NEURONAL INOSITOL 1,4,5-TRISPHOSPHATE RECEPTOR LOCALIZED TO THE PLASMA-MEMBRANE OF OLFACTORY CILIA

Both the cyclic adenosine 3',5'-monophosphate and the phosphoinositide second messenger systems are involved in olfactory signal transductio n. The inositol 1,4,5-trisphosphate receptor is one of the principal i ntracellular calcium channels responsible for mobilizing stored calciu m. The precise location of the 1,4,5-trisphosphate receptor (endoplasm ic reticulum vs surface) and its role in the events of olfactory signa l transduction need to be defined. By light microscopic and confocal i mmunohistochemistry we show expression of the olfactory-enriched G-pro tein, G(olf), associated with cyclic AMP responses, and of the inosito l 1,4,5-trisphosphate receptor in the dendritic projections and cilia of essentially all olfactory receptor neurons, indicating that individ ual neurons express components of both second messenger systems. By im munoelectron microscopy, we demonstrate that the inositol 1,4,5-trisph osphate receptor is localized to the surface membrane of rat olfactory cilia. This is the first morphological demonstration of the surface m embrane localization of inositol 1,4,5-trisphosphate receptor in olfac tory cilia. Our findings, taken in conjunction with electrophysiologic al data from other workers, are supportive of the inositol 1,4,5-trisp hosphate receptor playing a novel role in regulating calcium flux at t he ciliary surface membrane.