Voltage-gated Na+ channel EOIII-segment-like immunoreactivity in fish retinal ganglion cells

Although single-channel and whole-cell patch-clamp recordings have demonstr ated the presence of Na+ currents in retinal ganglion cell somata, it has n ot previously been reported that an anti-Naf-channel antiserum stains both retinal ganglion cell somata nod proteins with molecular weights correspond ing to complexes of alpha and beta subunits. We probed adult goldfish retin as for Na(+)channel-like immunoreactivity with a polyclonal antibody direct ed against the EOIII segment of vertebrate voltage-gated Na+ channels. In v ertical sections and whole mounts, this antibody consistently stained the s omata, axons, and proximal dendrites of retinal ganglion cells. Some somata in the proximal third of the inner nuclear layer were also stained. In Wes tern blots, this antibody specifically stained multiple protein bands from retina and optic nerve, all with apparent molecular weights between 200 and 315 kDa. The largest of these molecular weights agrees with that reported previously for complexes of alpha and beta subunits in mammalian neurons, i ncluding retinal ganglion cells. The intermediate and lowest molecular weig hts are consistent with the presence of multiple Na+ channel alpha subunits , either in individual proximal retinal neurons or in different morphologic al subtypes.