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The action of L-DOPA on the release of endogenous dopamine in striatal slices from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated C57BL mice
$122 EFFECFS
O!? IAP A N D
GTPrS
ON
K+-DEPENDENT
HYPERPOLARIZATION
INDUCED
BY D O P A M I N E
KAZUHIKO, SASAKI , MITSUHIKO MATSUMOTO , KOICHIRO, TAKASHIMA , MASANORI S H O Z U S H I M A * , and M A K O T O SATO., Dept. P h y s i o l . , Seh. Med., Iwate Med. Univ., M o r i o k a , I w a t e 020 Dopamine Aplysia
(DA)
is b l o c k e d
by
applications
of
islet
neuron
i.
Intracellular
under
irreversible resting
the
increase
of GTPrS.
3.
current.
The
since the
intra-
opening
Keiryokai
that
of
Fund.
the No.
IAP
clamp
state
of
outward
the
strongly
opening
of
DA-induced
application
voltage
of
dependent
Effects
current
current
studied
on
K +,
and
this
type
that
the
of
into
the
Na+-channel.
of
Li +
same
by the type
Supported
with
the
change of
the
by the
the
or
outward
GTP-binding
coupled
of
expeditied
(Ci=5-10 y M )
DA-induced
a certain
is c a u s e d
conductance
significanly
either of
2.
a gradual,
slope
DA
C.:2-5 ~g/l) i but it
30 m i n u t e s .
caused
and
K+-channels
response cAMP
were
within
amplitude
suggest the
in
toward
intracellular
membrane,
alone
applications
the
of
concentration;
receptor
application
depress
neurons
increase
method:
the
outward
identified
and G T P r S
(Ci=5-10 ~ M )
repetitive
not
(IAP)
(intracellular
Intracellular
did
the
cellular
voltage
in the
results
N i is r e g u l a t i n g is u n l i k e l y
protein
of G T P r S
both
in the
by p e r m e a b i l i t y
D2-antagonist.
DA-induced
However,
(Ci=5-10 ~ M )
It
of
resting
application
neomycine
like
is c a u s e d
a typical
modulated
above
hyperpolarization
activating
in the
membrane.
effect
slow
response
injection
blocked
Intracellular
the
the
no c h a n g e
irreversibly
This
sulpiride,
of
caused
induces
ganglion.
protein
DA-receptor. in
[cAMP]i,
cell
causes
I.M.U.
26.
DEPOLARIZATION-INDUCED
RELEASE
OF E N D O G E N O U S
DOPA
FROM
RAT
STRIATAL
SLICES.
Y O S H I O G O S H I M A * , T A K A O K U B O * and Y O S H I M I MISU, D e p a r t m e n t of P h a r m a c o l o g y , Y o k o h a m a C i t y U n i v e r s i t y S c h o o l of M e d i c i n e , Y o k o h a m a 236, J a p a n We p r e v i o u s l y d e m o n s t r a t e d the b i p h a s i c a c t i o n s of e x o g e n o u s l y a p p l i e d L - D O P A on d o p a m i n e (DA) r e l e a s e , f a c i l i t a t i o n ~ p r e s y n a p t i c 6 - a d r e n o c e p t o r s at 30 nM and inhibition u~ D A - r e c e p t o r s at 1 IJM. The p r i m a r y a c t i o n of L - D O P A w a s the f a c i l i t a t i o n of DA r e l e a s e 0{~ p r e s y n a p t i c i~-adrenoceptors r a t h e r t h a n the s y n t h e s i s a n d a c c u m u l a t i o n of DA in rat s } r i a t a l slices. In the s a m e s l i c e s , we f o u n d t h a t e l e c t r i c a l p u l s e s or h i g h K c o n c e n t r a t i o n s r e l e a s e d e n d o g e n o u s DOPA. The c h a r a c t e r i s t i c s of this D O P A r e l e a s e w e r e i n v e s t i g a t e d . S l i c e s (0.3 mm) w e r e s u p e r f u s e d w i t h K r e b s m e d i u m and ~ i e l d s t i m u l a t i o n s w i t h b i p h a s i c p u l s e s (0.5 - 5 Hz, 2 m s e c , 30 V, 3 min} or h i g h K stimulations (i0 - ~ mM, 5 min) w e r e g i v e n 45 (Sl) a n d 90 ($2) m i n a f t e r the s t a r t of s u p e r f u s i o n . C a - - - d e p r i v a t i o n and E G T A 2 m M - a d d i t i o n or T T X 0.3 I.M a p p l i c a t i o n w a s d o n e 30 or 12 m i n b e f o r e $2. D O P A and DA w e r e m e a s u r e d by H P L C - E C D . E l e c t r i c a l s