Fig. 1

Skinning/permeabilization of single muscle fibres and measurement of contractile force. Muscle fibres are chemically membrane-permeabilized with a glycerol-containing relaxing solution, to create ‘holes’ in the cell membrane (sarcolemma) [8]. Fibres are then either (a) fluorescently immunolabelled, or (b) assessed for contractile force generation attached via a force transducer. In the latter case, contraction is directly triggered by the addition of Ca²⁺ and ATP (facilitated by membrane permeabilization). Thus, upstream events that normally contribute to muscle contraction are bypassed (e.g. electrical stimulation or excitation–contraction coupling). Note that these skinned single muscle fibres retain all their peripheral and central nuclei (see also Figs. 2a, 3a, 4a)