BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Vo1.173, No. 1,1990
Pages 457-462
November 30,1990
EVIDENCE FOR DIRECT ARRHYTHMOGENIC ACTION OF ENDOTHELIN
Ryosuke ¥ o r i k a n e ,
H i r o s h i Shiga, Shigeki Miyake and Hiroyuki Koike*
B i o l o g i c a l Research L a b o r a t o r i e s , Sankyo Co., L t d . , 1-2-58, Hiromachi, Shinagawa-ku, Tokyo 140, Japan Received October 16, 1990
SUMMARY: We s t u d i e d e l e c t r o p h y s i o l o g i c a l e f f e c t s of e n d o t h e l i n on canine cardiac tissues. E n d o t h e l i n prolonged a c t i o n p o t e n t i a l d u r a t i o n and d e c r e a s e d spontaneous f i r i n g r a t e of the r i g h t bundle branch c e l l s . At ' a c o n c e n t r a t i o n of 2xlO-TM the p l a t e a u phase of a c t i o n p o t e n t i a l s was f l a t t e n e d , f o l l o w e d by the a b r u p t o c c u r r e n c e of e a r l y a f t e r d e p o l a r i z a t i o n s (EADs). ET, a t a c o n c e n t r a t i o n as low as 2xlO-gtl, was c a p a b l e of inducing EADs a l t h o u g h t h e i r i n c i d e n c e was low. The EADs were i n i t i a t e d from the membrane p o t e n t i a l l e s s n e g a t i v e than -30mY and were s u p p r e s s e d by n i c a r d i p i n e , s u g g e s t i n g the involvement of d i h y d r o p y r i d i n e - s e n s i t i v e Ca 2÷ channels in the i n d u c t i o n of EADs. Because EADs a r e c o n s i d e r e d to u n d e r l i e certain t y p e s of a r r h y t h m i a s e n d o t h e l i n per se may have a r r h y t h m o g e n i c action.
© 1 9 9 0 Academic Press, Inc.
INTRODUCTION:
Since
vasoconstrictor of
the
discovery
of
These i n c l u d e
kidney and n o n - v a s c u l a r smooth muscles 2. to
prolong
contractile to
an
force s .
intense
Recently
we
(ET) t,
p e p t i d e produced by v a s c u l a r e n d o t h e l i a l
a c t i o n s have been found f o r ET.
atria
endothelin
action potential
cells,
actions
on
ET has been shown
d u r a t i o n (APD) and
a
a variety the
heart,
in guinea pig increase
the
In i n t a c t animals ET produces myocardial ischemia
due
coronary vasoconstriction
and
causes
showed t h a t a c l o s e - c o r o n a r y a d m i n i s t r a t i o n
to
potent
cardiac of
ET
d e a t h 4'5 elicited
l e t h a l a r r h y t h m i a s in a n e s t h e t i z e d r a t s 6. Since t h e s e a r r h y t h m i a s could not solely had
be a t t r i b u t e d arrhythmogenic
electrophysiological
to myocardial ischemia, we s p e c u l a t e d t h a t ET per actions. effects
In
the
present
study
we
of ET on canine c a r d i a c t i s s u e s
se
investigated to c l a r i f y
the
mechanisms u n d e r l y i n g a r r h y t h m i a s caused by the agent.
