Effects of antidepressants on serotonin-evoked current in Xenopus oocytes injected with rat brain mRNA

Serotonin (5-HT, 1 microM) induced an inward current in Xenopus oocytes injected with rat brain mRNA under steady voltage clamp conditions of -60 mV. The 5-HT response was blocked by 0.1 microM mianserin, but neither buspirone, 8-hydroxy-dipropylaminotetralin (8-OH-DPAT), trifluoromethylphenyl piperazine (TFMPP), pindolol, propranolol, spiperone, ketanserin nor ICS 205-930 exerted effects, suggesting that the 5-HTIC subtype of 5-HT receptors is involved in the current. The 5-HT-induced current was inhibited by imipramine or desipramine with IC50 values of 60 nM or 20 microM, respectively. The response was also inhibited by setiptilline, maprotiline or amoxapine at a dose of 10 microM. Imipramine at 10 microM had no effect on the acetylcholine (ACh, 1 mM)-induced current response. It has been reported that inositol triphosphate (IP3) formation and intracellular Ca2+ are involved in the 5-HT- as well as ACh-induced current and that intracellular injection of either 50 pmol IP3 or 50 pmol Ca2+ mimics the 5-HT-induced current. The response induced by intracellular injection of either 50 pmol IP3 or 50 pmol Ca2+ was not affected by 10 microM imipramine. It is suggested that imipramine, and perhaps other antidepressant drugs tested, blocks 5-HTIC receptors, subsequently inhibiting the 5-HT-evoked current.     

Conantokin-G selectively inhibits N-methyl-D-aspartate-induced currents in Xenopus oocytes injected with mouse brain mRNA.

The conantokins are a family of peptides isolated from the venom of predatory marine snails of the genus Conus. Here we demonstrate that one of these peptides, conantokin-G, specifically inhibits the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors that are expressed in mouse brain mRNA-injected Xenopus oocytes. Increasing the concentration of conantokin-G causes the NMDA dose-response curve to shift to progressively higher concentrations. We therefore conclude that conantokin-G interacts with the glutamate binding site of the receptor. In contrast, the peptide does not compete with glycine, and this indicates that conantokin-G does not act at the binding site of this co-agonist of the NMDA receptor. Furthermore, the inhibitory effects of conantokin-G appear to be insensitive to membrane potential.     

Tryptophan inhibits the [3H]glutamate uptake into Xenopus oocytes injected with rat brain mRNA.

We characterized the glutamate (Glu) uptake in Xenopus oocytes injected with rat brain mRNA. The Glu uptake into oocytes was higher in mRNA-injected oocytes than in vehicle-injected ones. Na+ omission or addition of tryptophan inhibited the uptake in mRNA-injected oocytes, although it did not affect that in vehicle-injected oocytes. These results suggest that Glu transporters with a tryptophan sensitivity different from that of Glu transporters in native oocytes are expressed after injection of rat brain mRNA.     

Species-dependent functional properties of non-NMDA receptors expressed in Xenopus laevis oocytes injected with mammalian and avian brain mRNA.

1. Species-dependent variation in the functional properties of non-NMDA receptors was investigated by intracellular recording in Xenopus laevis oocytes injected with rat, chick and calf brain mRNA. 2. In all mRNA-injected oocytes, kainic acid (KA), domoic acid (Dom) and 5-bromowillardiine (BrW) evoked large, maintained membrane currents, in contrast to the smaller, desensitizing responses elicited by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), quisqualic acid (QA) and L-glutamic acid (L-Glu). Dose-response curves for KA in oocytes injected with calf (EC50 = 96.4 +/- 12.3 microM; mean +/- s.e. mean), chick (87.0 +/- 8.9 microM) or rat (88.7 +/- 4.3 microM) brain mRNA were similar. 3. Current-voltage (I-V) relationships determined with KA inwardly rectified in oocytes injected with calf or chick mRNA; whereas, outward rectification was observed in oocytes injected with rat brain mRNA. 4. In oocytes injected with rat brain mRNA, AMPA antagonized responses evoked by KA in a competitive manner. The absolute amplitudes of KA and AMPA responses in the same oocytes were significantly correlated, which is consistent with both agonists acting on the same receptor-ionophore complex. 5. In contrast, in oocytes injected with calf or chick brain mRNA, AMPA (QA and L-Glu) antagonized the response evoked by KA in a non-competitive manner. The response amplitudes of KA compared to AMPA, QA or L-Glu in the same oocytes were not correlated suggesting discrete receptor-ionophores. 6. This study favours the existence of distinct non-NMDA receptor subtypes that are equi-sensitive to KA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional expression of H1-histaminergic receptors in Xenopus laevis oocytes injected with bovine adrenal medullary mRNA.

