Further investigations of ATP release from human erythrocytes exposed to ultrasonically activated gas-filled pores.

Suspensions of human erythrocytes in a firefly-extract solution were exposed to 2.0 MHz ultrasound in the presence of 3.4 microns dia. gas-filled pores. Lysis of the cells during ultrasonic exposure resulted in the release of ATP which produced light upon interaction with the firefly extract. The response was approximately proportional to the square of the SPTA intensity I for both continuous and pulsed exposures (1 mu s pulses, 1:9 duty cycle) within the range 5-100 mW/cm2. One method of graphical data presentation yielded an apparent threshold for the effect at 0.31 bar pressure amplitude; however, a response could probably be obtained at any nonzero exposure level with a sufficiently sensitive apparatus. The response was also proportional to the exposure duration t for the range 0.03-3 s. The product I2 t may have some significance as a dosage parameter for this system in an, as yet, undefined "low-dose" range. Measurements for exposures with higher intensities, longer durations, lower duty factors and with pulses longer than 300 mu s deviated from these trends.