Platelet aggregation and change in intracellular Ca(2+) induced by low frequency ultrasound in vitro

Treatment of platelet-rich plasma and washed platelets with low frequency ultrasound (US, 22 kHz) at intensity range of 1.0-8.8 W/cm(2) resulted in intensity- and time-dependent platelet aggregation. The effect was absent in calcium-free medium and was initiated by adding supernatant from sonicated suspension (16 W/cm(2), 2 min) to non-treated platelets. A marked decrease in the rate of US-induced aggregation was observed in the presence of specific inhibitors of platelet activation dipyridamole, pentoxifillin, aspirin and verapamil. Concentration of intracellular calcium in washed platelets evaluated with fluorescent probe quin-2 acetoxymethyl ester (quin-2) increased upon sonication in both the calcium containing and calcium free media. It is suggested that US increase of [Ca(2+)](i) is involved in platelet aggregation induced by low frequency US.