Ion changes and signalling in perisynaptic glia.
ABSTRACT The maintenance of ion gradients across plasma membranes is a prerequisite for the establishment of cellular membrane potentials, electrical signalling, and metabolite transport. At active synapses, pre- and postsynaptic ion gradients are constantly challenged and used for signalling purposes. Perisynaptic glia, mainly represented by fine processes of astrocytes which get into close vicinity to neuronal synapses, are required to normalize the extracellular ionic milieu and maintain ion gradients. On the other hand, perisynaptic glia itself is activated by synaptically released transmitters binding to plasma membrane receptors and transmitter carriers, and experiences significant ion changes as well. In this review we present an overview of dynamic changes of the major ion species in astrocytes in response to neuronal, especially synaptic, activity. We will focus on calcium, sodium, and proton/hydroxyl ions that play key roles in signalling processes, and will discuss the functional consequences of the glial ion signals and homeostatic processes for synaptic transmission.
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ABSTRACT: Background Voltage-sensitive dye (VSD) imaging and intrinsic optical signals (IOS) are widely used methods for monitoring spatiotemporal neural activity in extensive networks. In spite of that, identification of their major cellular and molecular components has not been concluded so far. Results We addressed these issues by imaging spatiotemporal spreading of IOS and VSD transients initiated by Schaffer collateral stimulation in rat hippocampal slices with temporal resolution comparable to standard field potential recordings using a 464-element photodiode array. By exploring the potential neuronal and astroglial molecular players in VSD and IOS generation, we identified multiple astrocytic mechanisms that significantly contribute to the VSD signal, in addition to the expected neuronal targets. Glutamate clearance through the astroglial glutamate transporter EAAT2 has been shown to be a significant player in VSD generation within a very short (<5 ms) time-scale, indicating that astrocytes do contribute to the development of spatiotemporal VSD transients previously thought to be essentially neuronal. In addition, non-specific anion channels, astroglial K+ clearance through Kir4.1 channel and astroglial Na+/K+ ATPase also contribute to IOS and VSD transients. Conclusion VSD imaging cannot be considered as a spatially extended field potential measurement with predominantly neuronal origin, instead it also reflects a fast communication between neurons and astrocytes.Molecular Brain 06/2015; 8. DOI:10.1186/s13041-015-0127-9 · 4.35 Impact Factor
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ABSTRACT: Astroglial excitability is based on highly spatio-temporally coordinated fluctuations of intracellular ion concentrations, among which changes in Ca(2+) and Na(+) take the leading role. Intracellular signals mediated by Ca(2+) and Na(+) target numerous molecular cascades that control gene expression, energy production and numerous homeostatic functions of astrocytes. Initiation of Ca(2+) and Na(+) signals relies upon plasmalemmal and intracellular channels that allow fluxes of respective ions down their concentration gradients. Astrocytes express several types of TRP channels of which TRPA1 channels are linked to regulation of functional expression of GABA transporters, whereas TRPV4 channels are activated following osmotic challenges and are up-regulated in ischaemic conditions. Astrocytes also ubiquitously express several isoforms of TRPC channels of which heteromers assembled from TRPC1, 4 and/or 5 subunits that likely act as stretch-activated channels and are linked to store-operated Ca(2+) entry. The TRPC channels mediate large Na(+) fluxes that are associated with the endoplasmic reticulum Ca(2+) signalling machinery and hence coordinate Na(+) and Ca(2+) signalling in astroglia.Ergebnisse der Physiologie 06/2013; DOI:10.1007/112_2013_15 · 3.90 Impact Factor