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At least 19 recordsLinked to original sources

PubMed1977

Studies on the ionophorous antibiotics. XII. Effects of ionophore lysocellin on cation distribution and respiration in mitochondria.

The effects of the ionophore lysocellin on the movements of Ca2+, Mg2+ and alkali metal cations and its effect on energy utilization by rat liver mitochondria have been investigated. At a concentration of 0.05 micrometer, lysocellin induced dissociation of membrane-bound calcium, and an apparent steady state was established across the inner membrane between energy-linked calcium accumulation and the ionophore-induced depletion of calcium. No detectable efflux of intramitochondrial Ca2+ and Mg2+ was induced by 0.05 micrometer lysocellin, but the uptake of exogenously added calcium was significantly inhibited. The ionophore augmented Mg2+ release from mitochondria induced by Ca2+ addition and also caused rapid release of K+ from mitochondria preloaded with K+ by valinomycin or monazomycin. High levels (0.5 approximately 10 micrometer of lysocellin caused massive depletion of endogenous Ca2+, Mg2+ and K+ from mitochondria, resulting in disruption of mitochondrial functions including release of state 4 respiration, stimulation of ATPase and inhibition of ADP- or DNP-stimulated respiration. Structure-activity studies with chemically modified compounds of lysocellin indicated the important role of terminal carboxylic acid and C21 hydroxyl function in the activity of the ionophore, and there is a good correlation between the effect of lysocellin on mitochondrial cation movements and its ability to complex with cations determined in an organic solvent-water two-phase partition system.

Adenosine Triphosphatases↗

PubMed1978

Studies on the ionophorous antibiotics. XV The monovalent cation selective ionophorous activities of carriomycin, lonomycin and etheromycin.

The cations selectivity profiles of the carboxylic ionophores, carriomycin, lonomycin and etheromycin, have been investigated by measuring the complexation affinities for metal cations and the cation transport activity through an organic barrier. In a two-phase partition study, carriomycin and lonomycin formed complexes more readily with K+ than with NH4+, Rb+ or Na+, but not with Li+ or Cs+. On the other hand, etheromycin exhibited a great preference for K+ or NH4+ over Na+, Li+ or Rb+, but displayed no binding affinity for Cs+. The alklaine degradation product of lonomycin exhibited a preference for K+ or Na+, but its complexation affinities were much lower than those of the parent compound. Carriomycin, lonomycin and etheromycin efficiently transported K+, Rb+ and Na+ through a CCl4 barrier. But did not carry Ca2+. These antibiotics caused a massive release of K+, Rb+ or Na+, but not of Li+ and Cs+, from mitochondria previously loaded with these cations by valinomycin or monazomycin. Thus, it is concluded that carriomycin, lonomycin and etheromycin are monovalent cation selective ionophores.

Animals↗

PubMed1976

The effect of intracellular calcium ions on adrenaline-stimulated adenosine 3':5'-cyclic monophosphate concentrations in pigeon erythrocytes, studied by using the ionophore A23187.

