Aneural muscle cell cultures make synaptic basal lamina components

Abstract

The basal lamina that runs between the presynaptic and post-synaptic membranes at the neuromuscular junction has distinctive functional properties^1–3 amd differs in molecular composition from the extrasynaptic basal lamina to which it is attached^4,5. In regenerating muscle, synaptic basal lamina can direct the accumulation both of neuronal transmitter vesicles at specific sites near the presynaptic nerve terminal membrane and of acetylcholine receptors (AChRs) in the postsynaptic muscle membrane^1–3. Four components that are concentrated in synaptic basal lamina, but are not detectable in extrasynaptic basal lamina, have been recognized. The first is a particular form of acetylcholinesterase (AChE), the A₁₂ or 16S species, which is concentrated at the synapse in rats^6,7 and mice⁸; its distinctive feature is thought to be a long collagen-like tail⁹ that attaches it to the basal lamina¹⁰. Three other components of the synaptic basal lamina have been distinguished immunocytochemically using antisera raised against basement membrane extracts or collagen-rich preparations⁴. Although it has been previously reported that aneural muscle cell cultures may make the 16S form of AChE^11,12, the role of the nerve in the synthesis and organization of the synaptic basal lamina is unknown. We report here that cells of a mouse muscle line, in the absence of nerves, have surface accumulations of each of the four synaptic basal lamina components described above: the 16S AChE, and cross-reactive antigens recognized by each of the synapse-specific antisera.