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Comment |
Mason DE, et al 2002 reported the molecular basis of voltage-dependent potassium currents in
porcine granulosa cells.
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 (I-Ks) antagonized by clofilium, 293B,
L-735,821, and L-768,673; and 2) an ultrarapidly activating, slowly
inactivating current (I-Kur) antagonized completely by clofilium and
4-aminopyridine and partially by tetraethylammonium, charybdotoxin,
dendrotoxin, and kaliotoxin. The molecular identity of the K+ channel genes
underlying I-Ks and I-Kur was examined using reverse transcription-polymerase
chain reaction and immunoblotting to detect K+ channel transcripts and
proteins. It was 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, Kvbeta1.3, and Kvbeta2. 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
I-Ks. Extensive coassociation of the various Kv alpha- and beta-subunits was
also documented, suggesting that the diverse electrophysiological and
pharmacological properties of I-Kur 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. These 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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