Mitochondrial Rich Proton Pumping Cells in the Kidney and Epididymis are Highly Glycolytic
Authors: Ghazi Susan , Craigie Eilidh , Bourgeois Soline , Gomariz Alvaro , Bugarski Milica , Polesel Marcello , Nombela‐Arrieta César , Wagner Carsten , Hall Andrew 
Published: June 2021

The kidney collecting duct (CD) has a crucial role in regulating acid‐base balance. Alpha intercalated cells (ICs) of the CD maintain acid‐base homeostasis by acidifying the urine, via apical V‐ATPase H+ pumps. ICs are characterized in appearance by a very high density of mitochondria, but remarkably little is known about metabolism in these cells, due to a lack of suitable techniques to study this and the inability to generate a stable IC cell line. By using different innovative imaging techniques, we aimed to better understand how metabolism might be adapted in ICs to their specialized H+ pumping function.Using multiphoton microscopy of intact murine kidney slices, we have found that mitochondria in ICs have some highly unusual features compared with other tubular cells. IC mitochondria are considerably more mobile and dynamic, and display a high NADH signal but low uptake of voltage dependent dyes. Moreover, they are energized by a pH gradient that is functionally coupled to the proton pumping activity of the V‐ATPase. However, high resolution confocal microscopy and 3D electron microscopy (FIB‐SEM) in fixed mouse kidney tissue revealed that the mitochondria and V‐ATPase expressing vesicles were distant from each other, reducing the likelihood that the mitochondria are the only energy source for the V‐ATPase H+ pumps in ICs. Furthermore, we observed that the expression of respiratory chain complex V (ATP synthase) is lower in ICs than in surrounding cells, implying reduced oxidative capacity. Conversely, expression of enzymes in the glycolytic pathway, including lactate dehydrogenase, was markedly higher in ICs, consistent with high anaerobic ATP‐generating capacity. Interestingly, expression of glycolytic enzymes was also high in clear cells in the epididymis, suggesting that this is a common feature of proton pumping cells.As a surrogate of cellular ATP levels, we imaged cytosolic Ca2+ in kidney slices using a fluorescent reporter (GcaMP6s), and found that inhibition of mitochondrial ATP production with cyanide produced striking rises in Ca2+ in all tubular cell types except ICs. However, Ca2+ also increased in ICs when glycolysis was simultaneously inhibited. Finally, direct functional measurement of V‐ATPase function in microperfused isolated outermedullary collecting ducts (OMCDs) revealed that inhibition of glycolysis leads to a significant decrease in H+ pumping in ICs.In summary, we have provided several lines of evidence that mitochondrial rich cells in the kidney and epididymis are surprisingly glycolytic, and that glycolysis is functionally important for V‐ATPase activity. These findings provide new insights into coupling of transport and metabolism in proton pumping cells.Support or Funding InformationThis research is supported by The Swiss National Centre for Competence in Research Kidney Control of Homeostasis.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.