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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 - Korean J. Physiol. Pharmacol. (2015)

Bottom Line: Similar slow rising K(+) currents were observed in both genotypes, but their biophysical and pharmacological properties were quite different.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 Ca(2+) 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 Ca(2+) activated K(+) channels.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, College of Medicine, Dankook University, Cheonan 330-714, Korea.

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 Vhalf 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 Ca(2+) 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 Ca(2+) 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.

No MeSH data available.


Related in: MedlinePlus

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.
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Figure 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.

Mentions: In heterozygous (+/cir) mice, the K+ current recorded at 40 mV was reduced to 78.4±2.8% (n=5), 56.6±2.7% (n=5), and 13.9±2.1% (n=5) of the control by 1 mM, 10 mM, and 100 mM TEA, respectively (Fig. 3A). In homozygous (cir/cir) mice, the corresponding reductions were 62.7±4.8% (n=5), 38.7±3.8% (n=5), and 20.1±2.3% (n=5), respectively (Fig. 3B). The extent of inhibition by 1 mM and 10 mM TEA was significantly greater in homozygous (cir/cir) mice (repetitive-measured ANOVA and independent t-test, p<0.05).


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 - Korean J. Physiol. Pharmacol. (2015)

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.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4499651&req=5

Figure 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.
Mentions: In heterozygous (+/cir) mice, the K+ current recorded at 40 mV was reduced to 78.4±2.8% (n=5), 56.6±2.7% (n=5), and 13.9±2.1% (n=5) of the control by 1 mM, 10 mM, and 100 mM TEA, respectively (Fig. 3A). In homozygous (cir/cir) mice, the corresponding reductions were 62.7±4.8% (n=5), 38.7±3.8% (n=5), and 20.1±2.3% (n=5), respectively (Fig. 3B). The extent of inhibition by 1 mM and 10 mM TEA was significantly greater in homozygous (cir/cir) mice (repetitive-measured ANOVA and independent t-test, p<0.05).

Bottom Line: Similar slow rising K(+) currents were observed in both genotypes, but their biophysical and pharmacological properties were quite different.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 Ca(2+) 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 Ca(2+) activated K(+) channels.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, College of Medicine, Dankook University, Cheonan 330-714, Korea.

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 Vhalf 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 Ca(2+) 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 Ca(2+) 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.

No MeSH data available.


Related in: MedlinePlus