Fluorescence imaging reveals differences in mitochondrial function along the collecting duct

Abstract

The collecting duct (CD) consists of two different cell populations, principal cells (PCs) and intercalated cells (ICs), which have distinct solute transport functions. Transport and metabolism are closely coupled in the nephron, thus we hypothesised that intrinsic differences in PCs and ICs mitochondrial function might exist. Mitochondrial function can be measured in intact rat kidney slices using confocal and multiphoton microscopy (1,2); here we apply this approach to investigate our hypothesis.PCs and ICs have distinct morphological differences, which enabled their identification during live imaging. Heterogeneity was observed in mitochondrial signals along the CD. Mitochondrial membrane potential, measured using tetramethylrodamine methyl ester (TMRM), was higher in PCs (34.45±3.08) than ICs (16.82±8.23) (n=3, p=0.009), and this signal was not altered by dye efflux inhibitors. Fluorescence signals from the endogenous fluorophores NADH and FAD+ (substrates for complexes I and II in the respiratory chain, respectively) were higher in ICs than in PCs (p=0.03 and p=0.056 respectively).In summary, fluorescence imaging reveals intrinsic differences in mitochondrial function between PCs and ICs, which may be important in understanding (patho)physiology of the CD.Research supported by the Medical Research Council