Pharmacological characterization of ionophore X537A-induced contractile responses in isolated rabbit taenia coli and aorta

Pharmacological action of ionophore X537A was studied in taenia coli and aortic strips isolated from rabbit. These isolated smooth muscle preparations contracted by X537A (10(-5)-10(-4) M). A removal of Ca ions from the buffer solution considerably reduced the contraction of taenia coli but not that of aorta. D 600 (methoxyverapamil, 10(-6) M) was without any effect in the contraction of both tissues by X537A (10(-4) M). However, papaverine (10(-4) M) and Aspaminol (1, 1-diphenyl-3-piperidinobutanol hydrochloride, 10(-4) M) inhibited X537A (10(-4) M)-induced contraction markedly in taenia coli but slightly in aorta. Inhibitory effects of these drugs were reversed in taenia coli by increasing Ca ion concentration in buffer solution but not in aorta. X537A (10(-4) M)-induced contraction of aorta was not affected by a pretreatment of rabbit with reserpine and preincubation of the isolated preparations with guanethidine (10(-6) M) or prazosin (10(-7) M). These results suggest that ionophore X537A might produce the contraction through an increase of Ca influx in isolated rabbit taenia coli which are little or not affected by D 600, whereas the contraction of rabbit aorta induced by X537A is mainly due to facilitation of release of Ca sequestered intracellularly.

X-537A ionophore-mediated calcium transport and calcium phosphate formation in Pressman cells

The present study examined precipitate development induced in phosphate solutions by the ionophoric translocation of Ca2+ across a bulk organic solvent barrier. Experiments were conducted at pH 7.4 and 25 or 37 degrees in a three-compartment Pressman cell. The aqueous reaction (0, 2.2 or 22 mM phosphate, 100 mM K+) and donor (1.3 or 13 mM Ca2+, 0.8 mM Mg2+, 100 mM Na+) compartments were separated by a CHCl3 compartment rendered permeable to cations by the addition of the carboxylic ionophore X-537A (2 or 20 mM). The resultant cation movements increased Ca2+, Mg2+, and Na+ concentrations in the reaction compartment at the expense of K+ loss to the donor compartment. The magnitude of the K+ counterflow and the efficiency of the ionophore-mediated Ca2+ in equilibrium 2K+ exchange reaction resulted in appreciable Ca2+ overshoots in the reaction compartment. In the absence of phosphate, Ca2+ increases exceeded donor levels by several-fold. With phosphate present, the Ca2+ flux was sufficient to induced precipitation. Generally, the first solid formed was amorphous. The amorphous precipitate, however, was unstable and converted to an apatite-like crystalline phase. Both carbonate (26 mM) and Mg2+ (0.8 mM) in the reaction solution delayed but did not prevent the conversion. The possible relevance of these findings to matrix vesicle calcification is discussed.

The action of polyether ionophorous antibiotics (monensin, salinomycin, lasalocid) on developmental stages of Eimeria tenella (Coccidia, Sporozoa) in vivo and in vitro: study by light and electron microscopy

The effect of three polyether antibiotics (monensin, salinomycin, lasalocid) on developmental stages of Eimeria tenella (Coccidia, Sporozoa) was studied in vivo and in vitro by means of light and electron microscopy. It was found that these three drugs act against free merozoites, which are destroyed by bursting of the cell border (i.e. pellicle), endoplasmic reticulum and internal organelles even after very short exposure times (20 min) in media containing 1 ppm, 10 ppm or 100 ppm of these drugs. Sporozoites, however, survived these drug concentrations during an exposure time of 30 min (this would be sufficient to penetrate host cells and start development). Intracellular stages, which were situated in a parasitophorous vacuole within an intact host cell, were not attacked, apparently because these drugs are almost incapable of penetrating host cells. On the other hand, parasites (such as differentiated schizonts, gamonts) located within degenerating host cells showed slight disintegration, which did not necessarily led to their death. From these results it becomes clear why these polyether antibiotics have to be fed daily. Doses of 70 ppm salinomycin, 125 ppm monensin and 125 ppm lasalocid were found to bring about an equivalent protective effect against an infection with 40,000 Eimeria tenella oocysts.

