TRPA1 Is Expressed in Central But Not in Peripheral Glia

TRPA1 are cation channels expressed in sensory neurons and in several other cell types. This channel is specifically activated by ally isothiocyanate (AITC), the pungent component of mustard oil, as well as by other electrophilic compounds. Although TRPA1 expression in central glia has been reported, its subcellular localization and its expression in peripheral glia have not been investigated before. In this paper we report the molecular and functional expression of TRPA1 in rat cortical astrocytes. Real-time RT-PCR identified low but significant amounts of TRPA1 mRNA in cortical astrocytes while no signal was seen in peripheral glia isolated from dorsal root ganglia (DRG) or in a glial cell line (DITNC-1). Calcium imaging showed AITC-induced signals in astro-cytes while no response in peripheral glia. AITC induced calcium signals in astrocytes in the presence and in the absence of extracellular calcium, suggesting an intracellular localization of TRPA1 channels. Whole cell electrophysiological recordings were performed in astrocytes, in peripheral glia and in DITNC-1 cells transfected with TRPA1 during AITC application. In TRPA1-transfected DITNC-1 cells typical TRPA1 currents were recorded with a reversal potential near 0 mV, consistent with the opening of a non-selective cation channel. No such currents were recorded in untransfected DITNC-1 cells, in astrocytes and in peripheral glial cells, where even high concentrations of AITC (up to 10 mM) induced no significant outward current. In astrocytes AITC transiently induced an outward rectifying current with the reversal potential near ?90 mV, consistent with K channel activation, likely activated by intracellular release of calcium. Our results suggest that TRPA1 channels are molecularly and functionally expressed in calcium-containing organelles of rat cortical astrocytes, with no expression in the plasma membrane.