Ca-permeable AMPA receptors in mouse olfactory bulb astrocytes.

Ca signaling in astrocytes is considered to be mainly mediated by metabotropic receptors linked to intracellular Ca release. However, recent studies demonstrate a significant contribution of Ca influx to spontaneous and evoked Ca signaling in astrocytes, suggesting that Ca influx might account for astrocytic Ca signaling to a greater extent than previously thought. Here, we investigated AMPA-evoked Ca influx into olfactory bulb astrocytes in mouse brain slices using Fluo-4 and GCaMP6s, respectively. Bath application of AMPA evoked Ca transients in periglomerular astrocytes that persisted after neuronal transmitter release was inhibited by tetrodotoxin and bafilomycin A1. Withdrawal of external Ca suppressed AMPA-evoked Ca transients, whereas depletion of Ca stores had no effect. Both Ca transients and inward currents induced by AMPA receptor activation were partly reduced by Naspm, a blocker of Ca-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, Ca-permeable AMPA receptors contribute to Ca signaling in periglomerular astrocytes in the olfactory bulb.