Effect of lasalocid sodium on rumen fermentation and digestion in sheep

Four adult sheep were fed 4 diets successively according to a Latin-square design. They were fitted with a rumen cannula and with simple cannulae at the duodenum and ileum. The basal diet (L0) was composed of highly-pressed ensiled sugar beet pulp (56.2%), cereal (barley and corn: 27.6%), urea (1.5%) and wheat straw (14.1%). Lasalocid sodium was added to obtain the following respective amounts: 21 ppm for diet L1, 43 ppm for diet L2 and 64 ppm for diet L3 (table 1). In the rumen, lasalocid significantly increased the molar proportion of propionic acid in the volatile fatty acids (VFA) mixture at the expense of the acetic and butyric acid proportions. The total VFA concentration decreased, especially with 43 and 64 ppm (table 2). Accordingly, the proportion of methane in rumen gases decreased. The ciliate population was always lower in animals fed experimental diets L1, L2, and particularly L3. The non-food-particle-associated bacterial population also decreased; the differences were significant only with the highest doses of lasalocid (L3). At the same time, bacterial cellulolytic activity increased 10%, indicating that qualitative modifications had taken place in the rumen bacterial population (table 3). Overall digestive utilization of organic matter (OM) decreased when lasalocid was added to the diets. This was due to a considerable reduction in forestomach digestion (12% decrease) (table 4). A greater supply of OM rich in cell-wall carbohydrates in the duodenum would explain the lower digestibility in the small intestine of animals given diet L1 and especially the L2 and L3 diets. No significant shift in digestion was noted in the large intestine. The composition of the non-ammonia nitrogen that entered the duodenum of sheep given lasalocid differed from that noted with the control diet (L0) (table 5). The amount of microbial proteins was significantly lower, whilst the proportion of non-degraded feed proteins was higher. The efficiency of microbial synthesis (bacterial proteins/kg OM truly digested in the rumen) was not significantly modified by lasalocid. All these modifications in digestion observed with these diets, and resulting from changes in the qualitative and quantitative composition of flora and fauna in the rumen, have an effect on nitrogen and energy utilization in the ruminant.

Inactivation of the sarcoplasmic reticulum calcium-transport-ATPase by Lasolocid in combination with Triton X-100

The calcium-transport-ATPase of the sarcoplasmic reticulum membranes is irreversibly inactivated by the combined action of Lasolocid and Triton X-100 at concentrations which separately do not interfere with the enzyme's activity. In the presence of Lasolocid the enzyme is most susceptible to inactivation when the Triton X-100 concentration just exceeds its critical micellar concentration, approximately 0.2 mg . ml-1. Lasolocid becomes effective at a concentration of 10 microM and produces rapid inactivation at 100 microM. The enzyme is more rapidly inactivated in the active than in the inactive state.

Studies on the mechanism of an antibiotic ionophore, R02-2985 (X537A) in the conscious chronically instrumented dog: involvement of the prostaglandin synthetic pathway

Conscious dogs were pretreated with a large dose of indomethacin in order to test the hypothesis that prostaglandin synthesis may be involved in the mechanism of action of the inophore R02-2985. The increase in renal blood flow and decrease in renal vascular resistance usually produced by R02-2985 were inhibited by indomethacin. In fact, the calculated renal resistance doubled. In contrast to the effects on renal circulation, indomethacin did not affect coronary blood flow increases which occur independent of contractility changes produced by this ionophore. Effects associated with facilitated release of catecholamines, ie, increases in heart rate, central aortic pressure, and dP/dt were prolonged in comparison to the control study published earlier where these parameters returned to control levels within 2.5 h, thus suggesting that prostaglandin synthesis may somehow potentiate the effects of R02-2985 on the release of catecholamines in vivo.

The effect of X-537A (lasalocid) on potassium contracture in rat ventricular muscle

The effects of the carboxylic ionophore X-537A on contracture induced by high external K+ were determined in stimulated and unstimulated rat papillary muscles. X-537A (5 X 10(-6) M - 10(-5) M) increased peak K+-contracture force in stimulated but not unstimulated muscle. X-537A may alter myocardial force development by influencing transport of Ca2+ across the sarcolemma or Ca2+ release from sarcoplasmic reticulum.

