Biomedical Engineering Reference
In-Depth Information
Table 5.12.
Major voltage-gated potassium channels in the heart (Source: [
466
,
468
]). Inward-
rectifier (K
IR
), voltage-dependent (K
V
), and calcium-activated (K
Ca
)K
+
channels also regulate the
caliber of arteries and arterioles, especially in the cerebral territory. In the endocardium of human
heart, a small
i
K
,
to
component with slow recovery kinetics may correspond to K
V
1.4 channel.
Several inwardly rectifying currents in mammalian hearts include quasi-instantaneous rectifier
i
K1
,
ATP-inhibited
i
K
AT P
, and muscarinic receptor-stimulated
i
K
ACh
currents through K
IR
2.1, K
IR
6.2-
SUR1, and G-
protein-regulated K
IR
3.1-K
IR
3.4 (or GIRK1-GIRK4) complexes, res
pectively.
Type
Current
Subunits
(Genes)
Ultrarapid delayed rectifier
i
K
,
ur
K
V
1.5
(phases 1, 2)
(KCNA5)
Rapid delayed rectifier
i
K
,
r
K
V
11.1
(plateau end, phase 3)
(hERG, ERG1, KCNH2)
minK, MiRP1
(KCNE1, KCNE2)
Slow delayed rectifier
i
K
,
s
K
V
7.1
(plateau end, phase 3)
(K
V
LQT1, KCNQ1)
minK
(KCNE1)
Rapid transient outward
i
K
,
to
(
r
)
K
V
4.2/4.3
(phase 1)
(KCND2, KCND3)
KCNIP2
Slow transient outward
i
K
,
to
(
s
)
K
V
1.4
(phases 1, 2)
(KCNA4)
MiRP1
(KCNE2)
Inward rectifier
i
K1
K
IR
(phase 3, rest)
K
IR
2.1
(KCNJ2)
K
IR
2.2
(KCNJ12)
The long duration of cardiac action potentials (Sect.
6.5
) that results from a
coordinated action of numerous channels with diverse properties (gating mode,
activation and inactivation rate, ionic conductance, etc.) is needed to prevent
premature excitation. Three major potassium channels, with a varying concentration
in the sarcolemma according to the transmural location, contribute to ventricular
repolarization:
inward rectifier
(K
IR
,
i
K1
) that closes during depolarization,
rapid
(
i
K
,
r
)and
slow
(
i
K
,
s
current),
delayed rectifiers
,and
transient outward
K
+
(
i
K
,
to
current; Table
5.12
)
channels
.
The first group of K
+
channel subunits pertains to the 2TM and 1P class (K
2TM1P
)
of inwardly rectifying K
+
-selective channels K
IR
2.
i
,K
IR
3.
i
,andK
IR
6.
i
that cause
Search WWH ::
Custom Search