myo-inositol influx into human leucocytes: methods of measurement and the effect of glucose.
1. Low intracellular concentrations of myo-inositol in diabetic cells may contribute to the development of tissue damage. The cause of these low levels is unknown, but inhibition of a putative myo-inositol transporter by high concentrations of glucose has been proposed. We have developed a triple-isotope method for estimating myo-inositol influx into human leucocytes and so investigated both the kinetics of this uptake in normal volunteers and the effect of glucose upon it. 2. Uptake was composed of a passive component with a rate constant of 2.4 +/- 0.3 X 10(-2) min-1 and a saturable component with a Km of 61 +/- 23 mumol/l and Vmax of 11.3 +/- 4.5 X 10(-4) mmol min-1 l-1. Ouabain and low extracellular concentrations of sodium partly inhibited influx. Uptake was predominantly into the cytosolic fraction of the cell with 12% entering the membrane-associated fraction at both 5 and 10 min. 3. myo-Inositol influx was significantly inhibited by both D- and L-glucose but not by sucrose. Neither cytochalasin B nor ethyl isopropyl amiloride significantly inhibited uptake. 4. It is concluded that a myo-inositol transporter exists in human leucocytes which is similar to that found in other species and tissues. Our technique allows myo-inositol influx in diabetic subjects to be related to varying glycaemic control and tissue damage.
Simmons
D
D
Sheikh Rashid Diabetes Unit, Radcliffe Infirmary, Oxford, U.K.
Bomford
J
J
Ng
L L
LL
D000328:Adult; D001693:Biological Transport, Active / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007294:Inositol / Q000097:blood*; D007700:Kinetics; D007962:Leukocytes / Q000378:metabolism*; D008214:Lymphocytes / Q000378:metabolism; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D009504:Neutrophils / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013395:Sucrose / Q000494:pharmacology
D007294:Inositol; D013395:Sucrose; D010042:Ouabain; D012964:Sodium; D005947:Glucose