1. The bivalent cation ionophore A23187 was used to increase the intracellular concentration of Ca2+ in pigeon erythrocytes to investigate whether the increase in cyclic AMP content caused by adrenaline might be influenced by a change in intracellular Ca2+ in intact cells. 2. Incubation of cells with adrenaline, in the concentration range 0.55--55 muM, resulted in an increase in the concentration of cyclic AMP over a period of 60 min. The effect of adrenaline was inhibited by more than 90% with ionophore A23187 (1.9 muM) in the presence of 1 mM-Ca2+. This inhibition could be decreased by decreasing either the concentration of the ionophore or the concentration of extracellular Ca2+, and was independent of the concentration of adrenaline. 3. The effect of ionophore A23187 depended on the time of incubation. Time-course studies showed that maximum inhibition by ionophore A23187 was only observed when the cells were incubated with the ionophore for at least 15 min before the addition of adrenaline. 4. The inhibition by ionophore A23187 depended on the concentration of extracellular Ca2+. In the absence of Mg2+, ionophore A23187 (1.9 muM) inhibited the effect of adrenaline by approx. 30% without added Ca2+, by approx. 66% with 10 muM-Ca2+ and by more than 90% with concentrations of added Ca2+ greater than 30 muM. However, even in the presence of EGTA [ethanedioxybis(ethylamine)tetra-acetate](0.1--10 mM), ionophore A23187 caused an inhibition of the cyclic AMP response of at least 30%, which may have been due to a decrease in cell Mg2+ concentration. 5. The addition of EGTA after incubation of cells with ionophore A23187 resulted in a partial reversal of the inhibition of the effect of adrenaline. 6. Inclusion of Mg2+ (2 mM) in the incubation medium antagonized the inhibitory action of ionophore A23187. This effect was most marked when the ionophore A23187 was added to medium containing Mg2+ before the addition of the cells. 7. The cellular content of Mg2+ was decreased by approx. 50% after 20 min incubation with ionophore A23187 (1.9 muM) in the presence of Ca2+ (1 mM) but no Mg2+. When Mg2+ (2 mM) was also present in the medium, ionophore A23187 caused an increase of approx. 80% in cell Mg2+ content. Ionophore A23187 had no significant effect on cell K+ content. 8. Ionophore A23187 caused a decrease in cell ATP content under some conditions. Since effects on cyclic AMP content could also be shown when ATP was not significanlty lowered, it appeared that a decrease in ATP in the cells could not explain the effect of ionophore A23187 on cyclic AMP. 9. Ionophore A23187 (1.9 muM), with 1 mM-Ca2+, did not enhance cyclic AMP degradation in intact cells, suggesting that the effect of ionophore A23187 on cyclic AMP content was mediated through an inhibition of adenylate cyclase rather than a stimulation of cyclic AMP phosphodiesterase. 10. It was concluded that in intact pigeon erythrocytes adenylate cyclase may be inhibited by intracellular concentrations of Ca2+ in the range 1-10 muM.

Adenosine Triphosphate↗

PubMed1979

Effect of solvent on the histamine-releasing, enzyme-releasing, and mitogenic properties of the calcium ionophore A23187.

The potency of the calcium ionophore A23187 in inducing three activities of human leukocytes (histamine secretion from basophils, enzyme secretion from PMNs, and proliferation of lymphocytes) was markedly dependent on the solvent (DMSO versus ethanol versus aqueous buffer) used for its initial sonication. While 0.1 micrograms/ml of DMSO- and ethanol-solubilized A23187 induced maximal histamine release from basophils and histaminase release from PMNs, concentrations of aqueous buffer-sonicated ionophore of greater than or equal to 1 microgram/ml were required for an equivalent response. Ionophore sonicated in organic solvents caused a maximum release of 40% of PMN beta-glucuronidase, at an optimal concentration tenfold higher than that required for maximal histaminase release; ionophore sonicated in aqueous buffers, even at high concentrations, effected a release of less than 5% of cellular beta-glucuronidase. A23187 also induced lymphocyte proliferation over a narrow concentration range; 0.05 micrograms/l of DMSO-sonicated ionophore induced optimal proliferation and concentrations greater than or equal to 0.2 micrograms/ml were toxic. Twofold higher concentrations of ethanol-sonicated ionophore and fourfold higher concentrations of aqueous-sonicated ionophore were necessary for maximal proliferation, and the magnitude of the maximal response with aqueous-sonicated A23187 was only one-half that of DMSO-solubilized agent. Ionophore-induced release of histamine from basophils and enzymes from PMNs was not cytotoxic, since ionophore induced neither LDH nor histamine release from heat-treated (47 degrees C) cells. These results explain several previous, discordant reports on the presence or absence of an effect of A23187 on cellular secretory events, on differing dose-response relationships, and on cytotoxic versus noncytotoxic mechanisms of action.

