A nerve stump dependent appearance of junctional and perijunctional acetylcholine receptors in organ culture

Abstract

A rapid, nerve stump dependenl appearance of junctional and perijunctional acetylcholine receptors occurred after 42 h following the introduction of rat diaphragm into organ culture. Approximately2 × 10 6 or more acetylcholine receptors (assayed by [ 125I]alphabungarotoxin hinding) appeared at the endplate within a 2 h period, between 42 and 44 h, while only approximately2.5 × 10 3 acetylcholine receptors appeared in an equivalent area of extrajunctional membrane during the same time. Autoradiographic studies confirmed that most of the new acetylcholine receptor sites appeared at the endplate, although a small perijunctional component was also detected. The presence of a long nerve stump prevented the increase in the number of receptors specific to the endplate region, but had no effect on the appearance of extrajunctional acetylcholine receptors. Pharmacological studies showed that the nerve stump effect did not involve nerve impulse transmission, or the interaction of nicotinic acetylcholine receptors with acetylcholine. The findings suggest that junctional and extrajunctional acetylcholine receptors are controlled by different neuronal mechanisms and that junctional receptors are subject to