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Advances in Therapy Feb 2021Renal tubular acidosis (RTA) occurs when the kidneys are unable to maintain normal acid-base homeostasis because of tubular defects in acid excretion or bicarbonate ion... (Review)
Review
Renal tubular acidosis (RTA) occurs when the kidneys are unable to maintain normal acid-base homeostasis because of tubular defects in acid excretion or bicarbonate ion reabsorption. Using illustrative clinical cases, this review describes the main types of RTA observed in clinical practice and provides an overview of their diagnosis and treatment. The three major forms of RTA are distal RTA (type 1; characterized by impaired acid excretion), proximal RTA (type 2; caused by defects in reabsorption of filtered bicarbonate), and hyperkalemic RTA (type 4; caused by abnormal excretion of acid and potassium in the collecting duct). Type 3 RTA is a rare form of the disease with features of both distal and proximal RTA. Accurate diagnosis of RTA plays an important role in optimal patient management. The diagnosis of distal versus proximal RTA involves assessment of urinary acid and bicarbonate secretion, while in hyperkalemic RTA, selective aldosterone deficiency or resistance to its effects is confirmed after exclusion of other causes of hyperkalemia. Treatment options include alkali therapy in patients with distal or proximal RTA and lowering of serum potassium concentrations through dietary modification and potential new pharmacotherapies in patients with hyperkalemic RTA including newer potassium binders.
Topics: Acidosis, Renal Tubular; Bicarbonates; Humans; Hyperkalemia; Kidney; Potassium
PubMed: 33367987
DOI: 10.1007/s12325-020-01587-5 -
Advances in Immunology 2020Metals are essential components in all forms of life required for the function of nearly half of all enzymes and are critically involved in virtually all fundamental... (Review)
Review
Metals are essential components in all forms of life required for the function of nearly half of all enzymes and are critically involved in virtually all fundamental biological processes. Especially, the transition metals iron (Fe), zinc (Zn), manganese (Mn), nickel (Ni), copper (Cu) and cobalt (Co) are crucial micronutrients known to play vital roles in metabolism as well due to their unique redox properties. Metals carry out three major functions within metalloproteins: to provide structural support, to serve as enzymatic cofactors, and to mediate electron transportation. Metal ions are also involved in the immune system from metal allergies to nutritional immunity. Within the past decade, much attention has been drawn to the roles of metal ions in the immune system, since increasing evidence has mounted to suggest that metals are critically implicated in regulating both the innate immune sensing of and the host defense against invading pathogens. The importance of ions in immunity is also evidenced by the identification of various immunodeficiencies in patients with mutations in ion channels and transporters. In addition, cancer immunotherapy has recently been conclusively demonstrated to be effective and important for future tumor treatment, although only a small percentage of cancer patients respond to immunotherapy because of inadequate immune activation. Importantly, metal ion-activated immunotherapy is becoming an effective and potential way in tumor therapy for better clinical application. Nevertheless, we are still in a primary stage of discovering the diverse immunological functions of ions and mechanistically understanding the roles of these ions in immune regulation. This review summarizes recent advances in the understanding of metal-controlled immunity. Particular emphasis is put on the mechanisms of innate immune stimulation and T cell activation by the essential metal ions like calcium (Ca), zinc (Zn), manganese (Mn), iron (Fe/Fe), and potassium (K), followed by a few unessential metals, in order to draw a general diagram of metalloimmunology.
Topics: Animals; Calcium; Enzymes; Humans; Immunity, Innate; Immunotherapy; Ions; Iron; Manganese; Metals; Neoplasms; Potassium; Signal Transduction; Zinc
PubMed: 32081198
DOI: 10.1016/bs.ai.2019.11.007 -
Nutrients Jul 2016Potassium is an essential nutrient. It is the most abundant cation in intracellular fluid where it plays a key role in maintaining cell function. The gradient of... (Review)
Review
Potassium is an essential nutrient. It is the most abundant cation in intracellular fluid where it plays a key role in maintaining cell function. The gradient of potassium across the cell membrane determines cellular membrane potential, which is maintained in large part by the ubiquitous ion channel the sodium-potassium (Na+-K+) ATPase pump. Approximately 90% of potassium consumed (60-100 mEq) is lost in the urine, with the other 10% excreted in the stool, and a very small amount lost in sweat. Little is known about the bioavailability of potassium, especially from dietary sources. Less is understood on how bioavailability may affect health outcomes. Hypertension (HTN) is the leading cause of cardiovascular disease (CVD) and a major financial burden ($50.6 billion) to the US public health system, and has a significant impact on all-cause morbidity and mortality worldwide. The relationship between increased potassium supplementation and a decrease in HTN is relatively well understood, but the effect of increased potassium intake from dietary sources on blood pressure overall is less clear. In addition, treatment options for hypertensive individuals (e.g., thiazide diuretics) may further compound chronic disease risk via impairments in potassium utilization and glucose control. Understanding potassium bioavailability from various sources may help to reveal how specific compounds and tissues influence potassium movement, and further the understanding of its role in health.
