REDUCED NA-K+-ATPASE ACTIVITY AND PLASMA LYSOPHOSPHATIDYLCHOLINE CONCENTRATIONS IN DIABETIC-PATIENTS()

A fraction from normal human plasma inhibiting Na+-K+ ATPase has been recently identified as lysophosphatidylcholine (LPC). The aim of this study was to investigate the existence of a relationship between the a ctivity of the cellular membrane Na+-K+-ATPase and plasma LPC in human diabetes. We studied 10 patients with insulin-dependent diabetes mell itus (IDDM), 14 patients with non-insulin-dependent diabetes mellitus (NIDDM), and 10 sex- and age-matched control subjects. Plasma LPC conc entrations were increased in both IDDM and NIDDM patients compared wit h control subjects. Na+-K+-ATPase activity was reduced in both groups of patients in erythrocyte and platelet membranes. There was a signifi cant correlation between the concentrations of plasma LPC and N2(+)-K-ATPase activity in both erythrocyte and platelet membranes (P < 0.01) . To investigate the effect of LPC on the enzyme, Na+-K+-ATPase activi ty was determined in erythrocyte membranes obtained from six healthy s ubjects after in vitro incubation with increasing concentrations of LP C (1-10 mu M). Enzymatic activity was significantly reduced by in vitr o LPC at a concentration of 2.5 mu M, with a further decrease at 5 mu M. These data suggest that the decrease in Na+-K+-ATPase activity in d iabetes might be due to increased LPC concentrations.