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Dopaminergic modulation of the voltage-gated sodium current in the cochlear afferent neurons of the rat.

Valdés-Baizabal C, Soto E, Vega R - PLoS ONE (2015)

Bottom Line: Recordings of the INa showed that DA receptor activation induced a significant inhibition of the peak current amplitude, leading to a significant decrease in cell excitability.The action of the D1- and D2-like receptors was shown to be mediated by a Gαs/AC/cAMP/PKA and Gαq/PLC/PKC pathways respectively.These results showed that DA receptor activation constitutes a significant modulatory input to SGNs, effectively modulating their excitability and information flow in the auditory pathway.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, México.

ABSTRACT
The cochlear inner hair cells synapse onto type I afferent terminal dendrites, constituting the main afferent pathway for auditory information flow. This pathway receives central control input from the lateral olivocochlear efferent neurons that release various neurotransmitters, among which dopamine (DA) plays a salient role. DA receptors activation exert a protective role in the over activation of the afferent glutamatergic synapses, which occurs when an animal is exposed to intense sound stimuli or during hypoxic events. However, the mechanism of action of DA at the cellular level is still not completely understood. In this work, we studied the actions of DA and its receptor agonists and antagonists on the voltage-gated sodium current (INa) in isolated cochlear afferent neurons of the rat to define the mechanisms of dopaminergic control of the afferent input in the cochlear pathway. Experiments were performed using the voltage and current clamp techniques in the whole-cell configuration in primary cultures of cochlear spiral ganglion neurons (SGNs). Recordings of the INa showed that DA receptor activation induced a significant inhibition of the peak current amplitude, leading to a significant decrease in cell excitability. Inhibition of the INa was produced by a phosphorylation of the sodium channels as shown by the use of phosphatase inhibitor that produced an inhibition analogous to that caused by DA receptor activation. Use of specific agonists and antagonists showed that inhibitory action of DA was mediated both by activation of D1- and D2-like DA receptors. The action of the D1- and D2-like receptors was shown to be mediated by a Gαs/AC/cAMP/PKA and Gαq/PLC/PKC pathways respectively. These results showed that DA receptor activation constitutes a significant modulatory input to SGNs, effectively modulating their excitability and information flow in the auditory pathway.

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Effects of DA on the INa.A) Representative experiment showing the effect of 10 μM DA after control perfusion. B) Temporal course of the inhibitory action of DA 100 μM on the INa amplitude. Bar indicates the DA perfusion. C) Current-voltage relationship in control and with 10 μM DA. DA decreased the INa by 43 ± 8% at −20 mV (P = 0.001; n = 9). D) Activation and inactivation curves in control and after DA application. DA caused a hyperpolarizing shift of the V½ of the inactivation curve of 8 mV at 10 μM (P = 0.8). In this and following activation and inactivation curves the data were fitted with a Boltzmann function (solid lines). E) Concentration-response relationship of the effect of DA (1 nM to 100 μM), with at least n = 6 for each point. The data were fitted with a concentration response curve (solid line) with an IC50 of 2.5 x 10–6 M and a Hill coefficient of 1. F) Bar graph shows that a mixture of D1 and D2 antagonists (100 μM SCH-23390 + 1 μM eticlopride) completely blocks DA action (P = 0.006). Inset show a representative recording of the SCH-23390 (SCH) and eticlopride (E) actions. Calibration bars 0.2 nA and 1 ms. Asterisks denote a significant effect P < 0.05.
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pone.0120808.g002: Effects of DA on the INa.A) Representative experiment showing the effect of 10 μM DA after control perfusion. B) Temporal course of the inhibitory action of DA 100 μM on the INa amplitude. Bar indicates the DA perfusion. C) Current-voltage relationship in control and with 10 μM DA. DA decreased the INa by 43 ± 8% at −20 mV (P = 0.001; n = 9). D) Activation and inactivation curves in control and after DA application. DA caused a hyperpolarizing shift of the V½ of the inactivation curve of 8 mV at 10 μM (P = 0.8). In this and following activation and inactivation curves the data were fitted with a Boltzmann function (solid lines). E) Concentration-response relationship of the effect of DA (1 nM to 100 μM), with at least n = 6 for each point. The data were fitted with a concentration response curve (solid line) with an IC50 of 2.5 x 10–6 M and a Hill coefficient of 1. F) Bar graph shows that a mixture of D1 and D2 antagonists (100 μM SCH-23390 + 1 μM eticlopride) completely blocks DA action (P = 0.006). Inset show a representative recording of the SCH-23390 (SCH) and eticlopride (E) actions. Calibration bars 0.2 nA and 1 ms. Asterisks denote a significant effect P < 0.05.

