Modulation of myo-[3H]inositol uptake by glucose and sorbitol in cultured bovine lens epithelial cells. II. Characterization of high- and low-affinity myo-inositol transport sites.
Myo-[3H]inositol accumulation in cultured bovine lens epithelial cells (BLECs) occurred by high- and low-affinity, Na(+)-dependent transport sites. The high- and low-affinity transport systems had a Km of 27 +/- 4 and 157 +/- 22 mumol/l, respectively, and Vmax of 652 +/- 35 and 2952 +/- 308 pmol/mg protein/hr, respectively. The uptake of myo-[3H]inositol was lowered after chronic (20 hr) incubation of cultured cells in 40 mmol/l glucose throughout the concentration range for 1.5-400 mumol/l myo-inositol. The coadministration of sorbinil (0.1 mmol/l) to 40 mmol/l glucose partially prevented the inhibitory effect of glucose on myo-[3H]inositol uptake. Although the aldose reductase inhibitor prevented the inhibitory effect of glucose on the low-affinity transport site, a glucose-sensitive process for myo-[3H]inositol uptake on the high-affinity transport site was uncovered by Lineweaver-Burk analysis. Acute exposure (3 hr) of cultured BLECs maintained in physiologic medium (Eagle's minimal essential medium, 5.5 mmol/l glucose) to a range of 5.5-44 mmol/l glucose plus sorbinil also caused a decrease in myo-[3H]inositol uptake. Dixon plot analysis confirmed that the acute effect of glucose was the result of competitive inhibition of the high-affinity myo-inositol transport site. Acute exposure of cultured cells to 10-40 mmol/l sorbitol also diminished the accumulation of myo-[3H]inositol. Dixon plot analysis established that the acute effect of exogenous sorbitol was the result of competitive inhibition of the low-affinity myo-inositol transport site.(ABSTRACT TRUNCATED AT 250 WORDS)
Cammarata
P R
PR
Department of Anatomy and Cell Biology, Texas College of Osteopathic Medicine/University of North Texas, Fort Worth 76107.
Chen
H Q
HQ
Yang
J
J
Yorio
T
T
D000449:Aldehyde Reductase / Q000037:antagonists & inhibitors*; D000818:Animals; D001665:Binding Sites; D001692:Biological Transport / Q000187:drug effects; D002417:Cattle; D002478:Cells, Cultured; D004848:Epithelium / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D048289:Imidazolidines; D007294:Inositol / Q000378:metabolism*; D007700:Kinetics; D007908:Lens, Crystalline / Q000378:metabolism*; D013012:Sorbitol / Q000494:pharmacology*
D007093:Imidazoles; D048289:Imidazolidines; D007294:Inositol; D013012:Sorbitol; D000449:Aldehyde Reductase; C026411:sorbinil; D005947:Glucose