A slow calcium-dependent component of charge movement in Rana temporaria cut twitch fibres

Whole-cell voltage clamp on skeletal muscle fibers with the silicone-clamp technique

Control of membrane voltage and membrane current measurements are of critical importance for the study of numerous aspects of skeletal muscle physiology and pathophysiology. The silicone-clamp technique makes use of a conventional patch-clamp apparatus to achieve whole-cell voltage clamp of a restricted portion of a fully differentiated adult skeletal muscle fiber. The major part of an isolated muscle fiber is insulated from the extracellular medium with silicone grease and the tip of a single microelectrode connected to the amplifier is then inserted within the fiber through the silicone layer. The method is extremely easy to implement. It represents an alternative to the traditional vaseline-gap isolation and two or three microelectrodes voltage-clamp techniques. The present chapter reviews the benefits of the silicone-clamp technique and provides updated detailed insights into its practical implementation.

Association of the Igamma and Idelta charge movement with calcium release in frog skeletal muscle

Charge movement and calcium transient were measured simultaneously in stretched frog cut twitch fibers under voltage clamp, with the internal solution containing 20 mM EGTA plus added calcium and antipyrylazo III. When the nominal free [Ca2+]i was 10 nM, the shape of the broad I(gamma) hump in the ON segments of charge movement traces remained invariant when the calcium release rate was greatly diminished. When the nominal free [Ca2+]i was 50 nM, which was close to the physiological level, the I(gamma) humps were accelerated and a slow calcium-dependent I(delta) component (or state) was generated. The peak of ON I(delta) synchronized perfectly with the peak of the calcium release rate whereas the slow decay of ON I(delta) followed the same time course as the decay of calcium release rate. Suppression of calcium release by TMB-8 reduced the amount of Q(delta) concomitantly but not completely, and the effects were partially reversible. The same simultaneous suppression effects were achieved by depleting the sarcoplasmic reticulum calcium store with repetitive stimulation. The results suggest that the mobility of Q(delta) needs to be primed by a physiological level of resting myoplasmic Ca2+. Once the priming is completed, more I(delta) is mobilized by the released Ca2+ during depolarization.