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J Membr Biol. 1998 Sep 15;165(2):183-9.

Divalent cation effects on the Shaker K channel suggest a pentapeptide sequence as determinant of functional surface charge density.

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Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.


The effects of the divalent cations strontium and magnesium on Shaker K channels expressed in Xenopus oocytes were investigated with a two-electrode voltage-clamp technique. 20 mM of the divalent cation shifted activation (conductance vs. potential), steady-state inactivation and inactivation time constant vs. potential curves 10-11 mV along the potential axis. The results were interpreted in terms of the surface charge theory, and the surface charge density was estimated to be -0.27 e nm-2. A comparison of primary structure data and experimental data from the present and previous studies suggests that the first five residues on the extracellular loop between transmembrane segment 5 and the pore region constitutes the functional surface charges. The results further suggest that the surface charge density plays an important role in controlling the activation voltage range.

[Indexed for MEDLINE]

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