Effects of Pulsed Acoustic and Mechanical Stimuli on the Excitability of Isolated Neuronal and Cardiac Cells

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Abstract
This article presents the final results of a series of investigations conducted on the interaction of two specific forms of mechanical stimuli with isolated neuronal and cardiac cells: short bursts of focused, high peak-power ultrasound (1 to 7 MHz, 0.5 ms, 50 to 800 W/cm2 spatial-peak, pulse-average intensity, 3-mm half-power spot) and 0.5-ms direct pressure pulses applied with a transducer-driven glass stylus with a 1- to 6-μm peak displacement. The current study has investigated the effects of these stimuli on the mouse sciatic nerve trunk and cardiac preparations of the leopard frog. They are compared to those observed with the leopard frog sciatic nerve trunk and lobster axon, reported previously. These studies have revealed that each of these preparations exhibits brief and fully reversible modifications of cellular excitability within a 10- to 30-ms window following both single, submillisecond ultrasound bursts and appropriately applied direct mechanical stimuli. The high peak-power ultrasonic bursts used in this study have been shown micrographically to elicit a small but rapid stretch of the nerve preparation in the range of 3 to 10 μm in a manner similar to that of the direct mechanical stimuli; the result of this may be the gating of stretch-sensitive ion channels. These transmembrane structures, believed to be gated by a conformational change of a channel protein in response to membrane stretch, have been reported in a wide variety of cell types not normally involved in mechanotransduction.