The ionic environment and metabolic control

Ca-doping interfacial engineering and glycolysis enable rapid charge separation for efficient phototherapy of MRSA-infected wounds

Methicillin-resistant Staphylococcus aureus (MRSA) is the primary pathogenic agent responsible for epidermal wound infection and suppuration, seriously threatening the life and health of human beings. To address this fundamental challenge, we propose a heterojunction nanocomposite (Ca-CN/MnS) comprised of Ca-doped g-C3N4 and MnS for the therapy of MRSA-accompanied wounds. The Ca doping leads to a reduction in both the bandgap and the singlet state S1-triplet state T2 energy gap (ΔEST). The Ca doping also facilitates the two-photon excitation, thus remarkably promoting the separation and transfer of 808 nm near-infrared (NIR) light-triggered electron-hole pairs together with the built-in electric field. Thereby, the production of reactive oxygen species and heat are substantially augmented nearby the nanocomposite under 808 nm NIR light irradiation. Consequently, an impressive photocatalytic MRSA bactericidal efficiency of 99.98 ± 0.02 % is achieved following exposure to NIR light for 20 min. The introduction of biologically functional elements (Ca and Mn) can up-regulate proteins such as pyruvate kinase (PKM), L-lactate dehydrogenase (LDHA), and calcium/calmodulin-dependent protein kinase (CAMKII), trigger the glycolysis and calcium signaling pathway, promote cell proliferation, cellular metabolism, and angiogenesis, thereby expediting the wound-healing process. This heterojunction nanocomposite, with its precise charge-transfer pathway, represents a highly effective bactericidal and bioactive system for treating multidrug-resistant bacterial infections and accelerating tissue repair. STATEMENT OF SIGNIFICANCE: Due to the bacterial resistance, developing an antibiotic-free and highly effective bactericidal strategy to treat bacteria-infected wounds is critical. We have designed a heterojunction consisting of calcium doped g-C3N4 and MnS (Ca-CN/MnS) that can rapidly kill methicillin-resistant Staphylococcus aureus (MRSA) without damaging normal tissue through a synergistic effect of two-photon stimulated photothermal and photodynamic therapy. In addition, the release of trace amounts of biofunctional elements Mn and Ca triggers glycolysis and calcium signaling pathways that promote cellular metabolism and cell proliferation, contributing to tissue repair and wound healing.

Potassium Channels, Glucose Metabolism and Glycosylation in Cancer Cells

Potassium channels emerge as one of the crucial groups of proteins that shape the biology of cancer cells. Their involvement in processes like cell growth, migration, or electric signaling, seems obvious. However, the relationship between the function of K+ channels, glucose metabolism, and cancer glycome appears much more intriguing. Among the typical hallmarks of cancer, one can mention the switch to aerobic glycolysis as the most favorable mechanism for glucose metabolism and glycome alterations. This review outlines the interconnections between the expression and activity of potassium channels, carbohydrate metabolism, and altered glycosylation in cancer cells, which have not been broadly discussed in the literature hitherto. Moreover, we propose the potential mediators for the described relations (e.g., enzymes, microRNAs) and the novel promising directions (e.g., glycans-orinented drugs) for further research.

Assessing K+ ions and K+ channel functions in cancer cell metabolism using fluorescent biosensors

Cancer represents a leading cause of death worldwide. Hence, a better understanding of the molecular mechanisms causing and propelling the disease is of utmost importance. Several cancer entities are associated with altered K⁺ channel expression which is frequently decisive for malignancy and disease outcome. The impact of such oncogenic K⁺ channels on cell patho-/physiology and homeostasis and their roles in different subcellular compartments is, however, far from being understood. A refined method to simultaneously investigate metabolic and ionic signaling events on the level of individual cells and their organelles represent genetically encoded fluorescent biosensors, that allow a high-resolution investigation of compartmentalized metabolite or ion dynamics in a non-invasive manner. This feature of these probes makes them versatile tools to visualize and understand subcellular consequences of aberrant K⁺ channel expression and activity in K⁺ channel related cancer research.

Heat flows in rock cracks naturally optimize salt compositions for ribozymes

Catalytic nucleic acids, such as ribozymes, are central to a variety of origin-of-life scenarios. Typically, they require elevated magnesium concentrations for folding and activity, but their function can be inhibited by high concentrations of monovalent salts. Here we show that geologically plausible high-sodium, low-magnesium solutions derived from leaching basalt (rock and remelted glass) inhibit ribozyme catalysis, but that this activity can be rescued by selective magnesium up-concentration by heat flow across rock fissures. In contrast to up-concentration by dehydration or freezing, this system is so far from equilibrium that it can actively alter the Mg:Na salt ratio to an extent that enables key ribozyme activities, such as self-replication and RNA extension, in otherwise challenging solution conditions. The principle demonstrated here is applicable to a broad range of salt concentrations and compositions, and, as such, highly relevant to various origin-of-life scenarios.

