The amino terminus of Shaker K+ channels dictates both intracellular inactivation kinetics and extracellular pharmacological sensitivities, indicating transmembrane structural effects.
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Preclinical Shaker data warrant clinical caution; extends evidence that N-terminus modulates both inactivation and CTX sensitivity across the membrane.
Two members of the Shaker K+ channel family designated ShA2 and ShD2 were characterized in the Xenopus oocyte expression system. The predicted amino acid sequences of ShA2 and ShD2 differ only in the amino terminus, which is located intracellularly according to the present topological model of K+ channels. The differing amino termini have profound effects on the electrophysiological and pharmacological properties of the K+ channel. Most markedly, the nature of the amino terminus determines whether the K+ channel mediates rapidly inactivating or noninactivating K+ currents. It also affects the 4-aminopyridine, tetraethylammonium, and charybdotoxin sensitivities of the K+ channels. These results suggest that the amino terminus of Shaker proteins affects K+ channel structures on both sides of the membrane.
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Stocker et al. (1990) studied this question.
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