Inhibition of tetanus tension by elevated extracellular calcium concentration.

Extracellular [Ca2+] in the range of 5-20 mM produces a concentration-dependent reversible reduction in tetanus tension in single frog skeletal muscle fibers. Both peak tension and ability to sustain tension during tetanus is reduced. The effect is unrelated to osmotic effects and independent of stimulation frequency in the range 100-200 Hz. The effect occurs both at 8 and 24 degrees C. Tetanus tension is most strongly inhibited by elevated extracellular [Ca2+] at short muscle lengths, but the effect can be seen at all lengths. Microelectrode recordings during tetanus indicate that action potentials remain undiminished in amplitude and duration throughout the tetanus. The evidence suggests that the inhibition results from a failure of action potentials propagation within the transverse tubular system.