We prepared poly (A)+ mRNA from bovine adrenal medulla and electrophysiologically examined the expression of H1-histaminergic receptors in Xenopus laevis oocytes. Histamine dose-dependently induced inward currents in oocytes injected with the mRNA, but not in those injected with water or the non-injected oocytes. This response was also induced by H1-agonists and antagonized by H1-antagonists, while both an H2-agonist and an antagonist had no effect. These results clearly demonstrate that H1-histaminergic receptors are functionally expressed in oocytes injected with exogenous mRNA.     

Thiocyanate ions selectively antagonize AMPA-evoked responses in Xenopus laevis oocytes microinjected with rat brain mRNA.

1 Responses to kainate (KA), willardiine and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were recorded from rat brain mRNA-injected Xenopus laevis oocytes by use of a two-electrode voltage clamp. 2 Thiocyanate (SCN-; 50 microM-4 mM) ions reversibly and selectively inhibited the membrane current responses to AMPA in a non-competitive manner without affecting KA or willardiine-induced responses. 3 The inhibition of AMPA-induced responses by SCN- was dependent on the SCN- concentration with an estimated IC50 of 1 mM. The antagonism was not dependent on the AMPA concentration. 4 The response to a high concentration of AMPA (100-200 microM) exhibited a peak inward current which declined to a steady-state. SCN- inhibited the steady-state current more than the peak response. The inhibition was unaffected by prior incubation with concanavalin-A (Con-A; 10 microM). 5 Responses to KA were antagonized by AMPA in a competitive manner, suggesting that both agonists may activate a common receptor-channel complex. This interaction between two non-NMDA agonists was not affected by the SCN(-)-induced inhibition of the AMPA response. 6 AMPA-induced responses recorded from large cultured cerebellar neurones by whole-cell recording were also inhibited by SCN- in a non-competitive manner. The AMPA-induced peak current was less affected than the steady-state response. 7 We conclude that SCN- can inhibit the response to AMPA in expressed non-NMDA receptors in Xenopus oocytes and also in native receptors in cultured cerebellar neurones.(ABSTRACT TRUNCATED AT 250 WORDS)     

Functional expression of a novel ginsenoside Rf binding protein from rat brain mRNA in Xenopus laevis oocytes

We have shown that ginsenoside Rf (Rf) regulates voltage-dependent Ca(2+) channels through pertussis toxin (PTX)-sensitive G proteins in rat sensory neurons. These results suggest that Rf can act through a novel G protein-linked receptor in the nervous system. In the present study, we further examined the effect of Rf on G protein-coupled inwardly rectifying K(+) (GIRK) channels after coexpression with size-fractionated rat brain mRNA and GIRK1 and GIRK4 (GIRK1/4) channel cRNAs in Xenopus laevis oocytes using two-electrode voltage-clamp techniques. We found that Rf activated GIRK channel in a dose-dependent and reversible manner after coexpression with subfractions of rat brain mRNA and GIRK1/4 channel cRNAs. This Rf-evoked current was blocked by Ba(2+), a potassium channel blocker. The size of rat brain mRNA responding to Rf was about 6 to 7 kilobases. However, Rf did not evoke GIRK current after injection with this subfraction of rat brain mRNA or GIRK1/4 channel cRNAs alone. Other ginsenosides, such as Rb(1) and Rg(1), evoked only slight induction of GIRK currents after coexpression with the subfraction of rat brain mRNA and GIRK1/4 channel cRNAs. Acetylcholine and serotonin almost did not induce GIRK currents after coexpression with the subfraction of rat brain mRNA and GIRK1/4 channel cRNAs. Rf-evoked GIRK currents were not altered by PTX pretreatment but were suppressed by intracellularly injected guanosine-5'-(2-O-thio) diphosphate, a nonhydrolyzable GDP analog. These results indicate that Rf activates GIRK channel through an unidentified G protein-coupled receptor in rat brain and that this receptor can be cloned by the expression method demonstrated here.     

