Korean J Physiol Pharmacol.  2015 Jul;19(4):383-388. 10.4196/kjpp.2015.19.4.383.

Characteristics of K+ Outward Currents in the Cochlear Outer Hair Cells of Circling Mice within the First Postnatal Week

• Ahn JW
• Kang SW
• Ahn SC

• KMID: 2285582
• DOI: http://doi.org/10.4196/kjpp.2015.19.4.383

Abstract

K+ outward currents in the outer hair cells (OHCs) of circling mice (homozygous (cir/cir) mice), an animal model for human deafness (DFNB6 type), were investigated using a whole cell patch clamp technique. Littermate heterozygous (+/cir) mice of the same age (postnatal day (P) 0 -P6) were used as controls. Similar slow rising K+ currents were observed in both genotypes, but their biophysical and pharmacological properties were quite different. The values of V(half) for activation were significantly different in the heterozygous (+/cir) and homozygous (cir/cir) mice (-8.1+/-2.2 mV, heterozygous (+/cir) mice (n=7) and -17.2+/-4.2 mV, homozygous (cir/cir) mice (n=5)). The inactivation curve was expressed by a single first order Boltzmann equation in the homozygous (cir/cir) mice, while it was expressed by a sum of two first order Boltzmann equations in the heterozygous (+/cir) mice. The K+ current of homozygous (cir/cir) mice was more sensitive to TEA in the 1 to 10 mM range, while the 4-AP sensitivities were not different between the two genotypes. Removal of external Ca2+ did not affect the K+ currents in either genotype, indicating that the higher sensitivity of K+ current to TEA in the homozygous (cir/cir) mice was not due to an early expression of Ca2+ activated K+ channels. Our results suggest that the K+ outward current of developing homozygous (cir/cir) mice OHCs is different in both biophysical and pharmacological aspects than that of heterozygous (+/cir) mice.

Keyword

Circling mice; Deafness; DFNB6; K+ current; Outer hair cell

MeSH Terms

Animals
Deafness
Genotype
Hair*
Humans
Mice*
Models, Animal
Potassium Channels, Calcium-Activated
Tea
Potassium Channels, Calcium-Activated
Tea

Figure

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  Fig. 1 Whole cell K+ outward currents of P0-P6 mice OHCs. Current traces recorded from P5 heterozygous (+/cir) and P3 homozygous (cir/cir) mouse are shown in A and B. Currents were elicited by depolarizing voltage steps from -100 mV to 40 mV with 10 mV increment (holding potential: -60 mV). Voltage protocol is shown above the current traces. Current density-voltage curves are shown in C (filled circle: heterozygous (+/cir) mouse, hollow circle: homozygous (cir/cir) mouse). Cell capacitance changes from P0 to P6 are shown in D (filled circle: heterozygous (+/cir) mouse, hollow circle: homozygous (cir/cir) mouse). Cell capacitances are 5.09±0.4 (P2, n=13), 5.7±0.3 (P3, n=15), 5.7±0.3 (P4, n=15), 5.3±0.2 (P5, n=16), and 5.3±0.3 (P6, n=12) in heterozygous (+/cir) mice. They are 5.9±0.3 (P1, n=12), 5.9±0.2 (P3, n=21), 5.5±0.2 (P4, n=26), 5.6±0.1 (P5, n=30), and 5.9±0.1 (P6, n=29) in homozygous (cir/cir) mice.

• 

  Fig. 2 Inactivation (square) and activation (circle) curves for the K+ currents. Activation and inactivation curves for heterozygous (+/cir) mice and homozygous (cir/cir) mice are shown in A and B, respectively. Current trace examples for the inactivation curve fit are shown to the left of the plots. The activation curves in Figs. 2A and 2B were obtained by plotting the normalized conductance values against the commanding potentials.

• 

  Fig. 3 Effect of TEA on K+ currents. The effects of TEA (1 to 100 mM) on K+ currents are shown in A (P5 heterozygous (+/cir) mouse) and B (P3 homozygous (cir/cir) mouse). Currents were elicited by depolarizing voltage steps from -50 mV to 40 mV (the holding potential was -60 mV). Reduced currents were normalized (I/Imax) with the peak currents at 40 mV before drug application. Normalized currents - voltage curves are shown by the current traces (C). Marks above the current traces indicate the measuring points and TEA concentrations.

• 

  Fig. 4 Effect of 4-AP on K+ currents. The effects of 4-AP (0.1 to 10 mM) on K+ currents are shown in A (P4 heterozygous (+/cir) mouse) and B (P5 homozygous (cir/cir) mouse). Currents were elicited by depolarizing voltage steps from -50 mV to 40 mV (the holding potential was -60 mV). Reduced currents were normalized (I/Imax) with the peak currents at 40 mV before drug application. Normalized currents - voltage curves are shown by the current traces (C). Marks above the current traces indicate the measuring points and 4-AP concentrations.

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  Fig. 5 Effect of external Ca2+ removal on K+ currents. Nominal Ca2+-free solution did not changes the K+ currents of P6 heterozygous (+/cir) mouse (A) or P4 homozygous (cir/cir) mouse (B). Normalized current-voltage curves are shown by the current traces (filled circle represents control and hollow circle represents Ca2+-free).

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