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Inward rectifier potassium (Kir) current in dopaminergic periglomerular neurons of the mouse olfactory bulb.

Borin M, Fogli Iseppe A, Pignatelli A, Belluzzi O - Front Cell Neurosci (2014)

Bottom Line: The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP.We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors.These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences and Biotechnology, University of Ferrara Ferrara, Italy.

ABSTRACT
Dopaminergic (DA) periglomerular (PG) neurons are critically placed at the entry of the bulbar circuitry, directly in contact with both the terminals of olfactory sensory neurons and the apical dendrites of projection neurons; they are autorhythmic and are the target of numerous terminals releasing a variety of neurotransmitters. Despite the centrality of their position, suggesting a critical role in the sensory processing, their properties -and consequently their function- remain elusive. The current mediated by inward rectifier potassium (Kir) channels in DA-PG cells was recorded by adopting the perforated-patch configuration in thin slices; IKir could be distinguished from the hyperpolarization-activated current (I h ) by showing full activation in <10 ms, no inactivation, suppression by Ba(2+) in a typical voltage-dependent manner (IC50 208 μM) and reversal potential nearly coincident with EK. Ba(2+) (2 mM) induces a large depolarization of DA-PG cells, paralleled by an increase of the input resistance, leading to a block of the spontaneous activity, but the Kir current is not an essential component of the pacemaker machinery. The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP. We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors. These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

No MeSH data available.


Related in: MedlinePlus

Organic blockers of the Kir channels. (A) with a GIRK current activated by a cholinergic muscarinic agonist (oxotremorine 10 μM), the GIRK channels blocker tertiapin-Q (1 μM) completely suppresses the current (n = 11; see text for explanation); tertiapin-Q alone does not change the amplitude of hyperpolarization-activated (not shown; n = 13). In this as in the following panels, the steady-state (ss) current is calculated in relation to membrane capacity. (B) Quinacrine (100 μM) inhibition of hyperpolarization-activated current (n = 15). (C) With the KIR2.x channels blocked by quinacrine, a muscarinic cholinergic agonist (oxotremorine 10 μM) can activate a GIRK current (yellow dots), and this fraction can be completely suppressed by tertiapin (green dots; n = 7). *, ** and *** indicate significance levels of 0.05, 0.01 and 0.001, respectively. (D) Effect of quinacrine on membrane potential. Perforated patch recording in standard saline (EC1 solution). The blue bar indicates the time of application of 100 μM into the bath; to the right, a sequence recorded after injection of 35 pA hyperpolarizing current; (further explanation in the text). All recordings were realized at 34°C, in EC2, BL1, and BL2; statistical analysis performed with Two-Way ANOVA and post-hoc Bonferroni test.
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Figure 7: Organic blockers of the Kir channels. (A) with a GIRK current activated by a cholinergic muscarinic agonist (oxotremorine 10 μM), the GIRK channels blocker tertiapin-Q (1 μM) completely suppresses the current (n = 11; see text for explanation); tertiapin-Q alone does not change the amplitude of hyperpolarization-activated (not shown; n = 13). In this as in the following panels, the steady-state (ss) current is calculated in relation to membrane capacity. (B) Quinacrine (100 μM) inhibition of hyperpolarization-activated current (n = 15). (C) With the KIR2.x channels blocked by quinacrine, a muscarinic cholinergic agonist (oxotremorine 10 μM) can activate a GIRK current (yellow dots), and this fraction can be completely suppressed by tertiapin (green dots; n = 7). *, ** and *** indicate significance levels of 0.05, 0.01 and 0.001, respectively. (D) Effect of quinacrine on membrane potential. Perforated patch recording in standard saline (EC1 solution). The blue bar indicates the time of application of 100 μM into the bath; to the right, a sequence recorded after injection of 35 pA hyperpolarizing current; (further explanation in the text). All recordings were realized at 34°C, in EC2, BL1, and BL2; statistical analysis performed with Two-Way ANOVA and post-hoc Bonferroni test.

Mentions: The oxidation-resistant form of the drug, tertiapin-Q, was ineffective when tested alone at concentrations ranging from 100 nM to 3 μM (not shown). However, GIRK channels become activated only following the binding of ligands to their cognate G protein-coupled receptors, which causes the dissociation of the βγ subunits of a pertussis toxin-sensitive G protein which subsequently bind to and activate the GIRK channel (Walsh, 2011). Therefore, we tested the effect of tertiapin after activation of Kir current with oxotremorine, a metabotropic cholinergic receptor activator (see also below). In these conditions, tertiapin completely abolished the current increment promoted by the muscarinic receptor activation (Figure 7A), suggesting that functional GIRK channels are actually present in DA-PG cells.


