Intracellular Ca2+ store-operated influx of Ca2+ through TRP-R, a rat homolog of TRP, expressed in Xenopus oocytes.

To elucidate whether rat transient receptor potential (TRP-R), a rat TRP4 homolog, functions as a store-operated Ca2+ channel (SOC), we have measured the Ca2+ entry after thapsigargin treatment in Xenopus oocytes injected with mRNA for TRP-R. While non-injected oocytes elicited an SOC response, significantly larger responses were observed in the oocytes expressing TRP-R. The oocyte-native SOC response was inhibited by injection of antisense oligodeoxyribonucleotide for mammalian TRP1. When Ca2+ concentration-SOC response curve was examined, the EC50 value was much smaller in oocytes expressing TRP-R than that of non-injected oocytes. These results suggest that TRP-R functions as SOC having higher sensitivity to external Ca2+ than amphibian TRP1 channel.