In the Right Place at the Right Time: Regulation of Cell Metabolism by IP3R-Mediated Inter-Organelle Ca2+ Fluxes

In the last few years, metabolism has been shown to be controlled by cross-organelle communication. The relationship between the endoplasmic reticulum and mitochondria/lysosomes is the most studied; here, inositol 1,4,5-triphosphate (IP3) receptor (IP3R)-mediated calcium (Ca²⁺) release plays a central role. Recent evidence suggests that IP3R isoforms participate in synthesis and degradation pathways. This minireview will summarize the current findings in this area, emphasizing the critical role of Ca²⁺ communication on organelle function as well as catabolism and anabolism, particularly in cancer.

Electrolyte disorders

Electrolyte disorders can result in life-threatening complications. The kidneys are tasked with maintaining electrolyte homoeostasis, yet the low glomerular filtration rate of neonatal kidneys, tubular immaturity, and high extrarenal fluid losses contribute to increased occurrence of electrolyte disorders in neonates. Understanding the physiologic basis of renal electrolyte handling is crucial in identifying underlying causes and initiation of proper treatment. This article reviews key aspects of renal physiology, the diagnostic workup of disorders of plasma sodium and potassium, and the appropriate treatment, in addition to inherited disorders associated with neonatal electrolyte disturbances that illuminate the physiology of renal electrolyte handling.

Hypercalcemic and calcium-antagonistic effects on insulin release and oral glucose tolerance in man

The present investigation was carried out in order to study the acute effects of hypercalcemia on the carbohydrate metabolism in healthy subjects and in patients with non insulin-dependent diabetes mellitus (NIDDM). The combined effect of hypercalcemia and a calcium-antagonistic agent (verapamil) was also studied in healthy subjects, in patients with chronic hypercalcemia, e.g. primary hyperparathyroidism (PHPT). Calcium, infused intravenously to fasting diabetic patients, induced a significant decline in the blood glucose concentration. This was not the case in healthy individuals. When glucose was administered orally during exogenous hypercalcemia, glucose tolerance decreased significantly in the diabetic as well as in the healthy individuals. Verapamil, however, abolished this hypercalcemia effect, and even improved the tolerance for oral glucose when administered intravenously together with calcium in the patients with NIDDM. No such effect of verapamil was seen in the healthy subjects or in the patients with PHPT. Insulin activity was left unaffected by hypercalcemia and/or verapamil in all experimental situations. These findings thus imply that hypercalcemia decreases the tolerance for oral glucose in normoglycemic subjects, and further deteriorates the glucose tolerance in patients with an already impaired carbohydrate metabolism. Verapamil, on the other hand, appears to counteract this effect of hypercalcemia in diabetic patients. Since insulin remains unaffected by calcium and verapamil in the above mentioned situations, it is reasonable to assume that the calcium- and verapamil-induced effects on the glucose tolerance are due to glucose-regulatory factors other than insulin.

Reversible renal failure caused by hypercalcemia. A retrospective study

The influence of hypercalcemia on renal function was studied retrospectively in 13 patients suffering from primary hyperparathyroidism, sarcoidosis, vitamin D intoxication, malignant lymphoma or chronic lymphatic leucemia. Different kinds of treatment, depending upon the primary disease, often induced a rapid fall in the serum calcium concentration. The serum creatinine concentration always fell simultaneously. The serum phosphate concentration fell in all but two patients. Changes in serum calcium and serum creatinine correlated significantly (p less than 0.001), as did changes in serum calcium and serum phosphate concentrations (p less than 0.05). Serum calcium/serum creatinine and serum calcium/serum phosphate ratios were significantly higher in patients with primary hyperparathyroidism than in patients with hypercalcemia of non-hyperparathyroid origin (p less than 0.01, p less than 0.001). This suggests a different effect of calcium on the glomerular filtration rate in hyperparathyroid and non-hyperparathyroid patients, the latter group being more sensitive to the influence of hypercalcemia. Possible explanations for this difference, such as a protective effect of PTH on the glomerular filtration, are discussed.

