Background: C. elegans is a free-living nematode known for its utility in genomics research. A dominant gain-of-function mutation in unc-105, a putative mechano-sensitive ion channel of the ENaC/Degenerin family, causes mitochondrial fragmentation in body-wall muscles (Szewczyk et al. unpublished data) and a movement defect (1). These defects are ameliorated in unc-105; let-2 suppressed mutants (let-2 encodes a collagen). Objectives: Mitochondrial membrane potential and maximal rates of ATP production (MRAP) were determined in wild-type (WT) and unc-105 mutants to quantify disruption, if any, of mitochondrial function. The unc-105; let-2 mutants were also assessed to quantify any potential rescue of mitochondrial function. Methods: Mitochondrial membrane potential was quantified in vivo using JC-10 and Mitotracker® CMXRos, which reflect potential-dependent accumulation. JC-10 fluorescence was quantified using ImageJ. Membrane potential was also quantified in isolated mitochondria (n=10 assays of mixed-age worms; n≈300 per assay) using JC-1 and flow cytometry (2). MRAP and citrate synthase (CS) activity were also determined in similarly isolated mitochondria. MRAP was determined through incubation with a bioluminescent luciferase-based monitoring reagent, and a combination of respiratory substrates and ADP. All data were analysed using one-way ANOVA. Results: Mitochondrial accumulation of JC-10 was reduced in unc-105 versus WT (P <0.001), suggesting the loss of membrane potential in unc-105 mutants in vivo. Similarly, Mitotracker® CMXRos accumulated in vivo in WT (P <0.01) and unc-105; let-2 suppressed mutants (P <0.01), but not in unc-105 mutants. In keeping with these in vivo observations, JC-1 accumulation in isolated mitochondria was 25% lower in unc-105 than in WT and unc-105; let-2 (P <0.001). MRAP were reduced in unc-105 mutants vs. WT and unc-105; let-2 suppressed mutants (Figure 1). The respiratory substrate combinations were glutamate and succinate (GS), palmitoyl-L-carnitine and malate (PCM), pyruvate and malate (PM), succinate (S) and glutamate and malate (GM). Data were normalised for CS activity to account for mitochondrial content. * P <0.05 vs. WT and † P <0.05 vs. unc-105. Conclusion: Unc-105 mutants showed evidence of disrupted mitochondrial membrane potential compared to WT, which was accompanied by impaired MRAP. In unc-105; let-2 suppressed mutants, mitochondrial membrane potential and MRAP were similar to WT. Thus, as in mammalian cells (3), constitutive cationic influx leads to pathological changes in mitochondrial function in C. elegans muscle. These results establish that it is possible to use C. elegans to understand the genomic control of mitochondrial function.