*To whom c o r r e s p o n d e n c e should be a d d r e s s e d . 0006-291X/90 $1.50 457
Copyright © 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
Vol. 173, No. 1, 1990
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
METHODS AND MATERIALS
Adult male mongrel dogs were a n e s t h e t i z e d with sodium p e n t o b a r b i t a l and were a r t i f i c i a l l y v e n t i l a t e d . A f t e r thoracotomy the h e a r t was r a p i d l y removed and v e n t r i c u l a r s e p t a c o n t a i n i n g the r i g h t bundle branch were excised. The t i s s u e p r e p a r a t i o n was mounted in an a c r y l i c chamber f i l l e d with a 25ml K r e b s - H e n s e l e i t s o l u t i o n of the f o l l o w i n g c o m p o s i t i o n (mM): NaC1 128.7, NaHC03 22.0, KC1 2.2, KH2P04 1.8, CaC12 2.5, MgC12 0.5 and g l u c o s e 5.5. The s o l u t i o n was a e r a t e d with a mixture of 95~02 and 5~C02 gas and was m a i n t a i n e d a t 37"C. The transmembrane p o t e n t i a l s were measured with a g l a s s m i c r o e l e c t r o d e , filled with 3M KC1 and having r e s i s t a n c e of lO-20MOhm. The p r e p a r a t i o n s were exposed to 2xlO -8, 2xlO -8 or 2xlO-VM of ET-1 or v e h i c l e (0.05~ bovine serum albumin, BSA), and a c t i o n p o t e n t i a l s were o b s e r v e d f o r 1hr. E n d o t h e l i n (ET-1, P e p t i d e I n s t i t u t e , Osaka, Japan) was d i s s o l v e d in 0.05~ BSA. Bay k 8644 (Wako Pure Chemical, Osaka, Japan) and N i c a r d i p i n e (Sigma) were d i s s o l v e d in dimethyl s u l f o x i d e and were d i l u t e d by d i s t i l l e d water. RESULTS AND DISCUSSION Action bundle
potentials
r e c o r d e d from the most upper p o r t i o n of
branch showed a pacemaker a c t i v i t y .
At lower c o n c e n t r a t i o n s
2xlO -~ or 2xIO-SM, APD g r a d u a l l y i n c r e a s e d and reached a p l a t e a u a f t e r exposure (Fig. lB.C).
early
afterdepolarizations
(Fig. ID, E).
E A D s were
right of
ET,
30-40min
At a c o n c e n t r a t i o n of 2xlO-VM of ET the p l a t e a u
phase of a c t i o n p o t e n t i a l was f l a t t e n e d , of
the
followed by the a b r u p t
occurrence
(EADs) 24±6min a f t e r exposure to ET
elicited
in 5 out
of
8
preparations
(N=5)
at
concentration
and
each a c t i o n p o t e n t i a l had a s i n g l e EAD (in 4 out
preparations)
or m u l t i p l e EADs (in 1 out of 5, see Fig. lE) which were
this of
5 not
a b o l i s h e d by removing ET from the b a t h i n g s o l u t i o n . EADs were reached
a
from a t a k e - o f f p o t e n t i a l
peak v o l t a g e of - 8 . 9 ± 2 . 2 m V (N=5). The
potential the
initiated
of
- 2 4 . 5 ± 2 . 6 m V and
most n e g a t i v e
take-off
of EADs r e c o r d e d was -34mV. Peak v o l t a g e of EADs n e v e r
exceeded
zero p o t e n t i a l .
Action p o t e n t i a l d u r a t i o n (APD) a t 50~
repolarization
(APDso) j u s t p r i o r to the i n d u c t i o n of EADs was 460±26msec, which was about twice the c o n t r o l value. ET
at
2x10-8~, as well as a t 2xlO-~M, e l i c i t e d
preparations.
The c h a r a c t e r i s t i c s
of
similar
ET
were
preparations others EADs
EADs in 1
of EADs produced by lower
to t h o s e by the h i g h e s t one. The
in which EADs developed
plateau
APDs of
6
the
two
were much longer than the APDs of the
a s s o c i a t e d with l e n g t h e n i n g of APD, p a r t i c u l a r l y phase.
of
concentrations
in which EADs did not developed, s u g g e s t i n g t h a t the is
out
induction flattering
Other p a r a m e t e r s such as the maximum d i a s t o l i c 458
of of
potential,
Vol. 173, No. 1, 1990
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
40 min
Before
A
Vehicle
mY -80
~oOr~ 40 m~n
B Endothelin 2 x lO-SM
_8: &-mV
20 ~ n C 2 x 10-8M
mV
40 min D 0
40 rain E 2 x IO-~M
mV
Fi~.l. Effects of endothelin and vehicle on action potentials recorded the right bundle branch.
from
t a k e - o f f p o t e n t i a l and amplitude of a c t i o n p o t e n t i a l s were not a f f e c t e d
by
ET.
of
Spontaneous f i r i n g r a t e was d e c r e a s e d by the h i g h e s t c o n c e n t r a t i o n
ET, 2x10-7~. I t has been r e p o r t e d t h a t ET i n d i r e c t l y a c t i v a t e s the d i h y d r o p y r i d i n e s e n s i t i v e Ca ~÷ channels via the s p e c i f i c ET r e c e p t o r s , c e l l u l a r mechanisms a r e not known 2 ' 7 nicardipine
a l t h o u g h the p r e c i s e
We t h e r e f o r e examined the e f f e c t s
and Bay k 8644, a d i h y d r o p y r i d i n e Ca 2÷ channel a n t a g o n i s t
respectively,
involved
in the i n d u c t i o n of EADs by ET. In one study, EADs were i n i t i a l l y
the
by 2xlO-VM of ET, and
chamber.
