Changes in membrane microenvironment and signal transduction in platelets from NIDDM patients-a pilot study.
BACKGROUND
Non-insulin-dependent diabetes mellitus (NIDDM) is characterized by the presence of abnormally active platelets in the circulation, leading to increased incidence of thrombotic complications. In this study, we have attempted to understand the pathophysiology of the platelets in NIDDM.


METHODS
Platelet aggregation was induced by thrombin receptor-activating peptide or epinephrine. Membrane fluidity was derived from the steady-state fluorescence anisotropy of diphenylhexatriene incorporated in the membrane. The phosphotyrosine content of the platelet proteins was probed using specific monoclonal antibodies. The extent of calpain activity was assessed from the proteolysis of calpain substrates.


RESULTS
Aggregation was significantly enhanced (p<0.001) in the platelets obtained from the cases of NIDDM. Anisotropy measurements reflected a significant increase in the microviscosity of platelet membranes from 3.315 (+/-0.103) in the control to 4.153 (+/-0.119) in NIDDM. Proteins of relative mobilities of 131, 100, 47 and 38 kDa were found to remain phosphorylated on tyrosine in the resting platelets obtained from NIDDM patients, while they were not phosphorylated in the control counterparts. This was associated with heightened activity of the calcium-dependent thiol protease, calpain, in NIDDM.


CONCLUSIONS
Taken together, these data indicated significant changes in the signaling mechanism in the platelets obtained from NIDDM, which could lead to platelet hyperactivity in this disease.
Srivastava
Kalyan
K
Department of Biochemistry, Institute of Medical Sciences, Banaras Hindu University, 221005, Varanasi, India.
Dash
Debabrata
D
D000328:Adult; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002154:Calpain / Q000187:drug effects / Q000378:metabolism; D016022:Case-Control Studies; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000473:pathology; D004837:Epinephrine / Q000494:pharmacology; D006801:Humans; D008875:Middle Aged; D010766:Phosphorylation; D010865:Pilot Projects; D015539:Platelet Activation; D010974:Platelet Aggregation / Q000187:drug effects; D012016:Reference Values; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism
D000001:Calcimycin; D014443:Tyrosine; D002154:Calpain; D004837:Epinephrine