注射老龄大鼠脑皮层mRNA的爪蟾卵母细胞对乙酰胆碱，谷氨酸和5－羟色胺的反应

从老年（３２月龄）和成年（３月龄）大鼠大脑皮层提取多聚腺啤呤ｍＲＮＡ，注入非洲爪蟾卵母细胞表达有功能的神经递质受体。用电生理方法检测乙酰胆碱，谷氨酸和５－羟色胺诱发的去极化反应，揭示老化脑递质受休反应的变化。注射老年大鼠大脑皮层ｍＲＮＡ的卵母细胞对三种递质诱发反应去极化幅度下降，上升时间及潜伏期延长，Ｔ１／２缩短，与成年对照组有显著性差异；三种递质受体反应幅度约为成年对照组的４０％－６０％，其变化趋势相同，表明老年大鼠脑递质受体蛋白合成的翻译水平发生了改变     

Inhibition by ethanol of rat P2X(4) receptors expressed in Xenopus oocytes

1. The effect of ethanol on the function of P2X(4) receptors expressed in XENOPUS: oocytes was studied using two-electrode voltage-clamp recording. 2. The amplitude of current activated by 1 microM ATP was decreased by ethanol in a concentration-dependent manner over the concentration range 1 - 500 mM. The concentration of ethanol that produced 50% inhibition (IC(50)) of current activated by 1 microM ATP was 58 mM. 3. Ethanol inhibition of ATP-activated current was not dependent on membrane potential from -60 to +20 mV, and ethanol did not change the reversal potential of ATP-activated current. 4. Ethanol, 50 mM, shifted the ATP concentration-response curve to the right, increasing the EC(50) for ATP from 9.1 to 16.0 microM, but did not reduce the maximal response to ATP. 5. The results suggest that ethanol may inhibit P2X(4) receptors by decreasing the apparent affinity of the binding site for ATP. 6. Since the P2X(4) receptor is the most abundant P2X subunit in the brain, these receptors could be important effectors of ethanol action in the central nervous system.     

A comparison of the pharmacological properties of recombinant human and rat alpha(1)beta(2)gamma(2L) GABA(A) receptors in Xenopus oocytes

In the present study, we compared the pharmacology, particularly neurosteroid modulation of the GABA(A) receptor, between human and rat alpha(1)beta(2)gamma(2)(L) GABA(A) receptors and between human receptors containing the long (L) and short (S) forms of the gamma(2)-subunit. We observed that maximum responses to GABA were significantly higher with the human alpha(1)beta(2)gamma(2)(L) receptor compared with the rat receptor. In terms of neurosteroid modulation, increases in the EC(15) response to GABA induced by 3alpha-OH-5beta-pregnan-20-one (3alpha5betaP), 5alpha-androstane-3alpha,17beta-diol (3alpha5alphaADL) and 5alpha-pregnane-3alpha,20beta-diol (3alpha5alpha-diol) were significantly greater for the rat compared with the human receptor. Responses to 30 micromol/L GABA were inhibited by 3beta-OH-5alpha-pregnan-20-one (UC1010) and 5beta-pregnan-3beta,20(R)-diol (UC1020) to a greater degree for human and rat receptors, respectively. Responses to GABA + 3alpha5alphaTHDOC were inhibited by 5alpha-pregnan-3beta,20(S)-diol (UC1019) and pregnenolone sulphate to a greater degree for human and rat receptors, respectively. The GABA dose-response curves for human alpha(1)beta(2)gamma(2)(S) and alpha(1)beta(2)gamma(2)(L) receptors were identical. However, the maximum GABA-evoked current, the direct gating effect of pentobarbital and the allosteric potentiation of the GABA EC(15) response by 3alpha5alphaTHDOC and 3alpha5betaP were significantly higher with alpha(1)beta(2)gamma(2)(S) than alpha(1)beta(2)gamma(2)(L) receptors. Inhibition of the response to 30 micromol/L GABA by UC1010 and UC1020 was greater for a(1)beta(2)gamma(2)(L) and alpha(1)beta(2)gamma(2)(S) receptors, respectively. Inhibition of responses to 3alpha5alphaTHDOC + GABA by UC1019 and UC1010 was significantly higher for alpha(1)beta(2)gamma(2)(L) receptors. In conclusion, the site of activation by GABA and neurosteroid modulation differ between human and rat alpha(1)beta(2)gamma(2)(L) receptors, as well as between human receptors containing the L and S splice variants of the gamma(2)-subunit.     

