Analysis of IP3 receptors in and out of cells.
BACKGROUND
Inositol 1,4,5-trisphosphate receptors (IP3R) are expressed in almost all animal cells. Three mammalian genes encode closely related IP3R subunits, which assemble into homo- or hetero-tetramers to form intracellular Ca2+ channels.


OBJECTIVE
In this brief review, we first consider a variety of complementary methods that allow the links between IP3 binding and channel gating to be defined. How does IP3 binding to the IP3-binding core in each IP3R subunit cause opening of a cation-selective pore formed by residues towards the C-terminal? We then describe methods that allow IP3, Ca2+ signals and IP3R mobility to be examined in intact cells. A final section briefly considers genetic analyses of IP3R signalling.


CONCLUSIONS
All IP3R are regulated by both IP3 and Ca2+. This allows them to initiate and regeneratively propagate intracellular Ca2+ signals. The elementary Ca2+ release events evoked by IP3 in intact cells are mediated by very small numbers of active IP3R and the Ca2+-mediated interactions between them. The spatial organization of these Ca2+ signals and their stochastic dependence on so few IP3Rs highlight the need for methods that allow the spatial organization of IP3R signalling to be addressed with single-molecule resolution.


CONCLUSIONS
A variety of complementary methods provide insight into the structural basis of IP3R activation and the contributions of IP3-evoked Ca2+ signals to cellular physiology. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signaling.
Department of Pharmacology, Cambridge, UK.
Ana M
AM
Rossi
Stephen C
SC
Tovey
Taufiq
T
Rahman
David L
DL
Prole
Colin W
CW
Taylor
D000818:Animals; D001665:Binding Sites; D020013:Calcium Signaling; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000502:physiology; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials; D008856:Microscopy, Fluorescence; D018408:Patch-Clamp Techniques; D021381:Protein Transport; D059010:Single-Cell Analysis
D053496:Inositol 1,4,5-Trisphosphate Receptors; D015544:Inositol 1,4,5-Trisphosphate