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Cell-type-specific tuning of Cav1.3 Ca(2+)-channels by a C-terminal automodulatory domain.

Scharinger A, Eckrich S, Vandael DH, Schönig K, Koschak A, Hecker D, Kaur G, Lee A, Sah A, Bartsch D, Benedetti B, Lieb A, Schick B, Singewald N, Sinnegger-Brauns MJ, Carbone E, Engel J, Striessnig J - Front Cell Neurosci (2015)

Bottom Line: Alternative splicing generates short C-terminal channel variants lacking the CTM resulting in enhanced Ca(2+)-dependent inactivation and stronger voltage-sensitivity upon heterologous expression.CTM-elimination impaired Ca(2+)-dependent inactivation of Ca(2+)-currents in hair cells but increased it in chromaffin cells, resulting in hyperpolarized resting potentials and reduced pacemaking.CTM disruption did not affect hearing thresholds.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Toxicology, Institute of Pharmacy, Center for Molecular Biosciences, University of Innsbruck Innsbruck, Austria.

ABSTRACT
Cav1.3 L-type Ca(2+)-channel function is regulated by a C-terminal automodulatory domain (CTM). It affects channel binding of calmodulin and thereby tunes channel activity by interfering with Ca(2+)- and voltage-dependent gating. Alternative splicing generates short C-terminal channel variants lacking the CTM resulting in enhanced Ca(2+)-dependent inactivation and stronger voltage-sensitivity upon heterologous expression. However, the role of this modulatory domain for channel function in its native environment is unkown. To determine its functional significance in vivo, we interrupted the CTM with a hemagglutinin tag in mutant mice (Cav1.3DCRD(HA/HA)). Using these mice we provide biochemical evidence for the existence of long (CTM-containing) and short (CTM-deficient) Cav1.3 α1-subunits in brain. The long (HA-labeled) Cav1.3 isoform was present in all ribbon synapses of cochlear inner hair cells. CTM-elimination impaired Ca(2+)-dependent inactivation of Ca(2+)-currents in hair cells but increased it in chromaffin cells, resulting in hyperpolarized resting potentials and reduced pacemaking. CTM disruption did not affect hearing thresholds. We show that the modulatory function of the CTM is affected by its native environment in different cells and thus occurs in a cell-type specific manner in vivo. It stabilizes gating properties of Cav1.3 channels required for normal electrical excitability.

No MeSH data available.


Related in: MedlinePlus

Hearing function in Cav1.3DCRDHA/HA mice. (A) ABR thresholds (mean ± SD) of Cav1.3DCRDHA/HA mice were normal for click stimuli (WT and Cav1.3DCRDHA/HA: n = 8/16 animals/ears) and as a function of stimulus tone frequency (WT: n = 6/12 animals/ears and Cav1.3DCRDHA/HA: n = 7/13 animals/ears). Thresholds could be measured in (n = animals/ears, frequency in kHz): WT: 2/3, 2; 6/9, 2.8; 6/12, from 4 to 22.6; 3/6, 32; 3/6, 45.2; Cav1.3DCRDHA/HA: 2/3, 2; 7/13, from 2.8 to 32; 4/8, 45.2. (B) Mean DPOAE maximum amplitudes (signal to noise ratio) ± SD at f1 = 9.1 kHz, L1 = 55 dB SPL, f2 averaged over 10–18 kHz, and L2 = 45 dB SPL were normal in Cav1.3DCRDHA/HA (n = 7/14 animals/ears) compared with WT mice (n = 7/14 animals/ears, p = 0.12), indicating normal function of the cochlear amplifier.
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Figure 8: Hearing function in Cav1.3DCRDHA/HA mice. (A) ABR thresholds (mean ± SD) of Cav1.3DCRDHA/HA mice were normal for click stimuli (WT and Cav1.3DCRDHA/HA: n = 8/16 animals/ears) and as a function of stimulus tone frequency (WT: n = 6/12 animals/ears and Cav1.3DCRDHA/HA: n = 7/13 animals/ears). Thresholds could be measured in (n = animals/ears, frequency in kHz): WT: 2/3, 2; 6/9, 2.8; 6/12, from 4 to 22.6; 3/6, 32; 3/6, 45.2; Cav1.3DCRDHA/HA: 2/3, 2; 7/13, from 2.8 to 32; 4/8, 45.2. (B) Mean DPOAE maximum amplitudes (signal to noise ratio) ± SD at f1 = 9.1 kHz, L1 = 55 dB SPL, f2 averaged over 10–18 kHz, and L2 = 45 dB SPL were normal in Cav1.3DCRDHA/HA (n = 7/14 animals/ears) compared with WT mice (n = 7/14 animals/ears, p = 0.12), indicating normal function of the cochlear amplifier.

Mentions: To test if these changes in current properties also affect hearing function we recorded ABR (Figure 8A) and DPOAE (Figure 8B). Thresholds of click and frequency ABR recordings and DPOAE amplitudes were not changed in Cav1.3DCRDHA/HA compared with WT mice. The data indicate that reduced CDI in Cav1.3DCRDHA/HA IHCs does not cause detectable changes in hearing thresholds and the cochlear amplifier.


