title: Initiator-promoter coupling of phospholipases D and A2 in platelets upon cholesterol incorporation.
abstract: Since phospholipases exist within a membrane lipid environment, it is not unreasonable to assume that cholesterol capable of changing the lipid environment can effect the coupling relationship among the signal transducing components. Our previous study showed that the 'molecular switch' through which membrane cholesterol modulates cyclic nucleotide levels and Na+/H+ exchange within human platelets is phospholipase A2. We demonstrate here that membrane cholesterol initiates the activation of phosphatidyl choline phospholipase D and phosphatidic acid thus generated promotes the activation of its phospholipase A2 in the presence of extraplatelet calcium. More important, inhibition of phospholipase D by zinc blocks the activation of phosphatidic acid phospholipase A2 in platelets upon cholesterol incorporation. Our result led us to postulate that membrane cholesterol induced initiation promotion coupling of phospholipases D and A2 in human platelets may be responsible for the hypersensitized state of platelets in hypercholesterolemic patients.
authors.affiliation: Department of Experimental Medicine, PGIMER, Chandigarh, India.
authors.forename: N
authors.initials: N
authors.lastname: Kochhar
authors.forename: D
authors.initials: D
authors.lastname: Kaul
mesh_terms: D001792:Blood Platelets / Q000201:enzymology / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D006801:Humans; D010712:Phosphatidic Acids / Q000378:metabolism; D010739:Phospholipase D / Q000187:drug effects / Q000378:metabolism*; D010741:Phospholipases A / Q000187:drug effects / Q000378:metabolism*; D054467:Phospholipases A2; D010743:Phospholipids / Q000378:metabolism; D015398:Signal Transduction; D015032:Zinc / Q000494:pharmacology
chemical_list: D010712:Phosphatidic Acids; D010743:Phospholipids; D004533:Egtazic Acid; D002784:Cholesterol; D010741:Phospholipases A; D054467:Phospholipases A2; D010739:Phospholipase D; D015032:Zinc