Subcellular changes in rat hearts perfused with potassium-free medium

Role of claudins in idiopathic hypercalciuria and renal lithiasis

Paracellular transport in the kidney is mediated by a family of proteins located in the tight junctions called claudins which confers its ionic selectivity. Claudin-2 is highly expressed in the proximal tubule and descending limb of Henle and mediate paracellular reabsorption of sodium and calcium cations. In the thick ascending limb of Henle (TALH) calcium is reabsorbed by a paracellular channel formed by Claudin-16 and-19. Claudin-16 mediates cationic permeability while Claudin-19 increases the cationic selectivity of Claudin-16 by blocking anionic permeability. On the other hand, Claudin 14, that is also located in TALH, inhibits the paracellular permeability of Claudin-16 to calcium. Recent wide genomic association analysis studies have detected four common synonymous variants (genetic polymorphisms of a single nucleotide, SNPs) at the locus of Claudin-14 gene that were significantly associated with the presence of renal lithiasis. Another study of wide genomic association and nephrolithiasis was carried out in the general population but including chromosome X, where claudin-2 gene is located. They detected nine SNPs that had a significant association with renal lithiasis risk. A greater knowledge of the paracellular pathway controlled by claudins and its regulation will allow us to develop future new treatments for idiopathic hypercalciuria and renal lithiasis.

Mechanisms Underlying Calcium Nephrolithiasis

Nephrolithiasis is a worldwide problem with increasing prevalence, enormous costs, and significant morbidity. Calcium-containing kidney stones are by far the most common kidney stones encountered in clinical practice. Consequently, hypercalciuria is the greatest risk factor for kidney stone formation. Hypercalciuria can result from enhanced intestinal absorption, increased bone resorption, or altered renal tubular transport. Kidney stone formation is complex and driven by high concentrations of calcium-oxalate or calcium-phosphate in the urine. After discussing the mechanism mediating renal calcium salt precipitation, we review recent discoveries in renal tubular calcium transport from the proximal tubule, thick ascending limb, and distal convolution. Furthermore, we address how calcium is absorbed from the intestine and mobilized from bone. The effect of acidosis on bone calcium resorption and urinary calcium excretion is also considered. Although recent discoveries provide insight into these processes, much remains to be understood in order to provide improved therapies for hypercalciuria and prevent kidney stone formation. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Sodium Dichloroacetate Pharmacological Effect as Related to Na-K-2Cl Cotransporter Inhibition in Rats

The study objective was to investigate a possible sodium dichloroacetate (DCA) pharmacological mechanism causing an increase in diuresis in rats. The aim was to define characteristics of 24-hour urinary Na⁺, K⁺, Cl^-, Ca²⁺, and Mg²⁺ excretion in Wistar male rats and to evaluate effect of a single-dose DCA and repeated DCA dosage on diuresis. Six control and 6 DCA-treated male rats aged 5 to weeks after a single DCA dose and repeated dosage were tested. The single DCA dose treatment caused a significantly higher 24-hour diuresis when compared to control (P < .05), and it was related to increased Cl^-, Na⁺, and K⁺ urine excretion and a significant increase in Ca²⁺ and Mg²⁺ excretion (P < .05); after the repeated 4-week DCA dosage, the diuresis was not increased, but the excretion of the Na⁺, Cl^-, Ca²⁺, and Mg²⁺ ions was significantly higher. Kidney immunohistochemistry has revealed that DCA continuous treatment results in an increase in the size of Henle loop thick ascending limb epithelial cells (P < .001). The study results show a significantly reduced RNA expression of Na-K-2Cl co-transporter (NKCC1) in thymus of 4-week DCA-treated rats (P < .03). The study data have indicated a possible mechanism of such pharmacological effect to be NKCC inhibition.

Effect of diuretics on renal tubular transport of calcium and magnesium

Calcium (Ca2+) and Magnesium (Mg2+) reabsorption along the renal tubule is dependent on distinct trans- and paracellular pathways. Our understanding of the molecular machinery involved is increasing. Ca2+ and Mg2+ reclamation in kidney is dependent on a diverse array of proteins, which are important for both forming divalent cation-permeable pores and channels, but also for generating the necessary driving forces for Ca2+ and Mg2+ transport. Alterations in these molecular constituents can have profound effects on tubular Ca2+ and Mg2+ handling. Diuretics are used to treat a large range of clinical conditions, but most commonly for the management of blood pressure and fluid balance. The pharmacological targets of diuretics generally directly facilitate sodium (Na+) transport, but also indirectly affect renal Ca2+ and Mg2+ handling, i.e., by establishing a prerequisite electrochemical gradient. It is therefore not surprising that substantial alterations in divalent cation handling can be observed following diuretic treatment. The effects of diuretics on renal Ca2+ and Mg2+ handling are reviewed in the context of the present understanding of basal molecular mechanisms of Ca2+ and Mg2+ transport. Acetazolamide, osmotic diuretics, Na+/H+ exchanger (NHE3) inhibitors, and antidiabetic Na+/glucose cotransporter type 2 (SGLT) blocking compounds, target the proximal tubule, where paracellular Ca2+ transport predominates. Loop diuretics and renal outer medullary K+ (ROMK) inhibitors block thick ascending limb transport, a segment with significant paracellular Ca2+ and Mg2+ transport. Thiazides target the distal convoluted tubule; however, their effect on divalent cation transport is not limited to that segment. Finally, potassium-sparing diuretics, which inhibit electrogenic Na+ transport at distal sites, can also affect divalent cation transport.

