Acid sensing ion channels regulate neuronal excitability by inhibiting BK potassium channels

doi:10.1016/j.bbrc.2012.08.114

Biochemical and Biophysical Research Communications

Volume 426, Issue 4, 5 October 2012, Pages 511-515

https://doi.org/10.1016/j.bbrc.2012.08.114 Get rights and content

Abstract

Acid sensing ion channels (ASICs), Ca²⁺ and voltage-activated potassium channels (BK) are widely present throughout the central nervous system. Previous studies have shown that when expressed together in heterologous cells, ASICs inhibit BK channels, and this inhibition is relieved by acidic extracellular pH. We hypothesized that ASIC and BK channels might interact in neurons, and that ASICs may regulate BK channel activity. We found that ASICs inhibited BK currents in cultured wild-type cortical neurons, but not in ASIC1a/2/3 triple knockout neurons. The inhibition in the wild-type was partially relieved by a drop in extracellular pH to 6. To test the consequences of ASIC–BK interaction for neuronal excitability, we compared action potential firing in cultured cortical neurons from wild-type and ASIC1a/2/3 null mice. We found that in the knockout, action potentials were narrow and exhibited increased after-hyperpolarization. Moreover, the excitability of these neurons was significantly increased. These findings are consistent with increased BK channel activity in the neurons from ASIC1a/2/3 null mice. Our data suggest that ASICs can act as endogenous pH-dependent inhibitors of BK channels, and thereby can reduce neuronal excitability.

Highlights

► ASICs inhibit BK channels in neurons, this inhibition is relieved by acidification. ► Interaction with ASICs confers pH sensitivity on BK channel. ► ASIC–BK interaction regulates neuronal excitability.

Introduction

Neuronal excitability is an important factor in determining neuronal function. The activity of BK (Ca²⁺ and voltage-activated potassium channel) has profound effects on neuronal excitability. Functional or heritable gain of function of BK has been associated with change in the shape of action potentials, increased frequency of action potential firing, and spontaneous seizures in both humans and mice [1], [2]. ASIC channels, generally considered to be sensory channels, have also been implicated in changing neuronal action potential firing by contributing to membrane depolarization through small sustained inward currents induced by acidification of the environment [3], [4], [5]. Moreover, a number of studies report increases in the sensory response in ASIC knockout mice [6], [7], [8], [9], which is hard to understand if ASICs act as depolarizing channels.

We have previously shown that ASIC proteins, in addition to their channel properties, can directly interact with and regulate activity of BK channels in heterologous expression systems [10]. This regulation is pH dependent, and partial relief of BK inhibition by the more acid sensitive ASIC1a can be observed at pH 7 with the full effect at pH 6, whereas relief of inhibition by ASIC2 requires pH 5 and lower [10]. ASIC and BK channels co-exist in neurons in many parts of the brain [11], [12], [13], [14]. We hypothesized that an interaction between these channels may happen in vivo, that this interaction may regulate BK channel activity and, through this regulation, neuronal firing properties.

Section snippets

ASIC1a/2/3 null mice

The generation of ASIC1a/2/3 −/− mice has been described [9]. Each of previously generated ASIC1a, 2, and 3 null lines [6], [13], [15] was backcrossed for 10 generations onto a C57BL/6J background to generate congenic lines and then crossed to one another to generate a congenic C57BL/6J line missing ASIC1a and 2 (ASIC1a/2 null mice), and 3 (ASIC1a/2/3 −/− mice).

Antibodies

Anti-h/r/mBK monoclonal antibody was purchased from BD Biosciences Pharminogen (San Jose, CA). Anti-h/r/m Actin goat polyclonal

ASICs do not alter BK protein level in brain

ASIC and BK channels both display wide distributions throughout the brain [11], [12], [13], [14] indicating the potential for in vivo interaction. We used comparison between wild-type and triple knockouts (ASIC1a/2/3 −/−) because central neurons express ASIC1a, -2a, -2b, and small amounts of -3 [14], [18], [19], [20], all of which inhibit BK [10]. In cultured cortical neurons, disruption of these genes eliminated H⁺-evoked currents that are typical for ASICs (Fig. 1A). The BK protein levels in

Discussion

Our data suggest that at least some populations of ASIC and BK channels interact in neurons and that ASICs inhibit BK currents in the wild-type neurons. The lowering of the extracellular pH to 6 lead to an increase in outward K⁺ currents. This is consistent with the relief of inhibition of BK channels described previously [10] and, in addition, may possibly involve other potassium channels, such as voltage-gated potassium channels, that can also be inhibited by ASICs [10]. The observed increase

Acknowledgments

We thank Michael J. Welsh and Margaret P. Price for ASIC1a/2/3 null mice and fruitful discussions. This work was supported by NIH grants R15NS070260 to EP and HL14388 to FMA. The funders had no role in study design, data collection and analysis, preparation of the manuscript, or decision to publish.

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Published by Elsevier Inc.

Acid sensing ion channels regulate neuronal excitability by inhibiting BK potassium channels

Abstract

Highlights

Introduction

Section snippets

ASIC1a/2/3 null mice

Antibodies

ASICs do not alter BK protein level in brain

Discussion

Acknowledgments

Neuron

Neuron

J. Biol. Chem.

Neuropharmacology

J. Biol. Chem.

Neurobiol. Dis.

Biophys. J.

BK channel beta4 subunit reduces dentate gyrus excitability and protects against temporal lobe seizures

Nat. Neurosci.

Calcium-sensitive potassium channelopathy in human epilepsy and paroxysmal movement disorder

Nat. Genet.

Proinflammatory mediators, stimulators of sensory neuron excitability via the expression of acid-sensing ion channels

J. Neurosci. Off. J. Soc. Neurosci.

Acid-sensing ionic channels in the rat vestibular endorgans and ganglia

J. Neurophysiol.

Acid sensing ion channels in dorsal spinal cord neurons

J. Neurosci. Off. J. Soc. Neurosci.