Junctions between subsynaptic folds and rough sarcoplasmic reticulum of muscle fibres.

Serial sections through motor end plate regions of mouse muscle fibres demonstrated junctions between the subsynaptic folds and the rough sarcoplasmic reticulum of the sole plate nuclei. The shape of these structures resembles that of the well-known peripheral couplings, diads and triads of muscle fibres. However, the location of the new junctions between the surface membrane and the sole plate nuclei at a large distance from myofibrils, indicates a different function. The connection with the rough sarcoplasmic reticulum possibly influence the regulation of fibre protein metabolism, for example, gene expression of acetylcholine receptor synthesis.