Abstract
Ca2+ signaling in astrocytes is considered to be mainly mediated by metabotropic receptors linked to intracellular Ca2+ release. However, recent studies demonstrate a significant contribution of Ca2+ influx to spontaneous and evoked Ca2+ signaling in astrocytes, suggesting that Ca2+ influx might account for astrocytic Ca2+ signaling to a greater extent than previously thought. Here, we investigated AMPA-evoked Ca2+ influx into olfactory bulb astrocytes in mouse brain slices using Fluo-4 and GCaMP6s, respectively. Bath application of AMPA evoked Ca2+ transients in periglomerular astrocytes that persisted after neuronal transmitter release was inhibited by tetrodotoxin and bafilomycin A1. Withdrawal of external Ca2+ suppressed AMPA-evoked Ca2+ transients, whereas depletion of Ca2+ stores had no effect. Both Ca2+ transients and inward currents induced by AMPA receptor activation were partly reduced by Naspm, a blocker of Ca2+-permeable AMPA receptors lacking the GluA2 subunit. Antibody staining revealed a strong expression of GluA1 and GluA4 and a weak expression of GluA2 in periglomerular astrocytes. Our results indicate that Naspm-sensitive, Ca2+-permeable AMPA receptors contribute to Ca2+ signaling in periglomerular astrocytes in the olfactory bulb.
Highlights
Ca2+ signaling in astrocytes is considered to be mainly mediated by metabotropic receptors linked to intracellular Ca2+ release
100 μM Adenosine 5′-triphosphate (ATP) evoked a Ca2+-dependent increase in Fluo-4 fluorescence by 1.34 ± 0.08 ΔF/F0 (n = 53) in periglomerular astrocytes, while in neurons, ATP did not evoke Ca2+ signaling (Fig. 1a). 59.3% of ATP-sensitive astrocytes and all neurons responded to bath application of 50 μM amino-3-hydroxy-5-methyl-4-isoxazolephosphonic acid (AMPA) (Fig. 1a)
We have investigated the role of AMPA receptors in Ca2+ signaling in periglomerular astrocytes of the olfactory bulb
Summary
Ca2+ signaling in astrocytes is considered to be mainly mediated by metabotropic receptors linked to intracellular Ca2+ release. Our results indicate that Naspm-sensitive, Ca2+-permeable AMPA receptors contribute to Ca2+ signaling in periglomerular astrocytes in the olfactory bulb. It has become increasingly evident during the past decade that astrocytes are far more than supportive cells in the brain, but rather take active part in information processing such as synaptic transmission and synaptic plasticity[1,2]. All Ca2+ responses to neurotransmitters measured in olfactory bulb astrocytes were mediated by Ca2+ release from internal stores, while Ca2+ influx from the extracellular space has not been demonstrated so far[17]. The results indicate that olfactory bulb astrocytes possess both GluA2-containing and GluA2-lacking AMPA receptors, the latter being blocked by Naspm
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