Effects of ultrasound on the steady-state transmembrane pH gradient and the permeability of acetic acid through bilayer lipid membranes.

The irradiation of bilayer lipid membranes with continuous ultrasound of a frequency of 8.2 MHz and a spacial peak time average (SPTA) intensity of 0.4 W/cm2 reduces the thickness of the unstirred layer up to 40% of its initial value under our conditions. This result was obtained from measurements of the transmembrane potential which appears after the addition of a protonophore in the presence of a gradient of acetic acid. Ultrasound exposure decreases this potential when the pH of the buffer solutions is much higher than the pK of CH3COOH and has no effect at low pH values. The latter can be explained by a simultaneous increase of the permeability of acetic acid and the buffer substances, respectively, due to ultrasound irradiation.