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Biophys J, March 2001, p. 1262-1279, Vol. 80, No. 3
Departments of *Pharmacology and
Cellular and
Molecular Physiology, Yale University School of Medicine,
New Haven, Connecticut 06520-8066 USA
We report that voltage-gated Na+ channels
(NaV) from rat muscle (µ1) expressed in HEK293 cells
exhibit anomalous rectification of whole-cell outward current under
conditions of symmetrical Na+. This behavior gradually
fades with time after membrane break-in, as if a diffusible blocking
substance in the cytoplasm is slowly diluted by the pipette solution.
The degree of such block and rectification is markedly altered by
various mutations of the conserved Lys(III) residue in Domain III of
the NaV channel selectivity filter (DEKA locus), a
principal determinant of inorganic ion selectivity and organic cation
permeation. Using whole-cell and macropatch recording techniques, we
show that two ubiquitous polyamines, spermine and spermidine, are
potent voltage-dependent cytoplasmic blockers of µ1 NaV
current that exhibit relief of block at high positive voltage, a
phenomenon that is also enhanced by certain mutations of the Lys(III)
residue. In addition, we find that polyamines alter the apparent rate
of macroscopic inactivation and exhibit a use-dependent blocking
phenomenon reminiscent of the action of local anesthetics. In the
presence of a physiological Na+/K+ gradient,
spermine also inhibits inward NaV current and shifts the
voltage dependence of activation and inactivation. Similarities between
the endogenous blocking phenomenon observed in whole cells and
polyamine block characterized in excised patches suggest that polyamines or related metabolites may function as endogenous modulators of NaV channel activity.
Biophys J, March 2001, p. 1262-1279, Vol. 80, No. 3
© 2001 by the Biophysical Society 0006-3495/01/03/1262/18 $2.00
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