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Departments of Medicine and Pharmacology, University of Vermont, Burlington Vermont 05405
Small conductance Ca2+-activated K+
(SK) channels have been cloned from mammalian brain, but little is
known about the molecular characteristics of SK channels in
nonexcitable tissues. Here, we report the isolation from rat liver of
an isoform of SK3. The sequence of the rat liver isoform differs from
rat brain SK3 in five amino acid residues in the NH3
terminus, where it more closely resembles human brain SK3. SK3
immunoreactivity was detectable in hepatocytes in rat liver and in HTC
rat hepatoma cells. Human embryonic kidney (HEK-293) cells transfected
with liver SK3 expressed 10 pS K+ channels that were
Ca2+ dependent (EC50 630 nM) and were blocked
by the SK channel inhibitor apamin (IC50 0.6 nM); whole
cell SK3 currents inactivated at membrane potentials more positive than
40 mV. Notably, the Ca2+ dependence, apamin sensitivity,
and voltage-dependent inactivation of SK3 are strikingly similar to the
properties of hepatocellular and biliary epithelial SK channels evoked
by metabolic stress. These observations raise the possibility that SK3
channels influence membrane K+ permeability in
hepatobiliary cells during liver injury.
cloning; hepatocytes; immunofluorescence; ion channels; patch clamp; transfection
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