Inositol 1,3,4,5-tetrakisphosphate as a second messenger—a special role in neurones?

There has been much controversy over the possibility that inositol 1,3,4,5-tetrakisphosphate (Ins P 4) may have a second messenger function. A possible resolution to this controversy may stem from the recent cloning of two putative receptors for Ins P 4, GAP1 IP4BP and GAP1m. Both these proteins are expressed at high levels in neurones, as is inositol 1,4,5-trisphosphate 3-kinase, the enzyme that makes Ins P 4. In this review we discuss the possible relevance of these high expression levels to the complex way in which neurones control Ca 2+ and use it as a second messenger.