Introducing a special series: Membrane proteins, epithelial transport, and kidney physiology

Membrane proteins, facilitating transport across epithelia, are fundamental for a range of essential physiological processes throughout the organism. For instance, the regulation of epithelial transport is critically important for the homeostatic control of electrolyte and fluid balance, as well as many other solutes. Adjusting these epithelial transport mechanisms is at the core of a myriad of diverse physiological mechanisms, including the maintenance of blood pressure, glucose homeostasis, nutrient uptake, and the removal of waste products into urine. Knowledge of these epithelial transport mechanisms informs of their perturbations in pathophysiological conditions, as exemplified in cystic fibrosis, where the transmembrane conductance regulator anion channel disrupts epithelial chloride transport in airways and other organs,¹ or in familial hyperkalemia and hypertension where pathogenic variants in the with-no-lysine (WNK) protein kinases alter renal epithelial transport.² Understanding these epithelial transport processes open the door to targeted treatments.

Seminal discoveries of membrane proteins being essential components include the sodium-potassium ATPase by Jens Christian Skou³ and aquaporin water channels by Peter Agre.⁴ In recognition, both pioneers became Nobel laureates. Knowledge of the epithelial transport processes oftentimes precedes the identification of the responsible protein, while at other times the identification of a protein allows the identification of the transport process. These discoveries have shaped our understanding of epithelial transport physiology. None more so, than our understanding of the kidney and its central role in maintaining homeostasis.

The journal Acta Physiologica, previously titled Acta Physiologica Scandinavica (1940–2005) and Skandinavisches Archiv für Physiologie (1889–1939) provide longstanding contributions to this field. For instance, in 1929, Norn found that the diurnal rhythm of urinary sodium, chloride, potassium, and water excretion could be reversed when studying a nurse on night shift.⁵ In 1937, Krogh developed methods to study ion uptake and reported on the ability of the frog to absorb salt through the skin against large concentration gradients.⁶ In 1951, Ussing and Zerahn published the development of an apparatus to simultaneously determine electric current and sodium transport through isolated frog skin,⁷ now known as the Ussing chamber system. And in 1961 when Lassen et al, investigated the correlation between renal oxygen uptake and sodium reabsorption in the mammalian kidney.⁸ These are just a few highlights and by no means an exhaustive overview of manuscripts published in Acta Physiologica on these topics. Furthermore, many manuscripts have been published within these fields over the latest years, including multiple recent works.^9-11

To honor this tradition, we invite you to take part in a special series on the topic of membrane proteins and epithelial transport in physiology and pathophysiology. We look forward to receiving original articles for consideration for publication in this series. Naturally, reviews are also welcome. Given the importance of epithelial transport in the kidney, a particular focus is placed hereon. However, as editor of this special series, I welcome studies on epithelial transport from any organ system.

The author has no financial interests to declare.