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Proposed tertiary structure of the sodium channel
s57
l-07
PROPOSED TERTIARY STRUCTURE OF THE SODIUM CHANNEL., CHIKARA SAT0 AND GEN MATSUMOTO.El~technical Laboratorv.SupermolecularScience Divison.
Tsukuba
Ibaraki
On the basis of our recent results of the complete amino acid sequence of the squid Loligo bleekeri sodium channel deduced by cloning and sequence analysis of the complementary DNA (Sato, C. and Matsumoto, G. Biochem. Biophys. Res. Comm. in press), we have proposed a tertiary structure model of the sodium channel where the transmembrane segments are octagonally aligned and the four linkers of S5-6 between segments S5 and S6 play a crucial role in the activation gate, voltage sensor and ion selective pore, which can slide, depending on membrane potentials, along inner walls consisting of segments S2 and S4 alternately. The proposed model is contrasted with thatof Noda er al.(Nature320; 188-192,1986).
l-08
CAMP-MEDIATED EXPRESSION CULTURED MOUSE SCHWANN
OF
INWARDLY
RECTIFYING
POTASSIUM
CHANNELS
IN
CELLS. TETSURO KONISHI, Department of Neurology, Utano National Hospital, Narutaki, Kyoto 616. Japan
ionic currents were recorded from cultured Schwann cells Voltage-gated obtained from neonatal mouse sciatic nerves by the whole-cell variation of the patch-clamp technique. CAMP analogues or forskolin were added to the culture medium 4 days after the start of the culture, when inwardly rectifying potassium (Kir) currents were almost eliminated from cultured Schwann cells. Cultured Schwann cells restored the expression of Kir currents by co-culture with agents which elevate intracellular CAMP level. The dose response of 8%(4chlorophenylthio) CAMP (CPT CAMP) for the incidence of the expression of Kir currents showed a steep increase in the percentage of cells with Kir currents between 0.02 and 0.1 mM of external CPT CAMP and approximately two third of cells had Kir currents in higher concentrations more than 0.1 mM of CPT CAMP after 4 days of incubation. The simultaneous application of cycloheximide (1 ug/ml) with CPT CAMP suppressed the expression of Kir currents. These findings suggested that CAMP is an intracellular second messenger for the expression of functional Kir channels in Schwann cells.
l-09
THE ROLE OF POTASSIUMCHANNELIN AUTORECEPTOR-REGULATED DOPAMINERELEASEIN THE RAT STRIATUM
: IN VIVO MICRODIALYSIS STUDY.TAKAHIKOTANAKA,MASAMI YOSHIDA.HIDEYASUYOKOO.KATSIJHIRO MIZOGUCHI,MASATOSHITANAKA.Departmentof Pharmacology. KurumeUniversitySchoolof Medicine, Kurume,Fukuoka 830. Japan In vivo microdialysis was used to examinethe role of potassium(K')channelactivationon dopamine (DA)autoreceptorfunctionin the striatumof freelymovingrats. Local application of K’ DA channel blocker. quinine (PIN.10~5-10~3M) to the striatum through the dialysis membrane increased release in a dose-dependent manner. Local infusionof (-)-sulpiride (SLP.10-5M) also produced significantincreasesin levelsof DA and its metabolites.DOPAC and HVA. C!IN(10-3,10-4M but not 1O-5 M) completelyblockedthe SLP-inducedincreasesin DA and DOPAC levels. Local infusionof K' channel opener nicorandil(NIC,10~5-10~3M) reducedextracellular DA concentrations. NIC(1 mM) blockedPIN (1 ml)-inducedincreasesin DA levelsin the striatum. These resultsconfirmthat SLP increasesDA levelsby blocking the tonic activation of autoreceptors by endogenous DA. QIN blocksSLP-inducedincreasesin DA levelsby preventingthe K' channelopeningthat would normallyaccompanyendogenousautoreceptor activation.In addition,infusion of K' channelblocker.PIN.increases DA releasein the striatumand K' channelopener,NIC,decreases it. PIN-inducedincreasesin DA levelsare blockedby NIC. The findingssuggestthat endogenousDA inhibitsDA releaseby activatingK' channelcoupledto presynapticDA autoreceptors.
l-07
PROPOSED TERTIARY STRUCTURE OF THE SODIUM CHANNEL., CHIKARA SAT0 AND GEN MATSUMOTO.El~technical Laboratorv.SupermolecularScience Divison.
