Focused ultrasound transiently increases membrane conductance in isolated crayfish axon
Jen-Wei Lin, Feiyuan Yu, Wolfgang S. Müller, Gösta Ehnholm, Yoshio Okada
Journal of Neurophysiology 2019, 121, 480-489 · 10.1152/jn.00541.2018
Abstract
We report a novel phenomenon produced by focused ultrasound (US) that may be important for understanding its effects on cell membranes. When a US burst (2.1 MHz, 1-mm focal diameter, 0.1-1 MPa) was focused on a motor axon of the crayfish neuromuscular junction, it consistently produced a fast hyperpolarization, which was followed or superseded by subthreshold depolarizations or action potentials in a stochastic manner. The depolarization persisted in the presence of voltage-gated channel blockers [1 µM TTX ( I Na ), 50 µM ZD7288 ( I h ), and 200 µM 4-aminopyridine ( I K )] and typically started shortly after the onset of a 5-ms US burst, with a mean latency of 3.35 ± 0.53 ms (SE). The duration and amplitude of depolarizations averaged 2.13 ± 0.87 s and 10.1 ± 2.09 mV, with a maximum of 200 s and 60 mV, respectively. The US-induced depolarization was always associated with a decrease in membrane resistance. By measuring membrane potential and resistance during the US-induced depolarization, the reversal potential of US-induced conductance ( g us ) was estimated to be -8.4 ± 2.3 mV, suggesting a nonselective conductance. The increase in g us was 10-100 times larger than the leak conductance; thus it could significantly influence neuronal activity. This change in conductance may be due to stimulation of mechanoreceptors. Alternatively, US may perturb the lateral motion of phospholipids and produce nanopores, which then increase g us . These results may be important for understanding mechanisms underlying US-mediated modulation of neuronal activity and brain function. NEW & NOTEWORTHY We report a specific increase in membrane conductance produced by ultrasound (US) on neuronal membrane. When a 5-ms US tone burst was focused on a crayfish motor axon, it stochastically triggered either depolarization or a spike train. The depolarization was up to 60 mV in amplitude and 200 s in duration and therefore could significantly influence neuronal activity. Depolarization was still evoked by US burst in the presence of Na + and Ca 2+ channel blockers and had a reversal potential of -8.4 ± 2.3 mV, suggesting a nonselective permeability. US can be applied noninvasively in the form of a focused beam to deep brain areas through the skull and has been shown to modulate brain activity. Understanding the depolarization reported here should be helpful for improving the use of US for noninvasive modulation and stimulation in brain-related disease.
Abstract via europepmc.
Exposures
Exposure 1: Focused ultrasound burst applied to isolated crayfish motor axon
Target: crayfish neurons, neuromuscular junction — “motor axon of the crayfish opener neuromuscular junction”
Device: custom-built
| Waveform | continuous | |
|---|---|---|
| Fundamental frequency (kHz) | 2,100 | ✓✓✓ |
| Pulse duration (ms) | not applicable | |
| Pulse repetition frequency (Hz) | not applicable | |
| Duty cycle (%) | not applicable | |
| Sonication duration (s) | 0.005 | ✓✓✓ |
| Free-field pressure (kPa) | 100, 1,000swept | ✓✓✓⚑ |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | 0.0042, 0.0094swept | ✓✓✓ |
| In-situ estimate | not applicable | |
| In-situ pressure (kPa) | not applicable | |
| In-situ Isppa (W/cm²) | not applicable | |
| In-situ Ispta (W/cm²) | not applicable |
Unless otherwise specified, responses were evoked by a single 5-ms, 2.1-MHz US tone burst focused (1-mm focal diameter) on the axon. US stimuli were delivered in 20-s cycles, each cycle consisting of a 10-s recorded trace followed by a 10-s interval before the next recording, over 2-4 h recording sessions; some protocols delivered bursts repeatedly at a low rate (about every 10 s) within a session.
Flags from extraction
n_subjects— Quote covers Groups 2 and 3 (n=11, n=5); Group 1 (n=6) is described in the same paragraph with garbled source formatting and is included in the list but not separately quoted.exposures[0].free_field.pressure_kpa— 0.1-1 MPa is the overall pressure range used across experiments (from the abstract); individual figures cite specific intensities (e.g. 2.7-9.4 mW/cm2) for particular trials that are not individually itemised here.