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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

Inactivation (square) andactivation (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.
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Figure 2: Inactivation (square) andactivation (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.

Mentions: Figs. 2A and 2B show the voltage-dependent activation and inactivation of K+ currents. Inactivation curves were obtained by measuring the peak currents recorded at a potential of 30 mV after conditioning pulses (1s) from the holding potential of -60 mV. The conditioning pulses were from -100 mV to more depolarized voltage levels in 10 mV increments. Normalized peak currents were plotted against the different conditioning potentials and fitted by a modified first-order Boltzmann equation: y=A2+(A1-A2)/{1+exp(V-Vhalf/S)} where y is the normalized peak current, A2 is the minimal normalized peak current, A1 is the maximal normalized peak current, Vhalf is the potential of half-maximal inactivation, V is the commanding potential, and S is the voltage sensitivity of inactivation.


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)

Inactivation (square) andactivation (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.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Inactivation (square) andactivation (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.
Mentions: Figs. 2A and 2B show the voltage-dependent activation and inactivation of K+ currents. Inactivation curves were obtained by measuring the peak currents recorded at a potential of 30 mV after conditioning pulses (1s) from the holding potential of -60 mV. The conditioning pulses were from -100 mV to more depolarized voltage levels in 10 mV increments. Normalized peak currents were plotted against the different conditioning potentials and fitted by a modified first-order Boltzmann equation: y=A2+(A1-A2)/{1+exp(V-Vhalf/S)} where y is the normalized peak current, A2 is the minimal normalized peak current, A1 is the maximal normalized peak current, Vhalf is the potential of half-maximal inactivation, V is the commanding potential, and S is the voltage sensitivity of inactivation.

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