Calcium balance and mechanotransduction in rat cochlear OHCs quantified by fluorescence imaging and electrophysiology. Provides the primary quantitative source for PMCA Ca2+ extrusion rate and endogenous buffer capacity in the h05 model. The “Mammano 1999 Pflugers Arch” attribution in h05 scripts is wrong; this Beurg 2010 paper is the correct source for k_extrusion.
Key finding
Electrogenic PMCA current saturates at 18 pA → maximum Ca2+ extrusion rate of 3.7 fmol·s⁻¹. Ca2+ clearance time constant after bundle deflection ~50 ms for brief stimuli, 100–300 ms for prolonged. Endogenous mobile buffer equivalent to 1 mM BAPTA (~5 mM Ca2+-binding sites from parvalbumin-β + calbindin-D28k). PMCA density in stereociliary membrane ~6000 pumps/µm².
Numbers that matter
| Parameter | Value | Units | Conditions | Notes |
|---|---|---|---|---|
| Max PMCA extrusion rate | 3.7 | fmol/s | Rat OHC, saturating Ca2+ | Electrogenic current 18 pA |
| Ca2+ clearance τ (brief stimulus) | ~50 | ms | Rat OHC | Fast component; PMCA + diffusion |
| Ca2+ clearance τ (prolonged) | 100–300 | ms | Rat OHC | Slower recovery |
| Endogenous mobile buffer | ~1 | mM BAPTA-equivalent | OHC apical compartment | ~5 mM Ca2+-binding sites total |
| PMCA density (stereocilia) | ~6000 | pumps/µm² | Rat OHC | Higher than bullfrog (Yamoah 1998) |
| k_extrusion (derived estimate) | ~30 | /s | See note | Derived from 3.7 fmol/s ÷ V_apex×[Ca] — model parameter, not directly stated |
Derivation note for k_extrusion ~30 /s: At Ca_rest ~30 nM in V_apex = 50 fL, total Ca ~1.5 attomol. Max flux 3.7 fmol/s is 2500× higher than resting pool — so linear first-order approximation k_extrusion30/s is plausible as a near-saturation efficiency parameter, but is not a directly reported number. The paper reports flux not k.
Limitations
- Rat cochlear OHCs (P10-P14). Postnatal development may affect PMCA density.
- k_extrusion ~30 /s is a derived model parameter, not a directly reported rate constant from this paper.
- Buffer capacity measured via BAPTA analog; parvalbumin-β binding kinetics differ from BAPTA (faster on-rate).
Connections
[source]calcium-oscillation — primary source for k_extrusion and buffer_ratio estimates[see-also]2005-hackney-calcium-buffering-proteins — provides oncomodulin/calbindin concentrations[applies]STRC Calcium Oscillation Acoustic Therapy