The hydrogen ion in normal metabolism: a review

The production of hydrogen ions (H+) by metabolic processes is described, with particular emphasis on glycolysis and ketogenesis. Total metabolic production of H+ is approximately 150 g day-1 but utilization closely balances production, so that intracellular and extracellular H+ production is maintained within narrow limits. H+ is generated at several sites in glycolysis but no net H+ production occurs unless the ATP formed is hydrolysed. The other main source of metabolic H+ production is ketogenesis. Here H+ accumulation depends on both the relative dominance of ketone body production over utilization and the loss of base in urine. The H+ is produced during the synthesis of 3-hydroxy-3-methylglutaryl-CoA and not because of dissociation of acetoacetic acid. Lipolysis and re-esterification of fats are additional major producers of H+, while net H+ production also occurs with pathological accumulation and incomplete combustion of other organic acids. Many metabolic systems are sensitive to the changes in pH. These effects have been examined in vivo using an ammonium chloride acidaemia model in the rat. Severe insulin resistance and impaired glucose metabolism in liver and muscle were found. One mechanism involved inhibition, by H+, of the binding of insulin to its receptors. Further mechanisms include inhibition of key glycolytic enzymes including phosphofructokinase. It is concluded that too little attention is paid to metabolic production of hydrogen ions and to their effects, in turn, on metabolism.

Potassium transport in the maturing kidney

The distal nephron and colon are the primary sites of regulation of potassium (K(+)) homeostasis, responsible for maintaining a zero balance in adults and net positive balance in growing infants and children. Distal nephron segments can either secrete or reabsorb K(+) depending on the metabolic needs of the organism. In the healthy adult kidney, K(+) secretion predominates over K(+) absorption. Baseline K(+) secretion occurs via the apical low-conductance secretory K(+) (SK) channel, whereas the maxi-K channel mediates flow-stimulated net urinary K(+) secretion. The K(+) retention characteristic of the neonatal kidney appears to be due not only to the absence of apical secretory K(+) channels in the distal nephron but also to a predominance of apical H-K-adenosine triphosphatase (ATPase), which presumably mediates K(+) absorption. Both luminal and peritubular factors regulate the balance between K(+) secretion and absorption. Perturbation in any of these factors can lead to K(+) imbalance. In turn, these factors may serve as effective targets for the treatment of both hyper-and hypokalemia. The purpose of this review is to present an overview of recent advances in our understanding of mechanisms of K(+) transport in the maturing kidney.

Cyclic nucleotide-gated channels in non-sensory organs

Cyclic nucleotide-gated channels represent a class of ion channels activated directly by the binding of either cyclic-GMP or cyclic-AMP. They carry both mono and divalent cations, but select calcium over sodium. In the majority of the cases studied, binding of cyclic nucleotides to the channel results in the opening of the channel and the influx of calcium. As a consequence, cytosolic free calcium levels increase leading to the modifications of calcium-dependent processes. This represents and important link in the chain of events leading to the physiological response. Cyclic nucleotide-gated channels were discovered in sensory cell types, in the retina, and in olfactory cells, and were extensively studied in those cells. However, it is becoming increasingly evident that such channels are present not only in sensory systems, but in most, if not all, cell types where cyclic nucleotides play a role in signal transduction. A hypothesis is presented here which attributes physiological importance to these channels in non-sensory organs. Four examples of such channels in non-sensory cells are discussed in detail: those in the liver, in the heart, in the brain, and in the testis with the emphasis on the possible physiological roles that these channels might have in these organs.

Permeable analogues of cGMP promote hepatic calcium inflow induced by the synergistic action of glucagon and vasopressin but inhibit that induced by vasopressin alone

Treatment of perfused rat liver with the nitric oxide-generating reagent molsidomine led to substantial increases in cGMP without itself affecting basal Ca2+ fluxes. Under these conditions the ability of glucagon plus vasopressin to induce Ca2+ influx was greatly enhanced. The permeable analogue of cGMP (8-bromo-cGMP) enhanced glucagon plus vasopressin-induced Ca2+ influx to a similar extent as that with molsidomine. This suggests that the effect of the latter is attributable to the generation of cGMP which itself enhances the ability of the two hormones to induce synergistic Ca2+ influx. While 8-bromo-cGMP (or molsidomine) did not influence Ca2+ fluxes induced by glucagon, these agents strongly inhibited Ca2+ influx induced by vasopressin alone. These data show that while 8-bromo-cGMP has no effect on basal Ca2+ fluxes, it is able to modify the Ca2+ influx induced by glucagon and vasopressin action in hepatic tissue.