Paracellular calcium transport across renal and intestinal epithelia

Calcium (Ca(2+)) is a key constituent in a myriad of physiological processes from intracellular signalling to the mineralization of bone. As a consequence, Ca(2+) is maintained within narrow limits when circulating in plasma. This is accomplished via regulated interplay between intestinal absorption, renal tubular reabsorption, and exchange with bone. Many studies have focused on the highly regulated active transcellular transport pathways for Ca(2+) from the duodenum of the intestine and the distal nephron of the kidney. However, comparatively little work has examined the molecular constituents creating the paracellular shunt across intestinal and renal epithelium, the transport pathway responsible for the majority of transepithelial Ca(2+) flux. More specifically, passive paracellular Ca(2+) absorption occurs across the majority of the intestine in addition to the renal proximal tubule and thick ascending limb of Henle's loop. Importantly, recent studies demonstrated that Ca(2+) transport through the paracellular shunt is significantly regulated. Therefore, we have summarized the evidence for different modes of paracellular Ca(2+) flux across renal and intestinal epithelia and highlighted recent molecular insights into both the mechanism of secondarily active paracellular Ca(2+) movement and the identity of claudins that permit the passage of Ca(2+) through the tight junction of these epithelia.

Analysis of submicromolar concentrations of adenosine in plasma using reversed phase high-performance liquid chromatography

A method is described for the determination of adenosine in small samples of plasma (< 1 ml) using reversed-phase high-performance liquid chromatography (HPLC) in either a simple isocratic or a gradient elution system which gives a clear separation of adenosine from other plasma constituents. Acetone is used to deproteinize plasma and chloroform to remove unwanted lipid soluble material prior to HPLC. 6-Methyladenosine is used as an internal standard for making corrections for changes in concentration during sample processing. Adenosine in plasma could be reliably detected at concentrations lower than its minimum effector concentration as a vasodilator (4 x 10(-8) Mol l(-1) using the isocratic system and 1.9 x 10(-8) Mol l(-1) with gradient elution). The recoveries of adenosine added to blood at concentrations ranging from 2 x 10(-8) Mol l(-1) to 1.4 x 10(-6) Mol l(-1) were from 101.4 +/- 16.9% (n = 4) to 100.0 +/- 3.6% (n = 5). The present method provides a simple, sensitive and selective assay for submicromolar concentrations of adenosine in plasma with good recovery.

Discovery of alpha-Klotho unveiled new insights into calcium and phosphate homeostasis

alpha-Klotho was first identified as the responsible gene in a mutant mouse line whose disruption results in a variety of premature aging-related phenotypes. alpha-Klotho has been shown to participate in the regulation of parathyroid hormone secretion and trans-epithelial transport of Ca(2+) in the choroid plexus and kidney. alpha-Klotho, acting as a cofactor for FGF23, is also a major regulator of vitamin D biosynthesis and phosphate reabsorption in the kidney. These suggest that alpha-Klotho is a key player that integrates a multi-step regulatory system of calcium and phosphate homeostasis. Collectively, the molecular function of alpha-Klotho reveals a new paradigm that may change current concepts in mineral homeostasis and give rise to new insights in this field.

Effects of thiazide on the expression of TRPV5, calbindin-D28K, and sodium transporters in hypercalciuric rats

TRPV5 is believed to play an important role in the regulation of urinary calcium excretion. We assessed the effects of hydrochlorothiazide (HCTZ) on the expression of TRPV5, calbindin-D(28K), and several sodium transporters in hypercalciuric rats. Sprague-Dawley rats were divided into 4 groups; control, HCTZ, high salt, and high salt with HCTZ group in experiment 1; control, HCTZ, high calcium (Ca), and high Ca with HCTZ group in experiment 2. To quantitate the expression of TRPV5, calbindin-D(28K), and sodium transporters, western blotting was performed. In both experiments, HCTZ significantly decreased urinary calcium excretion. TRPV5 protein abundance decreased in all hypercalciuric rats, and restored by HCTZ in both high salt with HCTZ and high Ca with HCTZ group. Calbindin-D(28K) protein abundance increased in the high salt and high salt with HCTZ groups, but did not differ among groups in experiment 2. Protein abundance of NHE3 and NKCC2 decreased in all hypercalciuric rats, and were restored by HCTZ in only high Ca-induced hypercalciuric rats. In summary, protein abundance of TRPV5, NHE3, and NKCC2 decreased in all hypercalciuric rats. The hypocalciuric effect of HCTZ is associated with increased protein abundance of TRPV5 in high salt or calcium diet-induced hypercalciuric rats.

alpha-Klotho: a regulator that integrates calcium homeostasis

Intensive study on calcium homeostasis regulation over the past several decades has established a systematized construal of its role in living phenomena, leaving us with the impression that this field is fairly defined and understood. However, the unveiling of the molecular function of alpha-Klotho has recently given new insight into this field. alpha-Klotho is a unique molecule that plays pivotal roles in: (i) the rapid tuning of extracellular Ca(2+) concentration through transepithelial Ca(2+) transport; (ii) parathyroid hormone secretion and subsequent Ca(2+) increase in the serum, and (iii) the signal transduction of FGF23 that adjusts the calcium concentration by downregulating the production of 1,25(OH)(2)D(3). Through these pathways, alpha-Klotho participates in the regulation of calcium homeostasis of the CSF and blood/body fluids by its actions in the choroid plexus, parathyroid glands and DCT nephrons. In this regard, alpha-Klotho is a key player that integrates 'a multi-step regulatory system of calcium homeostasis' that rapidly adjusts the extracellular calcium concentration and continuously maintains its concentration within a narrow physiological range.

