Fig. 1. Single skeletal muscle fibres from adult honeybee leg muscle. (A) Micrographs of two cells bathed in Tyrode's solution taken using phase contrast (transmitted light) microscopy. (B) Part of a cell at a highest magnification, (in horizontal orientation). (C–F) Laser confocal micrographs of T-tubule system in isolated fibres. Single fibres bathed in Tyrode's solution were stained with the lipophilic fluorescent dye di-8 ANEPPS (10 µmol l^–1) for 20 min in order to reveal the transverse tubule network. (C) In longitudinal axial section, a central chain of nuclei interrupting T-tubules (double arrow) and tracheoles (arrow) are visible. (D) Longitudinal paraxial section, shows longitudinal connections between T-tubules (arrows) within the same or adjacent sarcomeres. The dotted line (i) shows the position at which the transverse fibre reconstruction shown in F was taken. (E) Continuity of T-tubules with the surface membrane. Two T-tubules per sarcomere penetrate the fibre volume, as emphasized by the profiles of pixel intensity (below) taken at positions ii and iii. (F) Transverse confocal section showing the shape of the fibre. (G) Another cylindrical fibre stained with the calcium fluorophore Fluo-3-AM. Scale bars, 100 µm (A); 20 µm (B); 20 µm (C,D,F,G); 4 µm (E).