Properties of Shaker-homologous potassium channels expressed in the mammalian brain.

Sixteen different K+ channel subtypes have been cloned from mammalian tissue. Considering their sequence homology to Drosophila Shaker, Shab, Shaw and Shal channels, they were classified into four corresponding classes Kv1-4. All K+ channels belonging to these classes consist of four subunits with each six hydrophobic segments (S1-S6) and a characteristic structure-function relationship of certain domains in their amino acid sequence. These domains are, the inactivation gate in the N-terminal region of the sequence, the voltage sensor in the fourth hydrophobic segment (S4), and the pore-region in the H5 segment between S5 and S6. In some functional properties K+ channels cloned from the mammalian brain, however, differ from Drosophila K+ channels. These are pharmacological differences, differences in the threshold of activation and in regulation of inactivation. Part of these differences are important to understand their physiological role in the brain. Based on their functional characteristics the expression pattern of cloned K+ channels in the rat brain can be correlated with the properties of K+ currents measured in central neurones.