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Vol. 61, Issue 1, 201-213, January 2002
Departments of Anatomy and Physiology (K.E.M., Y.L., M.R.F.,
L.C.F.) and Clinical Sciences (D.E.M.), College of Veterinary Medicine,
Kansas State University, Manhattan, Kansas
The major objective of this study was to elucidate the molecular bases
for K+ current diversity in porcine granulosa cells (GC).
Two delayed rectifier K+ currents with distinct
electrophysiological and pharmacological properties were recorded from
porcine GC by using whole-cell patch clamp: 1) a slowly activating,
noninactivating current (IKs) antagonized by clofilium,
293B, L-735,821, and L-768,673; and 2) an ultrarapidly activating,
slowly inactivating current (IKur) antagonized completely by clofilium and 4-aminopyridine and partially by tetraethylammonium, charybdotoxin, dendrotoxin, and kaliotoxin. The molecular
identity of the K+ channel genes underlying IKs
and IKur was examined using reverse transcription-polymerase chain reaction and immunoblotting to detect
K+ channel transcripts and proteins. We found that GC could
express multiple voltage-dependent K+ (Kv) channel
subunits, including KCNQ1, KCNE1, Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv1.5,
Kv1.6, Kv
1.3, and Kv2. Coimmunoprecipitation was used to
establish the hetero-oligomeric nature of granulosa cell Kv channels.
KCNE1 and KCNQ1 were coassociated in GC, and their expression coincided
with the expression of IKs. Extensive coassociation of the
various Kv 
- and -subunits was also documented, suggesting
that the diverse electrophysiological and pharmacological properties of
IKur currents may reflect variation in the composition and
stoichiometry of the channel assemblies, as well as differences in
post-translational modification of contributing Kv channel subunits.
Our findings provide an essential background for experimental definition of granulosa K+ channel function(s). It will be
critical to define the functional roles of specific GC K+
channels, because these proteins may represent either novel targets for
assisted reproduction or potential sites of drug toxicity.
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