Mentions: Perfusion of DA reduced the INa peak amplitude, an effect that took place during the first minute of its application (Fig. 2A-B). Comparing the values of the current amplitude at −10 mV, DA significantly decreased the Na+ current at 3 μM, 10 μM and 100 μM by 36 ± 12%, 40 ± 9% and 49 ± 5%, respectively, and shifted the V1/2 towards more negative potentials. When 10 μM of DA (n = 9) was perfused, the maximum INa amplitude decreased 43 ± 8%, P = 0.001 at −20 mV (Fig. 2C). DA caused a significant 7 mV, 12 mV, 8 mV, 9 mV and 14 mV hyperpolarizing shift in the V½ of the inactivation curve at 1 nM (P = 0.03), 100 nM (P = 0.001), 1 μM (P = 0.02), 3 μM (P = 0.01) and 100 μM (P < 0.001), respectively. With 10 μM DA non-significant changes of the activation or inactivation curves was found (n = 9; P > 0.05) (Fig. 2D). The concentration-response curve of the effect of DA on the INa showed that DA inhibits the INa in a concentration dependent manner (Fig. 2E). Data were fitted (solid line) by a dose-response function with an IC50 of 2.5 μM.


Dopaminergic modulation of the voltage-gated sodium current in the cochlear afferent neurons of the rat.

Valdés-Baizabal C, Soto E, Vega R - PLoS ONE (2015)

