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Originally published In Press as doi:10.1074/jbc.M302091200 on May 6, 2003
J. Biol. Chem., Vol. 278, Issue 28, 25940-25946, July 11, 2003
Small Conductance Ca2+-activated K+ Channels and Calmodulin
CELL SURFACE EXPRESSION AND GATING*
Wei-Sheng Lee ,
Thu Jennifer Ngo-Anh ,
Andrew Bruening-Wright ,
James Maylie and
John P. Adelman ¶
From the
Department of Obstetrics and Gynecology and
Vollum Institute, Oregon Health & Science
University, Portland, Oregon 97239
Small conductance Ca2+-activated K+
channels (SK channels) are heteromeric complexes of pore-forming
subunits and constitutively bound calmodulin (CaM). The binding of CaM is
mediated in part by the electrostatic interaction between residues Arg-464 and
Lys-467 of SK2 and Glu-84 and Glu-87 of CaM. Heterologous expression of the
double charge reversal in SK2, SK2 R464E/K467E (SK2:64/67), did not yield
detectable surface expression or channel activity in whole cell or inside-out
patch recordings. Coexpression of SK2:64/67 with wild type CaM or CaM1,2,3,4,
a mutant lacking the ability to bind Ca2+, rescued
surface expression. In patches from cells coexpressing SK2:64/67 and wild type
CaM, currents were recorded immediately following excision into
Ca2+-containing solution but disappeared within minutes
after excision or immediately upon exposure to Ca2+-free
solution and were not reactivated upon reapplication of
Ca2+-containing solution. Channel activity was restored
by application of purified recombinant Ca2+-CaM or
exposure to Ca2+-free CaM followed by application of
Ca2+-containing solution. Coexpression of the double
charge reversal E84R/E87K in CaM (CaM:84/87) with SK2:64/67 reconstituted
stable Ca2+-dependent channel activity that was not lost
with exposure to Ca2+-free solution. Therefore,
Ca2+-independent interactions with CaM are required for
surface expression of SK channels, whereas the constitutive association
between the two channel subunits is not an essential requirement for
gating.
Received for publication, February 27, 2003
, and in revised form, April 25, 2003.
* The costs of publication of this article were defrayed in part by the
payment of page charges. This article must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section 1734
solely to indicate this fact.
¶
To whom correspondence should be addressed: Vollum Institute, Oregon Health
& Science University, 3181 SW Sam Jackson Park Rd., Portland, OR 97239.
Tel.: 503-494-5450; Fax: 503-494-4353; E-mail:
adelman{at}ohsu.edu.

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Copyright © 2003 by the American Society for Biochemistry and Molecular Biology.
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