Nicardipine
channels
and
agonist,
generated
to examine i f the a c t i v a t i o n of Ca e÷
of
lxlO-eM of n i c a r d i p i n e was then added
completely
eliminated
EADs, s h o r t e n e d
prolonged APD (Fig. 2, upper panel) and i n c r e a s e d the f i r i n g r a t e 459
is
to the
slightly.
Vol.
173, No.
1, 1 9 9 0
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Endothelin 2 x I0-7M Before
+Nicardipine 1 x 10~M
20 min
30 min
7 rain
8: mV
400 m s Bay k 8644 2 x I0-6M Before
6 rain
+ Nicardipine 1x 10"6M 10 rain
7 min
400 ms
Fig, 2. Effects of endothelin (upper panel) and Bay k 8644 (lower panel) a c t i o n p o t e n t i a l s recorded f r o • the r i g h t bundle branch.
In
other
study,
Bay
k
8644
was
added
in
a
cumulative
on
manner
at
concentrations of 2xi0 -8, 2xi0 -v and 2xlO-eH. The agent increased APD in concentration related manner (Fig. 3) and elicited at
the
highest concentration in 1 but of 4 preparations.
suppressed (Fig. 2, EADs
single or multiple
and the prolonged APD was shortened by ixlO-SM
The of
EADs
EADs
were
nicardipine
lower panel). In other three preparations treated with Bay k
were
parameters
not of
induced,
although
action potentials
APD
was
markedly
prolonged.
were not a f f e c t e d by Bay
k
8644
8644 Other except
f i r i n g r a t e which was i n c r e a s e d s l i g h t l y .
@ Endothelin
200-
D 150. 13_ < ._c loo-
"-
50.
ii v
2x10"9 2×10~ 2x10-7 2xld 6 concentration (M)
Fig. 3. Effects of endothelin ( f i l l e d c i r c l e ) and Bay k 8644 ( f i l l e d square) on action p o t e n t i a l duration (APD) recorded from the r i g h t bundle branch. V:vehicle. Abscissa: concentrations of endothelin and Bay k 8644. Ordinate: percent changes in APD measured at 50~ r e p o l a r i z a t i o n (APDso).
APDso was measured before EADs were developed. 460
a
Vol. 173, No. 1, 1990
Recently, k
8644
January et al.
induces
steady
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
have shown in sheep p u r k i n j e f i b e r s t h a t
EADs by i n c r e a s i n g L - t y p e Ca 2÷
state 8's
"window"
current
EADs induced by ET and Bay k 8644 were s i m i l a r
Bay
during in
the
f o l l o w i n g a s p e c t s : l ) E A D s o c c u r r e d d u r i n g the l a t e p o r t i o n of p l a t e a u phase. 2)RADs
were
always a s s o c i a t e d with p r o l o n g a t i o n of APD, which
enough
for
t h e Ca 2÷ channels to r e c o v e r from t h e i n a c t i v e s t a t e .
take-off potential which
roughly
voltages
of
and peak p o t e n t i a l
corresponded the
long
3)Their
lay n e a r -30mY and OmV, r e s p e c t i v e l y ,
to the maximum
activation
Ca 2÷ channels i°. In view of t h e s e
c o n c e i v a b l e t h a t EADs e l i c i t e d
was
and
inactivation
similarities,
by ET i n v o l v e the a c t i v a t i o n
it
of L - t y p e
is Ca e÷
channels.
not
However,
the e l e c t r o p h y s i o l o g i c a l
entirely
the
prolongation much
1)Bay k 8644
at
2xlO-aM
r a t e of the r i g h t bundle branch c e l l s ,
These
observations
greater
suggest that
-30mY
The
first
and the
i o n i c mechanisms
Ha ÷
the second type.