Effects of DA on the INa.A) Representative experiment showing the effect of 10 μM DA after control perfusion. B) Temporal course of the inhibitory action of DA 100 μM on the INa amplitude. Bar indicates the DA perfusion. C) Current-voltage relationship in control and with 10 μM DA. DA decreased the INa by 43 ± 8% at −20 mV (P = 0.001; n = 9). D) Activation and inactivation curves in control and after DA application. DA caused a hyperpolarizing shift of the V½ of the inactivation curve of 8 mV at 10 μM (P = 0.8). In this and following activation and inactivation curves the data were fitted with a Boltzmann function (solid lines). E) Concentration-response relationship of the effect of DA (1 nM to 100 μM), with at least n = 6 for each point. The data were fitted with a concentration response curve (solid line) with an IC50 of 2.5 x 10–6 M and a Hill coefficient of 1. F) Bar graph shows that a mixture of D1 and D2 antagonists (100 μM SCH-23390 + 1 μM eticlopride) completely blocks DA action (P = 0.006). Inset show a representative recording of the SCH-23390 (SCH) and eticlopride (E) actions. Calibration bars 0.2 nA and 1 ms. Asterisks denote a significant effect P < 0.05.
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pone.0120808.g002: Effects of DA on the INa.A) Representative experiment showing the effect of 10 μM DA after control perfusion. B) Temporal course of the inhibitory action of DA 100 μM on the INa amplitude. Bar indicates the DA perfusion. C) Current-voltage relationship in control and with 10 μM DA. DA decreased the INa by 43 ± 8% at −20 mV (P = 0.001; n = 9). D) Activation and inactivation curves in control and after DA application. DA caused a hyperpolarizing shift of the V½ of the inactivation curve of 8 mV at 10 μM (P = 0.8). In this and following activation and inactivation curves the data were fitted with a Boltzmann function (solid lines). E) Concentration-response relationship of the effect of DA (1 nM to 100 μM), with at least n = 6 for each point. The data were fitted with a concentration response curve (solid line) with an IC50 of 2.5 x 10–6 M and a Hill coefficient of 1. F) Bar graph shows that a mixture of D1 and D2 antagonists (100 μM SCH-23390 + 1 μM eticlopride) completely blocks DA action (P = 0.006). Inset show a representative recording of the SCH-23390 (SCH) and eticlopride (E) actions. Calibration bars 0.2 nA and 1 ms. Asterisks denote a significant effect P < 0.05.
Mentions: Perfusion of DA reduced the INa peak amplitude, an effect that took place during the first minute of its application (Fig. 2A-B). Comparing the values of the current amplitude at −10 mV, DA significantly decreased the Na+ current at 3 μM, 10 μM and 100 μM by 36 ± 12%, 40 ± 9% and 49 ± 5%, respectively, and shifted the V1/2 towards more negative potentials. When 10 μM of DA (n = 9) was perfused, the maximum INa amplitude decreased 43 ± 8%, P = 0.001 at −20 mV (Fig. 2C). DA caused a significant 7 mV, 12 mV, 8 mV, 9 mV and 14 mV hyperpolarizing shift in the V½ of the inactivation curve at 1 nM (P = 0.03), 100 nM (P = 0.001), 1 μM (P = 0.02), 3 μM (P = 0.01) and 100 μM (P < 0.001), respectively. With 10 μM DA non-significant changes of the activation or inactivation curves was found (n = 9; P > 0.05) (Fig. 2D). The concentration-response curve of the effect of DA on the INa showed that DA inhibits the INa in a concentration dependent manner (Fig. 2E). Data were fitted (solid line) by a dose-response function with an IC50 of 2.5 μM.

Bottom Line: Recordings of the INa showed that DA receptor activation induced a significant inhibition of the peak current amplitude, leading to a significant decrease in cell excitability.The action of the D1- and D2-like receptors was shown to be mediated by a Gαs/AC/cAMP/PKA and Gαq/PLC/PKC pathways respectively.These results showed that DA receptor activation constitutes a significant modulatory input to SGNs, effectively modulating their excitability and information flow in the auditory pathway.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, México.

ABSTRACT
The cochlear inner hair cells synapse onto type I afferent terminal dendrites, constituting the main afferent pathway for auditory information flow. This pathway receives central control input from the lateral olivocochlear efferent neurons that release various neurotransmitters, among which dopamine (DA) plays a salient role. DA receptors activation exert a protective role in the over activation of the afferent glutamatergic synapses, which occurs when an animal is exposed to intense sound stimuli or during hypoxic events. However, the mechanism of action of DA at the cellular level is still not completely understood. In this work, we studied the actions of DA and its receptor agonists and antagonists on the voltage-gated sodium current (INa) in isolated cochlear afferent neurons of the rat to define the mechanisms of dopaminergic control of the afferent input in the cochlear pathway. Experiments were performed using the voltage and current clamp techniques in the whole-cell configuration in primary cultures of cochlear spiral ganglion neurons (SGNs). Recordings of the INa showed that DA receptor activation induced a significant inhibition of the peak current amplitude, leading to a significant decrease in cell excitability. Inhibition of the INa was produced by a phosphorylation of the sodium channels as shown by the use of phosphatase inhibitor that produced an inhibition analogous to that caused by DA receptor activation. Use of specific agonists and antagonists showed that inhibitory action of DA was mediated both by activation of D1- and D2-like DA receptors. The action of the D1- and D2-like receptors was shown to be mediated by a Gαs/AC/cAMP/PKA and Gαq/PLC/PKC pathways respectively. These results showed that DA receptor activation constitutes a significant modulatory input to SGNs, effectively modulating their excitability and information flow in the auditory pathway.

Show MeSH
Related in: MedlinePlus