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The effects of Tmc1 Beethoven mutation on mechanotransducer channel function in cochlear hair cells.

Beurg M, Goldring AC, Fettiplace R - J. Gen. Physiol. (2015)

Bottom Line: The Ca(2+)-dependent adaptation that adjusts the operating range of the channel was also impaired in Beethoven mutants, with reduced shifts in the relationship between MT current and hair bundle displacement for adapting steps or after lowering extracellular Ca(2+); these effects may be attributed to the channel's reduced Ca(2+) permeability.Moreover, the density of stereociliary CaATPase pumps for Ca(2+) extrusion was decreased in the mutant.The results suggest that a major component of channel adaptation is regulated by changes in intracellular Ca(2+).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706.

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MT channel conductance and Ca2+ selectivity in Tmc1Bth/Bth mice. (A) Four examples of single MT channel currents, recorded in a P5 apical IHC of Tmc1+/+ mice in response to 0.1-µm step displacements of the hair bundle; below is the ensemble average of 14 presentations. (B) Amplitude histogram showing single-channel current of 6.2 pA. (C) Four examples of single MT channel currents recorded in a P5 apical IHC of Tmc1Bth/Bth mice in response to 0.1-µm step displacements of the hair bundle; below is the ensemble average of 12 presentations. (D) Amplitude histogram showing single-channel current of 6.3 pA; both B and D were at a −84-mV holding potential in 1.5 mM of external Ca2+. (E) Bar plot showing collected single-channel currents in IHCs, apical OHCs, and basal OHCs for Tmc1+/+ and Tmc1Bth/Bth. Number of cells tested is shown above the columns. (F) Protocol for determining Ca2+ selectivity: mechanical hair bundle stimulus (top) evoking MT current (bottom) during voltage ramp from −40 to 70 mV. (G) Examples of MT current–voltage relationships recorded in apical OHCs from Tmc1+/+ and Tmc1Bth/Bth mice in the voltage region around reversal potential. (H) Collected reversal potentials (left ordinate) and PCa/PCs (right ordinate) for Tmc1+/+ and Tmc1Bth/Bth in Tmc2+/+ and Tmc2−/− backgrounds. Numbers of OHCs tested are shown above the columns. Apical OHCs: P4–P6 mice. Error bars represent means ± SD.
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fig1: MT channel conductance and Ca2+ selectivity in Tmc1Bth/Bth mice. (A) Four examples of single MT channel currents, recorded in a P5 apical IHC of Tmc1+/+ mice in response to 0.1-µm step displacements of the hair bundle; below is the ensemble average of 14 presentations. (B) Amplitude histogram showing single-channel current of 6.2 pA. (C) Four examples of single MT channel currents recorded in a P5 apical IHC of Tmc1Bth/Bth mice in response to 0.1-µm step displacements of the hair bundle; below is the ensemble average of 12 presentations. (D) Amplitude histogram showing single-channel current of 6.3 pA; both B and D were at a −84-mV holding potential in 1.5 mM of external Ca2+. (E) Bar plot showing collected single-channel currents in IHCs, apical OHCs, and basal OHCs for Tmc1+/+ and Tmc1Bth/Bth. Number of cells tested is shown above the columns. (F) Protocol for determining Ca2+ selectivity: mechanical hair bundle stimulus (top) evoking MT current (bottom) during voltage ramp from −40 to 70 mV. (G) Examples of MT current–voltage relationships recorded in apical OHCs from Tmc1+/+ and Tmc1Bth/Bth mice in the voltage region around reversal potential. (H) Collected reversal potentials (left ordinate) and PCa/PCs (right ordinate) for Tmc1+/+ and Tmc1Bth/Bth in Tmc2+/+ and Tmc2−/− backgrounds. Numbers of OHCs tested are shown above the columns. Apical OHCs: P4–P6 mice. Error bars represent means ± SD.

Mentions: MT currents from OHCs of wild-type (Tmc1+/+) and littermate mutant (Tmc1Bth/Bth) Beethoven mice were recorded during hair bundle displacements with a piezoelectric fluid jet (Kros et al., 1992; Kim and Fettiplace, 2013). The maximum amplitude of the MT current was similar at least up to postnatal day (P) 9 in all genotypes tested, indicating that, unlike dn mutation in Tmc1 (Kim and Fettiplace, 2013), the Beethoven mutation does not impair mechanotransduction in apical OHCs. Because early on the bundles have a normal shape, a corollary is that the single–MT channel conductance was unaffected by the Beethoven mutation (Fig. 1, A–E). Although, as observed previously, there was an increase in OHC MT channel conductance from apex to base (Beurg et al., 2014, 2015), the conductance at neither location was reduced relative to wild type in Tmc1Bth/Bth. The basal values are most diagnostic, because they show a marked twofold reduction in the Tmc1−/− (Beurg et al., 2014), but here there was no significant difference between the wild-type and Beethoven mutant. There was also no effect of the Beethoven mutation on the MT channel conductance in IHCs (Fig. 1 E).


