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Vol. 302, Issue 2, 545-550, August 2002
1.2 Subunit
Departments of Medicine and Pharmacology, Vanderbilt University
School of Medicine, Nashville, Tennessee
Kv1.5 is the principal molecular component of IKur, an
atrial-specific K+ current in human myocytes that is
suppressed by activation of protein kinase C (PKC). We examined the
effect of phorbol 12-myristate 13-acetate (PMA), a direct activator of
PKC, on Kv1.5 current. Although PMA had minimal effect when Kv1.5 was
expressed alone, K+ currents derived from coexpression of
Kv
1.2 (but not another closely related
subunit, Kv
1.3) with
Kv1.5 were markedly reduced by PMA, associated with a small
depolarizing shift in the voltage dependence of channel activation.
Additional experiments with an inactive stereoisomer, 4
-PMA, and the
PKC inhibitor chelerythrine indicated that the effects of PMA were
mediated by PKC activation. Assembly of Kv1.5 in vivo with both
subunits was demonstrated, and all three K+ channel
proteins were substrates for phosphorylation by PKC. These results
demonstrate that coexpression of Kv
1.2 enhances the response of
Kv1.5 to PKC activation and that direct phosphorylation of
K+ channel subunits is a potential molecular basis for the
effect. Furthermore, they suggest that Kv
1.2 may be a component of
the IKur complex in human atrium.
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