FIGURE 6.

Activation of TRPV4 in astrocytes enhances synaptic activity through release of excitatory glutamate. A, a representative trace of mEPSCs in TRPV4KO hippocampal neurons evoked after application of conditioned media from cultured astrocytes. The conditioned media (CM) were prepared after 4αPDD (10 μm) was applied. B, comparison of the amplitude and frequency of evoked mEPSCs to those detected in basal conditions. *, p < 0.01, t test (versus basal). C, a representative trace of the analysis of amino acids present in the conditioned media from WT or TRPV4KO astrocytes exposed to 10 μm 4αPDD. A.U., absorbance units. D, quantification of glutamate release (in basal media or conditioned media from cells exposed to 4αPDD) from WT or TRPV4KO astrocytes. *, p < 0.01, t test (versus WT basal). E and F, currents from NMDA receptor (NMDA-R) biosensor cells (GluN1- and GluN2B-expressing HEK293 cells). The biosensor cells sense glutamate release from TRPV4-positive or -negative astrocytes, which are identified by Ca²⁺ imaging after exposure to 10 μm 4αPDD (F). As a negative control, the mock biosensor cells (HEK293 cells transfected with the pCAG vector) did not display inward currents after 10 μm 4αPDD was applied to TRPV4⁺ astrocytes (E).