Interaction of ruthenium red with isolated sarcolemma

Selective neurotoxicity of ruthenium red in primary cultures

The inorganic dye ruthenium red (RuR) has been shown to be neurotoxic in vivo when injected intracerebrally. In this work the toxicity of RuR was compared in primary cultures of rat cortical neurons, cerebellar granule neurons and cerebellar astroglia. Microscopic examination of the cultures revealed that RuR penetrates the somata of both types of neurons used and produces vacuolization and loss and fragmentation of neurites. In contrast, no RuR was seen inside cultured astrocytes and no morphological signs of damage were observed in these cells. RuR toxicity was also assessed by immunocytochemistry of alpha-tubulin and by biochemical measurement of the reduction of (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) by the cultured cells. The morphological alterations in the neurons were closely correlated with loss of tubulin immunoreactivity and particularly with a notable decrement in the ability to reduce MTT. Using the latter parameter, it was found that neuronal damage was independent of the age of the cultures, augmented progressively with time of incubation with RuR, from 8 to 24 h, and showed a clear dose-response curve from 20 to 100 microM RuR. Astrocytes showed only a slight decrease in MTT reduction after 24 h of incubation with 100 microM RuR. It is concluded that RuR seems to be toxic for neurons but not for astroglia, and that this selectivity is probably related to the ability of the neurons to internalize the dye. The possible mechanisms of RuR penetration and neuronal damage are discussed.

Characterization of ruthenium red-binding sites of the Ca(2+)-ATPase from sarcoplasmic reticulum and their interaction with Ca(2+)-binding sites

Sarcoplasmic reticulum Ca(2+)-ATPase has previously been shown to bind and dissociate two Ca2+ ions in a sequential mode. This behaviour is confirmed here by inducing sequential Ca2+ dissociation with Ruthenium Red. Ruthenium Red binds to sarcoplasmic reticulum vesicles (6 nmol/mg) with a Kd = 2 microM, producing biphasic kinetics of Ca2+ dissociation from the Ca(2+)-ATPase, decreasing the affinity for Ca2+ binding. Studies on the effect of Ca2+ on Ruthenium Red binding indicate that Ruthenium Red does not bind to the high-affinity Ca(2+)-binding sites, as suggested by the following observations: (i) micromolar concentrations of Ca2+ do not significantly alter Ruthenium Red binding to the sarcoplasmic reticulum; (ii) quenching of the fluorescence of fluorescein 5'-isothiocyanate (FITC) bound to Ca(2+)-ATPase by Ruthenium Red (resembling Ruthenium Red binding) is not prevented by micromolar concentrations of Ca2+; (iii) quenching of FITC fluorescence by Ca2+ binding to the high-affinity sites is achieved even though Ruthenium Red is bound to the Ca(2+)-ATPase; and (iv) micromolar Ca2+ concentrations prevent inhibition of the ATP-hydrolytic capability by dicyclohexylcarbodi-imide modification, but Ruthenium Red does not. However, micromolar concentrations of lanthanides (La3+ and Tb3+) and millimolar concentrations of bivalent cations (Ca2+ and Mg2+) inhibit Ruthenium Red binding as well as quenching of FITC-labelled Ca(2+)-ATPase fluorescence by Ruthenium Red. Studies of Ruthenium Red binding to tryptic fragments of Ca(2+)-ATPase, as demonstrated by ligand blotting, indicate that Ruthenium Red does not bind to the A1 subfragment. Our observations suggest that Ruthenium Red might bind to a cation-binding site in Ca(2+)-ATPase inducing fast release of the last bound Ca2+ by interactions between the sites.

Dissociation between contractile function and oxidative metabolism in postischemic myocardium. Attenuation by ruthenium red administered during reperfusion

