The CamKKβ Inhibitor STO609 Causes Artefacts in Calcium Imaging and Selectively Inhibits BKCa in Mouse Carotid Body Type I Cells

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It has previously been reported that AMP-activated protein kinase (AMPK) may be critical for hypoxic chemotransduction in carotid body type I cells. This study sought to determine the importance of the regulatory upstream kinase of AMPK, CamKKβ, in the acute response to hypoxia in isolated mouse type I cells.

Initial data indicated several previously unreported artefacts associated with using the CamKKβ inhibitor STO609 and Ca2+ imaging techniques. Most importantly Fura-2 and X-Rhod1 imaging revealed that STO609 quenched emission fluorescence even in the absence of intracellular Ca2+([Ca2+]i). Furthermore, STO609 (100 μM) rapidly inhibited outward macroscopic currents and this inhibition was abolished in the presence of the selective BKCa inhibitor paxilline.

Taken together these data suggest that ST0609 should be used with caution during Ca2+ imaging studies as it can directly interact with Ca2+ binding dyes. The rapid inhibitory effect of STO609 on BKCa was unexpected as the majority of studies using this compound required an incubation of approximately 10 min to inhibit the kinase. Furthermore, as AMPK activation inhibits BKCa, inhibitingAMPK’s upstream kinases would, if anything, be predicted to have the opposite effect on BKCa. Future work will determine if the inhibition of BKCa is via CamKKβ or via an off target action of STO609 on the channel itself.



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