In vivo insulin effect on ATPase activities in erythrocyte membrane from insulin-dependent diabetics.

Na+-K+-dependent ouabain-sensitive ATPase and Mg2+-ATPase have been assayed in the erythrocyte membranes of control subjects and in uncontrolled type I (insulin-dependent) diabetics. A decrease in Na+-K+-ATPase activity was observed in the patients that was significantly correlated with glycemia. The Mg2+-ATPase was increased moderately, and no correlation with glycemia was found. To study the in vivo effect of insulin, ATPase activities were measured in uncontrolled diabetics before and after a 24-h continuous insulin perfusion administered by means of an artificial pancreas. ATPase activities were corrected after normalization of glycemia. It therefore seems that glycemia and/or insulinemia are involved in the regulation of erythrocyte Na+-K+ ouabain-sensitive ATPase and to a lesser extent in that of Mg2+-dependent ATPase.

Correction by insulin added in vitro of abnormal membrane fluidity of the erythrocytes from type 1 (insulin-dependent) diabetic patients.

Filtrability of erythrocytes obtained from uncontrolled Type 1 (insulin-dependent) diabetic patients is abnormal, but is corrected by insulin added in vivo or in vitro. As erythrocyte filtrability depends on several determinants, we chose to study a membrane property of erythrocytes from diabetic subjects. Membrane fluidity was studied by fluorescence polarization using a lipophilic probe, the diphenyl-hexatriene and the Coulter Epics V together with a laser Spectra-physics 2000. Fluorescence polarization values obtained for 31 normal subjects (0.253 +/- 0.043 SD) and 31 uncontrolled Type 1 diabetic patients (0.231 +/- 0.043 SD) were significantly different (p less than 0.01). Insulin (2.5.10(-9) mol/l) added in vitro increased the fluorescence polarization values of red cell membranes from diabetic patients (without insulin, fluorescence polarization values = 0.210 +/- 0.032 SD; with insulin, fluorescence polarization values = 0.253 +/- 0.024 SD, p less than 0.001, n = 15), but had no effect on normal membranes (without insulin fluorescence polarization values = 0.255 +/- 0.037 SD, with insulin, fluorescence polarization values = 0.251 +/- 0.026 SD; n = 12). Given a relationship between the lipid bilayer and membrane cytoskeleton proteins, this insulin-correctable abnormality of erythrocyte membrane fluidity may be an important determinant of the rheological behaviour of erythrocytes from diabetic patients.

Correction by pentoxifylline of the abnormal fluorescence polarization of erythrocyte membranes from diabetic patients.

Erythrocytes from diabetic patients show abnormal rheology. Pentoxifylline, a methylxanthine, improves the abnormal deformability of diabetic erythrocytes, but its mechanism of action remains unclear. We have studied the effect of pentoxifylline on the lipid order of erythrocyte membranes from controls and patients with Type I diabetes. We studied the structural organization of membrane lipids in individual erythrocyte ghosts by fluorescence polarization using a cell sorter. Fluorescence polarization values (P) for 17 controls (P = 0.244) and 20 diabetic patients (P = 0.215) were significantly different. Pentoxifylline added in vitro had no effect on normal membranes, but significantly increased at 10(-5) mol X l-1 (P = 0.233), and normalized at 10(-4) mol X l-1 (P = 0.243), the P value of membrane ghosts from diabetics.