McCarron, John G. and Chalmers, Susan and Wilson, Calum and Sandison, Mairi E. (2016) Calcium mobilization via intracellular ion channels, store organization and mitochondria in smooth muscle. In: Vascular Ion Channels

In smooth muscle, Ca release from the internal store into the cytoplasm occurs via inositol trisphosphate (IP3R) and ryanodine receptors (RyR). The internal Ca stores containing IP3R and RyR may be arranged as multiple separate compartments with various IP3R and RyR arrangements, or there may be a single structure containing both receptors. The existence of multiple stores is proposed to explain several physiological responses which include the progression of Ca waves, graded Ca release from the store and various local responses and sensitivities. We suggest that, rather than multiple stores, a single luminally-continuous store exists in which Ca is in free diffusional equilibrium throughout. Regulation of Ca release via IP3R and RyR by the local Ca 2+ concentration within the stores explains the apparent existence of multiple stores and physiological processes such as graded Ca release and Ca waves. Close positioning of IP3R on the store with mitochondria or with receptors on the plasma membrane creates ‘IP3 junctions’ to generate local responses on the luminally-continuous store.