Changes in Phosphoinositide Turnover, Ca2+ Mobilization, and Protein Phosphorylation in Platelets From NIDDM Patients

Abstract

Enhanced platelet functions have been demonstrated in patients with non-insulin-dependent diabetes mellitus (NIDDM). This study evaluated abnormalities in platelet signal transduction in diabetic patients, including turnover of phosphoinositides, mobilization of intracellular Ca2+, and phosphorylation of 20,000- and 47,000-Mr proteins (P20 and P47). Washed platelets were obtained from 6 patients with NIDDM whose platelet aggregation rates were abnormally elevated (DM-A group), 11 NIDDM patients with normal platelet aggregation rates (DM-B group), and 8 age-matched healthy control subjects. The mass and specific radioactivity of phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol (PI), and phosphatidic acid (PA) in 32P-labeled platelets were not different among the three groups. Hydrolysis of PIP2, PIP, and PI; accumulation of PA; and phosphorylation of P20 in platelets stimulated by 0.05 U/ml thrombin were significantly increased in the DM-A group compared with the control or DM-B group. There was no difference in P47 phosphorylation among the three groups. On the contrary, P20 and P47 phosphorylation induced by 50 nM of 12-O-tetradecanoylphorbol-13-acetate, an activator of protein kinase C, was significantly decreased in the DM-A group. Additionally, the intracellular free Ca2+ concentration [( Ca2+]i) was measured with the fluorescent Ca2+ indicator fura 2. Although the basal [Ca2+]i value was similar in the three groups, the rise in [Ca2+]i induced by 0.05 U/ml thrombin in the presence and the absence of extracellular Ca2+ was significantly higher in the DM-A group than the other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane Fluidity, Membrane Lipid Pattern, and Cytosolic Ca2+ Content in Platelets from a Group of Type II Diabetic Patients with Macrovascular Complications

“…An increase in this parameter, examined in resting intact platelets, was found in type II diabetic patients (28,29). Instead, our data are in agreement with the findings reported by Ishii et al (30,31), who examined platelet cytosolic Ca 2+ content in type II diabetic subjects, showing that the Ca 2+ content was similar to that of normal subjects under basal conditions, although its increase was significantly higher in type II diabetic patients when platelets were stimulated with thrombin (30) or platelet-activating factor and calcium ionophore A23187 (31).…”

Platelet Abnormalities in Diabetes Mellitus

“…The amount of thrombin that bound to its receptor on platelets from diabetic rats was not different from control rats (27); this result has not been examined with platelets from diabetic humans. In a recent study, thrombin induced greater phosphoinositide hydrolysis, intracellular Ca 2+ mobilization, and myosin light-chain kinase-mediated P20 phosphorylation in hypersensitive platelets from NIDDM patients compared with control subjects (28). However, in contrast, decreased phosphoinositide turnover in response to thrombin was reported in platelets from IDDM patients (29).…”

Platelet abnormalities in diabetes mellitus

“…Diabetic platelets were shown to have increased phosphoinositide turnover upon thrombin stimulation [61], along with decreased protein phosphorylation and raised free intracellular Ca 2+ concentration. When exposed to high glucose concentrations, both normal and diabetic platelets have increased DAG levels and increased stimulation of PKC and phospholipase A 2 [59].…”