Effects of enflurane on excitation-contraction coupling in frog skeletal muscle fibers.

The effect of enflurane on the excitation-contraction (E-C) coupling of frog skeletal muscle fiber was studied. Low (19.13 +/- 0.70 mg%) and high (108.52 +/- 4.52 mg%) concentrations of enflurane did not cause substantial changes of the resting membrane potential but a high concentration of enflurane reduced the peak of action potentials and prolonged the duration measured at 50% peak amplitude. During the twitch response, enflurane reduced the peak response of light signal measured with calcium-sensitive photoprotein, aequorin, but peak tension was not diminished by a low concentration of enflurane. A high concentration of enflurane remarkably inhibited both light signal and tension. During tetanus, a low concentration of enflurane partially abolished light signal and tension. At the high concentration, this inhibitory effect was pronounced and action potentials were only observed in the initial phase of tetanic stimulation. Enflurane enhanced the increase of light signal observed in rapid cooling contracture. In glycerinated muscle fiber, enflurane shifted the pCa-tension relation to the left in low calcium and suppressed maximally activated tension at high calcium concentration. Inhibitory effect of enflurane on light signal in twitch response without abolition of action potential suggests that enflurane might inhibit E-C coupling in frog skeletal muscle fiber (but it enhances direct calcium release from SR induced by caffeine) and increase calcium sensitivity of contractile element.