<s>
In	O
electrocardiography	B-Application
,	O
the	O
ventricular	O
cardiomyocyte	O
membrane	O
potential	O
is	O
about	O
−90mV	O
at	O
rest	O
,	O
which	O
is	O
close	O
to	O
the	O
potassium	O
reversal	B-Algorithm
potential	I-Algorithm
.	O
</s>
<s>
When	O
an	O
action	B-Algorithm
potential	I-Algorithm
is	O
generated	O
,	O
the	O
membrane	O
potential	O
rises	O
above	O
this	O
level	O
in	O
four	O
distinct	O
phases	O
.	O
</s>
<s>
The	O
beginning	O
of	O
the	O
action	B-Algorithm
potential	I-Algorithm
,	O
phase	O
0	O
,	O
specialized	O
membrane	O
proteins	O
(	O
voltage-gated	O
sodium	O
channels	O
)	O
in	O
the	O
cell	O
membrane	O
selectively	O
allow	O
sodium	O
ions	O
to	O
enter	O
the	O
cell	O
.	O
</s>
<s>
This	O
leads	O
to	O
repolarization	B-Algorithm
.	O
</s>
<s>
The	O
depolarization	B-Algorithm
of	O
the	O
membrane	O
allows	O
calcium	O
channels	O
to	O
open	O
as	O
well	O
.	O
</s>
<s>
This	O
outward	O
potassium	O
current	O
causes	O
a	O
small	O
dip	O
in	O
membrane	O
potential	O
shortly	O
after	O
depolarization	B-Algorithm
.	O
</s>
<s>
This	O
current	O
is	O
observed	O
in	O
human	O
and	O
dog	O
action	B-Algorithm
potentials	I-Algorithm
,	O
but	O
not	O
in	O
guinea	O
pig	O
action	B-Algorithm
potentials	I-Algorithm
.	O
</s>
<s>
Repolarization	B-Algorithm
is	O
accomplished	O
by	O
channels	O
that	O
open	O
slowly	O
and	O
are	O
mostly	O
activated	O
at	O
the	O
end	O
of	O
the	O
action	B-Algorithm
potential	I-Algorithm
(	O
slow	O
delayed-rectifier	O
channels	O
)	O
and	O
channels	O
that	O
open	O
quickly	O
but	O
are	O
inactivated	O
until	O
the	O
end	O
of	O
the	O
action	B-Algorithm
potential	I-Algorithm
(	O
rapid	O
delayed	O
rectifier	O
channels	O
)	O
.	O
</s>