A mathematical model of the diluting power of the cortical thick ascending limb of the loop of Henle

A mathematical model is presented that describes the ionic transport across the cortical thick ascending limb (cTAL) of the Henle's loop, taking into account its tubular geometry. A comprehensive description of the cTAL is given for the first time in terms of potential, ion concentrations and ion fluxes along the tubule. For given ion concentrations at the entrance of the tubule, the model simulates steady-state profiles and allows the fitting of existing experimentally measured values at its exit. Moreover, the model expands the potentialities of experiments in situ and enables testing the effect of different perturbations induced by drugs or mutation-altering transport activity. One of the main insights given by this model is the increase of the lumenal electrical potential from the entrance to the exit of the tubule with a profile determined by the transepithelial electrical potential difference and by the chemical gradients along the lumen, both reflecting transepithelial salt transport. Furthermore, model and experimental results are consistent, showing that when the TAL is perfused at high rates with a diluted NaCl solution in relation to the bath, the transepithelial electrical potential difference increases from 6.7 to 23.0 mV and the potential difference across the basolateral barrier changes very little. The model predicts that the same static head is obtained independently of the NaCl concentration at the entrance of the tubule. A final important insight concerns the lowest reported NaCl concentrations (20-30 mM) at the exit of the tubule, which is controlled by a very tight epithelium, where the back-leak is substantially reduced.

Pathophysiology of hypercalciuria in children

Urinary excretion of calcium is the result of a complex interplay between three organs-namely, the gastrointestinal tract, bone, and kidney-which is finely orchestrated by multiple hormones. Hypercalciuria is believed to be a polygenic trait and is influenced significantly by diet. This paper briefly reviews calcium handling by the renal tubule in normal and in hereditary disorders as it relates to the pathophysiology of hypercalciuria. The effects of dietary sodium, potassium, protein, calcium, and phosphate on calcium excretion, and the association of hypercalciuria with bone homeostasis is discussed, leading to recommendations on means to address excessive urinary calcium excretion.

Physiology of epithelial Ca2+ and Mg2+ transport

Ca2+ and Mg2+ are essential ions in a wide variety of cellular processes and form a major constituent of bone. It is, therefore, essential that the balance of these ions is strictly maintained. In the last decade, major breakthrough discoveries have vastly expanded our knowledge of the mechanisms underlying epithelial Ca2+ and Mg2+ transport. The genetic defects underlying various disorders with altered Ca2+ and/or Mg2+ handling have been determined. Recently, this yielded the molecular identification of TRPM6 as the gatekeeper of epithelial Mg2+ transport. Furthermore, expression cloning strategies have elucidated two novel members of the transient receptor potential family, TRPV5 and TRPV6, as pivotal ion channels determining transcellular Ca2+ transport. These two channels are regulated by a variety of factors, some historically strongly linked to Ca2+ homeostasis, others identified in a more serendipitous manner. Herein we review the processes of epithelial Ca2+ and Mg2+ transport, the molecular mechanisms involved, and the various forms of regulation.

Epithelial Ca2+and Mg2+Channels in Health and Disease

A near constancy of the extracellular Ca(2+) and Mg(2+) concentration is required for numerous physiologic functions at the organ, tissue, and cellular levels. This suggests that minor changes in the extracellular concentration of these divalents must be detected to allow the appropriate correction by the homeostatic systems. The maintenance of the Ca(2+) and Mg(2+) balance is controlled by the concerted action of intestinal absorption, renal excretion, and exchange with bone. After years of research, rapid progress was made recently in identification and characterization of the Ca(2+) and Mg(2+) transport proteins that contribute to the delicate balance of divalent cations. Expression-cloning approaches in combination with knockout mice models and genetic studies in families with a disturbed Mg(2+) balance revealed novel Ca(2+) and Mg(2+) gatekeeper proteins that belong to the super family of the transient receptor potential (TRP) channels. These epithelial Ca(2+) (TRPV5 and TRPV6) and Mg(2+) channels (TRPM6 and TRPM7) form prime targets for hormonal control of the active Ca(2+) and Mg(2+) flux from the urine space or intestinal lumen to the blood compartment. This review describes the characteristics of epithelial Ca(2+) and Mg(2+) transport in general and highlights in particular the distinctive features and the physiologic relevance of these new epithelial Ca(2+) and Mg(2+) channels in (patho)physiologic situations.