Anti-Bacterial Agents↗

PubMed1975

Separate effects of mercurial compounds on the ionophoric and hydrolytic functions of the (Ca++ +Mg++)-ATPase of sarcoplasmic reticulum.

We have shown that a Ca++-ionophore activity is present in the (Ca++ +Mg++)-ATPase of rabbit skeletal muscle sarcoplasmic reticulum (A. E. Shamoo & D. H. MacLennan, 1974. Proc. Nat. Acad. Sci. USA 71:3522). Methylmercuric chloride inhibited the (Ca++ +Mg++)-ATPase and Ca++ transport, but had no effect on the activity of the Ca++ ionophore. Mercuric chloride inhibited ATPase, transport and ionophore activity. The ATPase and transport functions were more sensitive to methylmercuric chloride than to mercuric chloride. The two functions were inhibited concomitantly by methylmercuric chloride but slightly lower concentrations of mercuric chloride were required to inhibit Ca++ transport than were required to inhibit ATPase. Methylmercuric chloride and mercuric chloride probably inhibited ATPase and Ca++ transport by blocking essential -SH groups. However, it appears that there are no essential -SH groups in the Ca++ ionophore and that mercuric chloride inhibited the Ca++ ionophore activity by competition with Ca++ for the ionophoric site. Blockage of Ca++ transport by mercuric chloride probably occurs both at sites of essential -SH groups and at sites of ionophoric activity. These data suggest the separate identity of the sites of ATP hydrolysis and of Ca++ ionophoric activity.

Adenosine Triphosphatases↗

PubMed1977

Ionophorous activity and murine B lymphocyte mitogens.

The relationship between ionophorous and B cell mitogen activity has been investigated. Most known ionophores were nonmitogenic for mouse spleen cells. In addition, when tested in a bilayer lipid membrane (BLM) apparatus, most types of B cell mitogens were nonionophorous. However, excitability-inducing material (EIM), a high m.w. polymeric protein, which is a channel-forming ionophore, was a potent mitogen for mouse B lymphocytes. Similarly, keyhole limpet hemocyanin (KLH), a high m.w. polymeric protein, which is a B cell mitogen, is a channelforming ionophore. The mitogenic activities of these two compounds were not due to contamination with endotoxin since they produced weak or absent responses in the limulus lysate clotting and rabbit pyrogenicity assays, and were also mitogenic for spleen cells of endotoxin-low responder C3H/HeJ mice. Both the mitogenic and ionophorous activities of EIM and KLH were dependent on their polymeric structure since dissociation of these compounds into monomeric subunits markedly decreased both activities. However, heat denaturation destroyed their ionophorous ability but preserved their mitogenicity, thereby demonstrating that ionophorous activity was not essential for B cell activation. These data suggest that B cell mitogens do not necessarily act as primary ionophores. However, we propose that these molecules intercalate into the lipid portion of the cell membrane, and that this interaction initiates the process of B cell activation.

Animals↗

PubMed1976

Bone resorption in organ culture: inhibition by the divalent cation ionophores A23187 and X-537A.

The ionophores A23187 and X-537A were used as probes to investigate the possible role of calcium uptake by bone as a mediator for the stimulation of bone resorption induced by parathyroid hormone (PTH) and other agents in cultured mouse calvaria. The ionophores alone at concentrations from 1 nM to 20 muM did not stimulate bone resorption, nor did they potentiate bone resorption stimulated by submaximal concentrations of PTH after either brief (15-60 min) or extended (1-3 day) exposure to the ionophores. Unexpectedly, we found that the ionophores inhibit in a dose-dependent manner bone resorption stimulated by PTH and a wide variety of other compounds (prostaglandin E2, 1alpha-hydroxycholecalciferol, 3-isobutyl-1-methyl-xanthine, and phorbol myristate acetate). This inhibition was not due to irreversible damage to the bones by the ionophores, because the inhibition was reversible even after 24 h of treatment. Inhibition of bone resorption by the ionophores was observed in media of both high and low calcium concentration, indicating that the inhibition was not due to a critical extracellular calcium concentration. Inhibition by the ionophores differs qualitatively in several ways from that produced by calcitonin, a natural inhibitor of bone resorption. Furthermore, A23187 at 1.0 mug/ml had no effect on the accumulation of cyclic AMP in the medium of either control, PTH- or calcitonin treated calvaria. We conclude that the ionophores A23187 or X537A do not stimulate bone resorption nor potentiate the effects of stimulators of bone resorption; instead they are inhibitors of bone resorption stimulated by a wide variety of compounds.

