Ashmore 1987 — Fast motile response in guinea-pig OHCs: cellular basis of cochlear amplifier
This is the founding paper of OHC electromotility. Ashmore isolated guinea-pig OHCs and showed they change length under voltage clamp at frequencies beyond 1 kHz — a rate far faster than any actin-myosin motor could achieve. He coined the term “fast motile response” and proposed the motor resides in the lateral wall cortex (later identified as prestin). This paper is the correct primary reference for OHC electromotility; it does NOT report specific membrane capacitance (which was quantified later by Gentet et al. 2000).
TL;DR. Guinea-pig OHCs elongate on hyperpolarization and shorten on depolarization; sensitivity 19.8 nm/mV or 2.11 nm/pA; kinetics with sub-ms latency exclude actin-myosin; motor is proposed to be in the lateral wall cortex.
Key finding. OHC length change is graded with command voltage over ±2 µm (~4% of cell length) in apical cells. Sinusoidal stimulation at frequencies above 1 kHz produces measurable movement, consistent with acoustic-frequency force generation.
Numbers that matter
| Parameter | Value | Units | Source location | Conditions |
|---|---|---|---|---|
| Maximum OHC length change | ±2 | µm (~4% cell length) | Abstract, Results | Apical-turn cells, voltage clamp |
| Electromechanical sensitivity | 19.8 | nm/mV | Abstract para 3 | Mean value; apical cells |
| Electromechanical sensitivity (current) | 2.11 | nm/pA | Abstract para 3 | Guinea-pig, apical turn |
| Response latency | 120–255 | µs | Abstract para 4 | Basal-end stimulation, apical cells |
| Fast time constant | 240 | µs | Abstract para 4 | Exponential elongation component |
| Intermediate time constant | 1.3–2.8 | ms | Abstract para 4 | Second exponential component |
| Slow time constant | 20–40 | ms | Abstract para 4 | Osmotic component |
| Phase delay (sinusoidal) | ~200 | µs (absolute delay) | Abstract para 5 | Above 1 kHz, phase grows with frequency |
Critical note for h02. The h02 scripts cite “Ashmore 1987” for OHC specific membrane capacitance (Cm = 0.9 µF/cm²). That value does not appear in this paper. Ashmore 1987 established electromotility origin and voltage-sensitivity; Cm = 0.9 µF/cm² is from Gentet et al. 2000 (neurons). The citation is misattributed in the scripts.
Limitations
- Guinea-pig preparation; mouse OHC sensitivities are similar but not identical.
- Short-term culture conditions; acute dissociation may alter lateral wall tension.
- Prestin not yet identified; molecular mechanism unknown at time of publication.
Connections
[source]piezoelectric-materials — cited (incorrectly) as origin of Cm = 0.9 µF/cm²; correct attribution is OHC electromotility[see-also]2026-04-25-santos-sacchi-1991-prestin-nlc-voltage — extends this work to NLC voltage dependence[see-also]2026-04-25-gentet-2000-specific-membrane-capacitance-neurons — actual source of Cm 0.9 µF/cm²[applies]STRC Piezoelectric TM Bioelectronic Amplifier