title: Intracellular receptor
text: # Intracellular receptor
  
  Intracellular receptors are globular protein receptors located inside the cell rather than on its cell membrane. The word intracellular means "within or inside a cell". Molecules that cross a cell membrane to bind with a receptor are generally nonpolar and may be relatively small. These molecules are also known as ligands. Hormones that use intracellular receptors include thyroid, aldosterone, and steroid hormones.
  
  Examples are the class of nuclear receptors located in the cell nucleus and cytoplasm and the $IP_3$ receptor located on the endoplasmic reticulum. The ligands that bind to them are usually intracellular second messengers like inositol trisphosphate $(IP_3)$ and extracellular lipophilic hormones like steroid hormones. Some intracrine peptide hormones also have intracellular receptors.
  
  ## Examples
  
  * transcription factors
     * nuclear receptors
  * other
     * $Sigma_1$ (neurosteroids)
     * $IP_3$ receptor (inositol triphosphate, $IP_3)$
  