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Delayed-rectifier potassium current in cultured bullfrog primary afferent neurons
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P H E N O T Y P I C E X P R E S S I O N OF RAT PINEAL CELLS IN VITRO IS C O N T R O L L E D BY CATECHOLAMINES. M A S A S U K E ARAKI, D e p a r t m e n t of Anatomy, Jichi Medical School, Minamikawachi, Tochi@i 329-04, Japan. During the course of p h y l o g e n e t i c development, the function of the pineal c o m p l e x undergoes a t r a n s i t i o n from a p h o t o r e c e p t o r organ to an endocrine organ. In mammals, the pineal is c o n s i d e r e d to function e x c l u s i v e l y as a m e l a t o n i n secreting organ, and no evidence has been shown in favor of the p h o t o - r e c e p t i v e function. By using a c e l l - c u l t u r e system, I have attempted to examine the potential of m a m m a l i a n pineal cells to d i f f e r e n t i a t e into p h o t o r e c e p t o r cells. Pineal glands of newborn rats were d i s s o c i a t e d by EDTA and/or trypsin, and were cultured for 7-14 days. S e r o t o n i n (5HT) i m m u n o h i s t o c h e m i s t r y showed numerous i m m u n o r e a c t i v e cells w h i c h had long neuritic p r o c e s s e s w i t h varicosities. W i t h opsin antibodies (both poly- and mono-clonal), positive cells were found in cultures, e s p e c i a l l y in E D T A - d i s s o c i a t e d cultures. These cells resembled cultured rod cells both in m o r p h o l o g y and opsin localization. In the presence of luM norepinephrine, opsin i m m u n o r e a c t i v e cells did not appear and 5HT immunoreactive cells altered in m o r p h o l o g y from neuronal to flat cells w i t h o u t neuritic processes. Other amines such as dopamine and 5HT did not have such effects. These results indicate that rat pineal cells retain the capacity to express photoreceptor as well as neuronal cell p r o p e r t i e s which may be suppressed in situ by massive sympathetic innervation.
V O L T A G E - D E P E N D E N T P O T A S S I U M C H A N N E L S IN T R E M B L E R SCHWANN CELLS. TETSURO KONISHI, HIROSHI N I S H I T A N I % D e p a r t m e n t of Neurology, Utano National H o s p i t a l . Narutaki. Kyoto 616, Japan In order to clarify e l e c t r o p h y s i o l o g i c a l abnormalities of Trembler Schwann cells, which were characterized as hypomyelinatlng and d e m y e l l n a t i n g in peripheral nerves, v o l t a g e - d e p e n d e n t K + currents were investigated in Schwann cells using whole-cell recordings. In m y e l l n a t i n g S c h w a n n cells obtained from f r e s h l y - d i s s o c l a t e d adult sciatic nerves of normal littermates or C57BL/6 mice at 4-weeks-old, voltage-dependent K + currents were not observed except in some m y e l l n a t i n g cells with small calibers. In contrast to normal Schwann cells, al| myelinating Trembler Schwann cells at the same age showed voltage-dependent K• currents. Although the magnitudes of K + currents in non-myellnating Trembler Schwann cells were not different from those in normal non-myelinating cells, zero-current membrane potentials were significantly low compared to those In normal Schwann cells. Under culture conditions of enzyme-treated adult sciatic nerves, magnitudes of voltage-dependent K- currents increased in both normal and Trembler myelinating cells during the first few days of culture. These results suggest that Trembler Schwann cells show a normal response to an early event of cell proliferation and that residual voltage-dependent K T channels in myelinating cells may reflect incomplete myelin formation by Trembler Schwann cells.
DELAYED-RECTIFIER
POTASSIUM
CURRENT
IN
CULTURED
BULLFROG
PRIMARY
TSURUSAKI , TAKAYUKI TOKIMASA~ AND TAKASHI AKASU~ Department
AFFERENT
of Physiolo~y~
NEURONS.
MASASHI
Kurume University
School of Medicine, 67 Asahi-machi~ Kurume 830~ Japan Whole-cell recordings were made from cultured bullfrog dorsal root ganglion
(DRG) cells.
Depolarizing step commands from a holding potential close to rest (typically -70 mV) evoked a slowly-inactivating potassium current (IK) in Ringer solution containing TTX (5 MM), barium mM), cesium (I mM), and 4-AP (3 mM). manner.
(2
IK was blocked by TEA (3-50 mM) in a concentratlon-dependent
IK reversed its polarity at -87.4 and -33.7 mV in the superfusate containing 2 and 20 mM
potassium, respectively.
The amplitude of IK at -30 mV was progressively increased at holding
potentials more negative than -70 mV, being maximum with step commands from -120 mV. activated, IK inactivated single-exponentially never occurred. It is suggested
When fully
(~ ~ 2 s at -30 mV) although complete inactivation
TEA (30 mM) produced an inward shift of the holding current (~ 500 pA at -30 mV). that the slowly-lnactivatlng
potassium current, probably an atypical delayed-
rectifier current, contributes to the resting membrane potential in bullfrog DRG cells.
