Santos-Sacchi 1991 — Reversible inhibition of voltage-dependent OHC motility and capacitance
This paper characterized the nonlinear capacitance (NLC) of isolated guinea-pig OHCs — the electrical signature of prestin motor charge movement. Using whole-cell voltage clamp with blocked ionic currents, Santos-Sacchi showed that OHC motility magnitude tracks the NLC-voltage (C-V) curve, that gadolinium reversibly abolishes both, and that NLC is not due to membrane deformation from length change. This paper establishes the biophysical framework for prestin as a voltage-sensitive motor (though prestin was not identified molecularly until 2000).
TL;DR. OHC NLC peaks at −40 mV (AC method, more accurate) or −23 mV step potential from −120 mV holding potential; maximum NLC 16–17 pF; motility and NLC are correlated and both blocked reversibly by 0.5–1 mM gadolinium, dissociating them from pure membrane mechanics.
Key finding. The Boltzmann-shaped C-V function means prestin operates over a wide voltage range (roughly −150 to +50 mV full range); the h02 model simplification of “10 mV threshold” is not in this paper — 10 mV is the signal modulation amplitude assumed sufficient for amplification around the operating point, not a threshold in the Santos-Sacchi framework. V_peak at −40 mV (AC) is the operating point; signals modulate around this.
Numbers that matter
| Parameter | Value | Units | Source location | Conditions |
|---|---|---|---|---|
| Peak NLC voltage (AC analysis) | −40 | mV (holding potential) | Abstract | AC method; most physiologically accurate |
| Peak NLC voltage (step analysis) | −23 | mV (step from −120 mV hold) | Abstract | Step method; less accurate for V_half |
| Maximum NLC | 16–17 | pF | Abstract | Low-frequency (apical) OHCs |
| Maximum charge movement | up to 2.5 | pC | Abstract | Apical OHCs, largest cells |
| Gadolinium block concentration | 0.5–1 | mM | Abstract | Reversible block of both motility and NLC |
| V_saturation | Not reported as single threshold | — | — | NLC is Boltzmann; “saturation” is ±2 mV tail of function |
Critical note for h02. The script uses “Prestin V_saturation = 70 mV (no citation)” — this is NOT in Santos-Sacchi 1991. The 70 mV value is unsourced. This paper provides V_half ≈ −40 mV and the shape of the Boltzmann, from which a practical saturation range can be calculated, but not a 70 mV discrete threshold.
Limitations
- Guinea-pig OHCs; mouse prestin (SLC26A5) has similar but not identical kinetics.
- Holding potential −120 mV is artificial (resting OHC Vm ~−70 mV); step-analysis V_half is shifted from true in-vivo operating point.
- Gadolinium experiments do not distinguish NLC from prestin-specific effects (Gd³⁺ is a broad-spectrum divalent blocker).
Connections
[source]piezoelectric-materials — cited for prestin NLC voltage dependence (V_half, operating range)[see-also]2026-04-25-ashmore-1987-ohc-electromotility-jphysiol — same phenomenon, earlier characterization[see-also]2026-04-25-gentet-2000-specific-membrane-capacitance-neurons — linear Cm background on which NLC is superimposed[applies]STRC Piezoelectric TM Bioelectronic Amplifier