Effects of change of posture on the diurnal renal excretory rhythm

Circadian gene expression in mouse renal proximal tubule

Circadian variability in kidney function is well recognized but is often ignored as a potential confounding variable in physiological experiments. Here, we have created a data resource consisting of expression levels for mRNA transcripts in microdissected proximal tubule segments from mice as a function of the time of day. Small-sample RNA sequencing was applied to microdissected S1 proximal convoluted tubules and S2 proximal straight tubules. After stringent filtering, the data were analyzed using JTK-Cycle to detect periodicity. The data set is provided as a user-friendly webpage at https://esbl.nhlbi.nih.gov/Databases/Circadian-Prox2/. In proximal convoluted tubules, 234 transcripts varied in a circadian manner (4.0% of the total). In proximal straight tubules, 334 transcripts varied in a circadian manner (5.3%). Transcripts previously known to be associated with corticosteroid action and with increased flow were found to be overrepresented among circadian transcripts peaking during the "dark" portion of the day [zeitgeber time (ZT)14-22], corresponding to peak levels of corticosterone and glomerular filtration rate in mice. To ask whether there is a time-of-day dependence of protein abundances in the kidney, we carried out LC-MS/MS-based proteomics in whole mouse kidneys at ZT12 and ZT0. The full data set (n = 6,546 proteins) is available at https://esbl.nhlbi.nih.gov/Databases/Circadian-Proteome/. Overall, 293 proteins were differentially expressed between ZT12 and ZT0 (197 proteins greater at ZT12 and 96 proteins greater at ZT0). Among the regulated proteins, only nine proteins were found to be periodic in the RNA-sequencing analysis, suggesting a high level of posttranscriptional regulation of protein abundances.NEW & NOTEWORTHY Circadian variation in gene expression can be an important determinant in the regulation of kidney function. The authors used RNA-sequencing transcriptomics and LC-MS/MS-based proteomics to identify gene products expressed in a periodic manner. The data were used to construct user-friendly web resources.

The Unappreciated Role of Extrarenal and Gut Sensors in Modulating Renal Potassium Handling: Implications for Diagnosis of Dyskalemias and Interpreting Clinical Trials

In addition to the classic and well-established "feedback control" of potassium balance, increasing investigative attention has focused on a novel and not widely recognized complementary regulatory paradigm for maintaining potassium homeostasis-the "feed-forward control" of potassium balance. This regulatory mechanism, initially defined in rumen, has recently been validated in normal human subjects. Studies are being conducted to determine the location for this putative potassium sensor and to evaluate potential signals, which might increase renal potassium excretion. Awareness of this more updated integrative control mechanism for potassium homeostasis is ever more relevant today, when the medical community is increasingly focused on the challenges of managing the hyperkalemia provoked by renin-angiotensin-aldosterone system inhibitors (RAASis). Recent studies have demonstrated a wide gap between RAASi prescribing guidelines and real-world experience and have highlighted that this gap is thought to be attributable in great part to hyperkalemia. Consequently we require a greater knowledge of the complexities of the regulatory mechanisms subserving potassium homeostasis. Sodium polystyrene sulfonate has long been the mainstay for treating hyperkalemia, but its administration is fraught with challenges related to patient discomfort and colonic necrosis. The current and imminent availability of newer potassium binders with better tolerability and more predictive dose-response potassium removal should enhance the management of hyperkalemia. Consequently it is essential to better understand the intricacies of mammalian colonic K+ handling. We discuss colonic transport of K+ and review evidence for potassium (BK) channels being responsible for increased stool K+ in patients with diseases such as ulcerative colitis.

Potassium homeostasis and dyskalemias: the respective roles of renal, extrarenal, and gut sensors in potassium handling

Integrated mechanisms controlling the maintenance of potassium homeostasis are well established and are defined by the classic "feedback control" of potassium balance. Recently, increasing investigative attention has focused on novel physiological paradigms that increase the complexity and precision of homeostasis. This review briefly considers the classic and well-established feedback control of potassium and then considers subsequent investigations that inform on an intriguing and not widely recognized complementary paradigm: the "feed-forward control of potassium balance." Feed-forward control refers to a pathway in a homeostatic system that responds to a signal in the environment in a predetermined manner, without responding to how the system subsequently reacts (i.e., without responding to feedback). Studies in several animal species, and recently in humans, have confirmed the presence of a feed-forward control mechanism that is capable of mediating potassium excretion independent of changes in serum potassium concentration and aldosterone. Knowledge imparted by this update of potassium homeostasis hopefully will facilitate the clinical management of hyperkalemia in patients with chronic and recurrent hyperkalemia. Awareness of this updated integrative control mechanism for potassium homeostasis is more relevant today when the medical community is increasingly focused on leveraging and expanding established renin-angiotensin-aldosterone system inhibitor treatment regimens and on successfully coping with the challenges of managing hyperkalemia provoked by renin-angiotensin-aldosterone system inhibitors. These new insights are relevant to the future design of clinical trials delineating renal potassium handling.

Clinical trial of mefruside, a new diuretic

A controlled clinical trial of a new diuretic-mefruside-is reported, in which it was compared with frusemide in 15 normal subjects and 15 patients with fluid retention. It was found to be an effective diuretic which, in the patients, produced a significantly greater excretion of water and electrolytes than an equal dose of frusemide. Its smooth prolonged action, maximal in the first 12 hours, made it of particular value for maintenance therapy. In a short-term trial on a further 15 hypertensive patients mefruside was shown to have a useful hypotensive action. The drug was well tolerated with minimal side effects.

Use of random specimens of urine to compare dietary intakes of African and British children

Specimens of urine were obtained during the forenoon from 45 Ugandan and 45 British boys and girls below 4 years of age who were attending clinics for healthy children. By employing known facts about the excretion of creatinine, and by making certain assumptions, it was possible to obtain a surprising amount of information about the nature of the food consumed. This agreed well with what was already known about it. The method has distinct possibilities and could be made more quantitative by using a reference group about which more was known.