Gentet et al. 2000 — Direct measurement of specific membrane capacitance in neurons
Specific membrane capacitance (Cm) determines how fast electrical signals propagate along dendrites and unmyelinated axons, but its true value had been controversial. Gentet et al. resolved this using nucleated patch-clamp: pull a small membrane patch, apply a voltage step, fit the capacitative transient, divide by observed patch area. The result is Cm = 0.9 µF/cm² across all neuronal classes tested.
TL;DR. Nucleated-patch technique in cortical, spinal, and hippocampal neurons — plus HEK-293 cells — yields Cm = 0.9 µF/cm² regardless of cell type or transmembrane protein density. Authors conclude Cm is a “biological constant” of the lipid bilayer.
Key finding. Cm is independent of membrane protein composition (tested by overexpressing glycine receptor channels in HEK-293 cells): transfected vs. untransfected Cm was indistinguishable. This means lipid bilayer geometry, not protein content, sets Cm.
Numbers that matter
| Parameter | Value | Units | Source location | Conditions |
|---|---|---|---|---|
| Specific membrane capacitance Cm | 0.9 | µF/cm² | Abstract, Results | Cortical pyramidal, spinal, hippocampal neurons; nucleated patch |
| Cm (HEK-293 control) | 0.9 | µF/cm² | Results | Untransfected HEK-293 cells |
| Cm (HEK-293 + glycine Rc) | 0.9 | µF/cm² | Results | High glycine-receptor expression; Cm unchanged |
Critical caveat for h02: This paper does NOT measure OHC membrane capacitance. The h02 scripts cite this value as OHC Cm = 0.9 µF/cm². That extrapolation is defensible (the “biological constant” claim spans neuron classes) but is an extrapolation. OHC-specific Cm measurements exist elsewhere (Santos-Sacchi 1991 measures total OHC nonlinear capacitance, not specific Cm). The 0.9 µF/cm² value is the correct order of magnitude for OHC modeling but should be flagged as general-neuron-derived, not OHC-measured.
Limitations
- Neuronal preparation only; no OHC or mechanosensory cells measured.
- “Biological constant” claim is for resting membrane; OHC membrane is crowded with prestin motors which may locally influence lipid packing and Cm.
- Paper does not address frequency dependence of Cm.
Connections
[source]piezoelectric-materials — provides OHC Cm = 0.9 µF/cm² parameter used in h02 scripts[see-also]2026-04-25-santos-sacchi-1991-prestin-nlc-voltage — OHC nonlinear capacitance; NLC is superimposed on background linear Cm[applies]STRC Piezoelectric TM Bioelectronic Amplifier