Acute regulation of Na+/H+ exchanger NHE3 by parathyroid hormone via NHE3 phosphorylation and dynamin-dependent endocytosis

Parathyroid hormone (PTH) is a potent inhibitor of mammalian renal proximal tubule Na(+) transport via its action on the apical membrane Na(+)/H(+) exchanger NHE3. In the opossum kidney cell line, inhibition of NHE3 activity was detected from 5 to 45 min after PTH addition. Increase in NHE3 phosphorylation on multiple serines was evident after 5 min of PTH, but decrease in surface NHE3 antigen was not detectable until after 30 min of PTH. The decrease in surface NHE3 antigen was due to increased NHE3 endocytosis. When endocytic trafficking was arrested with a dominant negative dynamin mutant (K44A), the early inhibition (5 min) of NHE3 activity by PTH was not affected, whereas the late inhibition (30 min) and decreased surface NHE3 antigen induced by PTH were abrogated. We conclude that PTH acutely inhibits NHE3 activity in a biphasic fashion by NHE3 phosphorylation followed by dynamin-dependent endocytosis.

Control of skeletal muscle perfusion at the onset of dynamic exercise

At the onset of exercise there is a rapid increase in skeletal muscle vascular conductance and blood flow. Several mechanisms involved in the regulation of muscle perfusion have been proposed to initiate this hyperemic response, including neural, metabolic, endothelial, myogenic, and muscle pump mechanisms. Investigators utilizing pharmacological blockade of cholinergic muscarinic receptors and sympathectomy have concluded that neither sympathetic cholinergic nor adrenergic neural mechanisms are involved in the initial hyperemia. Studies have also shown that the time course for vasoactive metabolite release, diffusion, accumulation, and action is too long to account for the rapid increase in vascular conductance at the initiation of exercise. Furthermore, there is little or no evidence to support an endothelium or myogenic mechanism as the initiating factor in the muscle hyperemia. Thus, the rise in muscle blood flow does not appear to be explained by known neural, metabolic, endothelial, or myogenic influences. However, the initial hyperemia is consistent with the mechanical effects of the muscle pump to increase the arteriovenous pressure gradient across muscle. Because skeletal muscle blood flow is regulated by multiple and redundant mechanisms, it is likely that neural, metabolic, and possibly endothelial factors become important modulators of mechanically induced exercise hyperemia following the first 5-10 s of exercise.

Dual mechanisms of regulation of Na/H exchanger NHE-3 by parathyroid hormone in rat kidney

Parathyroid hormone (PTH) is a potent inhibitor of mammalian renal proximal tubule sodium absorption via suppression of the apical membrane Na/H exchanger (NHE-3). We examined the mechanisms by which PTH inhibits NHE-3 activity by giving an acute intravenous PTH bolus to parathyroidectomized rats. Parathyroidectomy per se increased apical membrane NHE-3 activity and antigen. Acute infusion of PTH caused a time-dependent decrease in NHE-3 activity as early as 30 min. Decrease in NHE-3 activity at 30 and 60 min was accompanied by increased NHE-3 phosphorylation. In contrast to the rapid changes in NHE-3 activity and phosphorylation, decrease in apical membrane NHE-3 antigen was not detectable until 4-12 h after the PTH bolus. The decrease in apical membrane NHE-3 occurred in the absence of changes in total renal cortical NHE-3 antigen. Pretreatment of the animals with the microtubule-disrupting agent colchicine blocked the PTH-induced decrease in apical NHE-3 antigen. We propose that PTH acutely cause a decrease in NHE-3 intrinsic transport activity possibly via a phosphorylation-dependent mechanism followed by a decrease in apical membrane NHE-3 antigen via changes in protein trafficking.

Codependence of renal calcium and sodium transport

Calcium and sodium absorption by the kidney normally proceed in parallel. However, a number of physiological, pharmacological, pathological, and genetic conditions dissociate this relation. In each instance, the dissociation can be traced to the distal convoluted tubule, where calcium and sodium transport are inversely related. Based on the identification of the relevant sodium transporters in these cells and on analysis of the mechanism of calcium transport, an explanation for this inverse relation can be developed. Apical membrane calcium entry is mediated by voltage-sensitive calcium channels that are activated upon membrane hyperpolarization. Basolateral calcium efflux is effected primarily by Na+/Ca2+ exchange. According to the model, inhibition of sodium entry through either the Na-Cl cotransporter or the Na+ channel hyperpolarizes the cell, as does parathyroid hormone, thereby activating the calcium entry channel and increasing the driving force for diffusional entry. Membrane hyperpolarization also increases the driving force of calcium efflux through the Na+/Ca2+ exchanger. Thus sodium-dependent changes of calcium transport are indirect and occur secondarily through effects on membrane voltage.

The differential diagnostic value of urinary enzyme and amino acid excretion in children with nephrotic syndrome

Urinary enzymes N-acetyl-beta-D-glucosaminidase (NAG) and gamma-glutamyl transpeptidase (gamma-GT) are sensitive markers of specific renal cell damage. Excessive urinary amino acid excretion may also be an indicator of renal tubular damage. We have evaluated urinary excretion of NAG, gamma-GT and 37 amino acids, phospholipids and dipeptides in 30 children (aged 2.3-18.1 years) with nephrotic syndrome (NS), 23 with minimal change nephrotic syndrome (MCNS), 7 with focal segmental glomerulosclerosis (FSGS) and 16 healthy age-matched controls. Nine MCNS patients were in relapse and 14 in remission. Enzyme activity is expressed as micromoles per milligram urinary creatinine. In FSGS, NAG excretion correlated with the following: blood urea nitrogen (BUN) (r = 0.8), serum protein (r = 0.57), serum cholesterol (r = 0.85), serum albumin (r = -0.68) and proteinuria (r = 0.56). In FSGS the gamma-GT excretion was not significantly different from MCNS in remission or in relapse. In FSGS, gamma-GT excretion correlated with the following: BUN (r = 0.48), serum creatinine (r = -0.66), serum protein (r = -0.54), serum albumin (r = -0.68) and serum cholesterol (r = 0.87). Compared with controls, the urinary excretion of 5 amino acids was increased in FSGS patients as a possible indicator of tubular damage. The value for 7 amino acids was reduced in MCNS patients. Urinary amino acid excretion was not different from controls for the other amino acids in either FSGS or MCNS.(ABSTRACT TRUNCATED AT 250 WORDS)