Cell-type-specific tuning of Cav1.3 Ca(2+)-channels by a C-terminal automodulatory domain.

Scharinger A, Eckrich S, Vandael DH, Schönig K, Koschak A, Hecker D, Kaur G, Lee A, Sah A, Bartsch D, Benedetti B, Lieb A, Schick B, Singewald N, Sinnegger-Brauns MJ, Carbone E, Engel J, Striessnig J - Front Cell Neurosci (2015)

Hearing function in Cav1.3DCRDHA/HA mice. (A) ABR thresholds (mean ± SD) of Cav1.3DCRDHA/HA mice were normal for click stimuli (WT and Cav1.3DCRDHA/HA: n = 8/16 animals/ears) and as a function of stimulus tone frequency (WT: n = 6/12 animals/ears and Cav1.3DCRDHA/HA: n = 7/13 animals/ears). Thresholds could be measured in (n = animals/ears, frequency in kHz): WT: 2/3, 2; 6/9, 2.8; 6/12, from 4 to 22.6; 3/6, 32; 3/6, 45.2; Cav1.3DCRDHA/HA: 2/3, 2; 7/13, from 2.8 to 32; 4/8, 45.2. (B) Mean DPOAE maximum amplitudes (signal to noise ratio) ± SD at f1 = 9.1 kHz, L1 = 55 dB SPL, f2 averaged over 10–18 kHz, and L2 = 45 dB SPL were normal in Cav1.3DCRDHA/HA (n = 7/14 animals/ears) compared with WT mice (n = 7/14 animals/ears, p = 0.12), indicating normal function of the cochlear amplifier.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4547004&req=5

Figure 8: Hearing function in Cav1.3DCRDHA/HA mice. (A) ABR thresholds (mean ± SD) of Cav1.3DCRDHA/HA mice were normal for click stimuli (WT and Cav1.3DCRDHA/HA: n = 8/16 animals/ears) and as a function of stimulus tone frequency (WT: n = 6/12 animals/ears and Cav1.3DCRDHA/HA: n = 7/13 animals/ears). Thresholds could be measured in (n = animals/ears, frequency in kHz): WT: 2/3, 2; 6/9, 2.8; 6/12, from 4 to 22.6; 3/6, 32; 3/6, 45.2; Cav1.3DCRDHA/HA: 2/3, 2; 7/13, from 2.8 to 32; 4/8, 45.2. (B) Mean DPOAE maximum amplitudes (signal to noise ratio) ± SD at f1 = 9.1 kHz, L1 = 55 dB SPL, f2 averaged over 10–18 kHz, and L2 = 45 dB SPL were normal in Cav1.3DCRDHA/HA (n = 7/14 animals/ears) compared with WT mice (n = 7/14 animals/ears, p = 0.12), indicating normal function of the cochlear amplifier.
Mentions: To test if these changes in current properties also affect hearing function we recorded ABR (Figure 8A) and DPOAE (Figure 8B). Thresholds of click and frequency ABR recordings and DPOAE amplitudes were not changed in Cav1.3DCRDHA/HA compared with WT mice. The data indicate that reduced CDI in Cav1.3DCRDHA/HA IHCs does not cause detectable changes in hearing thresholds and the cochlear amplifier.

Bottom Line: Alternative splicing generates short C-terminal channel variants lacking the CTM resulting in enhanced Ca(2+)-dependent inactivation and stronger voltage-sensitivity upon heterologous expression.CTM-elimination impaired Ca(2+)-dependent inactivation of Ca(2+)-currents in hair cells but increased it in chromaffin cells, resulting in hyperpolarized resting potentials and reduced pacemaking.CTM disruption did not affect hearing thresholds.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Toxicology, Institute of Pharmacy, Center for Molecular Biosciences, University of Innsbruck Innsbruck, Austria.

ABSTRACT
Cav1.3 L-type Ca(2+)-channel function is regulated by a C-terminal automodulatory domain (CTM). It affects channel binding of calmodulin and thereby tunes channel activity by interfering with Ca(2+)- and voltage-dependent gating. Alternative splicing generates short C-terminal channel variants lacking the CTM resulting in enhanced Ca(2+)-dependent inactivation and stronger voltage-sensitivity upon heterologous expression. However, the role of this modulatory domain for channel function in its native environment is unkown. To determine its functional significance in vivo, we interrupted the CTM with a hemagglutinin tag in mutant mice (Cav1.3DCRD(HA/HA)). Using these mice we provide biochemical evidence for the existence of long (CTM-containing) and short (CTM-deficient) Cav1.3 α1-subunits in brain. The long (HA-labeled) Cav1.3 isoform was present in all ribbon synapses of cochlear inner hair cells. CTM-elimination impaired Ca(2+)-dependent inactivation of Ca(2+)-currents in hair cells but increased it in chromaffin cells, resulting in hyperpolarized resting potentials and reduced pacemaking. CTM disruption did not affect hearing thresholds. We show that the modulatory function of the CTM is affected by its native environment in different cells and thus occurs in a cell-type specific manner in vivo. It stabilizes gating properties of Cav1.3 channels required for normal electrical excitability.

No MeSH data available.


Related in: MedlinePlus