Studies on the stage of action of ionophorous antibiotics against Eimeria

Sporozoites of Eimeria tenella were treated with different anticoccidial drugs in vitro and their subsequent viability was tested by inoculating them into chicken embryos. Monensin, salinomycin, lasalocid, and arprinocid, at concentrations between 0.01 and 1.0 micrograms/ml, greatly reduced sporozoite viability as judged by mortality, hemorrhage and specific lesions in the embryo chorioallantois. Monensin was also effective in reducing the viability of sporozoites of E. mivati and E. tenella as judged by oocyst production occurring in embryos; activity of monensin was greater against E. tenella than against E. mivati. Monensin (0.1 mg) inoculated into embryos inhibited development of E. tenella. Oocysts which were produced in the presence of the drug sporulated normally and sporozoites obtained from them were fully infective. By initiating treatment of chickens with monensin at different times in relation to infection, it was shown that the drug exerts its anticoccidial effect on the primary invasive stage and on the gametogonous stage of E. tenella and E. necatrix. The effect of gametogony was tested by initiating infections with second generation merozoites of E. tenella. Significant reduction in oocyst production occurred in three of four strains of E. tenella tested. Medication with monensin initiated before merozoite inoculation was effective in inhibiting oocyst production, but medication starting 5 hr after merozoite inoculation was not. This differed from the effects of arprinocid and sulfaquinoxaline which were expressed both before and 5 hr after merozoite inoculation. The results show that the ionophorous anticoccidial drugs exert their anticoccidial action primarily against the invasive stages of Eimeria.

Effects of amine substances on susceptibility of cells to agglutination by concanavalin A and on paracrystal formation by vinblastine in untransformed 3T3 cells

The effects of a secondary amine (ketamine), tertiary amines (dibucaine, lidocaine, marcaine, propanidid, diazepam and chlorpromazine) and a quaternary amine (tetraethylammonium bromide, TEA) on mouse 3T3 cell agglutination by concanavalin A (Con A), on patch formation of Con A receptors on the cell surface, and on paracrystal formation by vinblastine in cytoplasm were studied. These amines enhanced the cell agglutination at low concentrations of Con A, as did the mixture of colchicine and cytochalasin B. Ca++, applied extracellularly, inhibited the effects of these amines on cell agglutination by Con A. The patch formation of Con A receptors on the cell surface as revealed by fluoresceinated Con A was enhanced by these amines. Ketamine, dibucaine and TEA inhibited the paracrystal formation in cytoplasm, as did Ca++ ionophores such as A-23187 and X-537-A. These results suggest that the amines tested affect the fluidity of Con A receptors by impairment of cell membrane structural proteins and result in the increase of the susceptibility of cells to agglutination by Con A.

Spontaneous sweat secretion in calcium-free strontium medium

Sr2+ substitutes for Ca2+ in methacholine (MCH)-evoked sweat secretion in isolated simian eccrine sweat glands, but four to eight times greater concentrations of Sr2+ were required to achieve the same effect as did a given Ca2+ concentration. In Ca2+-free Sr2+ medium the anticholinergic effect of atropine was reduced by about four orders of magnitude. In the Sr2+ medium, spontaneous sweat secretion (SSS) was also observed in the absence of any pharmacological stimuli. SSS occurs slowly, reaching a plateau after 30 min incubation. The maximal SSS is a saturation function of Sr2+ concentration reaching a maximum at 8 mM. Sr2+-induced SSS was inhibitable by removal of Sr2+, low bath temperature (10-14 degrees C), ouabain (5 X 10(-6) M), and D 600 (10(-3) M). Ca2+ was found to inhibit Sr2+-induced SSS, but a Schild plot for the Ca2+ and Sr2+ dose relationship failed to show a slope of unity. The data suggest that Sr2+-induced SSS represents actual secretory processes, which are triggered by Sr2+ leaking into the cell through as yet undefined membrane channels.

A 31P-NMR study of some metabolic and functional effects of the inotropic agents epinephrine and ouabain, and the ionophore R02-2985 (X537A) in the isolated, perfused rat heart

1. Some metabolic effects of increased mechanical activity by the Langendorff-perfused rat heart have been characterized using 31P-NMR. Mechanical activity was increased by infusion of ouabain (0.9-7.0.10(-5) M), the ionophore R02-2985 (1.10(-5) M) or epinephrine (5.10(-8) M). 2. Similar metabolic changes accompanied infusion of each of the positive inotropic agents into hearts perfused with buffer containing 11 mM glucose as the substrate. In each case phosphocreatine concentrations decreased. During the period of epinephrine infusion the phosphocreatine began to recover its original concentration, although there were no significant changes in mechanical activity. 3. Comparisons of the metabolic changes accompanying the positive inotropic and chronotropic effects of epinephrine were made between hearts perfused with either glucose (11 mM), acetate (5 mM) or lactate (5 mM). A time-dependent decrease in phosphocreatine concentrations also accompanied infusion of epinephrine into hearts perfused with lactate as the sole exogenous substrate, but no statistically significant metabolite changes were observed after identical epinephrine infusions with acetate as the substrate. 4. Calculations of the concentration of free ADP assuming equilibrium in the creatine phosphokinase reaction allows estimation of the cytosolic phosphate potential ([ATP]/[ADP][Pi]), which appears to be dependent on the number of factors, including the nature of the exogenous substrate and the level of mechanical activity. 5. Thus, we conclude that there is no general correlation between the phosphate potential and the mitochondrial respiratory rate in the perfused rat heart.