Progressive hypercalcemia during continuous arterio-venous ultrafiltration (SCUF)

A case report is described of a patient who developed severe hypercalcemia during slow continuous arterio-venous ultrafiltration (SCUF). Which was instituted because of refractory congestive heart failure with pulmonary edema. The hypercalcemia was due to a preexisting mild hyperparathyroidism and aggressive fluid removal by SCUF. The differential diagnosis of hypercalcemia in the intensive care ward is discussed.

Plasma concentrations of atrial natriuretic factor and hemodynamics in pregnancy-induced hypertension

Plasma values of atrial natriuretic factor (ANF) were evaluated in 31 women with pregnancy-induced hypertension (PIH) and 31 normal pregnant women at the same age of gestation. In 27 women with PIH and 27 normal pregnant women forearm venous tone (FVT) was evaluated by Strain Gauge Plethysmography. Forearm vascular resistance (FVR) was measured as the ratio of mean blood pressure (MBP) to forearm blood flow. In addition Cardiac Index (CI) by means of transthoracic electrical bioimpedance and total peripheral vascular resistance (TPR) (with the Frank Equation) were also measured. In comparison with the normal pregnant women, the women with PIH had similar values of hematocrit (as an index of plasma volume) and significantly higher levels of FVR and TPR, while ANF plasma values did not differ significantly. Subdividing the women with PIH in relation to the presence of proteinuria (greater than or equal to 0.3 g/l), those with proteinuria, in addition to significantly higher levels of FVR and TPR, had significantly higher levels of FVT than normal pregnant women, while ANF plasma values were higher even though the difference was only near the level of significance. Hypertensive women with proteinuria also had higher values of FVT than hypertensive women without proteinuria. By means of multiple regression ANF did not show any significant correlations with hematocrit or sodium excretion. Hypertension with proteinuria seems to represent a more severe form of the disease in which, in addition to the probable influence of other factors such as the renin-angiotensin and prostaglandin systems, a greater increase in peripheral sympathetic tone than in hypertension alone appears to be present, causing a reduction in venous compliance in addition to the elevation in FVR and TPR, with increase in central blood volume and atrial stretch. This may explain the higher ANF plasma levels in these patients in comparison with normal pregnant women, even though the absence of a significant correlation of ANF with hematocrit and the fact that ANF increase was only near the level of significance may suggest a change in the relation between ANF secretion and atrial volume receptors in pregnancy either normal or complicated by hypertension. ANF does not seem to play an important role in water and sodium excretion in PIH probably because of the presence of very high plasma levels of hormones such as aldosterone, progesterone and oestriol which, together with renal prostaglandins, seem to be involved in diuresis and natriuresis in pregnancy.

Effect of parathyroid hormone on the connecting tubule from the rabbit kidney: biphasic response of transmural voltage

The effect of parathyroid hormone (PTH) on ion transport was examined by observing transmural (VT) and basolateral membrane voltage (VB) in the in vitro perfused rabbit connecting tubule. Addition of 10 nmol/l PTH to the bath induced a biphasic response of VT, with hyperpolarization followed by depolarization. Chlorophenylthioadenosine cyclic 3',5'-monophosphate mimicked the effect of PTH, which did not change the VB in the connecting tubule cell, but mainly caused changes in the apical membrane voltage. The VT of distal convoluted tubule and the cortical collecting duct were not affected by PTH. Elimination of Na+ from the lumen abolished the PTH-induced VT responses in the connecting tubule. In the presence of 10 mumol/l amiloride, PTH caused an initial hyperpolarization but did not induce the late depolarization. The same was seen in the absence of luminal Ca2+. Either addition of 0.1 mmol/l ouabain to the bath or elimination of bath Na+ completely abolished the PTH-induced VT changes. The presence of 5 mmol/l Ba2+ in the lumen did not affect the response to PTH. These findings indicate that the initial hyperpolarization may be caused by an increase in Na+ influx across the luminal membrane through an amiloride-insensitive Na+ conductive pathway and that the late depolarization may be caused by the decrease in Na+ influx through the amiloride-sensitive Na+ conductive pathway. Luminal Ca2+ is necessary for the late depolarization caused by PTH.(ABSTRACT TRUNCATED AT 250 WORDS)

Potentiation of calcitonin by corticosteroids during the treatment of the hypercalcaemia of malignancy

Some patients treated for the hypercalcaemia of malignancy develop renal tubular resistance to the effects of calcitonin which is independent of concurrent changes in sodium excretion. This type of resistance can be overcome by the addition of corticosteroids. In other patients apparent renal resistance to calcitonin is a consequence of reduced sodium excretion and is unaffected by corticosteroids.