The oxidative metabolic rate may be disproportionately high compared with contractile function in postischemic reperfused myocardium. To study the potential involvement of intracellular calcium transport in high energy expenditure after reperfusion, we determined in isolated rat hearts the effect of ruthenium red, an inhibitor of mitochondrial calcium transport, on recovery of contractile function and oxidative metabolic rate. Hearts subjected to 60 minutes of no-flow ischemia exhibited, at 15 minutes after the onset of reperfusion, poor recovery of left ventricular pressure development to only 7% of the corresponding value measured in control hearts (p less than 0.01). However, myocardial oxygen consumption was recovered to 84% of control (p = NS). The ratio of isovolumic contractile performance (expressed as the product of heart rate and left ventricular pressure development) to myocardial oxygen consumption was severely depressed to 6% of control (p less than 0.01). Supplementation of the perfusate with 6 microM ruthenium red during the initial 40 minutes of reperfusion resulted in a reduction of myocardial oxygen consumption to 65% of the value measured after 15 minutes of reperfusion in hearts reperfused without ruthenium red (p less than 0.01), despite a threefold increase of left ventricular pressure development (p less than 0.05). Oxidation of both palmitate and glucose was reduced to a comparable extent by ruthenium red. The ratio of contractile performance to myocardial oxygen consumption increased progressively during infusion of ruthenium red and did not differ further from control hearts after 30 minutes of reperfusion. Cumulative myocardial release of creatine kinase was reduced by 47% (p less than 0.05) in hearts reperfused with ruthenium red-containing medium. The results provide circumstantial evidence for the hypothesis suggesting that enhanced energy expenditure by intracellular calcium transport may be involved in the mechanisms underlying the dissociation between left ventricular performance and myocardial oxidative metabolic rate early after postischemic reperfusion.

Interaction of ruthenium red with Ca2(+)-binding proteins

The interaction of ruthenium red, [(NH3)5Ru-O-Ru(NH3)4-O-Ru(NH3)5]Cl6.4H2O, with various Ca2(+)-binding proteins was studied. Ruthenium red inhibited Ca2+ binding to the sarcoplasmic reticulum protein, calsequestrin, immobilized on Sepharose 4B. Furthermore, ruthenium red bound to calsequestrin with high affinity (Kd = 0.7 microM; Bmax = 218 nmol/mg protein). The dye stained calsequestrin in sodium dodecyl sulfate-polyacrylamide gels or on nitrocellulose paper and was displaced by Ca2+ (Ki = 1.4 mM). The specificity of ruthenium red staining of several Ca2(+)-binding proteins was investigated by comparison with two other detection methods, 45Ca2+ autoradiography and the Stains-all reaction. Ruthenium red bound to the same proteins detected by the 45Ca2+ overlay technique. Ruthenium red stained both the erythrocyte Band 3 anion transporter and the Ca2(+)-ATPase of skeletal muscle sarcoplasmic reticulum. Ruthenium red also stained the EF hand conformation Ca2(+)-binding proteins, calmodulin, troponin C, and S-100. This inorganic dye provides a simple, rapid method for detecting various types of Ca2(+)-binding proteins following electrophoresis.

Ruthenium red effect on mechanical and electrical properties of mammalian skeletal muscle

In this work we studied the effect of ruthenium red (RR) on the mechanical and electrical properties of rat diaphragm bundles in vitro (30 degrees C). Two concentrations of RR were used: 5 and 10 microM. We measured: 1) twitches, tetanus and caffeine contracture; 2) relation between mechanical tension and resting membrane potential (Vm); 3) contraction threshold by visualization of the contraction around the stimulated area of the fiber. The main finding are the following: a) RR potentiates the twitch tension. The tetanic tension is not affected and the time course of the caffeine contracture is shortened in the RR containing solutions; b) the relationship between mechanical tension and resting membrane potential (Vm) is shifted toward more negative values of Vm in RR; c) the mechanical threshold is lowered about 7 mV in the presence of RR; d) the rates of depolarization and repolarization of the action potential are decreased in the test solutions. We suggested that the shift in the mechanical threshold and the prolongation of the action potential are the main factors involved in the potentiating effect of RR. The mechanism by which RR shifts the mechanical threshold is not known.

Three phase contractile response of rabbit pulmonary artery to norepinephrine: influence of ruthenium red and calcium

We recorded isometric contractile force of rabbit pulmonary artery after application of norepinephrine (50 microM), plotted semilogarithmic graphs of force development over time, and calculated rates of force development. The normal contractile response contained three phases: an initial fast, a short intermediate and a final slow. Correlation coefficients for each phase and differences between rates of force development of each phase were significant (P less than 0.05). Ruthenium red (1 mM) removed only the slow phase and significantly reduced the rates of the fast and intermediate phases. A calcium-free solution removed both the slow and intermediate phases and significantly reduced the rate of the fast phase.

