IP3 receptors are proteins found in the membranes of cells that play a crucial role in cellular signaling. They are activated by a molecule called inositol trisphosphate (IP3), which is produced when certain signals, like hormones, bind to cell surface receptors. Once activated, IP3 receptors release calcium ions from the endoplasmic reticulum into the cytoplasm, leading to various cellular responses. These receptors are important in many physiological processes, including muscle contraction, neurotransmitter release, and cell growth. Dysregulation of IP3 receptor function can contribute to various diseases, making them a significant focus of research in cell biology and pharmacology.