Effect of pentobarbital on the noradrenaline release induced by drugs and field electrical stimulation from cerebral and femoral arteries of the cat

The present studies showed that field electrical stimulation, high potassium (K+), tyramine and ionophore X537A induced tritium release from cerebral and femoral arteries of cat prelabelled with [3H]noradrenaline. The secretion caused by K+ or field stimulation was CA2+-dependent and was antagonized by high concentrations of pentobarbital (10(-4) and 10(-3) M), whereas that induced by the rest of the drugs was unchanged in the same situations. The noradrenaline uptake by these arteries was reduced by pentobarbital (10(-3) M and 10(-4) M). These results suggest that this barbiturate interferes with Ca2+ entry to the adrenergic nerve endings, and therefore antagonizes the noradrenaline release by Ca2+-dependent processes (exocytosis).

Oxalate transfer across the membranes of sarcoplasmic reticulum during the uptake of Ca++

The kinetic profile of Ca++ uptake in the presence of oxalate is biphasic. An initial phase independent on oxalate is followed by an oxalate-dependent phase delayed in time. The ionophore X-537A only abolishes the net Ca++ uptake if added before the onset of the oxalate phase. However, during this phase, X-537A suddenly releases an amount of Ca++ similar in quantity to that released in the initial phase. The delay of the oxalate-dependent phase is a function of pH. At pH of about 5.5, the oxalate phase and simultaneous calcium oxalate precipitation would theoretically start at the beginning, with no delay. Ejection of protons during Ca++ uptake is strongly depressed by oxalate, but not by other organic anions which do not trap Ca++. It is suggested that oxalate is transferred to the inside of the vesicles as a monoprotonated species at expense of protons ejected by the Ca++-pump during the uptake of Ca++.

Relation of cytoplasmic calcium to contractility in Physarum polycephalum

In a dumbbell-shaped plasmodium of Physarum polycephalum showing active shuttle streaming Ca was precipitated with potassium pyroantimonate (K[Sb(OH)6]), and the distribution of Ca between the cytoplasm and cellular organelles, especially vacuoles, was examined by electron microscopy. The contracting half-mass, where many empty vacuoles were present, was rich in the small Ca precipitates located in the cytoplasm. The relaxing half-mass, where many Ca-containing vacuoles were present, was poor in the cytoplasmic Ca precipitates. One half-mass of a dumbbell-shaped plasmodium was treated with Ca ionophore, X-537A, and its effect on the motive force for endoplasmic streaming and the distribution of Ca was investigated. The motive force was increased by X-537A, but the period of shuttle streaming was not changed. X-537A also induced a significant increase in the number of the cytoplasmic Ca precipitates in the X-537A-treated contracting half-mass, so that the asymmetry of the distribution of cytoplasmic Ca precipitates was enhanced. A large portion of the vacuoles were empty in the contracting half-mass, and Ca-containing in the relaxing one as in the case of the untreated plasmodium.

Relaxing and metabolic inhibitory action of X537A (Lasalocid) on the taenia of the guinea-pig caecum

