Clustering of GABAA receptors by rapsyn/43kD protein in vitro

Rapsyn, a 43-kDa protein on the cytoplasmic face of the postsynaptic membrane, is essential for clustering acetylcholine receptors (AChR) at the neuromuscular junction. When transfected into nonmuscle cells (QT-6), rapsyn forms discrete membrane domains and can cluster AChR into these same domains. Here we examined whether rapsyn can cluster other ion channels as well. When expressed in QT-6 cells, the GABAA receptor (human alpha 1, beta 1, and gamma 2 subunits) and the skeletal muscle sodium channel were each diffusely scattered across the cell surface. Rapsyn, when co-expressed, clustered the GABAA receptor as effectively as it clustered AChR in previous studies. Rapsyn did not cluster co-transfected sodium channel, confirming that it does not cluster ion channels indiscriminately. Rapsyn mRNA was detected at low levels in the brain by polymerase chain reaction amplification of reverse-transcribed RNA, raising the possibility of a broader role for rapsyn.