Itpr3 (rat, Q63269) - manual literature synthesis

No deep-research API was available; this synthesis was compiled by hand from the cached
publications in publications/ and the UniProt record (Itpr3-uniprot.txt).

Identity and structure

• Rat IP3R3 is 2,670 residues with ~62-64% identity to IP3R1/IP3R2 and eight predicted membrane-spanning
  segments at the C-terminus PMID:8388391.
• UniProt: N-terminal cytoplasmic domain, juxtamembrane domain and TM domain; homotetramer by similarity;
  IP3-, Ca2+-, ATP- and Zn2+-binding residues by similarity to human ITPR3 (Q14573) structures
  [file:rat/Itpr3/Itpr3-uniprot.txt "Homotetramer (By similarity)."].

Channel activity

• Recombinant rat IP3R3 recorded in planar bilayers: 74-80 pS, open probability 30-40%, apparent IP3 affinity 0.40 microM,
  low-affinity cooperative ATP site PMID:15533917.
• Rat IP3R3 recorded in the native ER/outer nuclear membrane of Xenopus oocytes; >90% of channels were rat homotetramers
  PMID:10694253.
• Ligand binding: IP3 > Ins(1,3,4,5)P4 > InsP6 PMID:8388391.

Regulation

• PKA phosphorylates IP3R3 in RINm5F cells and increases IP3 binding and Ca2+ release
  PMID:17373911.
• PKC phosphorylation reduces IP3R3 activity PMID:17320950.
• cAMP sensitises all IP3R subtypes, including rat IP3R3, independently of PKA PMID:20189985.
• Bok binds IP3R3 only weakly PMID:23884412.

Location

• ER: recombinant IP3R3 in ER PMID:8388391; RINm5F IP3R3 co-fractionates with calnexin
  PMID:19116207; FRAP shows free diffusion in ER membranes
  [PMID:15537642; PMID:21550988 "IP(3)R1 and IP(3)R3 were uniformly distributed within the membranes of the endoplasmic reticulum (ER)"].
• Apical concentration in intestinal epithelium PMID:8288584.
• Neuronal terminals in rat forebrain; Schwann cells [PMID:10096607; PMID:17091480].

Tissue distribution

• Predominant subtype in rat islets and RINm5F cells [PMID:8388391; PMID:17320950 "RINm5F cells who express almost exclusively (approximately 90%) the IP3R-3"].
• Dominant IP3R of rat colonic epithelium PMID:18005397.