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

License
getmorefigures.php?uid=PMC4499651&req=5

Figure 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).

Mentions: Though a Ca2+-activated K+ current has not been reported in P0-P6 mice OHCs, because a significant difference in the percentage reduction between the two groups was observed only with the application of TEA, we tested whether it was due to an early expression of the Ca2+-activated K+ channels in homozygous (cir/cir) mice. For that purpose, the amplitude of the K+ current was measured before and after the removal of external Ca2+. In both groups, the removal of the external Ca2+ did not affect the K+ current amplitude (Fig. 5), which suggested that the greater inhibition of K+ currents in homozygous (cir/cir) mice than in heterozygous (+/cir) mice might not be due to the early expression of Ca2+-activated K+ channels in homozygous (cir/cir) mice.


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

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

Figure 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).
Mentions: Though a Ca2+-activated K+ current has not been reported in P0-P6 mice OHCs, because a significant difference in the percentage reduction between the two groups was observed only with the application of TEA, we tested whether it was due to an early expression of the Ca2+-activated K+ channels in homozygous (cir/cir) mice. For that purpose, the amplitude of the K+ current was measured before and after the removal of external Ca2+. In both groups, the removal of the external Ca2+ did not affect the K+ current amplitude (Fig. 5), which suggested that the greater inhibition of K+ currents in homozygous (cir/cir) mice than in heterozygous (+/cir) mice might not be due to the early expression of Ca2+-activated K+ channels in homozygous (cir/cir) mice.

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