P H E N O T Y P I C E X P R E S S I O N OF RAT PINEAL CELLS IN VITRO IS C O N T R O L L E D BY CATECHOLAMINES. M A S A S U K E ARAKI, D e p a r t m e n t of Anatomy, Jichi Medical School, Minamikawachi, Tochi@i 329-04, Japan. During the course of p h y l o g e n e t i c development, the function of the pineal c o m p l e x undergoes a t r a n s i t i o n from a p h o t o r e c e p t o r organ to an endocrine organ. In mammals, the pineal is c o n s i d e r e d to function e x c l u s i v e l y as a m e l a t o n i n secreting organ, and no evidence has been shown in favor of the p h o t o - r e c e p t i v e function. By using a c e l l - c u l t u r e system, I have attempted to examine the potential of m a m m a l i a n pineal cells to d i f f e r e n t i a t e into p h o t o r e c e p t o r cells. Pineal glands of newborn rats were d i s s o c i a t e d by EDTA and/or trypsin, and were cultured for 7-14 days. S e r o t o n i n (5HT) i m m u n o h i s t o c h e m i s t r y showed numerous i m m u n o r e a c t i v e cells w h i c h had long neuritic p r o c e s s e s w i t h varicosities. W i t h opsin antibodies (both poly- and mono-clonal), positive cells were found in cultures, e s p e c i a l l y in E D T A - d i s s o c i a t e d cultures. These cells resembled cultured rod cells both in m o r p h o l o g y and opsin localization. In the presence of luM norepinephrine, opsin i m m u n o r e a c t i v e cells did not appear and 5HT immunoreactive cells altered in m o r p h o l o g y from neuronal to flat cells w i t h o u t neuritic processes. Other amines such as dopamine and 5HT did not have such effects. These results indicate that rat pineal cells retain the capacity to express photoreceptor as well as neuronal cell p r o p e r t i e s which may be suppressed in situ by massive sympathetic innervation.
V O L T A G E - D E P E N D E N T P O T A S S I U M C H A N N E L S IN T R E M B L E R SCHWANN CELLS. TETSURO KONISHI, HIROSHI N I S H I T A N I % D e p a r t m e n t of Neurology, Utano National H o s p i t a l . Narutaki. Kyoto 616, Japan In order to clarify e l e c t r o p h y s i o l o g i c a l abnormalities of Trembler Schwann cells, which were characterized as hypomyelinatlng and d e m y e l l n a t i n g in peripheral nerves, v o l t a g e - d e p e n d e n t K + currents were investigated in Schwann cells using whole-cell recordings. In m y e l l n a t i n g S c h w a n n cells obtained from f r e s h l y - d i s s o c l a t e d adult sciatic nerves of normal littermates or C57BL/6 mice at 4-weeks-old, voltage-dependent K + currents were not observed except in some m y e l l n a t i n g cells with small calibers. In contrast to normal Schwann cells, al| myelinating Trembler Schwann cells at the same age showed voltage-dependent K• currents. Although the magnitudes of K + currents in non-myellnating Trembler Schwann cells were not different from those in normal non-myelinating cells, zero-current membrane potentials were significantly low compared to those In normal Schwann cells. Under culture conditions of enzyme-treated adult sciatic nerves, magnitudes of voltage-dependent K- currents increased in both normal and Trembler myelinating cells during the first few days of culture. These results suggest that Trembler Schwann cells show a normal response to an early event of cell proliferation and that residual voltage-dependent K T channels in myelinating cells may reflect incomplete myelin formation by Trembler Schwann cells.
DELAYED-RECTIFIER
POTASSIUM
CURRENT
IN
CULTURED
BULLFROG
PRIMARY
TSURUSAKI , TAKAYUKI TOKIMASA~ AND TAKASHI AKASU~ Department
AFFERENT
of Physiolo~y~
NEURONS.
MASASHI
Kurume University
School of Medicine, 67 Asahi-machi~ Kurume 830~ Japan Whole-cell recordings were made from cultured bullfrog dorsal root ganglion
(DRG) cells.
Depolarizing step commands from a holding potential close to rest (typically -70 mV) evoked a slowly-inactivating potassium current (IK) in Ringer solution containing TTX (5 MM), barium mM), cesium (I mM), and 4-AP (3 mM). manner.
(2
IK was blocked by TEA (3-50 mM) in a concentratlon-dependent
IK reversed its polarity at -87.4 and -33.7 mV in the superfusate containing 2 and 20 mM
potassium, respectively.
The amplitude of IK at -30 mV was progressively increased at holding
potentials more negative than -70 mV, being maximum with step commands from -120 mV. activated, IK inactivated single-exponentially never occurred. It is suggested
When fully
(~ ~ 2 s at -30 mV) although complete inactivation
TEA (30 mM) produced an inward shift of the holding current (~ 500 pA at -30 mV). that the slowly-lnactivatlng
potassium current, probably an atypical delayed-
rectifier current, contributes to the resting membrane potential in bullfrog DRG cells.