Calcium: its modulation in liver by cross-talk between the actions of glucagon and calcium-mobilizing agonists

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Evaluation of glucose tolerance, insulin secretion, and insulin action in patients with primary hyperparathyroidism before and after surgery

Glucose tolerance, insulin secretion, and insulin sensitivity were evaluated in 8 asymptomatic patients with primary hyperparathyroidism (PHPT) before and at least 8 weeks after surgical correction of PHPT by means of the hyperglycemic clamp technique. In addition, 15 sex- and age-matched control subjects were investigated for comparative reasons by the same technique. Glucose metabolized (M) during the hyperglycemic clamp was not significantly (NS) different between patients with PHPT and controls (7.9 +/- 2.3 vs. 6.3 +/- 1.9 mg/kg/min). However, insulin secretion (I) was significantly elevated in patients with PHPT compared to controls (87 +/- 17 vs. 45 +/- 12 microU/ml, P less than 0.05). The calculated insulin sensitivity index (M/I) was significantly reduced in PHPT compared to controls (11.0 +/- 2.1 vs. 15.2 +/- 1.4 mg/kg/min per microU/ml x 100, P less than 0.05). Comparing patients with PHPT before and after surgery, the M value, which is a measure of glucose tolerance, was not significantly different (7.9 +/- 2.3 vs. 7.8 +/- 1.5 mg/kg/min). However, insulin secretion was significantly lower after surgical correction of PHPT compared to the preoperative situation (48 +/- 9 microU/ml vs. 87 +/- 17 microU/7 ml, P less than 0.01). The calculated M/I rose significantly after surgery compared to the preoperative value (11 +/- 2.1 vs. 17.6 +/- 2.7 mg/kg/min per microU/ml x 100, P less than 0.001). We conclude that disturbed carbohydrate metabolism, such as insulin hypersecretion and insulin resistance, in patients with PHPT is an early finding in this disease and that these early disturbances in glucose metabolism are, however, fully reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Kidney function in response to salt feeding in rainbow trout (Salmo gairdneri Richardson)

1. The effect of high levels of dietary salt up to 12% NaCl on kidney function in freshwater rainbow trout was investigated. 2. Renal response to dietary NaCl load includes increases in urinary flow rate and glomerular filtration rate, together with a slight reduction in ionic reabsorption capacity. 3. The renal salt excretion rate, which was doubled to about 100 microM/kg/hr, in fish fed the high salt diet, is not entirely a consequence of a reduction in tubular ionic reabsorption but also of increased glomerular filtration. 4. The role of the endocrine system in control of renal salt excretion is discussed.

Further observations on the effect of calcium ionophores on ascites tumor cells

The effect of the Ca2+ ionophore ionomycin on neoplastic thymocytes in comparison to its effect on normal thymus cells was studied. Ionomycin increases intracellular Ca2+ in normal lymphocytes but fails to increase Ca2+ in neoplastic thymocytes. In these cells the ionophore causes a transient increase in cytosolic free Ca2+. The lack of effect of ionomycin reproduces that of A23187, but it does not depend on reduced availability of intracellular Mg2+ to exchange with Ca2+; it appears to depend on the strong activity of the plasma membrane Ca2+-extruding pump that counteracts ionomycin permeabilization and that can be partly inhibited by the calmodulin inhibitor R24571 (calmidazolium). Neoplastic thymocytes show a high content of magnesium, the intracellular binding of which is efficiently regulated by endogenous ATP. The data show also an interesting correlation between the regulation of energy metabolism (aerobic glycolysis) and cation homeostasis in the neoplastic cells studied.

Short-term effects of mercury on survival, behaviour, bioaccumulation and ionic pattern in the catfish (Clarias lazera)

1. The fresh-water fish, Clarias lazera, was exposed to 13 lethal and sublethal concentrations of mercury. 2. The median tolerance limit (TLm) at different exposure periods, 24, 48, 72 and 96 hr, appears to be as follows: 0.96, 0.88, 0.81 and 0.72 ppm Hg2+/l, respectively. 3. From the subacute tests, the maximum acceptable toxicant concentration (MATC) for this fish was between 0.10 and 0.22 ppm Hg2+/l. 4. Behavioural changes, tissue Hg2+ distribution and serum ionic patterns were recorded during both the acute and subacute exposure periods.

