Apoptotic-like mitochondrial events associated to phosphatidylserine exposure in blood platelets induced by local anaesthetics.

Abstract

Phosphatidylserine exposure in platelets is required for normal haemostasis and is also a hallmark of apoptosis. It results from activation of a phospholipid scramblase, which has been shown to be differently stimulated by Ca(2+)-influx and during apoptosis, thus suggesting that mitochondria may be involved in phosphatidylserine exposure in platelets. It is also well known that local anaesthetics can expose phosphatidylserine in platelets and affect the mitochondrial metabolism in other cells. Thus, the present study was undertaken to evaluate the specific involvement of mitochondria in phosphatidylserine exposure in platelets. For this purpose, we stimulated phosphatidylserine exposure by local anaesthetics and avoided any external Ca(2+)-influx by performing all experiments in the absence of added Ca(2+). We report that phosphatidylserine exposure, induced by the lipophilic local anaesthetics dibucaine and tetracaine, was accompanied by depolarization of the mitochondrial membrane, cytochrome c release, calpain-processing of caspases 9 and 3 to active enzymes, as well as a prolonged increase in both cytosolic and mitochondrial Ca(2+) concentrations. In contrast, in the absence of extracellular Ca(2+), the Ca(2+)-ionophore A23187 induced a smaller transient increase in both cytosolic and mitochondrial Ca(2+) concentrations, but did not induce any other phenomena, nor phosphatidylserine exposure. However, phosphatidylserine exposure and depolarization induced by dibucaine still occurred in spite of inhibition of intracellular Ca(2+) elevation. Thus we conclude that phosphatidylserine exposure in platelets is associated with mitochondrial apoptotic-like events. Therefore, we propose that mitochondria engagement in an apoptotic pathway in platelets could lead to PS exposure without the participation of Ca(2+).