Extracts of electric lobe and electric organ from Torpedo californica increase the total number as well as the number of aggregates of chick myotube acetylcholine receptors

Saline extracts prepared from the electric lobe, the electromotor nerves, and the electric organ (the electromotor system) of Torpedo californica increase the number of ACh receptors on uninnervated chick myotubes in culture, while extracts from T. californica liver or skeletal muscle do not. The extracts also increase the ACh sensitivity of treated myotubes, indicating that newly synthesized receptors are functional. The active substance(s) is heat sensitive but not trypsin sensitive. Gel filtration on Bio-Gel P-150 shows that the activity is associated with a peak of low (<5,000-dalton) molecular weight activity. Labeling studies with rhodamine-conjugated α-bungarotoxin show that, in addition to their effect on receptor number, these extracts also cause aggregation of prelabeled ACh receptors on the myotube surface.