t i m u l a t i o n s r e l e a s e d DOPA, a n d the r e l e a s e at Sl w a s frequency-dependent f r o m 0.5 to 2 Hz. The s p o n t a n e o u s and e v o k e d r e l e a s e at 2 Hz was 0.198 ": 0.08 and 0.300 + 0.06 pmol, r e s p e c t i v e l y (n : 9). T h e s e v a l u e s w e ~ a b o u t 1/20 of t h o s e of DA. The e v o k e d D O P A r e l e a s e was m a r k e d l y r e d u c e d by Ca d e p r i v a t i o n an~ TTX. H i g h K - s t i m u l a t i o n s a l s o r e l e a s e d DOPA, a n d the r e l e a s e w a s d e p e n d e n t on K c o n c e n t r a t i o n s f r o m I0 to 20 mM. The e v o k e d [ ~ l e a s e at 20 m M w a s 0.325 : 0.067 p m o l (n = 6). The r e l e a s e was a l s o m a r k e d l y Ca- - d e p e n d e n t . D O P A rel e a s e and t y r o s i n e h y d r o x y l a s e {TH) a c t i v i t y w e r e t h e ~ m e a s u r e d s i m u l t a n e o u s l y . S l i c e s w e r e s u p e r f u s e d w i t ~ m e d i u m c o n t a i n i n g L-3, 5 - - H - t y r o s i n e 50 ~ C i / m l and TH a c t i v i t y was e v a l u a t e d by ~O c o n t e n t in s u p e r f u s a t e s . In the p r e s e n c e of_<~-methyl - i - t y r o s i n e 0.2 mM, 20 m M K Z e v o k e d D O P A w i t h o u t a d e t e c t a b l e i n c r e a s e in J H - H 2 0 f o r m a t i o n . T h i s f i n d i g ~ s u g g e s t s t h a t the p r o c e s s of TH a c t i v a t i o n is not the o n l y one @ ~ o n g p r o b a b l e C a - - - d e p e n d e n t p r o c e s s e s r e s p o n s i b l e for the D O P A r e l e a s e . A Ca - - d e p e n d e n t and T T X - s e n s i t i v e r e l e a s e of D O P A was e v i d e n t in rat s t r i a t a l s l i c e s . E v o k e d D O P A a p p e a r s to be a v a i l a b l e for a p h y s i o l o g i c a l a c t i o n of d u a l m o d i f i c a t i o n of DA r e l e a s e ~:~ p r e s y n a p t i c f a c i l i t a t o r y f~-adrenoceptors and inhibitory DA-receptors.
O!? IAP A N D
GTPrS
ON
K+-DEPENDENT
HYPERPOLARIZATION
INDUCED
BY D O P A M I N E
KAZUHIKO, SASAKI , MITSUHIKO MATSUMOTO , KOICHIRO, TAKASHIMA , MASANORI S H O Z U S H I M A * , and M A K O T O SATO., Dept. P h y s i o l . , Seh. Med., Iwate Med. Univ., M o r i o k a , I w a t e 020 Dopamine Aplysia
(DA)
is b l o c k e d
by
applications
of
islet
neuron
i.
Intracellular
under
irreversible resting
the
increase
of GTPrS.
3.
current.
The
since the
intra-
opening
Keiryokai
that
of
Fund.
the No.
IAP
clamp
state
of
outward
the
strongly
opening
of
DA-induced
application
voltage
of
dependent
Effects
current
current
studied
on
K +,
and
this
type
that
the
of
into
the
Na+-channel.
of
Li +
same
by the type
Supported
with
the
change of
the
by the
the
or
outward
GTP-binding
coupled
of
expeditied
(Ci=5-10 y M )
DA-induced
a certain
is c a u s e d
conductance
significanly
either of
2.
a gradual,
slope
DA
C.:2-5 ~g/l) i but it
30 m i n u t e s .
caused
and
K+-channels
response cAMP
were
within
amplitude
suggest the
in
toward
intracellular
membrane,
alone
applications
the
of
concentration;
receptor
application
depress
neurons
increase
method:
the
outward
identified
and G T P r S
(Ci=5-10 ~ M )
repetitive
not
(IAP)
(intracellular
Intracellular
did
the
cellular
voltage
in the
results
N i is r e g u l a t i n g is u n l i k e l y
protein
of G T P r S
both
in the
by p e r m e a b i l i t y
D2-antagonist.
DA-induced
However,
(Ci=5-10 ~ M )
It
of
resting
application
neomycine
like
is c a u s e d
a typical
modulated
above
hyperpolarization
activating
in the
membrane.
effect
slow
response
injection
blocked
Intracellular
the
the
no c h a n g e
irreversibly
This
sulpiride,
of
caused
induces
ganglion.
protein
DA-receptor. in
[cAMP]i,
cell
causes
I.M.U.
26.