Topics: Cardiovascular Diseases; Diabetes Mellitus, Type 2; Dietary Supplements; Evidence-Based Medicine; Global Health; Glucose Intolerance; Humans; Hypertension; Intestinal Absorption; Kidney; Models, Biological; Potassium; Potassium Deficiency; Potassium, Dietary; Renal Elimination; Renal Reabsorption
PubMed: 27455317
DOI: 10.3390/nu8070444 -
International Journal of Molecular... Feb 2020Aquaporin-4 (AQP4) is the main water channel protein expressed in the central nervous system (CNS). AQP4 is densely expressed in astrocyte end-feet, and is an important... (Review)
Review
Aquaporin-4 (AQP4) is the main water channel protein expressed in the central nervous system (CNS). AQP4 is densely expressed in astrocyte end-feet, and is an important factor in CNS water and potassium homeostasis. Changes in AQP4 activity and expression have been implicated in several CNS disorders, including (but not limited to) epilepsy, edema, stroke, and glioblastoma. For this reason, many studies have been done to understand the various ways in which AQP4 is regulated endogenously, and could be regulated pharmaceutically. In particular, four regulatory methods have been thoroughly studied; regulation of gene expression via microRNAs, regulation of AQP4 channel gating/trafficking via phosphorylation, regulation of water permeability using heavy metal ions, and regulation of water permeability using small molecule inhibitors. A major challenge when studying AQP4 regulation is inter-method variability. A compound or phosphorylation which shows an inhibitory effect in vitro may show no effect in a different in vitro method, or even show an increase in AQP4 expression in vivo. Although a large amount of variability exists between in vitro methods, some microRNAs, heavy metal ions, and two small molecule inhibitors, acetazolamide and TGN-020, have shown promise in the field of AQP4 regulation.
Topics: Acetazolamide; Animals; Aquaporin 4; Central Nervous System; Central Nervous System Diseases; Homeostasis; Humans; Ions; Metals; MicroRNAs; Niacinamide; Permeability; Phosphorylation; Potassium; Proteolipids; Thiadiazoles; Water
PubMed: 32111087
DOI: 10.3390/ijms21051603 -
Comprehensive Physiology Dec 2021Na,K-ATPase is an ubiquitous enzyme actively transporting Na-ions out of the cell in exchange for K-ions, thereby maintaining their concentration gradients across the...
Na,K-ATPase is an ubiquitous enzyme actively transporting Na-ions out of the cell in exchange for K-ions, thereby maintaining their concentration gradients across the cell membrane. Since its discovery more than six decades ago the Na-pump has been studied extensively and its vital physiological role in essentially every cell has been established. This article aims at providing an overview of well-established biochemical properties with a focus on Na,K-ATPase isoforms, its transport mechanism and principle conformations, inhibitors, and insights gained from crystal structures. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.
Topics: Cell Membrane; Humans; Ions; Potassium; Sodium; Sodium-Potassium-Exchanging ATPase
PubMed: 34964112
DOI: 10.1002/cphy.c200018 -
Cell Calcium Mar 2022The lysosome is an important membrane-bound acidic organelle that is regarded as the degradative center as well as multifunctional signaling hub. It digests unwanted... (Review)
Review
The lysosome is an important membrane-bound acidic organelle that is regarded as the degradative center as well as multifunctional signaling hub. It digests unwanted macromolecules, damaged organelles, microbes, and other materials derived from endocytosis, autophagy, and phagocytosis. To function properly, the ionic homeostasis and membrane potential of the lysosome are strictly regulated by transporters and ion channels. As the most abundant cation inside the cell, potassium ions (K) are vital for lysosomal membrane potential and lysosomal calcium (Ca) signaling. However, our understanding about how lysosomal Khomeostasis is regulated and what are the functions of Kin the lysosome is very limited. Currently, two lysosomal Kchannels have been identified: large-conductance Ca-activated Kchannel (BK) and transmembrane Protein 175 (TMEM175). In this review, we summarize recent development in our understanding of K homeostasis and Kchannels in the lysosome. We hope to guide the readers into a more in-depth discussion of lysosomal K channels in lysosomal physiology and human diseases.
Topics: Calcium; Humans; Intracellular Membranes; Ion Channels; Ions; Lysosomes; Potassium; Potassium Channels
PubMed: 35016151
DOI: 10.1016/j.ceca.2022.102536 -
Current Biology : CB May 2021Metals are vital for life as they are necessary for essential biological processes. Traditionally, metals are categorized as either dynamic signals or static cofactors.... (Review)
Review
Metals are vital for life as they are necessary for essential biological processes. Traditionally, metals are categorized as either dynamic signals or static cofactors. Redox-inactive metals such as calcium (Ca), potassium (K), sodium (Na), and zinc (Zn) signal through large fluctuations in their metal-ion pools. In contrast, redox-active transition metals such as copper (Cu) and iron (Fe) drive catalysis and are largely characterized as static cofactors that must be buried and protected within the active sites of proteins, due to their ability to generate damaging reactive-oxygen species through Fenton chemistry. Cu has largely been studied as a static cofactor in fundamental processes from cellular respiration to pigmentation, working through cytochrome c oxidase and tyrosinase, respectively. However, within the last decade, a new paradigm in nutrient sensing and protein regulation - termed 'metalloallostery' - has emerged, expanding the repertoire of Cu beyond the catalytic proteins to dynamic signaling molecules essential for cellular processes that impact normal physiology and disease states. In this Primer we introduce both the 'traditional' and emerging roles for Cu in biology and the many ways in which Cu intersects with human health.
