Abstract
We have reported that a thermosensitive-TRP channel, TRPV4 (activated by >35°C heat) is expressed in hippocampal neurons, and enhances the neural activities through its activation at body temperature. We also observed the TRPV4 mRNA expression in astrocytes. We hypothesized that TRPV4 might be an important ion channel to regulate the excitability of astrocytes. We prepared the cultured astrocytes, and examined the cellular distribution of TRPV4. TRPV4 mRNA and protein were observed in only subsets of the astrocytes, indicating that we can classify the characteristics of astrocytes dependings on the TRPV4 expression. We also examined whether functional-TRPV4 was expressed in the astrocytes by a Ca2+ imaging method with Fura2. The subsets of astrocytes responded to the all reported stimulus (heat, hypotonicity and 4αPDD, which is a TRPV4 specific agonist). Following the increased calcium level in only subsets of astrocytes, significant calcium oscillations were observed in among most of the astrocytes, indicating that communications among astrocytes were initiated through the TRPV4 activations. We hypothesized that the calcium oscillations among astrocytes might be a critical determinant to regulate the neural activities. Therefore, we examined how astrocytes communicate each other. Upon activation of TRPV4 by 4αPDD in astrocytes, we used a biosensor method, in which the HEK293 cells expressing various neurotransmitter receptors were used to detect the neurotransmitter release using a whole-cell patch-clamp method. [J Physiol Sci. 2007;57 Suppl:S82]
