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Circ Res. 2011 Sep 16;109(7):729-38. doi: 10.1161/CIRCRESAHA.111.247148. Epub 2011 Aug 11.

Fluorescence resonance energy transfer-based sensor Camui provides new insight into mechanisms of calcium/calmodulin-dependent protein kinase II activation in intact cardiomyocytes.

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Department of Pharmacology, University of California, Davis, CA 95616-8636, USA.



Calcium/calmodulin-dependent protein kinase II (CaMKII) is a key mediator of intracellular signaling in the heart. However, the tools currently available for assessing dynamic changes in CaMKII localization and activation in living myocytes are limited.


We use Camui, a novel FRET-based biosensor in which full-length CaMKII is flanked by CFP and YFP, to measure CaMKII activation state in living rabbit myocytes.


We show that Camui and mutant variants that lack the sites of CaMKII autophosphorylation (T286A) and oxidative regulation (CM280/1VV) serve as useful biosensors for CaMKII╬┤ activation state. Camui (wild-type or mutant) was expressed in isolated adult cardiac myocytes, and localization and CaMKII activation state were determined using confocal microscopy. Camui, like CaMKII╬┤, is concentrated at the z-lines, with low baseline activation state. Camui activation increased directly with pacing frequency, but the maximal effect was blunted with the T286A, consistent with frequency-dependent phosphorylation of CaMKII at T286 mainly at high-frequency and high-amplitude Ca transients. Camui was also activated by 4 neurohormonal agonists. Angiotensin II and endothelin-1 activated Camui, largely through an oxidation-dependent mechanism, whereas isoproterenol- and phenylephrine-mediated mechanisms had a significant autophosphorylation-dependent component.


Camui is a novel, nondestructive tool that allows spatiotemporally resolved measurement of CaMKII activation state in physiologically functioning myocytes. This represents a first step in using Camui to elucidate key mechanistic details of CaMKII signaling in live hearts and myocytes.

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