Minimal requirements for calcium oscillations driven by the IP3 receptor.
Hormones and neurotransmitters that act through inositol 1,4,5-trisphosphate (IP3) can induce oscillations of cytosolic Ca2+ ([Ca2+]c), which render dynamic regulation of intracellular targets. Imaging of fluorescent Ca2+ indicators located within intracellular Ca2+ stores was used to monitor IP3 receptor channel (IP3R) function and to demonstrate that IP3-dependent oscillations of Ca2+ release and re-uptake can be reproduced in single permeabilized hepatocytes. This system was used to define the minimum essential components of the oscillation mechanism. With IP3 clamped at a submaximal concentration, coordinated cycles of IP3R activation and subsequent inactivation were observed in each cell. Cycling between these states was dependent on feedback effects of released Ca2+ and the ensuing [Ca2+]c increase, but did not require Ca2+ re-accumulation. [Ca2+]c can act at distinct stimulatory and inhibitory sites on the IP3R, but whereas the Ca2+ release phase was driven by a Ca2+-induced increase in IP3 sensitivity, Ca2+ release could be terminated by intrinsic inactivation after IP3 bound to the Ca2+-sensitized IP3R without occupation of the inhibitory Ca2+-binding site. These findings were confirmed using Sr2+, which only interacts with the stimulatory site. Moreover, vasopressin induced Sr2+ oscillations in intact cells in which intracellular Ca2+ was completely replaced with Sr2+. Thus, [Ca2+]c oscillations can be driven by a coupled process of Ca2+-induced activation and obligatory intrinsic inactivation of the Ca2+-sensitized state of the IP3R, without a requirement for occupation of the inhibitory Ca2+-binding site.
Hajnóczky
G
G
Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Thomas
A P
AP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008099:Liver / Q000166:cytology / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D013324:Strontium / Q000378:metabolism; D014667:Vasopressins / Q000494:pharmacology
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D014667:Vasopressins; D015544:Inositol 1,4,5-Trisphosphate; C025700:strontium chloride; D002118:Calcium; D013324:Strontium