Animals↗

PubMed1977

Structural alterations of peripheral nerve induced by the calcium ionophore A23187.

Desheathed segments of rat peripheral nerve were incubated at 37 degrees C in oxygenated Ringer's solution with and without the addition of calcium ionophore, A23187, 10 microgram/ml. Nerve fibers incubated in the presence of both ionophore and calcium revealed extensive granular disintegration of their axonal microtubules and neurofilaments after 30 and 60 min incubation intervals. These changes were not seen following control incubations in Ringer's solution without ionophore or in calcium-free Ringer's solution containing ionophore and EGTA, 1 mmole/1. Ionophore-induced alterations were also noted in Schwann cell cytoplasm. The granular degradative alteration of axoplasm caused by exposure of nerve fibers to ionophore and calcium were believed to be due to an ionophore-mediated influx of calcium into the axoplasm with resultant elevation of intra-axoplasmic calcium concentration. These axoplasmic changes were indistinguishable from the axoplasmic alteration occurring in the distal portions of transpected neurites during Wallerian degeneration. The findings support the view that abnormal calcium influxes are determinants in the degeneration of peripheral nerve.

Animals↗

PubMed1975

Calcium-induced insulin release in monolayer culture of the endocrine pancreas. Studies with ionophore A23187.

The role of Ca2+ on insulin release has been studied by the use of ionophore A23187. The ionophore complexes divalent cations and permits Ca2+ entry into cells by acting as a carrier in the plasma membranes. Cultured cells obtained by enzymatic digestion of pancreases from newborn rats were studied on the 3rd day of culture. With Ca2+ in the incubation medium the ionophore induced sustained insulin release even in the absence of glucose. Optimal effects of the ionophore were observed at 3 and 10 mug per ml in the presence of 0.3 to 1.0 mM Ca-2+. Under these conditions the insulin release was greater than that caused by 16.7 mM glucose. A graded response was observed to changes in Ca-2+ concentration from 0.1 to 1.0 mM Ca-2+. Higher Ca-2+ concentrations caused a large amount of insulin to be released promptly, but the release was not sustained. Mg-2+ and Sr-2+ were not found to substitute for Ca-2+. Ba-2+ at 0.3 mM stimulated insulin release even in the absence of ionophore. Cyclic adenosine 3':5'-monophosphate was able to increase ionophore-induced insulin release. The alpha-adrenergic effect of epinephrine to inhibit insulin release was not observed in the presence of Ca-2+ and the ionophore, and a stimulatory effect of epinephrine was seen. This unusual stimulatory effect of epinephrine was blocked by propranolol indicating a beta-adrenergic mechanism for epinephrine. It is concluded that Ca-2+, which plays an essential role in the stimulus-secretion coupling, can alone initiate and cause sustained insulin release.

Animals↗

PubMed1977

Isolation of an electrogenic K+/Ca2+ ionophore from an ionophoroprotein of beef heart mitochondria.

