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General Comment |
Potassium ion channels are essential to many cellular functions in both excitable and
nonexcitable cells and show a high degree of diversity, varying in their
electrophysiologic and pharmacologic properties.
NCBI Summary:
Potassium channels represent the most complex class of voltage-gated ion channels from both functional and structural standpoints. Their diverse functions include regulating neurotransmitter release, heart rate, insulin secretion, neuronal excitability, epithelial electrolyte transport, smooth muscle contraction, and cell volume. Four sequence-related potassium channel genes - shaker, shaw, shab, and shal - have been identified in Drosophila, and each has been shown to have human homolog(s). This gene encodes a member of the potassium channel, voltage-gated, shaker-related subfamily. This member includes three distinct isoforms which are encoded by three alternatively spliced transcript variants of this gene. These three isoforms are beta subunits, which form heteromultimeric complex with alpha subunits and modulate the activity of the pore-forming alpha subunits.
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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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