Translocator protein in touch with mitochondrial chloride intracellular channel CLIC5

Cardiac arrhythmias rank among the leading causes of death worldwide. They frequently develop during ischemia/reperfusion, when fluctuations in oxygen and nutrient supply occur. Reperfusion can elevate levels of oxygen radicals, and both metabolic and oxidative stress have been shown to trigger arrhythmias by inducing cyclic changes in mitochondrial membrane potential. These fluctuations are mediated by chloride channels believed to correspond to the CLIC5 isoform of intracellular chloride channels. The cardioprotective effects have been observed following administration of 4-chlorodiazepam (4Cl-DZP), a specific ligand of the mitochondrial translocator protein TSPO, as well as after treatment with a non-specific anion channel inhibitor. Although 4Cl-DZP is thought to influence chloride channel activity indirectly through TSPO, the details of this interaction remain unclear. CLIC5 has been localized to the inner mitochondrial membrane. Based on the comparison of single-channel properties, it may represent a candidate for the molecular identity of the centum-pS channel. The potential physical association between CLIC5 and TSPO was investigated. To assess the spatial proximity of CLIC5 and TSPO, we performed Förster resonance energy transfer (FRET) measurements in immunolabeled cardiomyoblasts using acceptor photobleaching configuration. The observed FRET efficiency between CLIC5 and TSPO was 24%, comparable to the 28% efficiency measured in the positive control and substantially higher than the 7% efficiency observed in the negative control. These findings support the hypothesis that, if CLIC5 indeed constitutes the centum-pS channel, TSPO is positioned in sufficiently close proximity to modulate its activity.