Figure 1.

MT Currents and Receptor Potentials in Rat OHCs

(A) Saturating receptor currents with hair bundles exposed to saline containing Na⁺ and 1.5 mM Ca²⁺.

(B) Saturating receptor currents in a different OHC with hair bundles locally perfused with artificial endolymph containing K⁺ and 0.02 mM Ca²⁺. Note larger MT current amplitude and increased fraction on at rest compared to 1.5 mM Ca²⁺.

(C) Receptor potentials, V_m, for cell in (A) with hair bundles exposed to Na⁺, 1.5 mM Ca²⁺ saline.

(D) Receptor potentials for cell in (B) with hair bundles exposed K⁺, 0.02 mM Ca²⁺ endolymph. The sinusoidal stimulus (top), which applies to both receptor currents and potentials, was delivered with a fluid jet, hair bundle motion being calibrated by projection on a photodiode pair; holding potential in voltage clamp −84 mV.

(E) Relation between MT current (I) and bundle displacement (X) in (A) over one cycle of the response (dashed line).

(F) MT current versus bundle displacement in (B) over one cycle of the response (dashed line). I–X results fitted with single Boltzmann (continuous line): I = I_MAX/(1 + (exp((X₁ − X)/X_e)) where I_MAX = 1.51 nA, X_e = 0.017 μm, X₁ = 0.04 μm (C, perilymph); I_MAX = 2.4 nA, X_e = 0.035 μm, X₁ = 0.008 μm (D, endolymph). Apical cochlear location, P8 (A and C), P9 (B and D) rats, T = 22°C.