The sigma-1 receptor antagonist PB212 reduces the Ca2+-release through the inositol (1, 4, 5)-trisphosphate receptor in SK-N-SH cells

Abstract

Sigma-1 receptors are specifically located at the endoplasmic reticulum–mitochondrion interface, but upon stimulation by ligands or under prolonged cellular stress, they translocate to other areas of the cell. Sigma-1 receptors are involved in the regulation of intracellular [Ca2+] by affecting the Ca2+-influx or the release from intracellular stores. In SK-N-SH cells, we measured the affinity of 4-methyl-1-[4-(6-methoxynaphthalen-1-yl)butyl]piperidine (PB212) at sigma-1 receptor by using a competition binding assay with specific radioligand; we obtained a Ki value=316±19nM. PB212 also showed an antiproliferative effect in SK-N-SH cells (EC50=32±4μM) but had no effect in MCF7 cells, which only express sigma-2 receptor; these findings suggest that PB212 behaves as a sigma-1 receptor antagonist. We have studied the effect of PB212 on Ca2+ homeostasis of the SK-N-SH cell line with the fluorescent probe Fura-2. 100μM PB212 induced a Ca2+-efflux from the endoplasmic reticulum through the inositol (1, 4, 5)-trisphosphate (IP3) receptor. Moreover, [PB212] ranging from 1 to 100μM reduced the Ca2+-response, triggered by carbachol or bradykinin that engage the phospholipase C/IP3 pathway; such a response is generally increased by sigma-1 receptor agonists. On the other hand, PB212 did not reduce the Ca2+-response mediated by IP3 in LoVo cells, which do not express neither sigma-1 nor sigma-2 receptors, and in MCF7 cells. The fact that the activity of the sigma-1 receptor can be experimentally modulated by agonists and antagonists supports the intriguing hypothesis that some endogenous molecules, unknown at the moment, modulate the sigma-1 receptor and its cellular targets.