induced by a
than
Ca 2+
type
based on the l e v e l
has
a take-off
of t h e i r
potential
less
is mainly
i n v o l v e d in the f i r s t
is
type of
"window" c u r r e n t a n d / o r outward K÷ c u r r e n t a r e i n v o l v e d g A D s induced by
v a r i e t y of s u b s t a n c e s such
APD in i s o l a t e d c a r d i a c produce
other
second type more n e g a t i v e than -50mV. I t
proposed t h a t slow inward c u r r e n t gADs and t h a t
2)ET d e c r e a s e d the
may a l s o be i n v o l v e d in the a c t i o n s of ET.
p o t e n t i a l s l~.
n e g a t i v e than
to
a
were
whereas Bay k 8644 i n c r e a s e d
Two s u b t y p e s of EADs have been s u g g e s t e d , take-off
8644
of APD than ET a t 2xlO-TM, whereas the i n c i d e n c e of EADs was
channel a c t i v a t i o n
in
produced
h i g h e r f o r BT (5/6 vs 1/4 f o r Bay k 8644)(Fig. 3).
firing it.
same:
a c t i o n s of ET and Bay k
tissues.
QT p r o l o n g a t i o n ,
ET were of the f i r s t
t y p e . EADs a r e
as Cs ÷ and q u i n i d i n e t h a t prolong
They have been shown polymorphous
in i n t a c t
ventricular
animals
tachycardia
and
s o - c a l l e d " t o r s a d e s de p o i n t e s " i 2 Several
reports
produces v e n t r i c u l a r
have shown t h a t i n t r a c o r o n a r y a d m i n i s t r a t i o n fibrillation
t h e s e r e p o r t s have a t t r i b u t e d
that
Recently,
a d m i n i s t r a t i o n of ET e l i c i t e d
however, we
from
an
demonstrated that
VF in a n e s t h e t i z e d
VF developed a f t e r myocardial ischemia s u b s i d e d e. These 461
RW
The a u t h o r s of
V? to myocardial ischemia r e s u l t i n g
intense coronary vasoconstriction. close-coronary
(VF) in i n t a c t animals 4 ' 5 .
of
rats
and
observations
Vol. 173, No. 1, 1990
have
lead
us
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
to speculate that ET per se
has
a
direct
arrhythmogenic
action. The results of the present study suggested that this was the case. Although the concentration for lethal arrhythmias released
in
together with
in
situations
the coronary vascular potent
inducing where bed.
EADs was high,
a large
amount of it is locally
The arrhythmogenic
coronary vasoconstrictor action
peptide is involved in ischemic
arrhythmias
and
ET may cause
action of ET
implies
that
the
cardiac sudden death.
REFERENCES
1. 2.
3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Yanagisawa, M., Eurihara, H., Kimura, S., Tomobe,Y., Kobayashi,M., Mitsui,Y., Yazaki, Y., Goto, Z. and Masaki, T. (1988) Nature 332, 411415. Yanagisawa, M. and Masaki,T. Trends Pharmacol. Sci. (1989) 10, 374-
378. Ishikawa, T., Yanagisawa, M., Kimura, S., Goto, K. and Masaki,T. Am. J. Physiol. 255, H970-H973.
(1988)
Larkin, S.W., Clarke, J.G., Keogh, B.E., Araujo, K.L., Rhodes, C., Davies, G.J., Taylor, K.M. and Maseri, A. (1989) Am. J. cardiol. 64, 956958. Ezra, D., Goldstein, R.E., Czala, J.F., and Feuerstein, G.Z. (1989) Am. J. Physiol. 257, H339-H343. Yorikane, R. and Koike, H. (1990) Japan. J. Pharmacol. 53, 259-263. Inoue,¥., Oike, M., Nakao, K., Kitamura, K. and Kuriyam~,H. (1990) J. Physiol., Lend. 423, 171-191. January, C.T., Riddle, J.M. and Salata, J.J. (1988) Circ. Res. 62, 563571. January, C.T. and Riddle, J.~. (1989) Circ. Res. 64, 977- 990. Hirano, Y., Fozzard, H.A. and January, C,T. (1989) Am. J. Physiol. 256, H1478-H1492. Gintant,G.A. and Cohen, I.S. (1988) Ann. Rev. Pharmacol. Toxicol. 28, 61-81. Levine, J.H., Spear, J.F., Guarnieri,T., Weisfeldt, M.L., de Langen, C.D.J., Becker, L.C. and Moore, E.N. (1985) Circulation 72, 1092-1103.
