Ruthenium-red staining of skeletal and cardiac muscles

Introducing a mammalian nerve-muscle preparation ideal for physiology and microscopy, the transverse auricular muscle in the ear of the mouse

A new mammalian neuromuscular preparation is introduced for physiology and microscopy of all sorts: the intrinsic muscle of the mouse ear. The great utility of this preparation is demonstrated by illustrating how it has permitted us to develop a wholly new technique for staining muscle T-tubules, the critical conductive-elements in muscle. This involves sequential immersion in dilute solutions of osmium and ferrocyanide, then tannic acid, and then uranyl acetate, all of which totally blackens the T-tubules but leaves the muscle pale, thereby revealing that the T-tubules in mouse ear-muscles become severely distorted in several pathological conditions. These include certain mouse-models of muscular dystrophy (specifically, dysferlin-mutations), certain mutations of muscle cytoskeletal proteins (specifically, beta-tubulin mutations), and also in denervation-fibrillation, as observed in mouse ears maintained with in vitro tissue-culture conditions. These observations permit us to generate the hypothesis that T-tubules are the "Achilles' heel" in several adult-onset muscular dystrophies, due to their unique susceptibility to damage via muscle lattice-dislocations. These new observations strongly encourage further in-depth studies of ear-muscle architecture, in the many available mouse-models of various devastating human muscle-diseases. Finally, we demonstrate that the delicate and defined physical characteristics of this 'new' mammalian muscle are ideal for ultrastructural study, and thereby facilitate the imaging of synaptic vesicle membrane recycling in mammalian neuromuscular junctions, a topic that is critical to myasthenia gravis and related diseases, but which has, until now, completely eluded electron microscopic analysis. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

Ruthenium red as an effective blocker of calcium and sodium currents in guinea-pig isolated ventricular heart cells

1. The effect of ruthenium red on calcium and sodium currents was studied in guinea-pig isolated ventricular heart cells with the whole cell patch-clamp technique. 2. Ruthenium red very efficiently blocked the L-type calcium current in a dose-dependent manner. A significant block was observed for concentrations as low as 0.3 microM. Analysis of the dose-response curve with the logistic equation indicated an EC50 of 0.8 microM, a maximum inhibition of 85% reached at 5 microM, and a coefficient of 2.37. 3. There was no shift in the voltage-dependence of the Ca current activation, nor in that of its steady-state inactivation determined with a 1 s prepulse. However, removal of Ca current inactivation at positive voltage was considerably reduced in the presence of concentrations of ruthenium red above 1 microM. A slowing of the time-course of inactivation of the Ca current was also observed. 4. At 10 microM, a concentration generally used to block the sarcoplasmic Ca release channels or the mitochondrial Ca uptake, ruthenium red blocked 26.7+/-4.3% (n=8) of the sodium current, and slowed its inactivation time-course. No effect was observed on the voltage-dependence of the current activation or inactivation. The peak sodium current was also decreased at a 10 times lower concentration by 7.6+/-2.7% (n=3). 5. Thus, at concentrations used to assess intracellular Ca movements, ruthenium red induced in heart cells a significant block of both Ca and Na channels.

Ruthenium red-catalyzed degradation of peroxides can prevent mitochondrial oxidative damage induced by either tert-butyl hydroperoxide or inorganic phosphate

We have recently shown that ruthenium red, a non-competitive inhibitor of the mitochondrial Ca2+ uniporter, can reduce tert-butyl hydroperoxide via a Fenton-type reaction. In respiring mitochondrial preparations containing tert-butyl hydroperoxide, redox cycling of ruthenium red occurs and causes the amplification of methyl radical generation (Meinicke, A. R., Zavan, S. S., Ferreira, A. M. C., Vercesi, A. E., and Bechara, E. J. H. (1996) Arch. Biochem. Biophys. 328, 239-244). In this study we show that ruthenium red can act as an antioxidant preventing mitochondrial damage when the respiratory chain is reduced or when ascorbate is present. Ruthenium red can catalyze the degradation of hydrogen peroxide into H2O and O2. We show here that ruthenium red prevents both accumulation of mitochondrial generated H2O2 and swelling in the presence of the Ca2+ ionophore A23187. Under these conditions the damage induced by Ca2+ ions and either tert-butyl hydroperoxide or inorganic phosphate is promoted by mitochondrial-generated reactive oxygen species. Swelling induced by phenylarsine oxide, a thiol cross-linker, by a mechanism independent of free radicals is not inhibited by ruthenium red. These data provide evidence that the antioxidant behavior of ruthenium red under our conditions is due to its ability to destroy peroxides, which is related to its redox cycling and is prevalent over the Fenton-type reaction.

