Antibodies that bind specifically to synaptic sites on muscle fiber basal lamina.

Abstract

Basal lamina (BL) ensheathes each skeletal muscle fiber and passes through the synaptic cleft at the neuromuscular junction. Synaptic portions of the BL play important roles in the formation, function, and maintenance of the neuromuscular junction. Molecular differences exist between synaptic and extrasynaptic BL. Antisera to immunogens that might be derived from or share determinants with muscle fiber BL were obtained, and immunohistochemical techniques were used to study the binding of antibodies to rat skeletal muscle. Four antisera contained antibodies that distinguished synaptic from extrasynaptic portions of the muscle fiber''s surface. They were anti-anterior lens capsule, antiacetylcholinesterase, anti-lens capsule collagen and anti-muscle basement membrane collagen; the last 2 sera were selective only after antibodies binding to extrasynaptic areas were removed by adsorption with connective tissue from endplate-free regions of muscle. Synaptic antigens revealed by each of the 4 sera were present on the external cell surface and persisted after removal of nerve terminal, Schwann cell, and postsynaptic plasma membrane. The antigens are contained in or connected to BL of the synaptic cleft. Details of staining patterns, differential susceptibility of antigens to proteolysis, and adsorption experiments showed that the antibodies define at least 3 different determinants that are present in synaptic but not extrasynaptic BL.