RT PCR on mRNA from enzymatically dissociated, isolated bipolar cells showed that these neurons express the Shaker-like K+ channels Kv1.1, Kv1.2, and Kv1.3. Immunohistochemical localization showed each channel to have a unique subcellular distribution: Kv1.1 immunoreactivity was detected in the dendrites and axons terminal, whereas Kv1.2 and Kv1.3 subunits were localized to the axon and the postsynaptic membrane of the rod ribbon synapse, respectively. Whole-cell patch-clamp recordings indicated that the activation voltage of the delayed rectifier current of the isolated bipolar cell and the inhibitory constants for current blockade by TEA, 4-AP, and Ba2+ were similar to these same properties measured for Kv1.1 expressed in oocytes. However, the TEA and 4-AP inhibitory constants for the bipolar cell current differed from the inhibitory constants for Kv1.2 or Kv1.3. These results suggest that the current of the isolated rod bipolar cell is most similar to Kv1.1 but that all three channels may function in the intact retina to allow complex modulation of retinal synaptic signals.

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