Complex Subunit Assembly of Neuronal Voltage-gated K+Channels

Neurons require specific patterns of K+ channel subunit expression as well as the precise coassembly of channel subunits into heterotetrameric structures for proper integration and transmission of electrical signals. In vivo subunit coassembly was investigated by studying the pharmacological profile, distribution, and subunit composition of voltage-gated Shaker family K+(Kv1) channels in rat cerebellum that are labeled by125I-margatoxin (125I-MgTX;Kd, 0.08 pm). High-resolution receptor autoradiography showed spatial receptor expression mainly in basket cell terminals (52% of all cerebellar sites) and the molecular layer (39% of sites). Sequence-directed antibodies indicated overlapping expression of Kv1.1 and Kv1.2 in basket cell terminals, whereas the molecular layer expressed Kv1.1, Kv1.2, Kv1.3, and Kv1.6 proteins. Immunoprecipitation experiments revealed that all 125I-MgTX receptors contain at least one Kv1.2 subunit and that 83% of these receptors are heterotetramers of Kv1.1 and Kv1.2 subunits. Moreover, 33% of these Kv1.1/Kv1.2-containing receptors possess either an additional Kv1.3 or Kv1.6 subunit. Only a minority of the 125I-MgTX receptors (