An early stage in sodium channel clustering at developing rat neuromuscular junctions.

Voltage-gated sodium channels (VGSCs) are concentrated in the postsynaptic membrane at the adult rat neuromuscular junction (NMJ). We have used immunolabelling to determine the pattern of initial VGSC accumulation during development. At birth, but not 3 days before, VGSC labelling is detectable at the NMJ and in the perijunctional (periJ) membrane but not elsewhere. A much higher density cluster of VGSCs forms at the NMJ itself 1-2 weeks later. If the nerve is cut 2 days after birth, VGSC labelling persists in the periJ region for at least 4 weeks but the clustering of VGSCs at the NMJ fails to develop. Thus an early, stable accumulation of VGSCs develops near the NMJ at least a week before high density postsynaptic VGSC clusters form.