Ruthenium red: differential effects on excitation and excitation-contraction coupling in frog skeletal muscle

The effects of purified ruthenium red (RR6+) on action potentials, resting potentials, twitches, tetani and potassium contractures in fibre bundles dissected from frog leg muscles were compared to the effects of supranormal concentrations of Ca2+. The effects of RR6+ include a shift of action potential threshold and reduction in rates of depolarization, repolarization and conduction velocity. Resting potentials and action potential overshoots are unaffected by RR6+ in concentrations of 10 microM or less. Higher RR6+ concentrations cause membrane depolarization. Low concentrations of RR6+ cause twitch potentiation but do not affect tetanus tension. Unlike Ca2+, RR6+ has no effect on the mechanical activation curve. However, crude preparations of RR6+ contain an unidentified contaminant which does shift the mechanical activation curve to the right, i.e. it increases mechanical threshold. RR6+ itself appears to be largely excluded from the t-system.

Role of calcium in triggering the release of transmitters at the neuromuscular junction

Calcium ions have a key role in triggering the release of packaged transmitter at the amphibian neuromuscular junction and of the chromaffin granules at the adrenal medulla. It is suggested that (i) proteins on the vesicle and plasma membranes are of particular importance in promoting membrane fusion and exocytosis (ii) they may be divalent cation-stimulated ATPases, which form the calcium-binding sites or have a specific calcium-binding protein in close molecular apposition (iii) these ATPases in synaptic vesicles and chromaffin granules also generate a protonmotive force which is associated with the uptake of transmitter (iv) the osmotic properties of the vesicle may be important during fission, but it is not suggested that chemiosmotic effects are involved in Ca2+-triggered fusion (v) the action of calcium is markedly co-operative (vi) the adrenal medullary cell and the n.m.j. may differ in the Ca2+-binding site; there is evidence for the involvement of calmodulin in granule-plasmalemma fusion in the chromaffin cells, but not at present (surprisingly) for a role of this Ca2+-binding protein at the n.m.j. (vii) exocytosis requires MgATP (viii) phosphorylation of the ATPase may well be involved; phosphorylation via cAMP does not seem to be involved in fusion in either system (ix) the ATPase may undergo configurational changes during exocytosis and is markedly sensitive to the physical state of its phospholipid environment and to the oxidation of its -SH groups.

The interaction of ruthenium red with surface charges controlling excitation-contraction coupling in frog sartorius

Frog sartorii were incubated in choline Ringer solution containing different amounts of the cationic dye ruthenium red, and were subsequently superfused with ruthenium red-free solution. The contraction threshold was measured during and after the incubation at different calcium and magnesium concentrations. During incubation in ruthenium red the threshold potential is slowly shifted to more positive values depending on time of incubation and the ruthenium red concentration (10--300 microns). After ca. 40 min of incubation a saturation potential is reached. The threshold shift is already maximal (-38mV threshold potential) at 30 microns of ruthenium ret regardless of the calcium concentration up to 5 mM. Omitting calcium from the incubation solution or adding 0.5 mM magnesium instead of calcium resulted in a more negative saturation potential (-48 mV). Washing the muscle in ruthenium red-free solution for 60 min after the incubation fails to reverse the threshold shift completely. The irreversible component of the threshold shift does not depend on the divalent cation concentration during incubation as long as the saturation value during incubation is more positive than -50 mV. The contraction threshold achieved after incubation with ruthenium red is dependent on the divalent cation concentration with calcium being twice as effective as magnesium. The effect of ruthenium red is greatest at small divalent cation concentrations and not significant at 50 mM. Incubating muscles with 5 units of neuraminidase shifted the concentration threshold to more positive potentials to the same extent as incubation with ruthenium red. Subsequent treatment of the neuraminidase-treated muscles with 30 microns of ruthenium red has no further effect on contraction threshold. The alternative experiment, first incubation with ruthenium red and then treatment with neuraminidase, gives the same results. The results are explained by the interaction of ruthenium red with membrane-bound sialic acid. This interaction is thought to result in a decrease in negative charges which results in a shift of the surface potential and hence of the contraction threshold to more positive potentials.

Calcium-binding of synaptosomes isolated from rat brain cortex. IV. Effects of ruthenium red on the Co-operative nature of calcium-binding

Ruthenium red combines with isolated synaptosomes, resulting in strong inhibition of their Ca2+-binding. In isotonic saline media, however, the dye-induced inhibition of Ca2+-binding is significantly greater than that expected for the amount of bound dye and Hill's exponent of the Ca2+-binding decreases to 1 with an increase in the amount of the dye bound. On the other hand in isotonic mannitol-sucrose solution, inhibition of synaptosmal Ca2+-binding brought about by the dye is proportional to the amount of dye bound. Based on these results, the effects of the dye on the co-operative nature of synaptosomal Ca2+-binding is discussed.