Arrangement and density of junctional feet in crayfish muscle fibres.

Junctional feet in tubulo-reticular junctions of crayfish muscle fibres are arranged tetragonally with a centre-to-centre spacing of 30-34 nm. The resulting density of 860-1110 feet per 1 micron 2 of the junctional membrane is similar to that reported for other animal species. Using data of a previous stereological study, there are 150-190 feet per 1 micron 2 of the total T-tubule surface and 6000-7800 feet per 100 microns 3 of the fibre volume.