Separation and Characterization of Currents through Store-operated CRAC Channels and Mg2+-inhibited Cation (MIC) Channels
Open Access
- 29 April 2002
- journal article
- Published by Rockefeller University Press in The Journal of general physiology
- Vol. 119 (5) , 487-508
- https://doi.org/10.1085/jgp.20028551
Abstract
Although store-operated calcium release–activated Ca2+(CRAC) channels are highly Ca2+-selective under physiological ionic conditions, removal of extracellular divalent cations makes them freely permeable to monovalent cations. Several past studies have concluded that under these conditions CRAC channels conduct Na+and Cs+with a unitary conductance of ∼40 pS, and that intracellular Mg2+modulates their activity and selectivity. These results have important implications for understanding ion permeation through CRAC channels and for screening potential CRAC channel genes. We find that the observed 40-pS channels are not CRAC channels, but are instead Mg2+-inhibited cation (MIC) channels that open as Mg2+is washed out of the cytosol. MIC channels differ from CRAC channels in several critical respects. Store depletion does not activate MIC channels, nor does store refilling deactivate them. Unlike CRAC channels, MIC channels are not blocked by SKF 96365, are not potentiated by low doses of 2-APB, and are less sensitive to block by high doses of the drug. By applying 8–10 mM intracellular Mg2+to inhibit MIC channels, we examined monovalent permeation through CRAC channels in isolation. A rapid switch from 20 mM Ca2+to divalent-free extracellular solution evokes Na+current through open CRAC channels (Na+-ICRAC) that is initially eightfold larger than the preceding Ca2+current and declines by ∼80% over 20 s. Unlike MIC channels, CRAC channels are largely impermeable to Cs+(PCs/PNa= 0.13 vs. 1.2 for MIC). Neither the decline in Na+-ICRACnor its low Cs+permeability are affected by intracellular Mg2+(90 μM to 10 mM). Single openings of monovalent CRAC channels were not detectable in whole-cell recordings, but a unitary conductance of 0.2 pS was estimated from noise analysis. This new information about the selectivity, conductance, and regulation of CRAC channels forces a revision of the biophysical fingerprint of CRAC channels, and reveals intriguing similarities and differences in permeation mechanisms of voltage-gated and store-operated Ca2+channels.Keywords
This publication has 43 references indexed in Scilit:
- Dissociation of the store‐operated calcium current ICRAC and the Mg‐nucleotide‐regulated metal ion current MagNuMThe Journal of Physiology, 2002
- Potentiation and inhibition of Ca2+ release‐activated Ca2+ channels by 2‐aminoethyldiphenyl borate (2‐APB) occurs independently of IP3 receptorsThe Journal of Physiology, 2001
- Calcium Signaling Mechanisms in T LymphocytesAnnual Review of Immunology, 2001
- Plasma Membrane Ca2+ Release-Activated Ca2+ Channels With A High Selectivity for Ca2+ Identified by Patch–Clamp Recording in Rat Liver CellsHepatology, 2001
- TRP-PLIK, a Bifunctional Protein with Kinase and Ion Channel ActivitiesScience, 2001
- Stable Activation of Single Ca2+ Release-activated Ca2+ Channels in Divalent Cation-free SolutionsPublished by Elsevier ,2001
- Requirement of the Inositol Trisphosphate Receptor for Activation of Store-Operated Ca 2+ ChannelsScience, 2000
- Regulation of cellular magnesiumFrontiers in Bioscience-Landmark, 2000
- Single-channel properties of a volume-sensitive anion conductance. Current activation occurs by abrupt switching of closed channels to an open state.The Journal of general physiology, 1995
- Calcium channel selectivity for divalent and monovalent cations. Voltage and concentration dependence of single channel current in ventricular heart cells.The Journal of general physiology, 1986