Extracellular Fluid Homeostasis Research Articles

CLC-5 and KIF3B interact to facilitate CLC-5 plasma membrane expression, endocytosis, and microtubular transport: relevance to pathophysiology of Dent's disease

Renal tubular reabsorption is important for extracellular fluid homeostasis and much of this occurs via the receptor-mediated endocytic pathway. This pathway is disrupted in Dent’s disease, an X-linked renal tubular disorder that is characterized by low-molecular-weight proteinuria, hypercalciuria, nephrolithiasis, and renal failure. Dent's disease is due to mutations of CLC-5, a chloride/proton antiporter, expressed in endosomes and apical membranes of renal tubules. Loss of CLC-5 function alters receptor-mediated endocytosis and trafficking of megalin and cubilin, although the underlying mechanisms remain to be elucidated. Here, we report that CLC-5 interacts with kinesin family member 3B (KIF3B), a heterotrimeric motor protein that facilitates fast anterograde translocation of membranous organelles. Using yeast two-hybrid, glutathione-S-transferase pull-down and coimmunoprecipitation assays, the COOH terminus of CLC-5 and the coiled-coil and globular domains of KIF3B were shown to interact. This was confirmed in vivo by endogenous coimmunoprecipitation of CLC-5 and KIF3B and codistribution with endosomal markers in mouse kidney fractions. Confocal live cell imaging in kidney cells further demonstrated association of CLC-5 and KIF3B, and transport of CLC-5-containing vesicles along KIF3B microtubules. KIF3B overexpression and underexpression, using siRNA, had reciprocal effects on whole cell chloride current amplitudes, CLC-5 cell surface expression, and endocytosis of albumin and transferrin. Clcn5Y/− mouse kidneys and isolated proximal tubular polarized cells showed increased KIF3B expression, whose effects on albumin endocytosis were dependent on CLC-5 expression. Thus, the CLC-5 and KIF3B interaction is important for CLC-5 plasma membrane expression and for facilitating endocytosis and microtubular transport in the kidney.

Blood–brain interfaces and cerebral drug bioavailability

The low cerebral bioavailability of various drugs is a limiting factor in the treatment of neurological diseases. The restricted penetration of active compounds into the brain is the result of the same mechanisms that are central to the maintenance of brain extracellular fluid homeostasis, in particular from the strict control imposed on exchanges across the blood–brain interfaces. Direct drug entry into the brain parenchyma occurs across the cerebral microvessel endothelium that forms the blood–brain barrier. In addition, local drug concentration measurements and cerebral imaging have clearly shown that the choroid plexuses – the main site of the blood–cerebrospinal fluid (CSF) barrier – together with the CSF circulatory system also play a significant role in setting the cerebral bioavailability of drugs and contrast agents. The entry of water-soluble therapeutic compounds into the brain is impeded by the presence of tight junctions that seal the cerebral endothelium and the choroidal epithelium. The cerebral penetration of many of the more lipid-soluble molecules is also restricted by various classes of efflux transporters that are differently distributed among both blood–brain interfaces, and comprise either multidrug resistance proteins of the ATP-binding cassette superfamily or transporters belonging to several solute carrier families. Expression of these transporters is regulated in various pathophysiological situations, such as epilepsy and inflammation, with pharmacological consequences that have yet to be clearly elucidated. As for brain tumour treatments, their efficacy may be affected not only by the intrinsic resistance of tumour cells, but also by endothelial efflux transporters which exert an even greater impact than the integrity of the endothelial tight junctions. Relevant to paediatric neurological treatments, both blood–brain interfaces are known to develop a tight phenotype very early on in postnatal development, but the developmental profile of efflux transporters still needs to be assessed in greater detail. Finally, the exact role of the ependyma and pia-glia limitans in controlling drug exchanges between brain parenchyma and CSF deserves further attention to allow more precise predictions of cerebral drug disposition and therapeutic efficacy.

Na +/H + Exchangers in Renal Regulation of Acid-Base Balance

The kidney plays key roles in extracellular fluid pH homeostasis by reclaiming bicarbonate (HCO(3)(-)) filtered at the glomerulus and generating the consumed HCO(3)(-) by secreting protons (H(+)) into the urine (renal acidification). Sodium-proton exchangers (NHEs) are ubiquitous transmembrane proteins mediating the countertransport of Na(+) and H(+) across lipid bilayers. In mammals, NHEs participate in the regulation of cell pH, volume, and intracellular sodium concentration, as well as in transepithelial ion transport. Five of the 10 isoforms (NHE1-4 and NHE8) are expressed at the plasma membrane of renal epithelial cells. The best-studied isoform for acid-base homeostasis is NHE3, which mediates both HCO(3)(-) absorption and H(+) excretion in the renal tubule. This article reviews some important aspects of NHEs in the kidney, with special emphasis on the role of renal NHE3 in the maintenance of acid-base balance.