Alterations in calcium content and biochemical processes in cultured skin fibroblasts from aged and Alzheimer donors

Aging and Alzheimer disease lead to alterations in several biochemical properties of cultured skin fibroblasts. Total bound calcium increases in fibroblasts due to normal aging (+52%) and is elevated even further with Alzheimer disease (+197%). Processes that require mitochondrial function, such as glucose and glutamine oxidation, declined in cells from aged donors (-25%) and decreased even further in Alzheimer disease (-46%). In addition, biosynthetic processes that depend upon mitochondrial function, such as glucose or glutamine incorporation into protein and lipid, paralleled the oxidative decreases. Cytosolic and nuclear processes such as leucine incorporation into protein and thymidine into DNA were depressed more by aging than Alzheimer disease. These findings suggest that calcium homeostasis and mitochondrial functions are altered more by Alzheimer disease than normal aging.

The kinetics of calcium influx into rat liver slices

The unidirectional influx of calcium across rat liver slices is a carrier-mediated process which displays saturation kinetics. The presence of Mg2+ in the incubation medium competitively inhibits calcium influx into rat liver slices. Metabolic inhibitors such as ouabain and 2,4-dinitrophenol at a concentration of 1 X 10(-4) and 2.5 X 10(-4) M respectively, inhibited significantly (P less than 0.001) calcium influx across the liver slices. Calcium influx is dependent on the presence of sodium in the extracellular medium, and is significantly reduced (P less than 0.01) when sodium concentration in the preincubation solution is reduced to zero.

Internal reference standards in ionic regulation and the predictability of ionic concentrations in animals

The regulation of ions at similar concentrations in most individuals of a species suggests the existence of internal reference standards. Few have been identified, but many probably relate to cell membrane properties, including potentials, surface charge densities and equilibrium constants of receptor molecules. Solubility may sometimes determine the product [Ca2+] [CO2-3]. Reference standards must generally each relate to more than one ionic species. For some concentrations, including osmolality, there may be no direct reference standard.

Rainbow trout red cells in vitro

Washed rainbow trout erythrocytes incubated at 14 degrees C in Eagle's minimal essential medium and Cortland saline displayed sharp reductions in volume and water content, nucleoside triphosphate, K+ and Cl- concentrations. Mg2+ and, to a lesser extent, Na+ concentrations increased. Cellular to medium Cl- ratios were indicative of membrane hyperpolarization. Morphological irregularities were also observed. Oxygen consumption and hemoglobin system organization were not grossly affected. Supplementation with pyruvate stabilized nucleoside triphosphate concentrations for at least 24 hr, and reduced rates of volume and compositional change to some extent. Addition of norepinephrine at physiologically realistic levels led to stabilization of Cl- content and reductions in Mg2+ accumulation and water loss. Transient but modest increases in K+ and Ca2+ were coupled, under these circumstances, with some decrease in Na+ concentration. Factors which may contribute to the dysfunctional status of these cells in vitro are discussed.

Primary hyperparathyroidism is associated with decreased insulin receptor binding and glucose intolerance

We studied insulin receptor-binding and carbohydrate and metabolism in 15 patients with symptomatic primary hyperparathyroidism in comparison with 20 healthy controls. Insulin binding to monocytes and erythrocytes was measured by radioreceptor-ligand-assay. Furthermore, patients and controls were characterized by testing oral (100 g glucose load) glucose tolerance as well as insulin tolerance (0.1U insulin/kg body weight). Compared with controls, patients with primary hyperparathyroidism exhibited marked hyperinsulinemia (P less than 0.01) and significantly higher glucose levels (P less than 0.01) after an oral glucose load. The glucose lowering effect of intravenous insulin was significantly diminished in primary hyperparathyroidism compared with controls (P less than 0.01). Receptor studies revealed a significantly lower (P less than 0.01) insulin binding to monocytes and to erythrocytes in patients with primary hyperparathyroidism compared with controls. The present data indicate an insulin-resistant state in primary hyperparathyroidism, which is caused at least in part, by a downregulation of insulin receptors.

Peripheral insulin resistance in primary hyperparathyroidism

Carbohydrate metabolism was investigated in 9 patients with symptomatic primary hyperparathyroidism. Before and after parathyroidectomy intravenous and oral glucose tolerance test, tolbutamide test, arginine infusion test and insulin tolerance test were performed. During intravenous and oral glucose tolerance tests, patients with primary hyperparathyroidism exhibited hyperinsulinemia and impaired glucose tolerance without normalization after surgery. Tolbutamide-induced induced insulin release did not differ pre- or postoperatively. After restoration of normocalcemia and normocalcemia and normophosphatemia we found significantly lower glucose and insulin levels following arginine infusion and a significantly increased hypoglycemic response to parenterally administered insulin, probably indicating partial improvement of glucose tolerance after surgery. Our findings suggest that biochemical abnormalities associated with primary hyperparathyroidism, like hypercalcemia, hypophosphatemia, and elevated parathyroid hormone levels may cause and sustain a form of endogenous insulin resistance, which consequently leads to hyperinsulinemia and to impaired glucose tolerance. Since hyperinsulinemia as well as impaired glucose tolerance seem to be only slowly and partially reversible in symptomatic primary hyperparathyroidism, these data could be considered as an additional argument for early surgical intervention in this disorder.

