This chapter describes the current state of knowledge regarding the mechanisms and physiological ramifications of 1,4,5-trisphosphate receptor (IP3R) regulation by phosphorylation and ATP binding. Phosphorylation by various kinases represents a common mode of ion channel regulation. The transfer of phosphate allows rapid, reversible modification of channel function not provided by changes in gene transcription, which are more energetically demanding. Similar to other ion channels, IP3R are phosphorylated by several ser/thr kinases and tyr kinases that comprise the two major classes of mammalian protein kinases. Protein kinase (PKA) is activated by increases in the second messenger cyclic adenosine monophosphate (cAMP), and phosphorylation of IP3R allows interplay or crosstalk between the ubiquitous cAMP and Ca2+ signaling pathways. Other second messenger activated serine/threonine kinases, including cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG), protein kinase C (PKC), and Ca2+–calmodulin-activated kinase II (CaMKII) have been shown to phosphorylate IP3R1. PKG phosphorylates IP3R1 at the same residues as PKA but the functional effects of direct PKG phosphorylation were distinct from those of PKA phosphorylation.
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