A 14-year-old girl with renal abnormalities after brief intrauterine exposure to enalapril during late gestation

In addition to its important role in the regulation of extracellular fluid homeostasis, an intact renin– angiotensin system (RAS) is essential for normal kidney development [1]. Several case reports have described fatal acute renal failure and renal tubular dysplasia in fetuses and newborns exposed to angiotensin-converting enzyme (ACE) inhibitors [2] or angiotensin II type-1 (AT1) receptor antagonists [3] during the second or third trimester. Notably, nephrogenesis is completed at about gestational week 36 in humans. Experimental studies have shown that interruption of the RAS during ongoing nephrogenesis, either pharmacologically or by gene knockout techniques, produces abnormalities in renal morphology and function that bear similarities to those described in case reports, and that normal kidney development is mainly mediated through the AT1 receptor [1,4,5]. Renal morphological abnormalities in these animals are characterized by papillary atrophy, wall thickening of pre-glomerular arterioles, and tubular atrophy and dilatation [1,4,5]. Functional defects are mainly characterized by a marked impairment in urinary concentrating ability [1]. Recent studies have demonstrated important roles for the AT1 receptor in tubular growth [6], branching morphogenesis [5] and the establishment of normal tubular cell–cell and cell–matrix interactions [7] in the developing kidney. In addition, angiotensin II is important for normal development of the renal pelvis and ureter [4]. Although maternal use of drugs that block the RAS during the second and third trimester sometimes induces fatal acute renal failure and renal tubular dysplasia in newborns, it is not known what the longterm consequences are on the kidney in survivors. We here describe a patient who was exposed to the ACE inhibitor enalapril during gestational weeks 28–36 and who at 14 years of age presented with a marked impairment in urinary concentrating ability, proteinuria and a reduction in glomerular filtration rate (GFR). This renal phenotype resembles that described in laboratory animals exposed to ACE inhibitors during a corresponding interval of kidney development.

.GAMMA.-Tocopherol Enhances Sodium Excretion as a Natriuretic Hormone Precursor

Endogenous natriuretic factors are believed to be responsible for extracellular fluid homeostasis in mammals. A new endogenous natriuretic factor, Loma Linda University-alpha (LLU-alpha) has recently been proven to be a 2,7,8-trimethyl-2-(2'-carboxyethyl)-6-hydroxychroman (gamma-CEHC), which is a metabolite of gamma-tocopherol (gamma-Toc). The purpose of this study was to investigate whether gamma-Toc could accelerate sodium excretion into rat urine as a natriuretic hormone precursor. Male SD strain rats were divided into two groups; one was a control diet group, while the other was a high NaCl group (50 g/kg diet). Next, the two groups were each subdivided into two groups consisting of a placebo group and a gamma-Toc group. After the oral administration of one experimental dose of 20 mg gamma-Toc or placebo, rat urine was collected at 6 h intervals for 24 h, and then the urine volume, sodium and potassium and gamma-CEHC content were determined. gamma-Toc increased in the urine volume of the high-NaCl intake group. The sodium excretion in the high-NaCl group given gamma-Toc was 8.29+/-2.20 g, while in the control group given gamma-Toc it was 6.24+/-1.49 g from 12-18 h. In contrast, the potassium excretion in the rat urine did not change in any of the groups. Our findings suggested that gamma-Toc accelerates the degree of sodium excretion in rats with a high sodium intake.

Endogenous natriuretic factors 3: isolation and characterization of human natriuretic factors llu-α, LLU- β1, and llu-γ

A low molecular weight endogenous substance believed to be responsible for extracellular fluid homeostasis in mammals has been sought for many years. Our goal is to isolate and structurally characterize this putative “natriuretic hormone”. We have developed an assay using the conscious rat to measure prolonged natriuresis (Benaksas et al (1993) Life Sciences, 52, 1045–1054), the activity originally described for this putative substance. Using this assay we have identified a number of natriuretic compounds isolated from human uremic urine. The collected urine is processed by ultrafiltration (≤ 3 kDa), gel filtration chromatography (G-25) and extraction with isopropanol and diethyl ether. The organic soluble material is then subjected to sequential high-performance liquid chromatography. We report here the initial characterization of two pure isolates (LLU-α and LLU-γ) obtained by this method, and the structural elucidation of a third pure compound, LLU- β 1, a natriuretic and previously unreported metabolite of the drug diltiazem.

