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Kinetics of calcium channel opening by inositol 1,4,5-trisphosphate.
- Source :
-
Biochemistry [Biochemistry] 1990 Jan 09; Vol. 29 (1), pp. 32-7. - Publication Year :
- 1990
-
Abstract
- The subsecond mobilization of intracellular Ca2+ by IP3 was measured with rapid mixing techniques to determine how cells achieve rapid rises in cytosolic [Ca2+] during receptor-triggered calcium spiking. In permeabilized rat basophilic leukemia cells at 11 degrees C, more than 80% of the 0.7 fmol of Ca2+/cell sequestered by the ATP-driven pump could be released by IP3. Half of the stored Ca2+ was released within 200 ms after addition of saturating (1 microM) IP3. The flux rate was half-maximal at 120 nM IP3. Ca2+ release from fully loaded stores was highly cooperative; the Hill coefficient over the 2-40 nM range was greater than 3. The delay time of channel opening was inversely proportional to [IP3], increasing from 150 ms at 100 nM IP3 to 1 s at 15 nM, indicating that the rate-limiting step in channel opening is IP3 binding. Multiple binding steps are required to account for the observed delay and nonexponential character of channel opening. A simple model is proposed in which the binding of four IP3 molecules to identical and independent sites leads to channel opening. The model agrees well with the data for KD = 18 nM, kon = 1.2 X 10(8) M-1 s-1, and koff = 2.2 s-1. The approximately 1-s exchange time of bound IP3 indicates that the channel gating sites are distinct from binding sites having approximately 100-s exchange times that were previously found with radiolabeled IP3. The approximately 1-1s response time of [Ca2+] to a rapid increase in IP3 level can account for observed rise times of calcium spikes.
- Subjects :
- Animals
Binding Sites
Calcium metabolism
Cyclic Nucleotide-Gated Cation Channels
Dose-Response Relationship, Drug
Eye Proteins physiology
Homeostasis
Ion Channels physiology
Kinetics
Models, Biological
Rats
Receptors, Cholinergic physiology
Receptors, Nicotinic physiology
Rod Cell Outer Segment ultrastructure
Time Factors
Calcium Channels physiology
Inositol 1,4,5-Trisphosphate metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 0006-2960
- Volume :
- 29
- Issue :
- 1
- Database :
- MEDLINE
- Journal :
- Biochemistry
- Publication Type :
- Academic Journal
- Accession number :
- 1691015
- Full Text :
- https://doi.org/10.1021/bi00453a004