Identification of protein homologous to inositol trisphosphate receptor inciliate Blepharisma

The protozoan ciliate Blepharisma japonicum is thought to utilize an enzyma tic cascade in light signal transduction and inositol trisphosphate seems t o he one of the messengers that causes the cells' electrical and behavioura l responses. We have examined the presence and localization of putative ino sitol trisphosphate receptor (InsP(3)R) in the cell by means of confocal mi croscopy and immunoblotting to further elucidate the possible involvement o f the phosphoinositide signaling pathway in phototransduction of ciliate ce lls. The immunohistochemical examination indicated that the InsP(3)-binding sites are expressed in abundance exclusively in the cortex later of the ce ll and are spread over the entire cell body. The localization of InsP(3)R, primarily in the cortex of Blepharisma, was also revealed by immunoblot ana lysis which clearly showed the existence of InsP(3)R-like proteins of molec ular mass above 200 kDa in the cell cortex fraction. This is the first demo nstration of the existence of InsP(3)R in ciliated protozoa and its morphol ogical localization within the cell. The results presented. along with our earlier data, support further the possibility of participation of the phosp hoinositide second messenger system in light signal transduction in Blephar isma cells.