Korean J Physiol Pharmacol.  2017 Mar;21(2):251-257. 10.4196/kjpp.2017.21.2.251.

Inhibition of K⁺ outward currents by linopirdine in the cochlear outer hair cells of circling mice within the first postnatal week

• Kang SW
• Ahn JW
• Ahn SC

• KMID: 2371044
• DOI: http://doi.org/10.4196/kjpp.2017.21.2.251

Abstract

Inhibition of K⁺ outward currents by linopirdine in the outer hair cells (OHCs) of circling mice (homozygous (cir/cir) mice), an animal model for human deafness (DFNB6 type), was investigated using a whole cell patch clamp technique. Littermate heterozygous (+/cir) and ICR mice of the same age (postnatal day (P) 0 -P6) were used as controls. Voltage steps from -100 mV to 40 mV elicited small inward currents (-100 mV~-70 mV) and slow rising K⁺ outward currents (-60 mV ~40 mV) which activated near -50 mV in all OHCs tested. Linopirdine, a known blocker of K⁺ currents activated at negative potentials (I(K,n)), did cause inhibition at varying degree (severe, moderate, mild) in K⁺ outward currents of heterozygous (+/cir) or homozygous (cir/cir) mice OHCs in the concentration range between 1 and 100 µM, while it was apparent only in one ICR mice OHC out of nine OHCs at 100 µM. Although the half inhibition concentrations in heterozygous (+/cir) or homozygous (cir/cir) mice OHCs were close to those reported in I(K,n), biophysical and pharmacological properties of K⁺ outward currents, such as the activation close to -50 mV, small inward currents evoked by hyperpolarizing steps and TEA sensitivity, were not in line with I(K,n) reported in other tissues. Our results show that the delayed rectifier type K⁺ outward currents, which are not similar to I(K,n) with respect to biophysical and pharmacological properties, are inhibited by linopirdine in the developing (P0~P6) homozygous (cir/cir) or heterozygous (+/cir) mice OHCs.

Keyword

Circling mice; I(K,n); K⁺ current; Linopirdine; Outer hair cell

MeSH Terms

Animals
Deafness
Hair Cells, Auditory, Outer*
Humans
Mice*
Mice, Inbred ICR
Models, Animal
Tea
Tea

Figure

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  Fig. 1 Whole cell K+ currents of P0~P6 mice OHCs. Current traces recorded from P6 ICR mice is shown in A.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 curve of ICR mice is shown in B. Activation curves for ICR, heterozygous (+/cir), and homozygous (cir/cir) mice are shown in C (filled square: ICR, filled circle: heterozygous (+/cir) mouse (Hetero), hollow circle: homozygous (cir/cir) mouse (Homo)). The activation curves in C were obtained by plotting the normalized tail currents at -30 mV against different prepulse potentials (–90 mV~40 mV). The voltage protocol and tail currents are shown in inset.

• 

  Fig. 2 Effect of linopirdine on K+ currents in homozygous (cir/cir) mice OHCs.The varying degree of inhibition of K+ currents by linopirdine (1 to 100 µM) is shown in A, B, and C. Currents were elicited by depolarizing voltage steps from –60 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 in Ae, Be, and Ce. Marks above the current traces indicate the measuring points and linopirdine concentrations. Fig. 2C shows the linopirdine effects recorded in one cell. Fig. 2D shows the linopirdine effects recorded in one cell, currents were elicited by depolarizing voltage steps from –100 mV to 40 mV (the holding potential was –60 mV). Linopirdine was not effective at hyperpolarizing voltage range (–100 mV~–60 mV).

• 

  Fig. 3 Effect of linopirdine on K+ currents in heterozygous (+/cir) mice OHCs.The varying degree of inhibition of K+ currents by linopirdine is shown in A (1 to 100 µM) and B (1 to 10 µM). Currents were elicited by depolarizing voltage steps from –60 mV to 40 mV (the holding potential was –60 mV). Reduced currents were normalized (I/Imax) with peak currents at 40 mV before drug application. Normalized currents–voltage curves are shown in Ae and Bd. Marks above the current traces indicate the measuring points and linopirdine concentrations.

• 

  Fig. 4 Effect of linopirdine on K+ currents in ICR mice OHCs.The varying degree of inhibition of K+ currents by linopirdine is shown in A (1 to 100 µM) and B (1 to 10 µM). Currents were elicited by depolarizing voltage steps from –60 mV to 40 mV (the holding potential was –60 mV). Reduced currents were normalized (I/Imax) with peak currents at 40 mV before drug application. Normalized currents-voltage curves are shown in Ae and B. Marks above the current traces indicate the measuring points and linopirdine concentrations. Fig. 4Aa~4Ae show the linopirdine effects recorded in one cell. Fig. 4B shows normalized currents-voltage curves obtained from the cells treated with linopirdine up to 10 µM.

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