462
Vo1.173, No. 1,1990
Pages 457-462
November 30,1990
EVIDENCE FOR DIRECT ARRHYTHMOGENIC ACTION OF ENDOTHELIN
Ryosuke ¥ o r i k a n e ,
H i r o s h i Shiga, Shigeki Miyake and Hiroyuki Koike*
B i o l o g i c a l Research L a b o r a t o r i e s , Sankyo Co., L t d . , 1-2-58, Hiromachi, Shinagawa-ku, Tokyo 140, Japan Received October 16, 1990
SUMMARY: We s t u d i e d e l e c t r o p h y s i o l o g i c a l e f f e c t s of e n d o t h e l i n on canine cardiac tissues. E n d o t h e l i n prolonged a c t i o n p o t e n t i a l d u r a t i o n and d e c r e a s e d spontaneous f i r i n g r a t e of the r i g h t bundle branch c e l l s . At ' a c o n c e n t r a t i o n of 2xlO-TM the p l a t e a u phase of a c t i o n p o t e n t i a l s was f l a t t e n e d , f o l l o w e d by the a b r u p t o c c u r r e n c e of e a r l y a f t e r d e p o l a r i z a t i o n s (EADs). ET, a t a c o n c e n t r a t i o n as low as 2xlO-gtl, was c a p a b l e of inducing EADs a l t h o u g h t h e i r i n c i d e n c e was low. The EADs were i n i t i a t e d from the membrane p o t e n t i a l l e s s n e g a t i v e than -30mY and were s u p p r e s s e d by n i c a r d i p i n e , s u g g e s t i n g the involvement of d i h y d r o p y r i d i n e - s e n s i t i v e Ca 2÷ channels in the i n d u c t i o n of EADs. Because EADs a r e c o n s i d e r e d to u n d e r l i e certain t y p e s of a r r h y t h m i a s e n d o t h e l i n per se may have a r r h y t h m o g e n i c action.
© 1 9 9 0 Academic Press, Inc.
INTRODUCTION:
Since
vasoconstrictor of
the
discovery
of
These i n c l u d e
kidney and n o n - v a s c u l a r smooth muscles 2. to
prolong
contractile to
an
force s .
intense
Recently
we
(ET) t,
p e p t i d e produced by v a s c u l a r e n d o t h e l i a l
a c t i o n s have been found f o r ET.
atria
endothelin
action potential
cells,
actions
on
ET has been shown
d u r a t i o n (APD) and
a
a variety the
heart,
in guinea pig increase
the
In i n t a c t animals ET produces myocardial ischemia
due
coronary vasoconstriction
and
causes
showed t h a t a c l o s e - c o r o n a r y a d m i n i s t r a t i o n
to
potent
cardiac of
ET
d e a t h 4'5 elicited
l e t h a l a r r h y t h m i a s in a n e s t h e t i z e d r a t s 6. Since t h e s e a r r h y t h m i a s could not solely had
be a t t r i b u t e d arrhythmogenic
electrophysiological
to myocardial ischemia, we s p e c u l a t e d t h a t ET per actions. effects
In
the
present
study
we
of ET on canine c a r d i a c t i s s u e s
se
investigated to c l a r i f y
the
mechanisms u n d e r l y i n g a r r h y t h m i a s caused by the agent.
