. The uptake was examined for 2-12 min at 10-200 microM DHAA in either the presence of 134 mM Na(+) or in its absence (N-methyl D-glucamine, choline or sucrose replaced Na(+)). This inhibition of DHAA uptake by Na(+) removal was paradoxical because it was inhibited by 2-deoxyglucose and cytochalasin B, as expected of transport via the GLUT pathway. We tested the hypothesis that this paradox resulted from an inefficient intracellular reduction of [(14)C]DHAA into [(14)C]ascorbate upon intracellular acidosis caused by the Na(+) removal. Consistent with this hypothesis: (i) the Na(+)/H(+)-exchange inhibitors ethylisopropyl amiloride and cariporide also decreased the uptake, (ii) Na(+) removal and Na(+)/H(+)-exchange inhibitors lowered cytosolic pH, with the decrease being larger in 12 min than in 2 min, and (iii) less of the cellular (14)C was present as ascorbate (determined by HPLC) in cells in Na(+)-free buffer than in those in Na(+)-containing buffer. This inability to obtain ascorbate from extracellular DHAA may be detrimental to the coronary artery under hypoxia-induced acidosis during ischaemia/reperfusion.
Holmes
Melanie E
ME
Department of Medicine, McMaster University, Hamilton, Ontario, Canada L8N 3Z5.
Mwanjewe
James
J
Samson
Sue E
SE
Haist
James V
JV
Wilson
John X
JX
Dixon
S Jeffrey
SJ
Karmazyn
Morris
M
Grover
Ashok K
AK
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001692:Biological Transport; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000378:metabolism*; D003683:Dehydroascorbic Acid / Q000378:metabolism*; D006146:Guanidines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology; D013552:Swine
D000889:Anti-Arrhythmia Agents; D002250:Carbon Radioisotopes; D006146:Guanidines; D013450:Sulfones; D000584:Amiloride; C093373:cariporide; D000255:Adenosine Triphosphate; C039614:ethylisopropylamiloride; D003683:Dehydroascorbic Acid