This project delineates biochemical and pharmacological properties of sigma-1 receptors. Sigma-1 receptors are one-transmembrane proteins at the endoplasmic reticulum (ER) that bind neurosteroids, dextrobenzomorphans, and certain psychostimulants such as cocaine. In this fiscal year, we found that sigma-1 receptors form a trimeric complex with IP3 receptors and a cytoskeletal adaptor protein ankyrin on the ER. This was demonstrated by Western blotting and confocal microscopy. Further, neurosteroids and cocaine cause the dissociation of sigma-1 receptor/ankyrin as a complex from the IP3 receptors on the ER. The sigma-1 receptor/ankyrin complex translocates to the plasmalemmal regions and the nucleus. The dissociation of the complex also increases the IP3 affinity for IP3 receptors, thus causing an efflux of calcium from ER into the cytosol. The sigma-1 receptor antagonist NE-100 blocks the dissociation of the sigma-1/ankyrin from the ER and, as a result, blocks the calcium efflux from the ER. Immunocytohistochemistry demonstrated that sigma-1 receptors, ankyrins, and IP3 receptors are co-localized in high density in the smooth ER, the cell-cell contact regions, and growth cones. These results suggest that the intracellular signaling pathways of sigma-1 receptors may encompass the mobilization of intracellular calcium and the alteration of the dynamics of cytoskeletal proteins. The results also suggest that psychostimulants like cocaine may exert life-long effects, at least partly, via cytoskeletal proteins through an interaction with sigma-1 receptors.
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