*To whom c o r r e s p o n d e n c e should be a d d r e s s e d . 0006-291X/90 $1.50 457
Copyright © 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
Vol. 173, No. 1, 1990
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
METHODS AND MATERIALS
Adult male mongrel dogs were a n e s t h e t i z e d with sodium p e n t o b a r b i t a l and were a r t i f i c i a l l y v e n t i l a t e d . A f t e r thoracotomy the h e a r t was r a p i d l y removed and v e n t r i c u l a r s e p t a c o n t a i n i n g the r i g h t bundle branch were excised. The t i s s u e p r e p a r a t i o n was mounted in an a c r y l i c chamber f i l l e d with a 25ml K r e b s - H e n s e l e i t s o l u t i o n of the f o l l o w i n g c o m p o s i t i o n (mM): NaC1 128.7, NaHC03 22.0, KC1 2.2, KH2P04 1.8, CaC12 2.5, MgC12 0.5 and g l u c o s e 5.5. The s o l u t i o n was a e r a t e d with a mixture of 95~02 and 5~C02 gas and was m a i n t a i n e d a t 37"C. The transmembrane p o t e n t i a l s were measured with a g l a s s m i c r o e l e c t r o d e , filled with 3M KC1 and having r e s i s t a n c e of lO-20MOhm. The p r e p a r a t i o n s were exposed to 2xlO -8, 2xlO -8 or 2xlO-VM of ET-1 or v e h i c l e (0.05~ bovine serum albumin, BSA), and a c t i o n p o t e n t i a l s were o b s e r v e d f o r 1hr. E n d o t h e l i n (ET-1, P e p t i d e I n s t i t u t e , Osaka, Japan) was d i s s o l v e d in 0.05~ BSA. Bay k 8644 (Wako Pure Chemical, Osaka, Japan) and N i c a r d i p i n e (Sigma) were d i s s o l v e d in dimethyl s u l f o x i d e and were d i l u t e d by d i s t i l l e d water. RESULTS AND DISCUSSION Action bundle
potentials
r e c o r d e d from the most upper p o r t i o n of
branch showed a pacemaker a c t i v i t y .
At lower c o n c e n t r a t i o n s
2xlO -~ or 2xIO-SM, APD g r a d u a l l y i n c r e a s e d and reached a p l a t e a u a f t e r exposure (Fig. lB.C).
early
afterdepolarizations
(Fig. ID, E).
E A D s were
right of
ET,
30-40min
At a c o n c e n t r a t i o n of 2xlO-VM of ET the p l a t e a u
phase of a c t i o n p o t e n t i a l was f l a t t e n e d , of
the
followed by the a b r u p t
occurrence
(EADs) 24±6min a f t e r exposure to ET
elicited
in 5 out
of
8
preparations
(N=5)
at
concentration
and
each a c t i o n p o t e n t i a l had a s i n g l e EAD (in 4 out
preparations)
or m u l t i p l e EADs (in 1 out of 5, see Fig. lE) which were
this of
5 not
a b o l i s h e d by removing ET from the b a t h i n g s o l u t i o n . EADs were reached
a
from a t a k e - o f f p o t e n t i a l
peak v o l t a g e of - 8 . 9 ± 2 . 2 m V (N=5). The
potential the
initiated
of
- 2 4 . 5 ± 2 . 6 m V and
most n e g a t i v e
take-off
of EADs r e c o r d e d was -34mV. Peak v o l t a g e of EADs n e v e r
exceeded
zero p o t e n t i a l .
Action p o t e n t i a l d u r a t i o n (APD) a t 50~
repolarization
(APDso) j u s t p r i o r to the i n d u c t i o n of EADs was 460±26msec, which was about twice the c o n t r o l value. ET
at
2x10-8~, as well as a t 2xlO-~M, e l i c i t e d
preparations.
The c h a r a c t e r i s t i c s
of
similar
ET
were
preparations others EADs
EADs in 1
of EADs produced by lower
to t h o s e by the h i g h e s t one. The
in which EADs developed
plateau
APDs of
6
the
two
were much longer than the APDs of the
a s s o c i a t e d with l e n g t h e n i n g of APD, p a r t i c u l a r l y phase.
of
concentrations
in which EADs did not developed, s u g g e s t i n g t h a t the is
out
induction flattering
Other p a r a m e t e r s such as the maximum d i a s t o l i c 458
of of
potential,
Vol. 173, No. 1, 1990
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
40 min
Before
A
Vehicle
mY -80
~oOr~ 40 m~n
B Endothelin 2 x lO-SM
_8: &-mV
20 ~ n C 2 x 10-8M
mV
40 min D 0
40 rain E 2 x IO-~M
mV
Fi~.l. Effects of endothelin and vehicle on action potentials recorded the right bundle branch.
from
t a k e - o f f p o t e n t i a l and amplitude of a c t i o n p o t e n t i a l s were not a f f e c t e d
by
ET.
of
Spontaneous f i r i n g r a t e was d e c r e a s e d by the h i g h e s t c o n c e n t r a t i o n
ET, 2x10-7~. I t has been r e p o r t e d t h a t ET i n d i r e c t l y a c t i v a t e s the d i h y d r o p y r i d i n e s e n s i t i v e Ca ~÷ channels via the s p e c i f i c ET r e c e p t o r s , c e l l u l a r mechanisms a r e not known 2 ' 7 nicardipine
a l t h o u g h the p r e c i s e
We t h e r e f o r e examined the e f f e c t s
and Bay k 8644, a d i h y d r o p y r i d i n e Ca 2÷ channel a n t a g o n i s t
respectively,
involved
in the i n d u c t i o n of EADs by ET. In one study, EADs were i n i t i a l l y
the
by 2xlO-VM of ET, and
chamber.
