Effects of Osmolarity on Ultrasound-Induced Membrane Depolarization in Isolated Crayfish Motor Axon
Feiyuan Yu, Wolfgang S. Müller, Gösta Ehnholm, Yoshio Okada, Jen-Wei Lin
Ultrasound in Medicine & Biology 2022 · 10.1016/j.ultrasmedbio.2022.05.028
Abstract
We have previously identified a novel non-selective membrane conductance (g US ) opened by focused ultrasound (FUS) in crayfish motor axons. In the work described here, we studied g US properties further by comparing FUS-evoked depolarization (FUSD) in control and hypotonic saline with 75% of control osmolarity. The FUS was a train of 20 FUS bursts (2.1 MHz and 50 µs per burst) delivered at 1 kHz. The amplitude, onset latency, frequency of occurrence and duration of FUSD were compared in a 15-min time window before and after switching to hypotonic saline. Significant increases were observed for amplitude (p US is mediated by opening of nanopores in the lipid bilayer and that stretching of axonal membrane caused by swelling at low osmolarity should increase the probability of nanopore formation under FUS. The FUSD parameters, in addition, exhibited time-dependent trends when the window of observation was expanded to 45 min in each saline. The statistical significance of amplitude and duration differed between 15- and 45-min time windows, indicating the presence of adaptive responses of axonal membrane to osmotic manipulation.
Abstract via europepmc.
Exposures
Exposure 1: FUS tone-burst train applied to isolated motor axon
Target: excised nerve — “the motor axons of the crayfish opener neuromuscular junction”
Device: custom-built · Steminc Piezo (Steiner & Martins) · SMSF20C30F21 ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 2,100 | ✓✓✓ |
| Pulse duration (ms) | 0.05 | ✓✓✓⚑ |
| Pulse repetition frequency (Hz) | 1,000 | ✓✓✓ |
| Duty cycle (%) | 5pulse duration × PRF gives 5% | ✓✓✓ |
| Sonication duration (s) | 0.02 | ✓✓✓ |
| Free-field pressure (kPa) | 100, 300swept | ✓✓✓ |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | 0.00094 | ✓✓✓ |
| 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 |
A test current step to trigger action potentials was alternated with a trial testing the effect of the FUS tone burst; the time gap between the current step and the FUS tone burst was 0.5 s, FUSD was recorded as a 20-s-long trace, and there was a 10-s gap before the next test current step. The lowest FUS pressure capable of triggering FUSD in 10% of trials was chosen for each preparation.
Flags from extraction
exposures[0].timing.pulse_duration_ms— The Methods text states 'each pulse lasting 50 ms', which conflicts with the abstract and Fig. 1D legend ('50 μs per burst'/'50-μs tone bursts') and with the stated duty cycle: 5% duty cycle at a 1 kHz PRF (1 ms period) implies a 50 μs pulse, not 50 ms. This is very likely an OCR/typographic confusion of μ for m. Recorded as 0.05 ms (50 μs) per the abstract/figure and the burst-rule arithmetic; the conflicting 'each pulse lasting 50 ms' wording appears in the Methods body.exposures[0].free_field.pressure_kpa,exposures[0].free_field.ispta_w_cm2— The preparation is an isolated axon bathed directly in saline with no skull or intervening tissue path; the paper does not use free-field/in-situ terminology. Values are placed in free_field per the instruction that in a bath/dish preparation with no skull or tissue path, in_situ is null.