Temperature enhances activation and inactivation kinetics of potassium currents in inner hair cells isolated from Guinea-pig cochlea

Abstract

Objectives: Until recently, most patch-clamp recordings in inner hair cells (IHCs) have been performed at room temperature. The results acquired at room temperature should be corrected if they are to be related to in vivo findings. However, the temperature dependency to ion channels in IHCs is unknown. The aim of this study was to investigate the effect of temperature on the potassium currents in IHCs.

Methods: IHCs were isolated from a mature guinea-pig cochlea and potassium currents were recorded at room temperature (around 25℃) and physiological temperatures (35℃-37℃).

Results: IHCs showed outwardly rectifying currents in response to depolarizing voltage pulses, with only a slight inward current when hyperpolarized. The amplitude of both outward and inward currents demonstrated no temperature dependency, however, activation and inactivation rates were faster at 36℃ than at room temperature. Half-time for activation was shorter at 36℃ than at room temperature at membrane potentials of -10, +10, +20, +30, and +40 mV. Q10 for the activation rate was 1.83. The inactivation time constant in outward tetraethylammonium-sensitive potassium currents was much smaller at 36℃ than at room temperature between the membrane potentials of -20 and +60 mV. Q10 for the inactivation time constant was 3.19.

Conclusion: The results of this study suggest that the amplitude of potassium currents in IHCs showed no temperature dependence either in outward or inward-going currents, however, activation and inactivation accelerated at physiological temperatures.

Keywords: Activation; Cochlea; Inactivation; Inner hair cell; Patch-clamp; Potassium currents; Temperature.

Fig. 1

Potassium currents at room temperature and 36℃. Currents in response to hyperpolarizing and depolarizing voltage steps from a holding potential of -60 mV (A, lower panel). Voltage protocol (A, upper panel). The inward component of the currents by enlarging the scale (B).

Fig. 2

Comparison between the amplitudes of potassium currents at room temperature and 36℃. (A) Amplitudes of outward currents at 110 mV. Open squares indicate the mean values at room temperature (9.2 nA ) and 36℃ (8.5 nA). (B) Amplitudes of inward currents at -130 mV. Mean values were 0.63 nA at room temperature and 0.68 nA at 36℃. Open circles were maximum values and crosses were minimum values.

Fig. 3

Activation process of outward potassium currents at 25.8℃ (yellow trace) and 35.8℃ (blue trace) at 60 mV. Both currents were normalized by sustained currents.

Fig. 4

Half maximum time for activation at room temperature (open circles) and 36℃ (closed circles). Each value is plotted against various membrane potentials (n=9). ^*P<0.05, ^†P<0.01.

Fig. 5

Inactivation time constants of outward TEA-sensitive potassium currents at room temperature (open circles) and 36℃ (closed circles). Each value is plotted against various membrane potentials (n=9). ^*P<0.01.

Fig. 6

The degree of inactivation (I_ss/I_p) at room temperature (open circles) and 36℃ (closed circles). Each value is plotted against various membrane potentials (n=9).