Membrane damage effect of continuous wave ultrasound on K562 human leukemia cells

This study investigated the bioeffects of ultrasound with a frequency of 1.1 MHz on human chronic myelogenous leukemia cell line K562.

Membrane potential changes were evaluated by flow cytometry using fluorescent probe bis-(1,3-dibarbituric acid)-trimethine oxanol staining. Other related changes such as potassium ion efflux and intracellular calcium ion overload were also measured. The plasma membrane integrity was monitored by flow cytometry combined with fluorescein diacetate and propidium iodide double fluorescent dye staining. A cell-counting assay and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis were used to examine the viability of K562 cells after ultrasound exposure. The acoustic cavitation activity in ultrasound fields was assessed by monitoring hydroxyl radical production.

As the ultrasonic intensity increased, the hydroxyl radical produced in the medium increased, and cell membrane damage and cell viability loss were enhanced. The ultrasonic intensity at 0.64 W/cm(2) did not cause substantial cell damage, whereas ultrasound exposure at 1 and 2.1 W/cm(2) could induce serious cell death (14.0% and 40.7%, respectively). Moreover, ultrasound at 0.64 W/cm(2) did not cause substantial membrane potential changes, whereas ultrasound exposure at 1 W/cm(2) could induce depolarization, and fast hyperpolarization occurred when the ultrasonic intensity increased to 2.1 W/cm(2). In addition, compared with control cells, in different ultrasound-treated cells, the potassium ion continuously outflowed with a prolonged incubation time, whereas the intracellular calcium ion oscillations became more apparent.

The damaging effects of ultrasound on the cell membrane and cell viability were intensity dependent. The membrane potential changes may be due to acoustic cavitation accompanied by alterations in the balance of ions on opposite sides of the cellular membrane.