Figure 2. Maximal current response requires alignment of the bilayer and the ultrasound beam.

A. Current recorded from a POPE/POPG bilayer under voltage-clamp at −100 mV in response to a 50-ms, 13-W/cm² ultrasound pulse from a 43-MHz focused transducer with the focal spot aligned on the bilayer (blue current trace) and with the focal spot moved 2 mm away from the bilayer in the x-y plane (red current trace). The currents are normalized to the peak inward current and the baseline currents have been subtracted. The current scale bar is in normalized units. The peak positive and negative currents were 147 and −157 pA with the focal spot centered on the bilayer, and 15 and −13.7 with the focal spot translated 2 mm in the x-y plane. The capacitance of the bilayer was 153 pF. The currents are the average of 10 ultrasound applications. Mean peak positive and negative currents, relative to the peak current with the bilayer and ultrasound beam aligned, for the On and Off responses (respectively) after moving the transducer were 8.9±0.1% and 9.1±0.1% (mean ± SE, n = 7). B. The Off current response from A. on an expanded time scale. C. Approximate scale drawing indicating the position of the focal spot for the two current traces.