Are lysophosphatidic acids or phosphatidic acids involved in stimulus activation coupling in platelets?

Phosphatidic acids and/or lysophosphatidic acids are potentially pivotal compounds produced during metabolism of phosphatidylinositol. a very early event in the response of platelets to thrombin and other stimuli. In the present study, we have reevaluated the platelet aggregation produced by these agents to assess whether one or both could possibly function as intermediates in the transmission of the activating signal. Liposomes could be used to deliver lysophosphatidic acids but were not more effective than using 25% ethanol. dimethylsulfoxide. or even good suspensions in Hank’s balanced salt solution. Aggregation induced by lysophosphatidic acid was considerably influenced by the concentration of albumin in the medium, with the highest percentage of aggregation in the absence of albumin and decreasing degrees of aggregation as more albumin was present. Aggregation in 1 mg/mI albumin was optimum at 0.5-1 .0 mM Mg. when calcium was held constant at 0.5 mM. When magnesium was 0.5 mM. then