Nicardipine
channels
and
agonist,
generated
to examine i f the a c t i v a t i o n of Ca e÷
of
lxlO-eM of n i c a r d i p i n e was then added
completely
eliminated
EADs, s h o r t e n e d
prolonged APD (Fig. 2, upper panel) and i n c r e a s e d the f i r i n g r a t e 459
is
to the
slightly.
Vol.
173, No.
1, 1 9 9 0
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Endothelin 2 x I0-7M Before
+Nicardipine 1 x 10~M
20 min
30 min
7 rain
8: mV
400 m s Bay k 8644 2 x I0-6M Before
6 rain
+ Nicardipine 1x 10"6M 10 rain
7 min
400 ms
Fig, 2. Effects of endothelin (upper panel) and Bay k 8644 (lower panel) a c t i o n p o t e n t i a l s recorded f r o • the r i g h t bundle branch.
In
other
study,
Bay
k
8644
was
added
in
a
cumulative
on
manner
at
concentrations of 2xi0 -8, 2xi0 -v and 2xlO-eH. The agent increased APD in concentration related manner (Fig. 3) and elicited at
the
highest concentration in 1 but of 4 preparations.
suppressed (Fig. 2, EADs
single or multiple
and the prolonged APD was shortened by ixlO-SM
The of
EADs
EADs
were
nicardipine
lower panel). In other three preparations treated with Bay k
were
parameters
not of
induced,
although
action potentials
APD
was
markedly
prolonged.
were not a f f e c t e d by Bay
k
8644
8644 Other except
f i r i n g r a t e which was i n c r e a s e d s l i g h t l y .
@ Endothelin
200-
D 150. 13_ < ._c loo-
"-
50.
ii v
2x10"9 2×10~ 2x10-7 2xld 6 concentration (M)
Fig. 3. Effects of endothelin ( f i l l e d c i r c l e ) and Bay k 8644 ( f i l l e d square) on action p o t e n t i a l duration (APD) recorded from the r i g h t bundle branch. V:vehicle. Abscissa: concentrations of endothelin and Bay k 8644. Ordinate: percent changes in APD measured at 50~ r e p o l a r i z a t i o n (APDso).
APDso was measured before EADs were developed. 460
a
Vol. 173, No. 1, 1990
Recently, k
8644
January et al.
induces
steady
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
have shown in sheep p u r k i n j e f i b e r s t h a t
EADs by i n c r e a s i n g L - t y p e Ca 2÷
state 8's
"window"
current
EADs induced by ET and Bay k 8644 were s i m i l a r
Bay
during in
the
f o l l o w i n g a s p e c t s : l ) E A D s o c c u r r e d d u r i n g the l a t e p o r t i o n of p l a t e a u phase. 2)RADs
were
always a s s o c i a t e d with p r o l o n g a t i o n of APD, which
enough
for
t h e Ca 2÷ channels to r e c o v e r from t h e i n a c t i v e s t a t e .
take-off potential which
roughly
voltages
of
and peak p o t e n t i a l
corresponded the
long
3)Their
lay n e a r -30mY and OmV, r e s p e c t i v e l y ,
to the maximum
activation
Ca 2÷ channels i°. In view of t h e s e
c o n c e i v a b l e t h a t EADs e l i c i t e d
was
and
inactivation
similarities,
by ET i n v o l v e the a c t i v a t i o n
it
of L - t y p e
is Ca e÷
channels.
not
However,
the e l e c t r o p h y s i o l o g i c a l
entirely
the
prolongation much
1)Bay k 8644
at
2xlO-aM
r a t e of the r i g h t bundle branch c e l l s ,
These
observations
greater
suggest that
-30mY
The
first
and the
i o n i c mechanisms
Ha ÷
the second type.
