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Functional contributions of HCN channels in the primary auditory neurons of the mouse inner ear.

Kim YH, Holt JR - J. Gen. Physiol. (2013)

Bottom Line: We found that HCN1 is the most prominent subunit contributing to Ih in SGNs.Deletion of Hcn1 resulted in reduced conductance (Gh), slower activation kinetics (τfast), and hyperpolarized half-activation (V1/2) potentials.Together, our data indicate that Ih contributes to SGN membrane properties and plays a role in temporal aspects of signal transmission between the cochlea and the brain, which are critical for normal auditory function.

View Article: PubMed Central - HTML - PubMed

Affiliation: Neuroscience Graduate Program, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.

ABSTRACT
The hyperpolarization-activated current, Ih, is carried by members of the Hcn channel family and contributes to resting potential and firing properties in excitable cells of various systems, including the auditory system. Ih has been identified in spiral ganglion neurons (SGNs); however, its molecular correlates and their functional contributions have not been well characterized. To investigate the molecular composition of the channels that carry Ih in SGNs, we examined Hcn mRNA harvested from spiral ganglia of neonatal and adult mice using quantitative RT-PCR. The data indicate expression of Hcn1, Hcn2, and Hcn4 subunits in SGNs, with Hcn1 being the most highly expressed at both stages. To investigate the functional contributions of HCN subunits, we used the whole-cell, tight-seal technique to record from wild-type SGNs and those deficient in Hcn1, Hcn2, or both. We found that HCN1 is the most prominent subunit contributing to Ih in SGNs. Deletion of Hcn1 resulted in reduced conductance (Gh), slower activation kinetics (τfast), and hyperpolarized half-activation (V1/2) potentials. We demonstrate that Ih contributes to SGN function with depolarized resting potentials, depolarized sag and rebound potentials, accelerated rebound spikes after hyperpolarization, and minimized jitter in spike latency for small depolarizing stimuli. Auditory brainstem responses of Hcn1-deficient mice showed longer latencies, suggesting that HCN1-mediated Ih is critical for synchronized spike timing in SGNs. Together, our data indicate that Ih contributes to SGN membrane properties and plays a role in temporal aspects of signal transmission between the cochlea and the brain, which are critical for normal auditory function.

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Expression of Hcn mRNA in mouse SGNs. (A and B) Expression of Hcn1–4 in neonatal (A) and adult (B) WT mouse SGNs. qPCR was used to estimate the total mRNA copy number of Hcn genes present in both neonatal (P3) and adult stages (≥P40). Neonatal SGN samples were collected from a pool of 24 whole cochleas. Adult SGN samples were obtained from a pool of 16 whole cochleas. Each preparation was run in triplicate. Results are shown as mean total copies in thousands of Hcn mRNA transcripts per cochlea. Error bars represent SEM.
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fig1: Expression of Hcn mRNA in mouse SGNs. (A and B) Expression of Hcn1–4 in neonatal (A) and adult (B) WT mouse SGNs. qPCR was used to estimate the total mRNA copy number of Hcn genes present in both neonatal (P3) and adult stages (≥P40). Neonatal SGN samples were collected from a pool of 24 whole cochleas. Adult SGN samples were obtained from a pool of 16 whole cochleas. Each preparation was run in triplicate. Results are shown as mean total copies in thousands of Hcn mRNA transcripts per cochlea. Error bars represent SEM.

Mentions: To examine the contributions of HCN subunits to Ih in SGNs, we began with a qPCR analysis using primers that were selective for Hcn1–4 and mRNA harvested from P3 WT SGN tissue. As shown in Fig. 1 A, the qPCR analysis indicated expression of Hcn1, Hcn2, and Hcn4 in early postnatal SGNs. The total mRNA expression for Hcn1, Hcn2, and Hcn4 per cochlea was 700,000:200,000:400,000, respectively, with little expression of Hcn3. When normalized to Hcn3 mRNA copy number, the relative expression was as follows: Hcn1-Hcn2-Hcn3-Hcn4 21:6:1:12. Based on the expression ratio, it is evident that Hcn1 was the most highly expressed in neonatal SGNs, followed by Hcn4 and Hcn2. We speculate that the Hcn3 expression in SGNs is minimal or nonexistent based on the low mRNA copy number; thus, its functional contributions in neonatal SGNs are likely to be negligible.