1. In the isolated guinea-pig taenia, application of X537A to the muscle caused a relaxation, while A23187 caused a sustained contraction. 2. Treatment with adrenergic blocking agents and tetrodotoxin had no effect on the relaxing response to X537A. 3. In the presence of a low concentration (10(-6) M) of X537A or under hypoxic conditions (bubbled with 95% N2: 5% CO2), the taenia lost the ability to respond to a high concentration (40 mM) of potassium with a sustained tonic contraction, although the rapid phasic contraction was still present. 4. When a low concentration of X537A was applied the shape of the contractile response to A23187 was changed from a sustained development of tension to an oscillatory tension which was also observed under hypoxia. 5. In tissues treated with glycerol for 3 weeks, neither X537A nor A23187 had any effect on the contractile response induced by elevation of calcium concentration (pCa = 4) in the presence of magnesium and ATP. 6. Exposure to a low concentration (10(-6) M) of X537A, or hypoxia, slightly yet significantly decreased the ATP content of the muscle. A high concentration (10(-5) M) of X537A markedly decreased the ATP content to about half normal. A23187 did not alter the ATP content. 7. Application of X537A did not alter the calcium content of the muscle and inhibited the A23187-induced increase in content. Under hypoxia, A23187 failed to increase the calcium content of the muscle. 8. The results indicate that, in contrast to A23187, X537A has a relaxing and metabolic inhibitory action on the guinea-pig taenia. The action of low concentrations of X537A resembled that of the hypoxia, indicating that X537A might exert its relaxing action, at least in part, by inhibition of aerobic energy metabolism of the muscle.

Taurine-calcium interactions in frog rod outer segments: taurine effects on an ATP-dependent calcium translocation process

Frog rod outer segments (ROS) isolated in a Ca-free, EGTA-containing medium, showed a rapid ATP-dependent accumulation of 45Ca, GTP, CTP, ITP, UTP, GMP and beta-, gamma-methylene ATP did not substitute for ATP in energizing Ca uptake. This process required Mg, it was abolished in the presence of Ca ionophores A23187 and X537A and is not affected by external sodium. The Arrhenius activation energy was 7.9 kcal/mol and the pH optimum was approximately 7.2. The apparent Km for Ca uptake was 66 microM with a V max of 12.5 nmol/mg protein. 45Ca accumulation was reduced in illuminated ROS. The presence of 5-25 mM taurine, but not of GABA, glycine, histidine or proline, markedly enhanced Ca uptake by ROS.

Effect of lasalocid or monensin on lactate production from in vitro rumen fermentation of various carbohydrates

Lasalocid and monensin effectively reduced the lactate produced during in vitro fermentation of various sugars and ground grains with rumen fluid from either hay- or grain-fed cattle. The minimum effective dose was 6 micrograms/ml. Both lasalocid and monensin at 6 micrograms/ml reduced the fermentation rate of glucose, fructose, galactose, sucrose, lactate, mannose, ground corn, ground sorghum, and ground wheat, and raised the pH and substantially lowered lactate concentration compared with controls. Although both antibiotics decreased total lactate production, the proportion of D(-) lactate to L(+) lactate increased. Apparently both antibiotics were less inhibitory to the formation of D(-) than to L(+) lactate isomer. Lasalocid was more effective than monensin in inhibiting lactate production except when rumen fluid from grain-fed cattle was used in fermentation.

Noradrenaline contractions in rabbit mesenteric arteries skinned with saponin

1. In rings of small rabbit mesenteric arteries, noradrenaline induced oscillatory contractions. After depolarization with potassium, which produced in this preparation only a transient contraction, the arteries responded to noradrenaline with tonic contraction. 2. Artery rings, skinned for 6 min with saponin (0.5 mg/ml.), were highly sensitive to calcium (half-maximum contraction at 4 x 10(-7) M-Ca2+). In the skinned preparations, a contraction was still elicited by noradrenaline. 3. Treatment with saponin renders virtually all smooth muscle cells of the mesenteric artery preparation hyperpermeable as indicated by both physiological and morphological criteria. 4. While the Ca stores responsible for the noradrenaline-induced contraction of skinned arteries were depleted at a slow rate by 0.1 mM-EGTA, they were completely emptied by a 4 min exposure to 10 mM-EGTA. After release of intracellular Ca by noradrenaline, the Ca stores could be partially replenished by incubating the preparation in 10(-6) M-Ca2+ for 4 min. 5. Noradrenaline failed to contract skinned arteries after part of the intracellular Ca had been released by caffeine but not after Ca release by the ionophore X-537 A. 6. The mitochondrial uncoupler, carbonyl cyanide m-chlorophenylhydrazone, inhibited noradrenaline-induced contractions of skinned arteries. 7. Noradrenaline had no effect on 45Ca translocation in either membrane vesicles or mitochondria isolated from mesenteric arteries. 8. The present results show that in vascular smooth muscle a certain degree of structural integrity of the cell membrane, but not its selective permeability, is required for the coupling between alpha-adrenoceptors and Ca release from intracellular stores; the data also suggest that alpha-adrenoceptor stimulation results in release of Ca bound to the plasma membrane rather than indirect release of Ca accumulated in intracellular organelles.