induced by a
than
Ca 2+
type
based on the l e v e l
has
a take-off
of t h e i r
potential
less
is mainly
i n v o l v e d in the f i r s t
is
type of
"window" c u r r e n t a n d / o r outward K÷ c u r r e n t a r e i n v o l v e d g A D s induced by
v a r i e t y of s u b s t a n c e s such
APD in i s o l a t e d c a r d i a c produce
other
second type more n e g a t i v e than -50mV. I t
proposed t h a t slow inward c u r r e n t gADs and t h a t
2)ET d e c r e a s e d the
may a l s o be i n v o l v e d in the a c t i o n s of ET.
p o t e n t i a l s l~.
n e g a t i v e than
to
a
were
whereas Bay k 8644 i n c r e a s e d
Two s u b t y p e s of EADs have been s u g g e s t e d , take-off
8644
of APD than ET a t 2xlO-TM, whereas the i n c i d e n c e of EADs was
channel a c t i v a t i o n
in
produced
h i g h e r f o r BT (5/6 vs 1/4 f o r Bay k 8644)(Fig. 3).
firing it.
same:
a c t i o n s of ET and Bay k
tissues.
QT p r o l o n g a t i o n ,
ET were of the f i r s t
t y p e . EADs a r e
as Cs ÷ and q u i n i d i n e t h a t prolong
They have been shown polymorphous
in i n t a c t
ventricular
animals
tachycardia
and
s o - c a l l e d " t o r s a d e s de p o i n t e s " i 2 Several
reports
produces v e n t r i c u l a r
have shown t h a t i n t r a c o r o n a r y a d m i n i s t r a t i o n fibrillation
t h e s e r e p o r t s have a t t r i b u t e d
that
Recently,
a d m i n i s t r a t i o n of ET e l i c i t e d
however, we
from
an
demonstrated that
VF in a n e s t h e t i z e d
VF developed a f t e r myocardial ischemia s u b s i d e d e. These 461
RW
The a u t h o r s of
V? to myocardial ischemia r e s u l t i n g
intense coronary vasoconstriction. close-coronary
(VF) in i n t a c t animals 4 ' 5 .
of
rats
and
observations
Vol. 173, No. 1, 1990
have
lead
us
BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS
to speculate that ET per se
has
a
direct
arrhythmogenic
action. The results of the present study suggested that this was the case. Although the concentration for lethal arrhythmias released
in
together with
in
situations
the coronary vascular potent
inducing where bed.
EADs was high,
a large
amount of it is locally
The arrhythmogenic
coronary vasoconstrictor action
peptide is involved in ischemic
arrhythmias
and
ET may cause
action of ET
implies
that
the
cardiac sudden death.
REFERENCES
1. 2.
3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Yanagisawa, M., Eurihara, H., Kimura, S., Tomobe,Y., Kobayashi,M., Mitsui,Y., Yazaki, Y., Goto, Z. and Masaki, T. (1988) Nature 332, 411415. Yanagisawa, M. and Masaki,T. Trends Pharmacol. Sci. (1989) 10, 374-
378. Ishikawa, T., Yanagisawa, M., Kimura, S., Goto, K. and Masaki,T. Am. J. Physiol. 255, H970-H973.
(1988)
Larkin, S.W., Clarke, J.G., Keogh, B.E., Araujo, K.L., Rhodes, C., Davies, G.J., Taylor, K.M. and Maseri, A. (1989) Am. J. cardiol. 64, 956958. Ezra, D., Goldstein, R.E., Czala, J.F., and Feuerstein, G.Z. (1989) Am. J. Physiol. 257, H339-H343. Yorikane, R. and Koike, H. (1990) Japan. J. Pharmacol. 53, 259-263. Inoue,¥., Oike, M., Nakao, K., Kitamura, K. and Kuriyam~,H. (1990) J. Physiol., Lend. 423, 171-191. January, C.T., Riddle, J.M. and Salata, J.J. (1988) Circ. Res. 62, 563571. January, C.T. and Riddle, J.~. (1989) Circ. Res. 64, 977- 990. Hirano, Y., Fozzard, H.A. and January, C,T. (1989) Am. J. Physiol. 256, H1478-H1492. Gintant,G.A. and Cohen, I.S. (1988) Ann. Rev. Pharmacol. Toxicol. 28, 61-81. Levine, J.H., Spear, J.F., Guarnieri,T., Weisfeldt, M.L., de Langen, C.D.J., Becker, L.C. and Moore, E.N. (1985) Circulation 72, 1092-1103.
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