The perception of ambient temperature is a physiological process critical to the maintenance of body temperature and the avoidance of dangerous thermal extremes. Among six heat-activated channels, TRPV3 and TRPV4 are identified as warm receptors. In addition, P2X3 receptor, an ATP-gated cation-selective ion channel, was also proposed to have a role in warm sensing. We investigated the effects of warm temperature on intracellular Ca2+ by using three lines of cultured cell, fibroblasts (NIH3T3), neuronal cells (NG108-15) and keratinocytes (M308). The warmth stimulus was applied by increasing the temperature of the bath solution from 32 to 38 °C. M308 cells showed rapid increase of cytosolic Ca2+ in normal bath solution containing Ca2+. Without extracellular Ca2+, slow and reduced response was observed, suggesting contribution of Ca2+ mobilization from intracellular stores. NIH3T3 cells also responded to the warmth in the normal solution, but not in Ca2+-free solution. On the other hand, NG108-15 cells showed both slow Ca2+ influx and mobilization. Immunofluorescence microscopy showed expression of TRPV3 and 4 in M308 but not in NIH 3T3 and NG108-15 cells. The expression of four TRPVs was examined by RT-PCR using primers specific for mouse TRPV1-4. These three line of cells may have distinct Ca2+ influx pathway in response to warmth stimulus. [J Physiol Sci. 2008;58 Suppl:S78]