Endogenous Natriuretic Factors 2

It is our intention to isolate, purify, and characterize the putative low-molecular-weight "natriuretic hormone" responsible for extracellular fluid (ECF) homeostasis. Toward this end, we are purifying from human uremic urine, and identifying endogenous vasopressor and natriuretic compounds. Bioactive components from large volumes of pooled urine were purified by ultrafiltration (< or = 3 kDa), gel filtration chromatography, and sequential reverse-phase and normal-phase high-performance liquid chromatography (HPLC). After each HPLC step, the fractions were evaluated in vivo, were assayed for inhibition of Na+/K(+)-ATPase-mediated 86Rb+ uptake, and were checked for cross-reactivity with an anti-ouabain antibody. Fractions assayed in vivo were identified that induced natriuresis, altered mean arterial pressure, or increased plasma cyclic-GMP. Also, many fractions inhibited Na+/K(+)-ATPase and/or cross-reacted with anti-ouabain antibody. None of the in vitro assays correlates with natriuretic or pressor effects. This plethora of bioactivities, revealed only with increased sample purity, may account for much of the confusion and multiplicity of crude isolates claimed to be the putative hormone. Presently we are attempting to purify and identify these natriuretic materials. One of these, a 3-substituted indole, has been partially characterized.

Atrial natriuretic peptide may not play a role in diuresis and natriuresis after cardiac operations

Human atria through release of atrial natriuretic peptide play an important role in extracellular fluid homeostasis. This study investigates the perioperative role of atrial natriuretic peptide, renin, angiotensin, aldosterone, and vasopressin in patient response to cardiopulmonary bypass after coronary artery bypass operations. Serum levels of these hormones were measured, along with hemodynamic profiles, urine output, and urine electrolytes, before induction of anesthesia, after discontinuation of cardiopulmonary bypass, 1 hour postoperatively, and 3 hours postoperatively. Serum levels of atrial natriuretic peptide were found to be significantly elevated immediately after discontinuation of cardiopulmonary bypass. These elevations did not correspond temporally to elevated central venous pressure or tachycardia. Significant natriuresis and diuresis were observed during the first postoperative hour. This diuresis failed to correspond temporally with alterations noted in serum levels of atrial natriuretic peptide, renin, angiotensin, aldosterone, and vasopressin. The mechanism responsible for the increases in serum atrial natriuretic peptide and the postoperative natriuresis and diuresis after cardiopulmonary bypass remain unknown.

Electrolyte Disorders Associated with Respiratory Distress Syndrome and Bronchopulmonary Dysplasia

In understanding the various electrolyte disorders associated with respiratory failure, one has to appreciate how the otherwise healthy premature infant maintains extracellular fluid homeostasis. The same physiologic processes that regulate body fluids are affected to varying degrees in the infant with respiratory failure. Maintenance of sodium conservation by the kidney is of critical importance for survival and growth. The immature kidney tends to exhibit excessive sodium wasting especially early on, but appropriate positive sodium balance is achieved generally within the first week. Appropriate reduction in extracellular fluid occurring during the first week or so of life is expected and if it is not allowed to occur may result in dilutional hyponatremia and an increase in pulmonary interstitial water. Diuretics, when used to promote an increase in lung compliance, can themselves generate significant morbidity. Sodium depletion, hypokalemia, alkalosis, and calcium wasting all can either be caused by or exaggerated by the loop diuretics. Thus, one must consider the maturational state of the infant, the infant's response to pulmonary failure, and iatrogenic factors influencing the outcome.

Infusions of recombinant human interleukins 1 alpha and 1 beta cause hypercalcemia in normal mice.

