Ruthenium red reduces acetylcholine sensitivity and increases desensitization at the frog neuromuscular junction

Ruthenium red, a novel enhancer of K+ currents at mouse motor nerve terminals

The effects of ruthenium red (RR) on transmitter release and pre-synaptic currents were studied in the mouse neuromuscular junction. The action of RR (10 microM) was shown not only in the complete suppression of nerve-evoked muscle contractions associated with the depression of endplate potential amplitude but also in the partial inhibition of the amplitude of miniature-endplate potentials. However, the other ruthenium compounds, ruthenium chloride and tris (2,2-bipyridyl) ruthenium chloride did not significantly affect the neuromuscular transmission. In pre-synaptic waveform studies, the fast K(+)-current [IK(f)] as well as the ca(2+)-activated K(+)-current [IK(ca)] was significantly enhanced by 10 microM RR. Furthermore, 10 microM RR antagonized the action of beta-bungarotoxin (a blocker of slow K(+)-channel [IK(s)] in enhancing pre-synaptic Ca2+ currents. In contrast, the typical Ca(2+)-channel blockers, omega-agatoxin (0.5 microM), Gd3+ (0.5 mM) and CD2+ (0.3 mM) all suppressed the IK(ca). Although RR (1-30 microM) inhibited the Ca(2+)-currents of the nerve terminals induced by the combined treatment with the K(+)-channel blockers, 3,4-diaminopyridine plus tetraethylammonium chloride in a concentration-dependent manner, it is considered that RR-enhanced K+ currents were responsible for, at least in part, the observed inhibition of the Ca(2+)-current which led to the blockade of transmitter release.

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.