Distribution of macromolecules from the intercellular matrix in the electroplaque of Electrophorus electricus

Abstract

The elementary unit of intercellular comnumication in the nervous system, the synapse, is characterized by a welldefined and fured spatial distribution of a few macromolecular species. In a peripheral cholinergic synapse like the motor endplate [ 1,2] or the electroplaque synapse [3,4], the enzyme of acetylcholine biosynthesis, choline acetyltransferase, is located exclusively in the nerve ending; the acetylcholine receptor is concentrated with a very high density in the cytoplasmic membrane which faces the nerve terminal [2-S]; and~acetylcholinesterase is bound to the basal lamina which covers the postsynaptic membrane [6]. Denervation and muscle regeneration experiments carried out with adult skeletal muscle have led to the proposal that the basal lamina, or one of its components, might interact with the receptor protein and, therefore, play a role as an ‘organizing factor’ for the receptor’s dense and stable accumulation in the subsynaptic membrane [6-121. Chemical studies on basal lamina and interstitial connective tissue have shown that these structures are composed of several genetically distinct types of collagens and structural glycoproteins. Collagens of type I and III are present in interstitial connective tissues [ 131 and collagens of type IV and V in basement membranes [14,15]. Fibronectin [16,17] and laminin [18,19] are the two major structural glycoproteins present in basal lamina. The electroplaque from the electric organ of Electrophorus electricus is a highly specialised cell derived from skeletal muscle fibers but deprived of