title: Role of the inositol 1,4,5-trisphosphate receptor in Ca(2+) feedback inhibition of calcium release-activated calcium current (I(crac)).
abstract: We examined the activation and regulation of calcium release-activated calcium current (I(crac)) in RBL-1 cells in response to various Ca(2+) store-depleting agents. With [Ca(2+)](i) strongly buffered to 100 nM, I(crac) was activated by ionomycin, thapsigargin, inositol 1,4,5-trisphosphate (IP(3)), and two metabolically stable IP(3) receptor agonists, adenophostin A and L-alpha-glycerophospho-D-myoinositol-4,5-bisphosphate (GPIP(2)). With minimal [Ca(2+)](i) buffering, with [Ca(2+)](i) free to fluctuate I(crac) was activated by ionomycin, thapsigargin, and by the potent IP(3) receptor agonist, adenophostin A, but not by GPIP(2) or IP(3) itself. Likewise, when [Ca(2+)](i) was strongly buffered to 500 nM, ionomycin, thapsigargin, and adenophostin A did and GPIP(2) and IP(3) did not activate detectable I(crac). However, with minimal [Ca(2+)](i) buffering, or with [Ca(2+)](i) buffered to 500 nM, GPIP(2) was able to fully activate detectable I(crac) if uptake of Ca(2+) intracellular stores was first inhibited. Our findings suggest that when IP(3) activates the IP(3) receptor, the resulting influx of Ca(2+) quickly inactivates the receptor, and Ca(2+) is re-accumulated at sites that regulate I(crac). Adenophostin A, by virtue of its high receptor affinity, is resistant to this inactivation. Comparison of thapsigargin-releasable Ca(2+) pools following activation by different IP(3) receptor agonists indicates that the critical regulatory pool of Ca(2+) may be very small in comparison to the total IP(3)-sensitive component of the endoplasmic reticulum. These findings reveal new and important roles for IP(3) receptors located on discrete IP(3)-sensitive Ca(2+) pools in calcium feedback regulation of I(crac) and capacitative calcium entry.
authors.affiliation: Laboratory of Signal Transduction, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA. broad@niehs.nih.gov
authors.forename: L M
authors.initials: LM
authors.lastname: Broad
authors.forename: D L
authors.initials: DL
authors.lastname: Armstrong
authors.forename: J W
authors.initials: JW
authors.lastname: Putney
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005246:Feedback; D005453:Fluorescence; D016257:Fura-2 / Q000737:chemistry; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: C087840:1-(glycerophosphoryl)-myo-inositol 4,5-diphosphate P(4(5))-1-(2-nitrophenyl)ethyl ester; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D007476:Ionophores; D018160:Receptors, Cytoplasmic and Nuclear; C085029:adenophostin A; D015759:Ionomycin; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D000241:Adenosine; D002118:Calcium; D016257:Fura-2