Binding of cationized and native ferritin to cellular structures of the electric organ of Torpedo marmorata

Abstract

The distribution of polycationic and polyanionic binding sites in the electric organ of Torpedo marmorata was investigated by incubation of tissue with native (NF) ferritin. 1) Collagen fibrils from the electric organ carry rosettes of polyanionic sites on their surface with a periodicity of 60 nm, corresponding to the pattern of crossbanding in collagen fibrils. The CF-binding sites are abut 30 nm in size and project 20 nm beyond the surface of the fibril. 2) As revealed by incubation of tissue homogenates, CF heavily stains the intraperiod line of the axonal myelin and also tubular structures in the axonal cytoplasm. 3) Neither the extracellular aspects of the pre- nor the postsynaptic membrane became labeled with either NF or CF. After incubation of tissue homogenates. labeling of the electron-dense material of the cytoplasmic aspect of the postsynaptic membrane was observed with NF and, in particular, with CF. The ventral basal lamina of the electroplaque cell revealed uniform labeling with NF. In contrast, CF-binding sites were distributed in the lamina densa of the basal lamina as a lattice of discrete binding sites, approximately 45 nm in diameter. The presence of polyanionic sites in the basal lamina, which also proceeds through the synaptic cleft, suggests the existence of a diffusion barrier for the released neurotransmitter acetylcholine. It is proposed that this facilitates hydrolysis of acetylcholine in the synaptic cleft and recirculation of the products of hydrolysis to the axon terminal.