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Endotoxic lipid A induces intracellular Ca2+ increase in human platelets
M Romano1, M Molino, C Cerletti
1Istituto di Patologia Medica e Medicina Mediterranea, Università di Messina, Italy.
The Biochemical Journal
|August 15, 1991
Summary
Endotoxic lipid A activates human platelets by increasing intracellular calcium ([Ca2+]i) and activating protein kinase C. This process involves calcium release from stores and influx from outside, with protein kinase C playing a key role.
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Endotoxic lipid A is known to activate protein kinase C in platelets.
- The precise mechanisms by which lipid A affects platelet function, particularly intracellular calcium levels, require further elucidation.
Purpose of the Study:
- To investigate the effect of lipid A on intracellular calcium concentration ([Ca2+]i) in human platelets.
- To determine the role of protein kinase C and calcium mobilization in lipid A-induced platelet activation.
Main Methods:
- Human platelets loaded with fura-2 were stimulated with lipid A.
- Intracellular calcium levels ([Ca2+]i) were measured using fluorescence.
- The effects of EGTA, NiCl2, MnCl2, and staurosporine on [Ca2+]i and inositol trisphosphate (InsP3) levels were assessed.
Main Results:
- Lipid A induced a concentration-dependent rise in [Ca2+]i, indicating calcium mobilization and influx.
- EGTA and NiCl2 partially inhibited the [Ca2+]i rise, suggesting extracellular calcium influx.
- Staurosporine, a protein kinase C inhibitor, blocked the [Ca2+]i rise and InsP3 accumulation, implicating protein kinase C in the signaling pathway.
Conclusions:
- Platelet activation by lipid A involves a complex interplay between the elevation of intracellular calcium and protein kinase C activation.
- Lipid A triggers calcium release from Ins(1,4,5)P3-sensitive stores and promotes calcium influx.
- Protein kinase C activation is a critical component of the lipid A signaling cascade in platelets.