Assessment of renal and skeletal components of hypercalcemia

The management of hypercalcemia of malignancy is guided by assessments of its various components. Since the intestine usually makes no contribution to hypercalcemia under these circumstances, the problem is to measure the net efflux of calcium out of bone and the ability of the kidneys to excrete the unwanted calcium load. Established relationships between serum and urinary calcium excretion rates allow the quantitation of the relative contribution of an impaired glomerular filtration rate, of reduced renal tubular calcium reabsorption, and of increased bone resorption. Since the renal handling of calcium is closely related to that of sodium in the proximal nephron, the rate of sodium excretion is an important variable in these measurements. A practical approach to the separation of hypercalcemia into its renal and skeletal components is described in this article. Examples of how these measurements can be used to assess the responses to various types of therapy for malignancy-associated hypercalcemia are also given.

Contribution of amino acids in protective solutions to postischemic functional recovery of canine kidneys

Amino acids are known to increase glomerular filtration rate (GFR). There is also an early resumption of filtration following 2-h renal ischemic stress under protection by histidine-buffered histidine-tryptophan-ketoglutarate solution (HTK), possibly due in part to an amino acid effect. Hence, we have examined the possibility of further enhancing the postischemic GFR by adding 32 (ASP I; 4 mM Mg2+) or 36 (ASP II; 6 mM Mg2+) mM L-aspartate (asp) or 32 mM DL-aspartate (ASP III) to the HTK solution in place of chloride. After infusion of 500 ml 5% glucose, canine kidneys were protected by an 8-min perfusion with HTK (n = 5), ASP I (n = 4), ASP II (n = 5) or ASP III-solution (n = 3). The subsequent ischemia lasted for 2 h at 27-31 degrees C. During reperfusion, both GFR and filtration fraction (FF) were higher in kidneys protected by L-aspartate-containing solutions. ASP III showed no improvement against HTK. An additional preischemic intra-aortal application of HTK or ASP I solution just above the exit of the renal arteries prior to the intrinsic protective perfusion further raised the postischemic GFR. The present results suggest that L-aspartate but also histidine may have favorable amino acid effects in renal protective solutions in addition to known positive effects of histidine.

Amino acid metabolism in uremia

The uremic syndrome is multifactorial, and affects most tissues and organs. Disturbances in protein and amino acid metabolism may play important roles, especially in chronic uremia, either directly or by production of toxic metabolites, with resultant negative nitrogen (N) balance, muscle wasting, reduced protein synthesis, and characteristically abnormal intracellular free amino acid concentrations. There are also grossly abnormal amino acid levels in the plasma of uremic patients, e.g., increases in conjugated amino acids, high levels of several nonessential and low levels of essential amino acids. The ratios of tyrosine/phenylalanine and of valine/glycine are decreased. The low tryptophan levels may contribute to encephalopathy as a result of an imbalance in neurotransmitter synthesis. Citrulline is found in excess; the explanation is unresolved. There are elevated concentrations of the sulfur-containing amino acids: cystine, taurine, cystathionine, and homocysteine. Excess of the latter is implicated in the atherogenesis of renal failure. Disturbed metabolism and interorgan exchange of amino acids in the uremic state explains some of the abnormalities in tissue and plasma concentrations of individual amino acids. Enzymatic defects are involved in the disturbed metabolism of branched chain amino acids (BCAA), with possible antagonism among them, which impairs growth and amino acid utilization. Carbohydrate intolerance, associated with insensitivity of peripheral tissues to insulin and hyperinsulinemia, elicits decreased plasma BCAA. Protein synthesis rates in normal and pathological conditions are more closely related to the intracellular amino acid pool than to plasma amino acid levels. Concentrations of individual amino acids in the plasma pool are poor indicators of their intracellular concentrations. Muscle contains the largest pool of protein and free amino acids in the body. In chronic renal failure patients, the intracellular concentrations of valine, threonine, lysine, and carnosine are low. With low protein diets and in hemodialysis, serine, tyrosine, and taurine often are also low. The low taurine may be related to fatigue and to uremic cardiomyopathies. The commonly used amino acid supplements generally fail to correct the intracellular amino acid deficits. A "New Formula" has been developed to correct these intracellular amino acid abnormalities, and to supplement a low protein diet. It provides more valine than leucine, increased tyrosine and threonine, and less histidine, leucine, isoleucine, lysine, methionine, and phenylalanine than in formulas customarily used for patients with chronic renal failure. It is uncertain whether other ap

Clinical and biochemical aspects of pregnancy-induced hypertension

In order to study what characteristics accompany the development of pregnancy-induced hypertension (PIH) and what parameters, if any, differentiate hypertension alone from hypertension with proteinuria, we evaluated 119 women with PIH who had hypertension alone, 73 women with PIH who had hypertension and proteinuria greater than or equal to 0.3 g/l, 63 women with normal pregnancy, 20 normal non-pregnant women. In comparison with normal pregnant women and normal non-pregnant women, women with PIH showed an increase in heart rate, suggesting an increased peripheral sympathetic tone, and an initial derangement in renal function as shown by the increase in serum uric acid and reduction in sodium excretion and total and fractional calcium excretion at any given level of sodium excretion. These changes were more marked in patients with hypertension and proteinuria. Higher levels of systolic blood pressure (SBP) were present in women with hypertension alone who subsequently developed proteinuria, compared with those who had only hypertension until term. According to our data hypertension alone and hypertension with proteinuria seem to be two aspects of only differing severity of the same disease.