A K+/Ca2+ electrogenic ionophore has been isolated from an ionophoroprotein of beef heart mitochondria and identified as a neutral peptide of molecular weight 1600. The amino acid composition and cationic specificity of the ionophore have been determined. The free ionophore was released from the ionophoroprotein as a consequence of tryptic digestion. The ionophoroprotein can be converted to an ionophoro peptide (molecular weight 5,100) by proteolysis without release of the free ionophore. The isolation of a K+/Ca2+ ionophore thus provides an introduction to the general technology of extracting ionophoro proteins and ofreleasing ionophores from these proteins by proteolytic digestion.

Animals↗

PubMed1976

Localization of ionophore activity in a 20,000-dalton fragment of the adenosine triphosphatase of Sarcoplasmic reticulum.

The (Ca2+ + Mg2+)-dependent ATPase of sarcoplasmic reticulum has been shown to ast as a Ca2+-dependent and selective ionophore in artificial lipid bilayers. Four fragments of 55,000, 45,000, 30,000, and 20,000 daltons have been purified from tryptic digests of the enzyme and it has been shown that the 55,000- and 45,000-dalton fragments are obtained from a single cleavage of the 100,000-dalton ATPase, while the 30,000- and 20,000-dalton fragments are obtained subsequently by a cleavage of the 55,000-dalton fragment. The 55,000- and 20,000-dalton fragments have ionophore activity inhibited by ruthenium red and by mercuric chloride but not by methylmercuric chloride, an inhibitor of the hydrolytic site of the enzyme. Under standard conditions the 45,000-dalton fragment was not active as an ionophore, while the 30,000-dalton fragment acted as a nonselective ionophore. The 55,000- and 30,000-dalton fragments have been shown to contain the site of phosphorylation and of N-ethyl [2-3H]-maleimide binding indicative of the hydrolytic site in the enzyme, and this site is absent from the 20,000-dalton fragment. Therefore, the ionophoric and hydrolytic sites are localized in separate regions of the ATPase molecule and they have now been physically separated. The 20,000-dalton fragment was degraded with cyanogen bromide and fragments were separated by molecular sieving. Ionophore activity was found in fragments of molecular mass less than 2,000 daltons.

Adenosine Triphosphatases↗

PubMedDate not supplied

Ionophores. Chemistry, physiology and potential applications to bone biology.

Ionophores are substances which facilitate the movement of ions into and/or through organic phases. The two major classes of compounds are the neutral ionophores, which form charged clathrate complexes with ions, and the carboxylic polyether ionophores which are neutral in the complexed state. Many of the ionophores exclusively bind organic monovalent cations. Selectivity for divalent metal cations or for anions is less common. One carboxylic polyether, X-537A, forms complexes with small organic cations as well as a variety of metals. Ionophores selective for monovalent cations have been used primarily for studies of mitochondrial metabolism. Compounds like X-537A and A23187, which show high affinity for biologically active divalent cations, are being widely used as tools to study the physiologic roles of these cations. These studies have confirmed the central role of calcium in many biological processes. The major problem encountered with X537A is a lack of selectivity. A23187 has produced variable results in studies of bone as well as other tissues. Despite these difficulties, the ionophores offer promise of being useful tools in studies of bone metabolism.

Animals↗

PubMed1979

Conditions limiting the use of ionophore A23187 as a probe of divalent cation involvement in biological reactions. Evidence from the slow fluorescence quenching of type A spinach chloroplasts.

The conditions under which ionophore A23187 can be used as a probe of Mg2+ involvement in the reactions of intact (Type A) spinach chloroplasts have been investigated by monitoring ionophore-induced reversal of slow fluorescence quenching. The following observations were made: (1) A23187-dependent reversal of quenching is a strong function of pH. This is consistent with competition between protons and divalent cations for the carboxylic acid moiety of the ionophore. (2) In the presence of exogenous Mg2+, quenching reversal by A23187 is significantly slowed. It is suggested that formation of the dimeric A23187 . Mg2+ complex delays action of the ionophore at the thylakoid membrane by slowing equilibration of the ionophore among chloroplast membrane phases. (3) In the absence of Mg2+, significant interaction of A23187 with certain monovalent cations--Li+ and Na+, but not K+--is observed. Evaluations of the interaction of ionophore A23187 with specific biological systems and inferences of divalent cation involvement, or lack thereof, must take these limitations into account.