Tsukuba
Ibaraki
On the basis of our recent results of the complete amino acid sequence of the squid Loligo bleekeri sodium channel deduced by cloning and sequence analysis of the complementary DNA (Sato, C. and Matsumoto, G. Biochem. Biophys. Res. Comm. in press), we have proposed a tertiary structure model of the sodium channel where the transmembrane segments are octagonally aligned and the four linkers of S5-6 between segments S5 and S6 play a crucial role in the activation gate, voltage sensor and ion selective pore, which can slide, depending on membrane potentials, along inner walls consisting of segments S2 and S4 alternately. The proposed model is contrasted with thatof Noda er al.(Nature320; 188-192,1986).
l-08
CAMP-MEDIATED EXPRESSION CULTURED MOUSE SCHWANN
OF
INWARDLY
RECTIFYING
POTASSIUM
CHANNELS
IN
CELLS. TETSURO KONISHI, Department of Neurology, Utano National Hospital, Narutaki, Kyoto 616. Japan
ionic currents were recorded from cultured Schwann cells Voltage-gated obtained from neonatal mouse sciatic nerves by the whole-cell variation of the patch-clamp technique. CAMP analogues or forskolin were added to the culture medium 4 days after the start of the culture, when inwardly rectifying potassium (Kir) currents were almost eliminated from cultured Schwann cells. Cultured Schwann cells restored the expression of Kir currents by co-culture with agents which elevate intracellular CAMP level. The dose response of 8%(4chlorophenylthio) CAMP (CPT CAMP) for the incidence of the expression of Kir currents showed a steep increase in the percentage of cells with Kir currents between 0.02 and 0.1 mM of external CPT CAMP and approximately two third of cells had Kir currents in higher concentrations more than 0.1 mM of CPT CAMP after 4 days of incubation. The simultaneous application of cycloheximide (1 ug/ml) with CPT CAMP suppressed the expression of Kir currents. These findings suggested that CAMP is an intracellular second messenger for the expression of functional Kir channels in Schwann cells.
l-09
THE ROLE OF POTASSIUMCHANNELIN AUTORECEPTOR-REGULATED DOPAMINERELEASEIN THE RAT STRIATUM
: IN VIVO MICRODIALYSIS STUDY.TAKAHIKOTANAKA,MASAMI YOSHIDA.HIDEYASUYOKOO.KATSIJHIRO MIZOGUCHI,MASATOSHITANAKA.Departmentof Pharmacology. KurumeUniversitySchoolof Medicine, Kurume,Fukuoka 830. Japan In vivo microdialysis was used to examinethe role of potassium(K')channelactivationon dopamine (DA)autoreceptorfunctionin the striatumof freelymovingrats. Local application of K’ DA channel blocker. quinine (PIN.10~5-10~3M) to the striatum through the dialysis membrane increased release in a dose-dependent manner. Local infusionof (-)-sulpiride (SLP.10-5M) also produced significantincreasesin levelsof DA and its metabolites.DOPAC and HVA. C!IN(10-3,10-4M but not 1O-5 M) completelyblockedthe SLP-inducedincreasesin DA and DOPAC levels. Local infusionof K' channel opener nicorandil(NIC,10~5-10~3M) reducedextracellular DA concentrations. NIC(1 mM) blockedPIN (1 ml)-inducedincreasesin DA levelsin the striatum. These resultsconfirmthat SLP increasesDA levelsby blocking the tonic activation of autoreceptors by endogenous DA. QIN blocksSLP-inducedincreasesin DA levelsby preventingthe K' channelopeningthat would normallyaccompanyendogenousautoreceptor activation.In addition,infusion of K' channelblocker.PIN.increases DA releasein the striatumand K' channelopener,NIC,decreases it. PIN-inducedincreasesin DA levelsare blockedby NIC. The findingssuggestthat endogenousDA inhibitsDA releaseby activatingK' channelcoupledto presynapticDA autoreceptors.