DEPOLARIZATION-INDUCED
RELEASE
OF E N D O G E N O U S
DOPA
FROM
RAT
STRIATAL
SLICES.
Y O S H I O G O S H I M A * , T A K A O K U B O * and Y O S H I M I MISU, D e p a r t m e n t of P h a r m a c o l o g y , Y o k o h a m a C i t y U n i v e r s i t y S c h o o l of M e d i c i n e , Y o k o h a m a 236, J a p a n We p r e v i o u s l y d e m o n s t r a t e d the b i p h a s i c a c t i o n s of e x o g e n o u s l y a p p l i e d L - D O P A on d o p a m i n e (DA) r e l e a s e , f a c i l i t a t i o n ~ p r e s y n a p t i c 6 - a d r e n o c e p t o r s at 30 nM and inhibition u~ D A - r e c e p t o r s at 1 IJM. The p r i m a r y a c t i o n of L - D O P A w a s the f a c i l i t a t i o n of DA r e l e a s e 0{~ p r e s y n a p t i c i~-adrenoceptors r a t h e r t h a n the s y n t h e s i s a n d a c c u m u l a t i o n of DA in rat s } r i a t a l slices. In the s a m e s l i c e s , we f o u n d t h a t e l e c t r i c a l p u l s e s or h i g h K c o n c e n t r a t i o n s r e l e a s e d e n d o g e n o u s DOPA. The c h a r a c t e r i s t i c s of this D O P A r e l e a s e w e r e i n v e s t i g a t e d . S l i c e s (0.3 mm) w e r e s u p e r f u s e d w i t h K r e b s m e d i u m and ~ i e l d s t i m u l a t i o n s w i t h b i p h a s i c p u l s e s (0.5 - 5 Hz, 2 m s e c , 30 V, 3 min} or h i g h K stimulations (i0 - ~ mM, 5 min) w e r e g i v e n 45 (Sl) a n d 90 ($2) m i n a f t e r the s t a r t of s u p e r f u s i o n . C a - - - d e p r i v a t i o n and E G T A 2 m M - a d d i t i o n or T T X 0.3 I.M a p p l i c a t i o n w a s d o n e 30 or 12 m i n b e f o r e $2. D O P A and DA w e r e m e a s u r e d by H P L C - E C D . E l e c t r i c a l s t i m u l a t i o n s r e l e a s e d DOPA, a n d the r e l e a s e at Sl w a s frequency-dependent f r o m 0.5 to 2 Hz. The s p o n t a n e o u s and e v o k e d r e l e a s e at 2 Hz was 0.198 ": 0.08 and 0.300 + 0.06 pmol, r e s p e c t i v e l y (n : 9). T h e s e v a l u e s w e ~ a b o u t 1/20 of t h o s e of DA. The e v o k e d D O P A r e l e a s e was m a r k e d l y r e d u c e d by Ca d e p r i v a t i o n an~ TTX. H i g h K - s t i m u l a t i o n s a l s o r e l e a s e d DOPA, a n d the r e l e a s e w a s d e p e n d e n t on K c o n c e n t r a t i o n s f r o m I0 to 20 mM. The e v o k e d [ ~ l e a s e at 20 m M w a s 0.325 : 0.067 p m o l (n = 6). The r e l e a s e was a l s o m a r k e d l y Ca- - d e p e n d e n t . D O P A rel e a s e and t y r o s i n e h y d r o x y l a s e {TH) a c t i v i t y w e r e t h e ~ m e a s u r e d s i m u l t a n e o u s l y . S l i c e s w e r e s u p e r f u s e d w i t ~ m e d i u m c o n t a i n i n g L-3, 5 - - H - t y r o s i n e 50 ~ C i / m l and TH a c t i v i t y was e v a l u a t e d by ~O c o n t e n t in s u p e r f u s a t e s . In the p r e s e n c e of_<~-methyl - i - t y r o s i n e 0.2 mM, 20 m M K Z e v o k e d D O P A w i t h o u t a d e t e c t a b l e i n c r e a s e in J H - H 2 0 f o r m a t i o n . T h i s f i n d i g ~ s u g g e s t s t h a t the p r o c e s s of TH a c t i v a t i o n is not the o n l y one @ ~ o n g p r o b a b l e C a - - - d e p e n d e n t p r o c e s s e s r e s p o n s i b l e for the D O P A r e l e a s e . A Ca - - d e p e n d e n t and T T X - s e n s i t i v e r e l e a s e of D O P A was e v i d e n t in rat s t r i a t a l s l i c e s . E v o k e d D O P A a p p e a r s to be a v a i l a b l e for a p h y s i o l o g i c a l a c t i o n of d u a l m o d i f i c a t i o n of DA r e l e a s e ~:~ p r e s y n a p t i c f a c i l i t a t o r y f~-adrenoceptors and inhibitory DA-receptors.