Proteoglycans are present in the transverse tubule system of skeletal muscle

The transverse tubule system (T-tubule, T-system) of skeletal muscle is a membranous network that penetrates the interior of myofibers. The T-system is continuous with the sarcolemma and therefore provides a path for membrane excitation to reach internal myofibrils. In this study we demonstrate that T-tubules in elasmobranch fish, frog, and rat skeletal muscle contain a matrix of chondroitin sulfate proteoglycans. We used anti-T1, a mouse monoclonal antibody that recognizes a rare chondroitin sulfate epitope, for immunolocalization and biochemical studies. First, we find that T1 immunoreactivity colocalizes with a T-tubule marker, the dihydropyridine receptor alpha 2 subunit, in both frog and fish muscle. Secondly, the distribution of T1 immunoreactivity exactly matches the different distribution of T-tubules in rat and frog muscle. In rat muscle, two bands of T1 immunoreactivity are detected per sarcomere, a distribution that corresponds to the T-tubules located at the two A-I junctions of each sarcomere. In frog muscle, we detect one band of T1 immunoreactivity per sarcomere that corresponds to the one T-tubule per sarcomere located at the Z line. Lastly, we have isolated and biochemically characterized T1 antigenicity from fish skeletal muscle. Like extracellular matrix proteoglycans of cartilage, T1 antigenicity requires denaturing conditions to be solubilized. In fish muscle, two chondroitin sulfate proteoglycans bear T1: a heavily glycosylated proteoglycan with a molecular mass of about 1000 kDa, and a smaller proteoglycan that has a mobility on SDS-PAGE like a protein of molecular mass 280 kDa. We propose that proteoglycans function as structural components in the T-system. The proteoglycans may form a matrix, like the one formed by the cartilage proteoglycans they resemble, that can withstand the cytosolic osmotic pressures present in muscle cells and therefore may prevent the T-tubule from collapsing. We present a quantitative argument in support of this hypothesis.

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.

Calcium-gated calcium channels in sarcoplasmic reticulum of rabbit skinned skeletal muscle fibers

The action of ruthenium red (RR) on Ca2+ loading by and Ca2+ release from the sarcoplasmic reticulum (SR) of chemically skinned skeletal muscle fibers of the rabbit was investigated. Ca2+ loading, in the presence of the precipitating anion pyrophosphate, was monitored by a light-scattering method. Ca2+ release was indirectly measured by following tension development evoked by caffeine. Stimulation of the Ca2+ loading rate by 5 microM RR was dependent on free Ca2+, being maximal at pCa 5.56. Isometric force development induced by 5 mM caffeine was reversibly antagonized by RR. IC50 for the rate of tension rise was 0.5 microM; that for the extent of tension was 4 microM. RR slightly shifted the steady state isometric force/pCa curve toward lower pCa values. At 5 microM RR, the pCa required for half-maximal force was 0.2 log units lower than that of the control, and maximal force was depressed by approximately 16%. These results suggest that RR inhibited Ca2+ release from the SR and stimulated Ca2+ loading into the SR by closing Ca2+-gated Ca2+ channels. Previous studies on isolated SR have indicated the selective presence of such channels in junctional terminal cisternae.

Suppression of cellular injury during the calcium paradox in rat heart by factors which reduce calcium uptake by mitochondria

Isolated Langendorff perfused rat hearts were used to study changes in the Ca, Na and K content, contractile force and the loss of cellular material during the Ca paradox. Five minutes perfusion with Ca-free solution containing 1 mM EGTA, followed by 10 min of reperfusion in 1.8 mM Ca causes irreversible contracture, K loss, increase in Na and Ca and a massive release of myoglobin and other cellular material into the perfusate (the calcium paradox). During the Ca-free perfusion the ventricles gain Na but the K content decreases slightly. The size of the Na gain appears to depend upon the buffer used and is larger in bicarbonate than in Tris. When HCO3- or H2PO4- ions are omitted from the bathing solution (in Tris, HEPES, or TES buffered salines) the adverse effects of Ca readmission are reduced. Tris buffer gives the best protection. Metabolic inhibition with FCCP (5 X 10(-7) M), or with CN-(2 X 10(-3) M) together with iodoacetic acid (2 X 10(-3) M), decreases Ca uptake during the Ca paradox and inhibits the release of cellular material. In both cases a contracture is observed. Ruthenium red (10(-4) M) does not inhibit the Ca readmission contracture but reduces the release of cellular material and the gain of Ca and Na. The results suggest that the loss of cellular constituents during the calcium paradox, is related to an active uptake of Ca by the mitochondria and may lead to massive changes in the cellular ion concentration, during Ca-repletion.

