Xestospongin C is a marine natural product which was first isolated from Pacific basin sponges, and noted to have vasodilatory properties. Xestospongin C antagonizes the calcium-releasing action of inositol-1,4,5-trisphosphate (IP3) at the receptor level. Inositol phosphates are important signal transduction messengers acting via IP3 receptors to promote the mobilization of Ca2+ from intracellular stores. Xestospongin C blocks the increase in intracellular calcium in vascular smooth muscle cells completely at a concentration of 25 μM. Xestospongin C also inhibits the sarcoplasmic reticulum Ca2+ ATPase pump at concentrations of 700 nM.
