Co-localization of Shaker A-type K+ channel (Kv1.4) and AMPA-glutamate receptor (GluR4) immunoreactivities to dendrites of OFF-bipolar cells of goldfish retina

Immunocytochemical methods were used to determine the comparative distribut ion of Shaker Kv1.4 and Shal Kv4.2 A-type voltage-gated K+ channels and AMP A-type GluR4 glutamate receptors in the goldfish retina. Kv1.4-immunoreacti vity (IR) was restricted to a very narrow band of bright puncta and filamen tous processes in the outer plexiform layer (OPL), whereas GluR4-IR was fou nd in radial processes of Muller cells in addition to a narrow band in the OPL. Kv4.2-IR was most prominent over cell bodies of horizontal cell, amacr ine cells and ganglion cells, with very weak labeling over the synaptic ter minal of cone photoreceptors. Double label experiments revealed complete co -localization of Kv1.4-IR and GluR4-IR in the OPL and showed that the Kv1.4 puncta in the OPL appeared enclosed by the Kv4.2-IR cone terminals. Electr on microscopical immunocytochemistry showed that Kv1.4-IR and GluR4-IR were restricted to the dendrites of OFF-bipolar cells that innervated cone phot oreceptor terminals and thin processes that coursed between the rod and con e terminals in the OPL. These data are consistent with other studies demons trating the selective clustering of A-type voltage-gated K+ channels and io notropic glutamate receptors. However, they differ from mammalian preparati ons in which Shal-like Kv4.2 rather than Shaker-like Kv1.4 co-localize post synaptically with glutamate receptors.