COMPLEX SUBUNIT ASSEMBLY OF NEURONAL VOLTAGE-GATED K- BASIS FOR HIGH-AFFINITY TOXIN INTERACTIONS AND PHARMACOLOGY( CHANNELS )

Neurons require specific patterns of K+ channel subunit expression as well as the precise coassembly of channel subunits into heterotetramer ic structures for proper integration and transmission of electrical si gnals, In vivo subunit coassembly was investigated by studying the pha rmacological profile, distribution, and subunit composition of voltage -gated Shaker family K+ (K(v)1) channels in rat cerebellum that are la beled by I-125-margatoxin (I-125-MgTX; K-d, 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 overlappi ng expression of K(v)1.1 and K(v)1.2 in basket cell terminals, whereas the molecular layer expressed K(v)1.1, K(v)1.2, K(v)1.3, and K(v)1.6 proteins, Immunoprecipitation experiments revealed that all I-125-MgTX receptors contain at least one K(v)1.2 subunit and that 83% of these receptors are heterotetramers of K(v)1.1 and K(v)1.2 subunits, Moreove r, 33% of these K(v)1.1/K(v)1.2-containing receptors possess either an additional K(v)1.3 or K(v)1.6 subunit, Only a minority of the I-125-M gTX receptors (<20%) seem to be homotetrameric K(v)1.2 channels, Heter ologous coexpression of K(v)1.1 and K(v)1.2 subunits in COS-1 cells le ads to the formation of a complex that combines the pharmacological pr ofile of both parent subunits, reconstituting the native MgTX receptor phenotype, Subunit assembly provides the structural basis for toxin b inding pharmacology and can lead to the association of as many as thre e distinct channel subunits to form functional K+ channels in vivo.