Effects of Rare Earths and Yttrium on Striated Muscle and the Neuromuscular Junction

Effects of several rare earths and yttrium on isolated frog sartorius muscles were investigated. Lanthanum (La), praseodymium, neodymium (Nd), samarium, gadolinium, dysprosium, erbium, thulium, ytterbium, and yttrium (Y) inhibited twitch tension of indirectly stimulated preparations. Concentrations required to reduce twitch tension to 50% of control tension in 15 min ranged between 0.52 mM and 1.10 mM (Ringer solution; pH 6.0). Similar concentrations (La, Nd, and Y) also inhibited twitch tension of directly stimulated, curarized preparations. A relationship between effect on twitch tension and atomic number was not found. La (0.3 mM) and Y (0.3 mM) reduced the amplitude, but did not appear to alter the time course, of extracellularly recorded end-plate potentials (E.P.P.'s). Amplitudes of intracellularly recorded E.P.P.'s were reduced by La (0.0125–0.05 mM) and Y (0.0125 and 0.025 mM). Effect on quantal contents of E.P.P.'s indicated that the principal action of both agents was an inhibition of transmitter release. La (0.025 and 0.05 mM) and Y (0.05 mM) significantly increased the frequency of miniature end-plate potentials. It is concluded that the prejunctional membrane does not differentiate significantly between the action of the trivalent rare earth ion lanthanum and the action of the trivalent rare-earth-like ion yttrium.