Calcium chelation independent effects of BAPTA on endogenous ANO6 channels in HEK293T cells

Selective calcium chelator 1,2-Bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA) is a common tool to investigate calcium signaling. However, BAPTA expresses various effects on intracellular calcium signaling, which are not related to its ability to bind Ca2+. In patch clamp experiments, we investigated calcium chelation independent effects of BAPTA on endogenous calcium-activated chloride channels ANO6 (TMEM16F) in HEK293T cells. We have found that application of BAPTA to intracellular solution led to two distinct effects on channels properties. On the one hand, application of BAPTA acutely reduced amplitude of endogenous ANO6 channels induced by 10 μM Ca2+ in single channel recordings. On the other hand, BAPTA application by itself induced ANO6 channel activity in the absence of the intracellular calcium elevation. Open channel probability was enhanced by increasing the intracellular BAPTA concentration from 0.1 to 1 and 10 mM. Another calcium chelator EGTA did not demonstrate chelation independent effects on the ANO6 activity in the same conditions. Due to off-target effects BAPTA should be used with caution when studying calcium-activated ANO6 channels.

1,2,3,4-dithiadiazole derivatives as a novel class of calcium signaling modulators

Aberrant calcium signaling is associated with a diverse range of pathologies, including cardiovascular and neurodegenerative diseases, diabetes, cancer, etc… So, therapeutic strategies based on the correction of pathological calcium signaling are becoming extremely in demand. Thus, the development of novel calcium signaling modulators remains highly actual. Previously we found that 1,2,3,4-dithiadiazole derivative 3-(4-nitrophenyl)-5-phenyl-3H-1,2,3,4-dithiadiazole-2-oxide can strongly reduce calcium uptake through store-operated calcium (SOC) channels. Here we tested several structurally related compounds and found that most of them can effectively affect SOC channels and attenuate calcium content in the endoplasmic reticulum, thus, establishing 1,2,3,4-dithiadiazoles as a novel class of SOC channel inhibitors. Comparing different 1,2,3,4-dithiadiazole derivatives we showed that previously published 3-(4-nitrophenyl)-5-phenyl-3H-1,2,3,4-dithiadiazole-2-oxide and newly tested 3-(3,5-difluorophenyl)-5-phenyl-3H-1,2,3,4-dithiadiazole 2-oxide demonstrated the highest efficacy of SOC entry reduction, supposing the important role of electron-withdrawing substituents to realize the inhibitory activity of 1,2,3,4-dithiadiazoles.