The influence of renal prostaglandins on urinary calcium excretion in idiopathic urolithiasis

Hypercalciuria is well recognized as an important factor in the cause of idiopathic calcium stone disease. Identification of the exact mechanism for the renal tubular handling of calcium has proved elusive, hence, treatment methods to alter the concentration of urine calcium in hypercalciuric stone formers have hitherto been non-specific. It is now well established that renal prostaglandins influence intrarenal hemodynamics and tubular electrolyte excretion. As the renal handling of sodium and calcium is intimately related, the possibility that the mechanism underlying hypercalciuria may be prostaglandin mediated was considered. Experiments were performed in conscious Sprague-Dawley rats (n = 10) to determine the changes in calcium excretion following prostaglandin synthetase inhibition with indomethacin. Calcium excretion was significantly reduced (p less than 0.01), compared with control animals (n = 10). Further experiments were performed in anesthetized monkeys (Macaca fascicularis) to see if the inhibitory effect of indomethacin was reversible. Exogenous prostaglandin (PGE2) infusion resulted in a marked calciuretic response without producing changes in glomerular filtration rate or blood pressure. Forty-three hypercalciuric patients were treated with a prostaglandin inhibitor for periods ranging from 2 to 4 weeks, and all showed a significant fall in urinary calcium excretion to within the normal range. This clinical and experimental study suggests that prostaglandin (PGE2) is a hormone which determines the renal handling of calcium by influencing renal tubular function.

Hydrogen ion dynamics and cancer: an appraisal

The concentration of hydrogen ions plays a critical role in all biochemical processes, including multiple enzymatic reactions, and in the regulation of metabolism. The acid-base aspects of metabolism as applied to cancer are considered. Preliminary data are presented. The primary concept of hydrogen ion dynamics is related to prevention, development, and etiology of carcinogenicity, as well as to the regression of certain malignant malignant tumors. The present overview summarizes, in terms of H+ dynamics, many related concepts in oncologic research and associates and integrates a variety of basic and clinical observations toward better understanding of cancer cell behavior, biology, and host-tumor relationships.

Active calcium transport in red cell ghosts resealed in dextran solutions

1. Human erythrocytes when lysed and resealed to Ca in the presence of dextran can be readily separated from the suspending medium by low-speed centrifugation. 2. Ghosts trapped Ca and EGTA at the same ratio as present in the haemolytic medium and remained tight to Ca after washing and subsequent incubation for up to 90 min at 37 degrees C. 3. Ca extrusion could be promoted by substrates other than ATP only from ghosts that had been loaded with low free Ca concentrations (1--22 microM). The order of activation by the various substrates employed was ATP greater than adenine + inosine greater than inosine. 4. The kinetics of extrusion depended markedly on internal free Ca. The system showed a high affinity state (KCa about 3 microM; V = 0.34 mumol Ca/ml ghosts per min) at low concentrations (1--22 microM) and a low affinity state (KCa about 250 microM; V = 0.17 mumol Ca/ml ghosts per min) at high concentrations (0.2--4.0 mM). 5. Both at low and at high free Ca, La-sensitive ATP hydrolysis was closely correlated with La-dependent Ca efflux, in keeping with an stoichiometry of 1.6. The rate of extrusion was maximal in the presence of 160 mM KCl and decreased to various extents when K was fully replaced by different cations, following the order K greater than Na = choline greater than Mg. 7. The efflux rate of high-K ghosts, resealed to alkaline cations, was stimulated by external Na, whilst Mg and choline was practically without effect. 8. The results indicate that human red cells possess a powerful Ca extrusion mechanism, the activity of which can be modulated by alkaline cations.