Quantitative microchemical imaging of calcium in Na-K pump inhibited heart cells

Quantitative electron probe X-ray imaging techniques have been utilized to determine simultaneously the element content within a single cultured embryonic chick heart cell and its intracellular compartments as well as the average elemental content of several heart cells within a population. These features of microchemical imaging have permitted establishment of data regarding: (1) the heterogeneity of calcium accumulation in mitochondrial, cytoplasmic and nuclear compartments under conditions which elevate total cell calcium without producing irreversible cell injury; and (2) the variability of calcium accumulation from cell to cell within the population sampled. The results indicate that during Na-K pump inhibition (K-free HT-BSS, 10(-4) M ouabain, 60 min) elevation of mitochondrial calcium, measured in situ by electron probe X-ray microanalysis, to levels more than 100 times greater than in the basal state, may not cause irreversible mitochondrial uncoupling and cell death.

Local changes in fractional saturation of cGMP- and cAMP-receptors in intestinal microvilli in response to cholera toxin and heat-stable Escherichia coli toxin

Cyclic nucleotide modulation of electrolyte transport across intestinal brushborder membranes is initiated by binding of cGMP and cAMP to high-affinity receptors at the interior of the microvilli. Previously these receptors have been identified by photoaffinity-labelling techniques as regulatory domains of cGMP- and cAMP-dependent protein kinases. In the present study, the receptor concentration in isolated brushborder membrane vesicles and their fractional saturation in absorptive and secretory states of the tissue were estimated. In microvillous membrane vesicles isolated from rat small intestine in the absorptive state, about 10% of the total number of cGMP receptors (25.5 pmol/mg protein) and 40% of all cAMP receptors (28.7 pmol/mg protein) were occupied by endogenous cyclic nucleotides. Luminal exposure of the intestinal segments in vivo to heat-stable Escherichia coli toxin for 3-5 min increased the occupancy of cGMP receptors by about 5-fold without affecting receptor-bound cAMP levels. In contrast, incubation with cholera toxin for 2 h increased the fractional saturation solely of cAMP receptors by 2-fold. Addition of heat-stable E. coli toxin to cholera toxin-pretreated segments, again raising the cGMP levels by 5-fold, did not reduce the amount of receptor-bound cAMP. This finding argues against the concept that increased levels of cAMP during cholera would mimick cGMP effects on ion transport by low-affinity binding to microvillar cGMP receptors. This analysis of local changes in cyclic nucleotide levels at the microvillous level might help to explore the mechanism of action of other secretagogues or antidiarrhoeal agents and to delineate a possible compartmentation of cGMP and cAMP pools within the intestinal mucosa responding differently to external signals.

ATP-dependent Ca2+ transport and Na+/Ca2+ exchange system in renal basolateral plasmamembranes of spontaneously hypertensive rats

A common abnormality of cellular Ca2+ handling in most tissues of spontaneously hypertensive rats (SHR) has been suggested. Therefore we investigated the ATP-dependent Ca2+ transport and Na+/Ca2+ exchange system in basolateral membrane vesicles (BLMV) of renal cortices from SHR and normotensive Wistar-Kyoto rats (WKY) at 12 and 20 weeks of age. In WKY the maximal transport rate of the ATP-dependent Ca2+ transport was 5.7 nmol/min/mg prot with an affinity for Ca2+ of 0.14 microM. These values were not significantly different in SHR at both ages studied. High concentrations of Na+ inhibited ATP-dependent Ca2+ uptake by 40% in BLMV of SHR and WKY. Low concentrations of Na+ stimulated ATP-dependent Ca2+ transport 20% in both rats. These findings suggest equal Na+/Ca2+ exchange activity in WKY and SHR. The present study failed to show a significant change in ATP-dependent Ca2+ transport and Na+/Ca2+ exchange activity in renal BLMV in SHR, suggesting that the Ca2+ homeostasis of the cortical cells is normal in SHR as far as the plasmamembrane is concerned.

Intracellular adenosine in isolated rat liver cells

Our objective was to determine whether a non-extracellular pool of adenosine exists in mammalian cells. Rat liver cells were dispersed by a collagenase perfusion technique and suspended in buffered salt solution. The adenosine content of these suspensions rose during hypoxia. Exogenous adenosine deaminase prevented or reversed the hypoxic increment but failed to reduce suspension adenosine levels to zero. This residual adenosine pool (average size = 85 +/- 10 pmol/mg protein) was not located in the extracellular medium, on surface adenosine receptors or in solution in the cytoplasm. A likely locus is the adenine-analog binding protein which has been described for liver and other tissues. Thus, our study supports the existence of an intracellular adenosine pool in isolated rat liver cells which is a large fraction of the total tissue adenosine. This situation may exist in other cell types as well, based on the ubiquity of the adenosine binding protein. Tissue adenosine content may not, therefore, accurately reflect interstitial adenosine concentration; thus, such measurements must be interpreted cautiously. It is not clear what, if any, functional role this putative, intracellular, bound adenosine pool plays in local vasoregulation.

