Ca2+イメージセンサーを用いた海馬の細胞外Ca²⁺の可視化

抄録

Extracellular calcium ion ([Ca²⁺]o) change occurring during physiological and pathological conditions play important roles in regulation of brain functions, but has received limited attention due to the lack of easy to use device. Here, we show the development and application of highly selective calcium image sensor for the imaging of glutamate-induced [Ca²⁺]o change in hippocampal slices. Using this sensor, we found that glutamate decreased [Ca²⁺]o by more than 50 % with different spatiotemporal patterns. The glutamate-evoked decrease in [Ca²⁺]o was inhibited by a NMDA receptor antagonist D-AP5 but not AMPA receptor antagonist CNQX, and mimicked by NMDA. The spatial pattern of the glutamate-evoked [Ca²⁺]o decrease was associated with that of distribution of NMDA receptors in the hippocampus. Moreover, using an ATP-imaging fluorescent probe, we found that the stimulation with NMDA triggered increase in ATP release from astrocytes via either connexin hemichannels or chloride channels. The NMDA-evoked ATP release was mediated by decrease in [Ca²⁺]o because the astrocytic ATP release was mimicked by Ca²⁺-free medium. Taken together, using the newly developed Ca²⁺ image sensor, we demonstrated that [Ca²⁺]o is dramatically decreased during excitatory synaptic transmission by glutamate, and [Ca²⁺]o decrease act as a signal that transmits neuronal excitation to astrocytes via ATP release. The application of this Ca²⁺ sensor is expected to clarify the physiological and pathophysiological roles of [Ca²⁺]o , which have received limited attention so far.