Inhibition and stimulation of respiration-linked Mg2+ efflux in rat heart mitochondria

Respiration-driven Mg2+ efflux from rat heart mitochondria has been studied in different conditions. Almost total release of Mg2+ from the mitochondria occurs upon addition of a proton/bivalent cation exchanger, A23187. The content of Mg2+ remaining in mitochondria after A23187 treatment is the same if part of the mitochondrial Mg2+ has already been extruded through the energy-linked mechanism. Some inhibition of Mg2+ efflux is observed in the presence of high concentrations of La3+ (100 micro M). A proton/monovalent cation exchanger, nigericin, completely prevents Mg2+ efflux, whereas a cation conductor, valinomycin, considerably stimulates it. The results indicate that the main part of mitochondrial Mg2+ is present in the membrane-bounded compartment, probably in the matrix space. The driving force of the Mg2+ efflux appears to be the proton gradient (deltapH) created by mitochondrial respiration.

Lack of effect of the Ca2+ ionophore A23187 on tumour cells

The Ca2+ ionophore A23187 increases intracellular calcium content in normal thymic cells, while it is without effect on the corresponding neoplastic cell (Ascites thymoma) and on Ehrlich ascites tumour cells. The A23187-induced total cell calcium increase in normal thymocytes takes place both in control and energy-depleted cells, while it is lacking in neoplastic cells. In addition the ionophore stimulates aerobic glycolysis of normal thymocytes, whereas it is ineffective on neoplastic cells. The study of intracellular calcium exchange properties reveals that in normal cells the ionophore A23187 provokes a 60% increase of the exchangeable pool together with a more significant, 4-fold enlargement of the unexchangeable pool. These effects are lacking in cancer cells. The data give rise to interesting considerations concerning the regulation and compartmentalization of calcium in neoplastic cells. The results will be also discussed in relation to the models that predict altered cell calcium metabolism as a cause of cancer cell high aerobic glycolysis and uncontrolled growth.

Effect of ammonium ions on the aerobic glycolysis in Ehrlich ascites tumor cells

The effect of ammonium ions on aerobic glycolysis has been studied in Ehrlich ascites tumor cells. The inhibition of respiration caused by 5-25 mM glucose, fructose or mannose is increased by the presence of 0.5-20 mM NH4+. Under these conditions, more glucose is used and a crossover analysis of intermediate metabolites of glycolysis indicates an increase in the glycolytic flux. In spite of the stimulation of glycolysis, the production of lactate decreases in the presence of ammonium ions, although the concentration of free alanine (glutamate and aspartate) is increased. Ammonium ions enhance the oxidation of cytochromes c and a caused by glucose, and decrease the adenine nucleotide pool and the ATP/ADP ratio. These effects of ammonium ions are observed when glucose is present in the incubation medium, and do not occur when only ammonium salts were supplied to the cells metabolizing endogenous substrates.

Further observations on calcium and other divalent cations metabolism in intact Ehrlich ascites tumour cells

The metabolism of calcium has been investigated in the Ehrlich Ascites Tumour Cells (ATC). ATC extrude Ca2+ actively by an energy-dependent mechanism, supported by both respiration and glycolysis. Extrusion takes place even against a very steep concentration gradient (10 mM Ca2+). Cell calcium content is decreased by monovalent cations (Na+,K+ and Li+), which act independently from their metabolic effects. La3+ inhibits ATC Ca2+ extrusion whereas Ruthenium Red slightly decreases cell calcium content. The antibiotic ionophore A 23187 strongly increases ATC Ca2+ level. the metabolism of other divalent cations (Mg2+, Sr2+ and Mn2+) has been studied. Mg2+ does not show appreciable changes in the various metabolic conditions tested, while Mn2+ and Sr2+ behave quite differently from Ca2+, suggesting a different distribution of these cations in ATC. The experimental findings indicate that Ehrlich Ascites Tumour Cells regulate their calcium content by mechanisms related to plasma membranes while the size and activity of mitochondrial compartment is of minor importance.

Alteration of smooth muscle contractility after muscarinic agonist-induced K+ loss

1. After stimulation of the longitudinal smooth muscle of the guinea-pig ileum by an optimal dose (2 x 10(-7) M) of a muscarinic agent, cis-2-methyl-4-dimethylaminomethyl-1,3-dioxolane methiodide (CD), the muscles failed to regain their normal spontaneous activity for 20 to 30 min. During the recovery period, subsequent contractions induced by either CD or 60 mM KCl were altered, particularly when only short times (15 min or less) were allowed between exposures. 2. Altered responses to CD had depressed phasic but increased tonic tensions and were characteristic of responses induced by lower doses of CD. The altered responsiveness probably represented an early phase of muscle 'densensitization'. 3. In contrast to muscarinic stimulation, the smooth muscles gave identical responses after repeated stimulation by 60 mM KCl, even when only 2 min were allowed between exposures. 4. Whereas K+ levels increased in muscles exposed to 60 mM KCl, they decreased during contractions to CD. The K+ levels remained low until the muscles recovered their normal responsiveness. 5. Increasing the extracellular K+ concentration (5 to 13 mM) hastened the recovery of the muscle responsiveness after CD, whereas lowering external K+ concentration to 1.35 mM or the addition of ouabain (5 x 10(-7) M) delayed the recovery. The results suggested that the Na+, K+-pump is rate-limiting in the recovery of the normal ionic balance of the muscles after stimulation by muscarinic agonists.