Topics: Animals; Calcium; Copper; Health; Humans; Ions; Iron; Potassium; Zinc
PubMed: 33974864
DOI: 10.1016/j.cub.2021.03.054 -
Science Translational Medicine Aug 2018Hyperphosphatemia is common in patients with chronic kidney disease and is increasingly associated with poor clinical outcomes. Current management of hyperphosphatemia... (Randomized Controlled Trial)
Randomized Controlled Trial
Hyperphosphatemia is common in patients with chronic kidney disease and is increasingly associated with poor clinical outcomes. Current management of hyperphosphatemia with dietary restriction and oral phosphate binders often proves inadequate. Tenapanor, a minimally absorbed, small-molecule inhibitor of the sodium/hydrogen exchanger isoform 3 (NHE3), acts locally in the gastrointestinal tract to inhibit sodium absorption. Because tenapanor also reduces intestinal phosphate absorption, it may have potential as a therapy for hyperphosphatemia. We investigated the mechanism by which tenapanor reduces gastrointestinal phosphate uptake, using in vivo studies in rodents and translational experiments on human small intestinal stem cell-derived enteroid monolayers to model ion transport physiology. We found that tenapanor produces its effect by modulating tight junctions, which increases transepithelial electrical resistance (TEER) and reduces permeability to phosphate, reducing paracellular phosphate absorption. NHE3-deficient monolayers mimicked the phosphate phenotype of tenapanor treatment, and tenapanor did not affect TEER or phosphate flux in the absence of NHE3. Tenapanor also prevents active transcellular phosphate absorption compensation by decreasing the expression of NaPi2b, the major active intestinal phosphate transporter. In healthy human volunteers, tenapanor (15 mg, given twice daily for 4 days) increased stool phosphorus and decreased urinary phosphorus excretion. We determined that tenapanor reduces intestinal phosphate absorption predominantly through reduction of passive paracellular phosphate flux, an effect mediated exclusively via on-target NHE3 inhibition.
Topics: Adult; Aged; Animals; Base Sequence; Cell Membrane Permeability; Cells, Cultured; Electric Impedance; Epithelium; Female; Gastrointestinal Tract; Healthy Volunteers; Humans; Hydrogen-Ion Concentration; Intestinal Absorption; Ions; Isoquinolines; Male; Mice; Middle Aged; Phosphates; Potassium; Protons; Rats; Sodium; Sodium-Hydrogen Exchanger 3; Sulfonamides; Tight Junction Proteins; Young Adult
PubMed: 30158152
DOI: 10.1126/scitranslmed.aam6474 -
Pediatric Nephrology (Berlin, Germany) Jul 2017The kidney plays an essential role in maintaining homeostasis of ion concentrations in the blood. Because the concentration gradient of potassium across the cell... (Review)
Review
The kidney plays an essential role in maintaining homeostasis of ion concentrations in the blood. Because the concentration gradient of potassium across the cell membrane is a key determinant of the membrane potential of cells, even small deviations in serum potassium level from the normal setpoint can lead to severe muscle dysfunction, resulting in respiratory failure and cardiac arrest. Less severe hypo- and hyperkalemia are also associated with morbidity and mortality across various patient populations. In addition, deficiencies in potassium intake have been associated with hypertension and adverse cardiovascular and renal outcomes, likely due in part to the interrelated handling of sodium and potassium by the kidney. Here, data on the beneficial effects of potassium on blood pressure and cardiovascular and renal outcomes will be reviewed, along with the physiological basis for these effects. In some patient populations, however, potassium excess is deleterious. Risk factors for the development of hyperkalemia will be reviewed, as well as the risks and benefits of existing and emerging therapies for hyperkalemia.
Topics: Aldosterone; Cation Exchange Resins; Cell Membrane; Child; Heart Failure; Homeostasis; Humans; Hyperkalemia; Hypertension; Hypokalemia; Kidney; Membrane Potentials; Polymers; Potassium; Potassium, Dietary; Protein Serine-Threonine Kinases; Recommended Dietary Allowances; Renal Elimination; Renin-Angiotensin System; Respiratory Insufficiency; Risk Factors; Signal Transduction; Silicates; Sodium; Sodium Chloride Symporters; WNK Lysine-Deficient Protein Kinase 1
PubMed: 27194424
DOI: 10.1007/s00467-016-3411-8 -
World Review of Nutrition and Dietetics 2021
Review
Topics: Chlorides; Humans; Potassium; Potassium Chloride; Sodium; Water
PubMed: 34352776
DOI: 10.1159/000514770