Anti-Bacterial Agents↗

PubMed1979

Fatty acid and glycerol labeling of glycerolipids of leukocytes in response to ionophore A23187.

The effect of divalent cation ionophore, A23187, on the incorporation of [1-14C]palmitic acid, [1-14C]linoleic acid and [U-14C]glycerol into glycerolipids of polymorphonulcear leukocytes was examined. Ionophore A23187 stimulated the labeling of phosphatidic acid, phosphatidylglycerol, phosphatidylinositol, and diacylglycerol by both labeled fatty acids and glycerol. [1-14C]Palmitic acid and [1-14C]linoleic acid incorporation into phosphatidylcholine and triacylglycerol was reduced by the presence of the ionophore in the incubation medium, while [U-14C]glycerol labeling of these lipids was not significantly changed under identical conditions. These data reflect that the acylation of sn-glycerol 3-phosphate is activated, and the acylations of lysophosphatidyl-choline and endogenous diacylglycerol are inhibited in cells incubated with ionophore A23187. External calcium was not required for the ionophore effect on the incorporation of labeled fatty acids and glycerol. It is suggested that the ionophore alters the metabolism of the fatty acid and glycerol moieties of glycerolipids by changing the distribution of intracellular calcium of leukocytes.

Animals↗

PubMed1977

A comparison of the effects of phytohaemagglutinin and of calcium ionophore A23187 on the metabolism of glycerolipids in small lymphocytes.

1. The effects of phytohaemagglutinin and of a Ca2+ ionophore (A23187) on glycerolipid metabolism in lymphocytes from pig lymph nodes were compared (a) by studying the incorporation of [32P]Pi and [3H]glycerol, and (b) by following the redistribution of [3H]glycerol among the lipids caused by these agents in pulse-chase experiments. 2. Phytohaemagglutinin only stimulated 32P incorporation into phosphatidylinositol and, to a slight extent, phosphatidate. Removal of most of the extracellular Ca2+ somewhat decreased this response. 3. Ionophore A23187 stimulated the labelling of phosphatidate and phosphatidylinositol with 32P to a much greater extent than did phytohaemagglutinin: the increase in phosphatidate labelling, but not that of phosphatidylinositol, was almost abolished by the removal of extracellular Ca2+. 4. The combined effects of phytohaemagglutinin and ionophore appeared to be additive, rather than synergistic. 5. Treatment with ionophore A23187 somewhat decreased the total incorporation of [3H]glycerol into glycerolipids, possibly because it lowered cell ATP content. In these experiments di- and tri-acylglycerol behaved anomalously, triacylglycerol labelling being suppressed completely, whereas that of diacylglycerol was enhanced. The pulse-chase results revealed that triacylglycerol was converted into diacylglycerol in the ionophore-treated cells, and the availability of this diacylglycerol probably led to the enhanced labelling of phosphatidate and phosphatidylinositol in the these cells. 6. Thus an increase in intracellular Ca2+ concentration appeared to have three effects on glycerolipid metabolism: (a) slight inhibition of some metabolic step preceding phosphatidate synthesis, (b) inhibition of diacylglycerol acyltransferase and (c) activation of a triacylglycerol lipase. 7. In contrast, it seems likely that the only effect of phytohaemagglutinin is to stimulate phosphatidylinositol breakdown. 8. Pig polymorphonuclear leucocytes treated with ionophore A23187 showed metabolic changes that were similar to those demonstrated with lymphocytes. 9. A possible similarity is suggested between Ca2+-stimulated triacylglycerol lipase in lymphocytes and polymorphonuclear leucocytes and previous observations of enhanced triacylglycerol metabolism in stimulated cells whose metabolic functions involve membrane fusion.