The effects of Tmc1 Beethoven mutation on mechanotransducer channel function in cochlear hair cells.

Beurg M, Goldring AC, Fettiplace R - J. Gen. Physiol. (2015)

MT channel conductance and Ca2+ selectivity in Tmc1Bth/Bth mice. (A) Four examples of single MT channel currents, recorded in a P5 apical IHC of Tmc1+/+ mice in response to 0.1-µm step displacements of the hair bundle; below is the ensemble average of 14 presentations. (B) Amplitude histogram showing single-channel current of 6.2 pA. (C) Four examples of single MT channel currents recorded in a P5 apical IHC of Tmc1Bth/Bth mice in response to 0.1-µm step displacements of the hair bundle; below is the ensemble average of 12 presentations. (D) Amplitude histogram showing single-channel current of 6.3 pA; both B and D were at a −84-mV holding potential in 1.5 mM of external Ca2+. (E) Bar plot showing collected single-channel currents in IHCs, apical OHCs, and basal OHCs for Tmc1+/+ and Tmc1Bth/Bth. Number of cells tested is shown above the columns. (F) Protocol for determining Ca2+ selectivity: mechanical hair bundle stimulus (top) evoking MT current (bottom) during voltage ramp from −40 to 70 mV. (G) Examples of MT current–voltage relationships recorded in apical OHCs from Tmc1+/+ and Tmc1Bth/Bth mice in the voltage region around reversal potential. (H) Collected reversal potentials (left ordinate) and PCa/PCs (right ordinate) for Tmc1+/+ and Tmc1Bth/Bth in Tmc2+/+ and Tmc2−/− backgrounds. Numbers of OHCs tested are shown above the columns. Apical OHCs: P4–P6 mice. Error bars represent means ± SD.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4555472&req=5

fig1: MT channel conductance and Ca2+ selectivity in Tmc1Bth/Bth mice. (A) Four examples of single MT channel currents, recorded in a P5 apical IHC of Tmc1+/+ mice in response to 0.1-µm step displacements of the hair bundle; below is the ensemble average of 14 presentations. (B) Amplitude histogram showing single-channel current of 6.2 pA. (C) Four examples of single MT channel currents recorded in a P5 apical IHC of Tmc1Bth/Bth mice in response to 0.1-µm step displacements of the hair bundle; below is the ensemble average of 12 presentations. (D) Amplitude histogram showing single-channel current of 6.3 pA; both B and D were at a −84-mV holding potential in 1.5 mM of external Ca2+. (E) Bar plot showing collected single-channel currents in IHCs, apical OHCs, and basal OHCs for Tmc1+/+ and Tmc1Bth/Bth. Number of cells tested is shown above the columns. (F) Protocol for determining Ca2+ selectivity: mechanical hair bundle stimulus (top) evoking MT current (bottom) during voltage ramp from −40 to 70 mV. (G) Examples of MT current–voltage relationships recorded in apical OHCs from Tmc1+/+ and Tmc1Bth/Bth mice in the voltage region around reversal potential. (H) Collected reversal potentials (left ordinate) and PCa/PCs (right ordinate) for Tmc1+/+ and Tmc1Bth/Bth in Tmc2+/+ and Tmc2−/− backgrounds. Numbers of OHCs tested are shown above the columns. Apical OHCs: P4–P6 mice. Error bars represent means ± SD.
Mentions: MT currents from OHCs of wild-type (Tmc1+/+) and littermate mutant (Tmc1Bth/Bth) Beethoven mice were recorded during hair bundle displacements with a piezoelectric fluid jet (Kros et al., 1992; Kim and Fettiplace, 2013). The maximum amplitude of the MT current was similar at least up to postnatal day (P) 9 in all genotypes tested, indicating that, unlike dn mutation in Tmc1 (Kim and Fettiplace, 2013), the Beethoven mutation does not impair mechanotransduction in apical OHCs. Because early on the bundles have a normal shape, a corollary is that the single–MT channel conductance was unaffected by the Beethoven mutation (Fig. 1, A–E). Although, as observed previously, there was an increase in OHC MT channel conductance from apex to base (Beurg et al., 2014, 2015), the conductance at neither location was reduced relative to wild type in Tmc1Bth/Bth. The basal values are most diagnostic, because they show a marked twofold reduction in the Tmc1−/− (Beurg et al., 2014), but here there was no significant difference between the wild-type and Beethoven mutant. There was also no effect of the Beethoven mutation on the MT channel conductance in IHCs (Fig. 1 E).

Bottom Line: The Ca(2+)-dependent adaptation that adjusts the operating range of the channel was also impaired in Beethoven mutants, with reduced shifts in the relationship between MT current and hair bundle displacement for adapting steps or after lowering extracellular Ca(2+); these effects may be attributed to the channel's reduced Ca(2+) permeability.Moreover, the density of stereociliary CaATPase pumps for Ca(2+) extrusion was decreased in the mutant.The results suggest that a major component of channel adaptation is regulated by changes in intracellular Ca(2+).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706.

Show MeSH
Related in: MedlinePlus