Local accumulation of acetylcholine receptors is neither necessary nor sufficient to induce cluster formation

Abstract

Acetylcholine receptors (AChRs) accumulate at developing neuromuscular junctions in part via lateral migration of diffusely expressed receptors. Using a model system--cultured Xenopus muscle cells exposed to electric fields--we have shown that AChRs, concentrated at the cathode-facing cell pole, continue to aggregate there after the field is terminated (Stollberg and Fraser, 1988). These observations are consistent with the possibility that the field-induced increase in receptor concentration triggers the aggregation event. Only 2 other molecular events could initiate the electric field-induced receptor aggregation: (1) a local increase in the density of some other molecules, or (2) a voltage-sensitive mechanism. Treatment of muscle cell cultures with neuraminidase changes the cell surface charge and has been reported to reverse the direction of electromigration for AChRs and concanavalin A binding sites (Orida and Poo, 1978). Using digitally analyzed fluorescence videomicroscopy, we find that AChRs in neuraminidase-treated cultures accumulate at both cell poles in an electric field. After termination of the field, the AChR continues to aggregate at the cathode-facing pole, as in cells not treated with neuraminidase. However, receptor density decreases at the anode-facing pole, indicating that elevated AChR density does not initiate receptor aggregation. Cells pretreated with neuraminidase and trypsin (which blocks receptor aggregation) display reversed receptor distributions compared to untreated controls, indicating that electromigration has indeed been reversed. The rate at which neuraminidase- and trypsin- treated cells approach steady-state distributions indicates a receptor diffusion constant of approximately 1.2 x 10(-9) cm2/sec, consistent with a diffusion trap mechanism of receptor aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of EGFR and RTK Signaling in the Electrotaxis of Lung Adenocarcinoma Cells under Direct-Current Electric Field Stimulation

“…The generally accepted hypothesis of electrotaxis mechanism is that dcEF-induced membrane receptor polarization results in directional ligand sensing [2] or initiation of ligand-independent activation [58,59]. The signaling discrepancy initiates polarized intracellular signaling cascades leading to directed cell migration.…”

Animal models of transcranial direct current stimulation: Methods and mechanisms

“…This factor may contribute to an augmentation of the development towards the cathode but is not a necessary mechanism, since without filopodia there is still galvanotropic behavior. Another possible mechanism could rely on electric field-induced receptor migration (McCaig, 1986, Stollberg et al, 1988, 1990b). Acetylcholine (Ach) receptors present in the axon’s terminal can increase the intracellular calcium concentration via second messenger pathways, therefore interacting with the growth of neural processes.…”

“…In a set of studies, Stollberg and Fraser applied a 400 V/m DC electric field to Xenopus muscle cells for 20–40 min, and Ach receptors clustered towards both the anode and the cathode during stimulation. Afterward, Ach receptors continued to accumulate towards the cathodal side (Stollberg et al, 1988, 1990b). Receptor clustering after application of electric fields may be caused by electromigration of the Ach receptors, which is a slow and linear process (Stollberg et al, 1990a).…”

Electrical fields, nerve growth and nerve regeneration

“…This is not simply a function of increasing receptor density, as conditions have been found in which ACh receptors accumulate both anodally and cathodally, but only continue to accumulate cathodally once the field has been switched off (Stollberg & Fraser, 1990a). Two other mechanisms which could trigger this type of receptor clustering have been investigated using alternating or pulsed fields.…”

“…A recent elegant series of investigations of the ACh receptor has shown that once receptor clustering is initiated by the field, it will continue in the absence of an applied field (Stollberg & Fraser, 1988). This is not simply a function of increasing receptor density, as conditions have been found in which ACh receptors accumulate both anodally and cathodally, but only continue to accumulate cathodally once the field has been switched off (Stollberg & Fraser, 1990a). Two other mechanisms which could trigger this type of receptor clustering have been investigated using alternating or pulsed fields.…”