Persistence of Excitation Contraction Coupling in “Slow” Muscle Fibres after a Treatment that destroys Transverse Tubules in “Twitch” Fibres

Abstract

A TREATMENT that disrupts the structure of the transverse tubular (T) system in skeletal “twitch” fibres has been shown to uncouple membrane excitation from contraction^1,2. Muscles were held at resting length and bathed in 400 mM glycerol in Ringer for 1 h. After that, when muscles were returned from glycerol–Ringer to ordinary Ringer, the “uncoupling” occurred¹. In twitch fibres subjected to this treatment, action potentials and passive electrical properties were modified in a way consistent with the destruction of the T system^2,3. In “slow” fibres of the frog, the T system is present but reduced in extent, and the triads formed by apposition of the T and the sarcoplasmic reticular systems are not developed^4,5. Thus a treatment that uncouples excitation from contraction in “twitch” fibres by disrupting the T system might not work in slow fibres.