Functional contributions of HCN channels in the primary auditory neurons of the mouse inner ear.

Kim YH, Holt JR - J. Gen. Physiol. (2013)

Expression of Hcn mRNA in mouse SGNs. (A and B) Expression of Hcn1–4 in neonatal (A) and adult (B) WT mouse SGNs. qPCR was used to estimate the total mRNA copy number of Hcn genes present in both neonatal (P3) and adult stages (≥P40). Neonatal SGN samples were collected from a pool of 24 whole cochleas. Adult SGN samples were obtained from a pool of 16 whole cochleas. Each preparation was run in triplicate. Results are shown as mean total copies in thousands of Hcn mRNA transcripts per cochlea. Error bars represent SEM.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3753603&req=5

fig1: Expression of Hcn mRNA in mouse SGNs. (A and B) Expression of Hcn1–4 in neonatal (A) and adult (B) WT mouse SGNs. qPCR was used to estimate the total mRNA copy number of Hcn genes present in both neonatal (P3) and adult stages (≥P40). Neonatal SGN samples were collected from a pool of 24 whole cochleas. Adult SGN samples were obtained from a pool of 16 whole cochleas. Each preparation was run in triplicate. Results are shown as mean total copies in thousands of Hcn mRNA transcripts per cochlea. Error bars represent SEM.
Mentions: To examine the contributions of HCN subunits to Ih in SGNs, we began with a qPCR analysis using primers that were selective for Hcn1–4 and mRNA harvested from P3 WT SGN tissue. As shown in Fig. 1 A, the qPCR analysis indicated expression of Hcn1, Hcn2, and Hcn4 in early postnatal SGNs. The total mRNA expression for Hcn1, Hcn2, and Hcn4 per cochlea was 700,000:200,000:400,000, respectively, with little expression of Hcn3. When normalized to Hcn3 mRNA copy number, the relative expression was as follows: Hcn1-Hcn2-Hcn3-Hcn4 21:6:1:12. Based on the expression ratio, it is evident that Hcn1 was the most highly expressed in neonatal SGNs, followed by Hcn4 and Hcn2. We speculate that the Hcn3 expression in SGNs is minimal or nonexistent based on the low mRNA copy number; thus, its functional contributions in neonatal SGNs are likely to be negligible.

Bottom Line: We found that HCN1 is the most prominent subunit contributing to Ih in SGNs.Deletion of Hcn1 resulted in reduced conductance (Gh), slower activation kinetics (τfast), and hyperpolarized half-activation (V1/2) potentials.Together, our data indicate that Ih contributes to SGN membrane properties and plays a role in temporal aspects of signal transmission between the cochlea and the brain, which are critical for normal auditory function.

View Article: PubMed Central - HTML - PubMed

Affiliation: Neuroscience Graduate Program, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.

ABSTRACT
The hyperpolarization-activated current, Ih, is carried by members of the Hcn channel family and contributes to resting potential and firing properties in excitable cells of various systems, including the auditory system. Ih has been identified in spiral ganglion neurons (SGNs); however, its molecular correlates and their functional contributions have not been well characterized. To investigate the molecular composition of the channels that carry Ih in SGNs, we examined Hcn mRNA harvested from spiral ganglia of neonatal and adult mice using quantitative RT-PCR. The data indicate expression of Hcn1, Hcn2, and Hcn4 subunits in SGNs, with Hcn1 being the most highly expressed at both stages. To investigate the functional contributions of HCN subunits, we used the whole-cell, tight-seal technique to record from wild-type SGNs and those deficient in Hcn1, Hcn2, or both. We found that HCN1 is the most prominent subunit contributing to Ih in SGNs. Deletion of Hcn1 resulted in reduced conductance (Gh), slower activation kinetics (τfast), and hyperpolarized half-activation (V1/2) potentials. We demonstrate that Ih contributes to SGN function with depolarized resting potentials, depolarized sag and rebound potentials, accelerated rebound spikes after hyperpolarization, and minimized jitter in spike latency for small depolarizing stimuli. Auditory brainstem responses of Hcn1-deficient mice showed longer latencies, suggesting that HCN1-mediated Ih is critical for synchronized spike timing in SGNs. Together, our data indicate that Ih contributes to SGN membrane properties and plays a role in temporal aspects of signal transmission between the cochlea and the brain, which are critical for normal auditory function.

Show MeSH
Related in: MedlinePlus