Na+,K+,2Cl− Cotransport and Intracellular Chloride Regulation in Rat Primary Sensory Neurons: Thermodynamic and Kinetic Aspects

Rocha-González, Héctor Isaac; S, Mao; Álvarez-Leefmans, Francisco J.

doi:10.1152/jn.01007.2007

Cited by 79 publications

(95 citation statements)

References 87 publications

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“…In case of an inhibitory feedback the plot in Fig. 5B would deviate from linearity at elevated [Cl − ] i levels (19). Our results demonstrate the lack of feedback inhibition on NKCC1 at elevated levels of [Cl − ] i , a finding that is consistent with the lack of WNK3 expression in ORNs.…”

Section: Nkcc1 Expressionsupporting

confidence: 83%

Molecular components of signal amplification in olfactory sensory cilia

Hengl

Kaneko

Dauner

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

100

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The mammalian olfactory system detects an unlimited variety of odorants with a limited set of odorant receptors. To cope with the complexity of the odor world, each odorant receptor must detect many different odorants. The demand for low odor selectivity creates problems for the transduction process: the initial transduction step, the synthesis of the second messenger cAMP, operates with low efficiency, mainly because odorants bind only briefly to their receptors. Sensory cilia of olfactory receptor neurons have developed an unusual solution to this problem. They accumulate chloride ions at rest and discharge a chloride current upon odor detection. This chloride current amplifies the receptor potential and promotes electrical excitation. We have studied this amplification process by examining identity, subcellular localization, and regulation of its molecular components. We found that the Na + /K + /2Cl − cotransporter NKCC1 is expressed in the ciliary membrane, where it mediates chloride accumulation into the ciliary lumen. Gene silencing experiments revealed that the activity of this transporter depends on the kinases SPAK and OSR1, which are enriched in the cilia together with their own activating kinases, WNK1 and WNK4. A second Cl − transporter, the Cl − /HCO 3 − exchanger SLC4A1, is expressed in the cilia and may support Cl − accumulation. The calcium-dependent chloride channel TMEM16B (ANO2) provides a ciliary pathway for the excitatory chloride current. These findings describe a specific set of ciliary proteins involved in anion-based signal amplification. They provide a molecular concept for the unique strategy that allows olfactory sensory neurons to operate as efficient transducers of weak sensory stimuli.chloride | olfaction | sensory transduction | transport | kinase M ammalian olfactory receptor neurons (ORNs) present to the air a tuft of sensory cilia equipped with odorant receptors. Upon contact with odorants, these receptors actuate a transduction cascade that leads to firing of action potentials. This cascade has an unusual, two-stage organization (1). First, the activated odorant receptors induce a rise of the second messengers cAMP and Ca 2+ in the cilia, a process that involves cAMP-gated, Ca 2+ -permeable ion channels. In the second stage, inflowing Ca 2+ opens Cl − channels. By conducting a depolarizing Cl − efflux from the cilia, these channels amplify the receptor potential approximately 10-fold, thus helping to excite the neuron even when stimulation is weak. ORNs accumulate chloride through the Na + /K + /2Cl − cotransporter NKCC1 and maintain an elevated intracellular Cl − concentration (2, 3) to support amplification. Accordingly, gene ablation of NKCC1, as well as the pharmacologic suppression of Cl − accumulation or Cl − efflux, strongly inhibits the sensory response of ORNs (3-5). Although these observations provide a robust concept for signal amplification, several points are still unclear. These concern both the Cl − accumulation process and the excitatory Cl − currents. First, ...

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Section: Nkcc1 Expressionsupporting

confidence: 83%

Molecular components of signal amplification in olfactory sensory cilia

Hengl

Kaneko

Dauner

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

100

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“…However, this study does not address the mechanism by which this factor regulates intracellular chloride concentration. Possible mechanisms include regulation of a large number of proteins, including cation-chloride cotransporters (12), namely the Na + -K + -2Cl − cotransporters that increase [Cl − ] i (10,(31)(32)(33)(34)(35) (42), and a variety of chloride channels (13). In contrast to the hippocampus, RGCs do not express Na + -K + -2Cl − cotransporter 1 (23) and they do not express Cl − /HCO 3 + exchangers until later in development (43).…”

Section: Discussionmentioning

confidence: 99%

Non–cell-autonomous factor induces the transition from excitatory to inhibitory GABA signaling in retina independent of activity

Barkis

Ford²,

Feller³

2010

Proc. Natl. Acad. Sci. U.S.A.

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During development, the effect of activating GABA A receptors switches from depolarizing to hyperpolarizing. Several environmental factors have been implicated in the timing of this GABA switch, including neural activity, although these observations remain controversial. By using acutely isolated retinas from KO mice and pharmacological manipulations in retinal explants, we demonstrate that the timing of the GABA switch in retinal ganglion cells (RGCs) is unaffected by blockade of specific neurotransmitter receptors or global activity. In contrast to RGCs in the intact retina, purified RGCs remain depolarized by GABA, indicating that the GABA switch is not cell-autonomous. Indeed, purified RGCs cocultured with dissociated cells from the superior colliculus or cultured in media conditioned by superior collicular cells undergo a normal switch. Thus, a diffusible signal that acts independent of local circuit activity regulates the maturation of GABAergic inhibition in mouse RGCs.A lthough GABA is the principal inhibitory neurotransmitter in the mature CNS, it is a robust source of excitation during development that is important for many developmental processes (1-4). The transition from excitatory to inhibitory action of GABA has been observed in a number of neural circuits and in many vertebrate species (5, 6) and the primary mechanisms underlying the switch are fairly well understood (7-11; reviewed in refs. 12-14). However, whether the timing of the GABA switch is modulated by local circuit activity (8,(15)(16)(17)(18) or occurs independent of activity (19,20) and is therefore intrinsic to developmental program of the cell remains controversial.Retinal ganglion cells (RGCs) undergo a switch in their response to GABA during the first two postnatal weeks of development (21-23). In vivo recordings in zebrafish demonstrate that the timing of the GABA switch is critical for the timing of the development of light responses (24) and therefore might be linked to the onset of visual experience. Chronic blockade of GABA A receptors (GABA A Rs) in turtle retina prevents the normal maturation of spontaneous firing patterns termed retinal waves and the maturation of adult-like chloride gradients, implicating early GABA signaling in the normal maturation of inhibitory circuits in retina (15). Based on these results, it has been proposed that the maturation of GABAergic inhibition is influenced by local network activity and is critical for the cessation of retinal waves (25).Here we explore factors that influence the timing of the GABA switch in mouse RGCs. By using three different preparations, we test whether the timing of the GABA switch is regulated by (i) local circuit activity in the retina, (ii) an intrinsic developmental program, or (iii) a diffusible, non-cell autonomous factor that operates independent of retinal activity. Results GABA Switch Occurs Normally in Nicotinic Acetylcholine Receptor-KORetinas. The timing of the GABA switch in retinal neurons in the ganglion cell layer (GCL) was determined by calcium imagi...

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“…Because chloride is actively loaded into the cell, primary afferents normally have E anion values near À35 mV. 43,52 Under these conditions, GABA A receptor activation will trigger efflux of both bicarbonate and chloride, leading to PAD. Although depolarization is typically equated with excitation, PAD reduces spike propagation and synaptic transmission in the affected axon, and is therefore inhibitory.…”

Section: Mechanisms Of Inhibitionmentioning

confidence: 99%