Research ArticleCalcium signaling

All three IP3 receptor isoforms generate Ca2+ puffs that display similar characteristics

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Sci. Signal.  18 Dec 2018:
Vol. 11, Issue 561, eaau0344
DOI: 10.1126/scisignal.aau0344

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Different isoforms, similar Ca2+ puffs

Cells express three different isoforms of the inositol trisphosphate receptor (IP3R), which underlie Ca2+ signals ranging from local puffs to global waves. Lock et al. used CRISPR-Cas9 gene editing to create HEK-293 cell lines that expressed individual IP3R isoforms. Despite their reported divergent functional properties, each isoform produced Ca2+ puffs with similar characteristics. Future work is required to determine how these conserved Ca2+ puffs give rise to different global Ca2+ signals.

Abstract

Inositol 1,4,5-trisphosphate (IP3) evokes Ca2+ release through IP3 receptors (IP3Rs) to generate both local Ca2+ puffs arising from concerted openings of clustered IP3Rs and cell-wide Ca2+ waves. Imaging Ca2+ puffs with single-channel resolution yields information on the localization and properties of native IP3Rs in intact cells, but interpretation has been complicated because cells express varying proportions of three structurally and functionally distinct isoforms of IP3Rs. Here, we used TIRF and light-sheet microscopy to image Ca2+ puffs in HEK-293 cell lines generated by CRISPR-Cas9 technology to express exclusively IP3R type 1, 2, or 3. Photorelease of the IP3 analog i-IP3 in all three cell lines evoked puffs with largely similar mean amplitudes, temporal characteristics, and spatial extents. Moreover, the single-channel Ca2+ flux was similar among isoforms, indicating that clusters of different IP3R isoforms contain comparable numbers of active channels. Our results show that all three IP3R isoforms cluster to generate local Ca2+ puffs and, contrary to findings of divergent properties from in vitro electrophysiological studies, display similar conductances and gating kinetics in intact cells.

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