Energy-dependent accumulation of Ca2+ by human embryonic lung fibroblasts

Human embryonic fibroblasts accumulate Ca2+ in the presence of extracellular ATP and Mg2+, the uptake being maximal at 3 mM ATP. Iodoacetic acid, oligomycin and temperatures of 2 degrees C all inhibit the ATP-potentiated uptake suggesting that an active process may be involved in the transport of Ca2+ into these cells under certain conditions.

Calcium metabolism in intact isolated thymocytes

Isolated rat thymocytes incubated under proper metabolic conditions extrude Ca2+ previously taken up under metabolically unfavourable conditions. The extrusion can be supported by both respiratory and glycolytic energy but glycolysis seems to be more efficient for this purpose. La3+ (50--200 micron) and the ionophore A 23187 inhibit cell Ca2+ extrusion. Ruthenium Red (1--100 micron) does not influence cell Ca2+ extrusion while it inhibits the in situ mitochondrial cation uptake. All the results are consistent with a cell regulation model of Ca2+ content in which both plasma membrane and mitochondria co-operate, acting in opposite directions, in order to decrease cytosolic Ca2+ concentration. The possibility of Na+-Ca2+ hetero-exchange participation to cell Ca2+ homeostasis regulation is also discussed.

Calcium-ion transport by intact Ehrlich ascites-tumour cells. Role of respiratory substrates, Pi and temperature

1. The interaction of intact Ehrlich ascites-tumour cells with Ca2+ at 37 degrees C consists of Ca2+ uptake followed by efflux from the cells. Under optimum conditions, two or three cycles of uptake and efflux are observed in the first 15 min after Ca2+ addition. 2. The respiratory substrates malate, succinate and ascorbate plus p-phenylenediamine support Ca2+ uptake. Ca2+ uptake at 37 degrees C is sensitive to the respiratory inhibitors rotenone and antimycin A when appropriate substrates are present. Ca2+ uptake and retention are inhibited by the uncoupler S-13. 3. Increasing extracellular Pi (12 to 30 mM) stimulates uncoupler-sensitive Ca2+ uptake, which reaches a maximum extent of 15 nmol/mg of protein when supported by succinate respiration. Ca2+ efflux is partially inhibited at 30 mM-Pi. 4. Optimum Ca2+ uptake occurs in the presence of succinate and Pi, suggesting that availability of substrate and Pi are rate-limiting. K. Ca2+ uptake occurs at 4 degrees C and is sensitive to uncouplers and oligomycin. Ca2+ efflux at this temperature is minimal. These data are consistent with a model in which passive diffusion of Ca2+ through the plasma membrane is followed by active uptake by the mitochondria. Ca2+ uptake is supported by substrates entering respiration at all three energy-coupling sites. Ca2+ efflux appears to be an active process with a high temperature coefficient.

The effects of magnesium on state 3 respiration of liver mitochondria from control and cold-acclimated rats and hamsters

1. Increasing the Mg2+ concentration results in a depression of succinoxidase-linked state 3 respiration of liver mitochondria from both control and cold-acclimated rats and hamsters. 2. It appears that in the cold-acclimated hamster, liver mitochondrial respiration is more sensitive to changes in Mg2+ levels than that of the rat.

Effects of adenine nucleotide translocase inhibitors on dinitrophenol-induced Ca2+ efflux from pig heart mitochondria

Bongkrekic acid and atractyloside, inhibitors of adenine nucleotide translocase, do not inhibit Ca2+ uptake and H+ production by pig heart mitochondria. However, bongkrekic acid, but not atractyloside, inhibits dinitrophenol-induced Ca2+ efflux and H+ uptake. Conversely, ruthenium red blocks Ca2+ uptake and H+ production but does not prevent dinitrophenol-induced Ca2+ efflux and H+ uptake by mitochondria. These results suggest that mitochondrial Ca2+ uptake and release exist as two independent pathways. The efflux of Ca2+ from mitochondria is mediated by a bongkrekic acid sensitive component which is apparently not identical to the ruthenium red sensitive Ca2+ uptake carrier.