Ultrastructure and architecture of the sarcoplasmic reticulum in frog sino-atrial fibres: a comparative study with various preparatory procedures

Various preparatory procedures were tested to preserve the ultrastructure of the sarcoplasmic reticulum (SR) by the best possible method within frog sino-atrial muscle fibres. These procedures were: conventional aldehyde fixation with or without tannic acid, cryofracture, metallic impregnation and quick-freezing followed by freeze-substitution. Our results illustrated that, when optimally preserved, the SR architecture and ultrastructure of frog sino-atrial fibres were not fundamentally different from those described in many other vertebrate muscle fibres, particularly cardiac fibres. The three-dimensional arrangement of the SR and the structure of its main compartments were situated in a precise fashion: the peripheral SR, located close to the plasma membrane, was made of a tight network of tubules and showed typical couplings; the juxtafibrillar SR was made of a loose network of tubules, small cisternae and some tubules near Z-lines; the intermediary SR, associated with the mitochondria, was made of tubules and fenestrated cisternae. Contacts between SR and mitochondrial membranes were also studied; cryofractures revealed no special intramembrane particles at this level. Collapsed portions of the SR were found after quick-freezing. Because of its relative importance and its three-dimensional arrangement, the SR of frog sino-atrial fibres may have comparable functional significance to the SR of other cardiac muscle fibres.

Comparative studies on the role of calcium in triggering subcellular damage in cardiac muscle

Isolated cardiac muscle strips from amphibians and mammals, together with isolated frog hearts, have been used as model systems for studying the action of elevated [Ca2+]i in promoting severe damage. A23187 and caffeine are believed to cause a rise in [Ca2+]i. Elevated [Ca2+]i causes characteristic damage which has been categorized and includes hypercontraction, Z-line damage and myofilament dissolution. The damage closely resembles that described in the isolated mammalian heart and in skeletal muscle preparations when [Ca2+]i is raised dramatically. Damage can therefore be triggered by releasing Ca2+ from intracellular sites, as distinct from increasing Ca2+ entry (as in the Ca2+-paradox). DNP and ruthenium red also cause identical damage and the results suggest that whilst the fall in pHi associated with ischaemia is probably the consequence of Ca2+/2H+ exchange at the mitochondria, coupled with ATP hydrolysis, lowered pHi by mitochondrial action is probably not the only cause of myofilament dissolution. Damage is not prevented by pretreatment with leupeptin, an inhibitor of Ca2+-activated neutral proteases, and it is concluded that the latter are probably not implicated in rapid and dramatic damage. The possible involvement of lysosomal enzymes in damage triggered by high [Ca2+]i is discussed.

Oxidation of ruthenium red for use as an intercellular tracer

When ruthenium red (RR) is combined with OsO4, an electron-opaque complex forms which readily binds to the cell surface coat. However, the RR-OsO4 complex is often excluded from intercellular spaces in many cell types, and thus is not dependable as a tracer of regions continuous with the extracellular space. Postfixation of erythrocytes agglutinated by the lectin helix (Helix promatia) and intact carotid artery endothelium with a freshly prepared mixture of 1% OsO4 containing 0.1% ruthenium red (RR) resulted in a dense surface deposit of these cells, but intercellular regions were penetrated to a minimal degree by the stain. When a similar mixture of RR-OsO4 was allowed to stand 3 h before use, RR is oxidized by OsO4 to yield a ruthenium compound that has a spectrophotometric absorbance maximum at 365 nm. This RR molecule has a reduced number of cationic sites due to binding with osmium dioxide OsO2=. Postfixation of agglutinated RBCs and carotid artery endothelium with this oxidized ruthenium-OsO4 mixture resulted in a 50-80% decrease in surface deposition but markedly enhanced penetration into intercellular regions. The enhanced penetration is attributed to decreased binding affinity of the oxidized ruthenium for anionic surface membrane components, permitting effective stain penetration of cell-to-cell contact rather than extensive surface deposition. These studies indicate that the ruthenium compound formed by OsO4 oxidation of ruthenium red may be a useful tracer for ultrastructural visualization of intercellular spaces and junctions.

Focal laminate segments in cytoplasmic processes of mouse myocardial fibroblasts

In mouse ventricular myocardium, we have found unusual fibroblasts whose cellular processes in some regions are particularly flattened and which contain linearly-arranged, electron-opaque structures ('central laminae"). The morphology of these focal laminate segments of fibroblast processes suggests that the intracellular laminae are adhesive entities which hold the plasmalemmata above and below them in close parallel apposition for short distances.