The immune cell products interleukins 1 alpha and -beta, which stimulate osteoclast activity in vitro, are among the most potent bone resorbing factors so far described. Although it appears likely that these cytokines are involved in regulation of trabecular bone turnover, nothing is known of their effects on extracellular fluid calcium concentration. In this report, we show the effects of 72-hr subcutaneous infusions of interleukins 1 alpha and -beta on plasma calcium and bone morphology in mice. Both interleukins 1 caused a marked dose-dependent increase in the plasma calcium. In higher doses, which cause the animals to die, the plasma calcium fell preterminally. Quantitative histomorphometry of bone sections showed evidence of increased numbers of osteoclasts and bone resorption surfaces. The effects were similar to those obtained with infusions of parathyroid hormone. These data suggest that in addition to its potential influence on trabecular bone volume, interleukin 1 may also modulate extracellular fluid calcium homeostasis under conditions in which it is produced excessively.

Comparative Physiology of the Renal Proximal Tubule

The comparative physiology of the renal proximal tubule (PT) is reviewed in the context of vertebrate evolution and vertebrate strategies of salt and water balance. Though extrarenal mechanisms of salt and water balance contribute importantly to extracellular fluid (ECF) homeostasis in the lower vertebrates, the kidney acquires these functions with evolutionary progress and becomes the dominant organ of ECF homeostasis in mammals. In acquiring the major responsibility over the ECF compartment the kidney favored filtration-reabsorption as the preferred mechanism for the rapid turnover of ECF with the advantage of providing quick renal regulatory responses. In spite of this specialization the structure and function of the PT do not appear to have undergone major evolutionary changes. In present-day vertebrates the PT remains as an immensely diverse transport epithelium with impressive capacities for both reabsorptive and secretory work, as exemplified by the mammalian PT with mostly reabsorptive functions and the PT of aglomerular kidneys with mostly secretory functions. The recent evidence for NaCl and fluid secretion in the PT of, unexpectedly, glomerular kidneys is consistent with the functional diversity and the conservative nature of evolution in the case of the PT.

Effects of Prostaglandin E2 and Prostaglandin F2α Upon Urinary Kallikrein Excretion in Rats

1. In normally hydrated rats prostaglandin F2alpha (PGF2alpha) in doses of 5 microgram/100 g body weight given subcutaneously every 2 h (three times) induced a significant increase in urinary kallikrein activity, and in sodium, potassium and water excretion for 8 h after the first injection. In moderately hyperhydrated rats loaded 2.5% of body wt. with 0.5% NaCl solution, PGF2alpha produced similar changes in kallikrein activity and electrolyte excretion. 2. In normally hydrated rats prostaglandin E2 (PGE2) in the same conditions and doses as in 1 had no effect on kallikrein activity, showing a tendency to decrease potassium and water excretion. 3. PGE2 in doses of 5, 12.5 and 25 microgram/100 g body wt. in overhydrated rats given 2.5% and 0.5% NaCl and 5% of tap water/100 g body wt. 1 h later, significantly increased kallikrein activity in the urine collected for 120 min after the injections. A significant decrease in potassium and water excretion was observed with the highest dose. 4. PGF2alpha, had no effect on kallikrein activity in overhydrated rats, but an increase in sodium and a decrease in potassium excretion was seen at the highest dose. 5. The different actions of PGE2 and PGF2alpha may be part of a regulatory mechanism associated with the kallikrein-kinin system which contributes maintainance of extracellular fluid homeostasis.

Observations and Experiments on Dragon-Flies in Brackish Water

Next article FreeObservations and Experiments on Dragon-Flies in Brackish WaterRaymond C. OsburnRaymond C. Osburn Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 40, Number 474Jun., 1906 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/278632 Views: 226Total views on this site Citations: 4Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Kyle M. Knysh, Mark D. Saunders, Leah P. Macintyre, Simon C. Courtenay, Michael R. van den Heuvel Sometimes You Can Add a Bit of Salt: Additional Freshwater Insect Species in Canadian Estuaries, Northeastern Naturalist 29, no.11 (Mar 2022).https://doi.org/10.1656/045.029.0110Klaus W. Beyenbach The plasticity of extracellular fluid homeostasis in insects, The Journal of Experimental Biology 219, no.1717 (Aug 2016): 2596–2607.https://doi.org/10.1242/jeb.129650 William A. Dunson Adaptations of Nymphs of a Marine Dragonfly, Erythrodiplax berenice, to Wide Variations in Salinity, Physiological Zoology 53, no.44 (Sep 2015): 445–452.https://doi.org/10.1086/physzool.53.4.30157882E. M. Walker A PRELIMINARY LIST OF THE ODONATA OF SASKATCHEWAN, The Canadian Entomologist 72, no.22 (May 2012): 26–35.https://doi.org/10.4039/Ent7226-2