Abstract
Cardiac inward rectifier K$^+$ currents (IK1) play an important
role in maintaining resting membrane potential and contribute to
late phase repolarization. Members of the Kir2.x channel family appear
to encode for IK1. The purpose of this study was to determine the
molecular composition of cardiac IK1 in rabbit ventricle. Western
blots revealed that Kir2.1 and Kir2.2, but not Kir2.3, are expressed
in rabbit ventricle. Culturing rabbit myocytes resulted in an approximately
50\% reduction of IK1 density after 48 or 72 h in culture which was
associated with an 80\% reduction in Kir2.1, but no change in Kir2.2,
protein expression. Dominant-negative (DN) constructs of Kir2.1,
Kir2.2 and Kir2.3 were generated and tested in tsA201 cells. Adenovirus-mediated
over-expression of Kir2.1dn, Kir2.2dn or Kir2.1dn plus Kir2.2dn in
cultured rabbit ventricular myocytes reduced IK1 density equally
by 70\% 72 h post-infection, while AdKir2.3dn had no effect, compared
to green fluorescent protein (GFP)-infected myocytes. Previous studies
indicate that the Ba2+ required for half-maximum block (IC50) differs
significantly between Kir2.1, Kir2.2 and Kir2.3 channels. The dependence
of IK1 on Ba2+ revealed a single binding isotherm which did not
change with time in culture. The IC50 for block of IK1 was also unaffected
by expression of the different DN genes after 72 h in culture. Taken
together, these results demonstrate functional expression of Kir2.1
and Kir2.2 in rabbit ventricular myocytes and suggest that macroscopic
IK1 is predominantly composed of Kir2.1 and Kir2.2 heterotetramers.
- ,
- 12794173
- adenoviridae,
- animals,
- cardiac,
- cell
- channels,
- electric
- electrophysiology,
- gov't,
- heart
- heterozygote,
- immunoblotting,
- inwardly
- line,
- membrane
- mutagenesis,
- mutation,
- myocytes,
- non-u.s.
- patch-clamp
- pota,
- potentials,
- rabbits,
- rectifying,
- research
- site-directed,
- ssium
- stimulation,
- support,
- techniques,
- ventricles,
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