Monovalent cation channel required for maintenance of rapid intracellular calcium release. May act as a potassium counter-ion channel that functions in synchronization with calcium release from intracellular stores. Homotrimer; trimerization probably requires binding to phosphatidylinositol 4,5-bisphosphate (PIP2). Widely expressed. Mice are neonatal lethal. Mice lacking Tmem38a and Tmem38b show a weak heartbeat at E9.5 followed by loss of cardiomyocyte viability and embryonic lethality around 10.5 dpc. Belongs to the TMEM38 family.