The interaction between ruthenium red and the isolated sarcoplasmic reticulum

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.

The role of mitochondria and sarcoplasmic reticulum calcium handling upon reoxygenation of hypoxic myocardium

The mechanism of twitch prolongation of hypoxic myocardium after reoxygenation was studied before and after interventions that affect cellular cyclic nucleotide levels, subcellular calcium handling, or oxygen-derived free radical production/survival. Right ventricular ferret papillary muscles were subjected to two 20-minute periods of hypoxia, each followed by 1 hour of reoxygenation. The first sequence of hypoxia/reoxygenation was done without intervention. Before the second sequence, the pharmacological agent under study was added to the superfusate or the superfusate calcium concentration was increased from 2.5 to 8 mM. Time from peak to 80% decline in twitch tension was measured in the presence and absence of each intervention immediately before each period of hypoxia and after reoxygenation at maximal twitch prolongation. Interventions that affect Ca2+ flux across the sarcolemma (verapamil and 8 mM [Ca2+]o) or agents that affect oxygen free radical production/survival (dimethyl sulfoxide and allopurinol) did not affect twitch prolongation. Pharmacological agents that increase cyclic AMP levels (forskolin and milrinone) or those that inhibit mitochondrial activity (oligomycin B and ruthenium red) attenuated twitch prolongation. Pharmacological agents that decrease cyclic AMP levels (carbachol) or inhibit function of the sarcoplasmic reticulum (ryanodine) augmented twitch prolongation. The effect of mitochondrial inhibitors on intracellular calcium handling during hypoxia and reoxygenation was examined using muscles loaded with the bioluminescent calcium indicator aequorin. Mitochondrial inhibitors abbreviated the calcium transient and maximal twitch prolongation after hypoxia. We conclude that alterations in sarcoplasmic reticulum and mitochondria calcium handling contribute to the prolonged relaxation seen upon reoxygenation of hypoxic myocardium.

Ruthenium red and caffeine affect the Ca2+-ATPase of the sarcoplasmic reticulum

Effects of ruthenium red and caffeine (a Ca2+ release blocker and an inducer, respectively) on Ca2+ uptake by sarcoplasmic reticulum (SR) vesicles and formation of the phosphorylated intermediate (EP) of the Ca2+-ATPase were studied using fast-kinetic techniques. Ruthenium red increased the rate and the maximum level of EP formation, while caffeine decreased both. Similarly, ruthenium red accelerated rapid Ca2+ uptake, while caffeine inhibited it. These drugs affected EP formation also with detergent solubilized Ca2+-ATPase. The concentrations required for half maximal effects on these functions (0.2 microM ruthenium red, 1.0 mM caffeine) are about the same as those for altering Ca2+ release. These results indicate that these reagents affect both the Ca2+-pump as well as the Ca2+ release mechanism, suggesting that the Ca2+-pump and Ca2+ release have some mechanisms in common.

Effects of Mg2+ on calcium accumulation by two fractions of sarcoplasmic reticulum from rabbit skeletal muscle

Calcium accumulation by two fractions of sarcoplasmic reticulum presumably derived from longitudinal tubules (light vesicles) and terminal cisternae (heavy vesicles) was examined radiochemically in the presence of various free Mg2+ concentrations. Both fractions of sarcoplasmic reticulum exhibited a Mg2+-dependent increase in phosphate-supported calcium uptake velocity, though half-maximal velocity in heavy vesicles occurred at a much higher free Mg2+ concentration than that in light vesicles (i.e., approx. 0.90 mM vs. approx. 0.02 mM Mg2+). Calcium uptake velocity in light vesicles correlated with Ca2+-dependent ATPase activity, suggesting that Mg2+ stimulated the calcium pump. Calcium uptake velocity in heavy vesicles did not correlate with Ca2+-dependent ATPase activity, although a Mg2+-dependent increase in calcium influx was observed. Thus, Mg2+ may increase the coupling of ATP hydrolysis to calcium transport in heavy vesicles. Analyses of calcium sequestration (in the absence of phosphate) showed a similar trend in that elevation of Mg2+ from 0.07 to 5 mM stimulated calcium sequestration in heavy vesicles much more than in light vesicles. This difference between the two fractions of sarcoplasmic reticulum was not explained by phosphoenzyme (EP) level or distribution. Analyses of calcium uptake, Ca2+-dependent ATPase activity, and unidirectional calcium flux in the presence of approx. 0.4 mM Mg2+ suggested that ruthenium red (0.5 microM) can also increase the coupling of ATP hydrolysis to calcium transport in heavy vesicles, with no effect in light vesicles. These functional differences between light and heavy vesicles suggest that calcium transport in terminal cisternae is regulated differently from that in longitudinal tubules.