Abstract
Nicotinic acetylcholine receptors serve a variety of signaling functions in the nervous system depending on cellular location, but little is known about mechanisms responsible for tethering them at specific sites. Among the most interesting are receptors containing the alpha7 gene product, because of their abundance and high relative permeability to calcium. On chick ciliary ganglion neurons alpha7-containing receptors are highly concentrated on somatic spines folded into discrete patches on the cell. We show that the spines contain filamentous actin and drebrin. After cell dissociation, the actin slowly redistributes, the spines retract, and the alpha7-containing receptors disperse and are subsequently lost from the surface. Latrunculin A, a drug that depolymerizes filamentous actin, accelerates receptor dispersal, whereas jasplikinolide, a drug that stabilizes the actin cytoskeleton, preserves large receptor clusters and prevents receptor loss from the surface. The receptors are resistant to extraction by nonionic detergent even after latrunculin A treatment. Other, less abundant, nicotinic receptors on the neurons are readily solubilized by the detergent even though these receptors are located in part on the spines. The results demonstrate that the actin cytoskeleton is important for retaining receptor-rich spines and indicate that additional cytoskeletal elements or molecular interactions specific for alpha7-containing receptors influence their fate in the membrane. The cytoskeletal elements involved are not dependent on the architecture of the postsynaptic density because alpha7-containing receptors are excluded from such sites on ciliary ganglion neurons.