Inward rectifier potassium (Kir) current in dopaminergic periglomerular neurons of the mouse olfactory bulb.

Borin M, Fogli Iseppe A, Pignatelli A, Belluzzi O - Front Cell Neurosci (2014)

Organic blockers of the Kir channels. (A) with a GIRK current activated by a cholinergic muscarinic agonist (oxotremorine 10 μM), the GIRK channels blocker tertiapin-Q (1 μM) completely suppresses the current (n = 11; see text for explanation); tertiapin-Q alone does not change the amplitude of hyperpolarization-activated (not shown; n = 13). In this as in the following panels, the steady-state (ss) current is calculated in relation to membrane capacity. (B) Quinacrine (100 μM) inhibition of hyperpolarization-activated current (n = 15). (C) With the KIR2.x channels blocked by quinacrine, a muscarinic cholinergic agonist (oxotremorine 10 μM) can activate a GIRK current (yellow dots), and this fraction can be completely suppressed by tertiapin (green dots; n = 7). *, ** and *** indicate significance levels of 0.05, 0.01 and 0.001, respectively. (D) Effect of quinacrine on membrane potential. Perforated patch recording in standard saline (EC1 solution). The blue bar indicates the time of application of 100 μM into the bath; to the right, a sequence recorded after injection of 35 pA hyperpolarizing current; (further explanation in the text). All recordings were realized at 34°C, in EC2, BL1, and BL2; statistical analysis performed with Two-Way ANOVA and post-hoc Bonferroni test.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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Figure 7: Organic blockers of the Kir channels. (A) with a GIRK current activated by a cholinergic muscarinic agonist (oxotremorine 10 μM), the GIRK channels blocker tertiapin-Q (1 μM) completely suppresses the current (n = 11; see text for explanation); tertiapin-Q alone does not change the amplitude of hyperpolarization-activated (not shown; n = 13). In this as in the following panels, the steady-state (ss) current is calculated in relation to membrane capacity. (B) Quinacrine (100 μM) inhibition of hyperpolarization-activated current (n = 15). (C) With the KIR2.x channels blocked by quinacrine, a muscarinic cholinergic agonist (oxotremorine 10 μM) can activate a GIRK current (yellow dots), and this fraction can be completely suppressed by tertiapin (green dots; n = 7). *, ** and *** indicate significance levels of 0.05, 0.01 and 0.001, respectively. (D) Effect of quinacrine on membrane potential. Perforated patch recording in standard saline (EC1 solution). The blue bar indicates the time of application of 100 μM into the bath; to the right, a sequence recorded after injection of 35 pA hyperpolarizing current; (further explanation in the text). All recordings were realized at 34°C, in EC2, BL1, and BL2; statistical analysis performed with Two-Way ANOVA and post-hoc Bonferroni test.
Mentions: The oxidation-resistant form of the drug, tertiapin-Q, was ineffective when tested alone at concentrations ranging from 100 nM to 3 μM (not shown). However, GIRK channels become activated only following the binding of ligands to their cognate G protein-coupled receptors, which causes the dissociation of the βγ subunits of a pertussis toxin-sensitive G protein which subsequently bind to and activate the GIRK channel (Walsh, 2011). Therefore, we tested the effect of tertiapin after activation of Kir current with oxotremorine, a metabotropic cholinergic receptor activator (see also below). In these conditions, tertiapin completely abolished the current increment promoted by the muscarinic receptor activation (Figure 7A), suggesting that functional GIRK channels are actually present in DA-PG cells.

Bottom Line: The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP.We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors.These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences and Biotechnology, University of Ferrara Ferrara, Italy.

ABSTRACT
Dopaminergic (DA) periglomerular (PG) neurons are critically placed at the entry of the bulbar circuitry, directly in contact with both the terminals of olfactory sensory neurons and the apical dendrites of projection neurons; they are autorhythmic and are the target of numerous terminals releasing a variety of neurotransmitters. Despite the centrality of their position, suggesting a critical role in the sensory processing, their properties -and consequently their function- remain elusive. The current mediated by inward rectifier potassium (Kir) channels in DA-PG cells was recorded by adopting the perforated-patch configuration in thin slices; IKir could be distinguished from the hyperpolarization-activated current (I h ) by showing full activation in <10 ms, no inactivation, suppression by Ba(2+) in a typical voltage-dependent manner (IC50 208 μM) and reversal potential nearly coincident with EK. Ba(2+) (2 mM) induces a large depolarization of DA-PG cells, paralleled by an increase of the input resistance, leading to a block of the spontaneous activity, but the Kir current is not an essential component of the pacemaker machinery. The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP. We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors. These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

No MeSH data available.


Related in: MedlinePlus