SIGMA-RECEPTORS (“σ-RECEPTORS”)

Sigma receptors were discovered by Martin et al. 1976 and were first classified as a subtype of opioid receptors. Later the availability of newer and more selective ligands established sigma receptors as distinct from opiate receptors or the phencyclidine (PCP) binding site. Based on the specific pharmacological characteristics of the sigma ligands, sigma receptors were further divided into two subtypes denoted sigma-1 and sigma-2. The sigma receptors and its agonists have been implicated in many cellular functions, biological processes and diseases. Although the exact molecular functions of sigma receptors are not fully defined and the endogenous ligand(s) still not known, there is evidence for a role of sigma receptors in regulation of neurotransmitter release, modulation of neurotransmitter receptor function, endocrine and immune system functions or apoptosis and, therefore, in movement and posture, in psychosis, in learning and memory or in cancer.

Sigma Receptors’ Interactions with Ion Channels

The most prominent action of sigma receptors in biological systems including cell lines, primary cultures, and animals is the regulation and modulation of voltage-regulated and ligand-gated ion channels, including Ca2^+-, K^+-, Na⁺, Cl^-, and SK channels, and NMDA and IP3 receptors. The final output of the action of sigma receptor agonists is to inhibit all above-mentioned voltage-gated ion channels, while they potentiate ligand-gated channels.
Source: The Pharmacology of Sigma-1 receptors, Anavex publications

The Role of Sigma-1 Receptor in Neurological Diseases

Originally considered an enigmatic protein, the sigma-1 receptor has recently been identified as a unique ligand-regulated molecular chaperone in the endoplasmic reticulum of cells. This discovery causes to look back at the many proposed roles of this receptor, even before its molecular function was identified, in many neurological diseases such as Alzheimer's disease, amnesia, pain, depression, schizophrenia, and retinal neuroprotection.
Source: The Pharmacology of Sigma-1 receptors, Anavex publications

The Role of Sigma-1 and Sigma-2 Receptors in Cancer

The discovery of the presence of sigma-1 and sigma-2 receptors in many human and rodent cell lines opens up this new area of cancer research, which is the most attractive for sigma-2 receptors. The most prominent fact is the involvement of these receptors in the death signalling of cancer cells.
Source: The Pharmacology of Sigma-1 receptors, Anavex publications