[Effect of ultrasound on membrane surface potentials]

The electrostatic equilibrium on the surface of an ion-impermeable membrane was not influenced by ultrasound fields. Only after incorporation of an ion transporter did the ultrasound induce changes of the membrane surface potential. Because the ultrasound effect was completely reversible, measurements of the surface potential of a flat lipid bilayer membrane containing the calcium transporter calcimycin were performed, simultaneously to the ultrasound exposure. The ultrasound-induced volume flow, also called quartz wind, favored the mass transfer through the diffusion boundary close to the membrane, thereby leading to increased calcium concentrations in the immediate vicinity of the membrane. This, in turn, became manifest as a reduction of the negative surface charge density.