Animals↗

PubMed1979

Monovalent ionophores inhibit secretion of procollagen and fibronectin from cultured human fibroblasts.

Procollagen and fibronectin are major products of confluent fibroblasts in culture and both are released from the cells. Procollagen is secreted by known pathways, while the mechanism of fibronectin release is controversial. We find that the secretion of both these proteins can be reduced to 20% by low concentrations (0.1-1 muM) of ionophores that have affinity for monovalent cations. In contrast, little effect upon secretion was found for similar concentrations of an ionophore that binds divalent cations. Electron microscopy showed that the inhibition of secretion is accompanied by accumulation of membranous vacuoles. We believe that the ionophores impede secretion by acting on the secretory structures rather than on the proteins themselves. Biochemical studies supported this interpretation because no changes were detected in hydroxylation or glycosylation of procollagen or glycosylation of fibronectin, nor were significant changes in cellular amino acid incorporation observed. Pulse-chase studies indicated that the rates of secretion were impaired by the ionophore without enhancing intracellular degradation. The decreased secretory rates accounted for the lower levels of procollagen and fibronectin in the culture medium; no evidence for increased catabolism of the secreted proteins was found. Secretion could be readily restored by removing the ionophore from the culture medium. The results indicate that procollagen and fibronectin may be simultaneously secreted, possibly utilizing a common pathway for secretion; the ionophores effectively interfere with cellular secretory pathways without impairing protein synthesis or protein glycosylation or altering protein catabolism.

Anti-Bacterial Agents↗

PubMed1975

Effects of calcium ionophore (A-23187) on glucose oxidation and iodide transport in dog thyroid slices.

A calcium ionophore (A-23187, 20 mug/ml) stimulted 14C-1-glucose oxidation in dog thyroid slices to an extent equivalent to that obtained by the optimal concentration of dibutyryl cyclic AMP (1mM). Furthermore, the ionophore augmented the stimulation by dibutyryl cyclic AMP much more than the simple additive effect. The ionophore also enhanced the effect of TSH, but to a lesser extent. Under conditions where organic binding was blocked, T/M ratio of radioiodine concentration was lowered in slices by the ionophore; the findings similar to those obtained with TSH and dibutyryl cyclic AMP. The ionophore exhibited a slightly depressive effect on the basal cyclic AMP level. The elevation by TSH of cyclic AMP levels was also slightly depressed by the ionophore, but statistically insignificant in most cases. These results indicate that calcium ion may play an important role in the TSH regulation of iodide transport and glucose metabolism in the thyroid, in some cases by augmenting the effects of cyclic AMP.

Animals↗

PubMed1975

Mechanism of action of "ruthenium red" compounds on Ca2+ ionophore from sarcoplasmic reticulum (Ca2+ + Mg2+)- adenosine triphosphatase and lipid bilayer.

Sarcoplasmic reticulum (Ca2+ + Mg2+)-ATPase was previously shown to have Ca2+-dependent and -selective ionophoric activity when tested in oxidized cholesterol lipid bilayer membranes (Shamoo, A. E., and MacLennan, D. H. (1974) Proc. Natl. Acad. Sci. U. S. A. 71, 3522). ruthenium red, a known inhibitor of (Ca2+ + Mg2+)-ATPase, is found to inhibit the Ca2+-ionophoric activity associated with (Ca2+ + Mg2+)-ATPase. Furthermore, ruthenium red alone acts as an anion-selective ionophore in lipid bilayers with the the following selectivity sequence for anions: l- greater than Cl-, Br- greater than F- greater than NO3-. The PCl-/PNa+ ratio was approximately 4/l. The presence of ruthenium red in excess of Ca2+ ionophore in lipid bilayer experiments converts the cation selectivity of the bilayer due to Ca2+ ionophore into anion selectivity.

Adenosine Triphosphatases↗