Pharmacodynamics and pharmacokinetics of xipamide in patients with normal and impaired kidney function

The effect of a single oral dose of 40 mg xipamide on urinary excretion of Na+, K+, Cl-, Ca2+ and Mg2+ in healthy subjects and in patients with varying degrees of renal impairment was compared with various conventional diuretics. Xipamide caused marked excretion of Na+ and Cl-, whereas the diuretic produced only moderate kaliuresis; urinary excretion of Ca2+ was increased in proportion to Na+, like the loop diuretics. Xipamide affected electrolyte excretion even in patients with a creatinine clearance below 30 ml/min, as do the loop diuretics, too. Therefore, the pharmacodynamic characteristics of xipamide are more like those of a loop diuretic than of a thiazide. Xipamide was good bioavailable, its t 1/2 beta was 7 h and urinary recovery of the undegraded drug was 40% of the given dose. In renal insufficiency, t 1/2 beta increased from 7 to only 9h, yielding a moderate increase in the AUC. Urinary recovery of the drug was reduced in proportion to the reduction in the creatinine clearance of the patient. Therefore, significant extrarenal elimination of the diuretic must be postulated, which suffices to prevent significant drug accumulation in renal failure.

Dietary calcium in human hypertension

A pilot survey was made of the dietary calcium intake of normotensive and hypertensive individuals. Compared to 44 normotensive controls, 46 subjects with essential hypertension reported significantly less daily calcium ingestion (668 +/- 55 milligrams compared to 886 +/- 89 milligrams). The intake of other nutrients, including sodium and potassium, was very similar in the two groups. The hypertensives differed from the controls primarily in their consumption of nonfluid dairy products. The data suggest that inadequate calcium intake may be a previously unrecognized factor in the development of hypertension.

The effects of altered cation balance on the fine structure of hypoxic myocardial cells

To determine whether the changes in intracellular/extracellular cation balance which develop in ischaemic myocardium are responsible for the fine structural changes seen in such tissue, thin slices of normal canine ventricle were incubated under hypoxic conditions at 37 degrees C and physiological pH in balanced salt solution (BSS), isotonic NaCl and isotonic KCl. Slices from each solution were fixed at 10-120 min intervals and examined by light and electron microscopy. For 60 min, tissue from both NaCl and KCl showed good overall preservation of cell architecture and only mild subcellular alterations including aggregation of nuclear chromatin, disappearance of glycogen granules, and swelling of sarcoplasmic reticulum. Tissue from BSS showed early development of intramitochondrial dense inclusions together with focal contraction-band damage similar to that seen in temporarily ischaemic, re-perfused heart muscle and at the margins of infarcts. These changes thus appear to be promoted by divalent cations. The progressive reversal of monovalent cation balance in an area of permanent and severe ischaemia does not appear to be a major determinant of fine structural change.

Effect of calcium, furosemide and chlorothiazide on net volume reabsorption and basolateral membrane potential of the distal tubule

In the distal tubule of the isolated kidney of Amphiuma net volume reabsorption (split-oil droplet method) and basolateral membrane potential (psi b) were measured. Luminal perfusion solution could be changed rapidly from 108 mmol . 1-1 NaCl plus 0.1 mmol . 1-1 calcium to solutions containing 103 or 97 mmol . 1-1 NaCl plus 3.6 or plus 7.2 mmol . 1-1 calcium. Furthermore, 10(-4) mol . 1-1 furosemide or chlorothiazide were applied luminally. (1) Addition of 7.2 mmol . 1-1 calcium hyperpolarized psi b from -73.4 mV to -108.3 mV and inhibited net volume reabsorption. (2) Similarly, when furosemide was injected, psi b was hyperpolarized and net volume reabsorption reduced. Application of both high calcium and furosemide further inhibited volume reabsorption. (3) The effects of chlorothiazide were similar to those of furosemide. However, when both high calcium and chlorothiazide were administered psi b and volume reabsorption were almost normalized. (4) The data are consistent with the hypothesis that calcium and the diuretics interfere primarily with chloride uptake across the luminal membrane and thus reduce sodium chloride transport. When chlorothiazide in the presence of high luminal calcium almost normalized chloride transport, it is likely that its effects were by stimulating calcium transport and thus increasing intracellular calcium activity.

Post-mortem elemental redistribution in rat studied by x-ray microanalysis and electron microscopy

Post-mortem elemental redistribution in various tissues from rat was studied by means of electron probe X-ray microanalysis, and correlated with morphological changes in these tissues. Pancreas, liver and cardiac muscle were removed from the animal either immediately, or after some hours after death. Elemental distribution at the cellular level was studied by X-ray microanalysis of thick cryosections. Calcium redistribution at the subcellular level was studied using tissue fixed with glutaraldehyde/oxalate. In all tissues, post-mortem redistribution of electrolytes had taken place within 2 h. The cellular concentrations of Na, Cl and Ca increased markedly, those of Mg and K decreased; no significant changes were found in the concentrations of P and S. The number of oxalate precipitates (indicating the presence of calcium) increased both in the mitochondria and in the cytoplasm and endoplasmic reticulum, reaching a maximum at 2 h. Morphological changes included mitochondrial swelling and vesiculation of the endoplasmic reticulum. Since the post-mortem ion shifts are similar to those encountered in some diseases and types of cell injury, great care has to be taken in the interpretation of X-ray microanalytical results from autopsy material.