3,4-methylenedioxymethamphetamine (MDMA, ecstasy)-induced egr-1 mRNA in rat brain: pharmacological manipulation

Using in situ hybridization and immunohistochemical techniques, we examined the expression pattern of egr-1 mRNA and Egr-1 protein in several brain regions following administration of 3, 4-methylenedioxymethamphetamine (MDMA). Furthermore, we also studied the role of N-methyl-D-aspartate (NMDA) receptor, dopamine D(1) receptor, 5-hydroxytryptamine (5-HT) transporter or 5-HT(2A) receptor in the induction of egr-1 mRNA by MDMA. Basal constitutive levels of egr-1 mRNA were detected in control rat brains. A single administration of MDMA (10 mg/kg) caused marked induction of egr-1 mRNA in the prefrontal cortex, striatum and hippocampal dentate gyrus. However, no changes in the egr-1 mRNA levels were detected in the CA1 region of hippocampus and occipital cortex after administration of MDMA (10 mg/kg). Furthermore, the expression of egr-1 mRNA in the prefrontal cortex, striatum and hippocampal dentate gyrus after administration of MDMA (10 mg/kg) was blocked significantly by pretreatment with NMDA receptor antagonist (5R, 10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,b]-cyclohepten-5, 10-imine ((+)-MK801; 1 mg/kg), dopamine D(1) receptor antagonist SCH 23390 (1 mg/kg) or 5-HT uptake inhibitor paroxetine (5 mg/kg), but not by 5-HT(2A) receptor antagonist SR46349B (5 mg/kg). However, high basal levels of Egr-1 immunoreactivity in the rat brain were not altered by administration of MDMA (10 mg/kg). These results suggest that MDMA alters the expression of egr-1 mRNA in several regions of rat brain, and that the expression of egr-1 mRNA by MDMA in the prefrontal cortex, striatum and hippocampal dentate gyrus appears to be mediated, at least in part, by NMDA receptor, dopamine D(1) receptor and 5-HT transporter.     

Differential blocking action of dihydropyridine Ca2+ antagonists on a T-type Ca2+ channel (alpha1G) expressed in Xenopus oocytes

Recent reports show that efonidipine, a dihydropyridine Ca2+ antagonist, has blocking action on T-type Ca2+ channels, which may produce favorable actions on cardiovascular systems. However, the effects of other dihydropyridine Ca2+ antagonists on T-type Ca2+ channels have not been investigated yet. Therefore, in this study, we examined the effects of dihydropyridine compounds clinically used for treatment of hypertension on a T-type Ca2+ channel subtype, alpha1G, expressed in Xenopus oocytes. These effects were compared with those on T-type Ca2+ channel. Rabbit L-type (alpha1Calpha2/deltabeta1a) or rat T-type (alpha1G) Ca2+ channel was expressed in Xenopus oocytes by injection of cRNA for each subunit. The Ba currents through expressed channels were measured by conventional 2-microelectrode voltage-clamp methods. Twelve DHPs (amlodipine, barnidipine, benidipine, cilnidipine, efonidipine, felodipine, manidipine, nicardipine, nifedipine, nilvadipine, nimodipine, nitrendipine) and mibefradil were tested. Cilnidipine, felodipine, nifedipine, nilvadipine, minodipine, and nitrendipine had little effect on the T-type channel. The blocks by drugs at 10 microM were less than 10% at a holding potential of -100 mV. The remaining 6 drugs had blocking action on the T-type channel comparable to that on the L-type channel. The blocking actions were also comparable to that by mibefradil. These results show that many dihydropyridine Ca2+ antagonists have blocking action on the alpha1G channel subtype. The action of dihydropyridine Ca2+ antagonists in clinical treatment should be evaluated on the basis of subtype selectivity.     

Binary combinations of propofol and barbiturates on human alpha(1) glycine receptors expressed in Xenopus oocytes

To test whether there is a common site of action for intravenous anaesthetics at the glycine receptor, the effects of binary combinations of thiopentone, pentobarbitone, methohexitone, and propofol have been tested on human alpha(1) glycine receptors expressed in Xenopus laevis oocytes using two-electrode voltage-clamp techniques. Thiopentone (5-40 microM), pentobarbitone (25-400 microM) and propofol (2-100 microM) (but not methohexitone), potentiated the glycine-induced (50 microM) current in a dose-dependent manner, with the maximum potentiation observed to be 218%, 400%, and 576%, respectively. In binary combination with thiopentone, pentobarbitone or propofol, methohexitone reduced potentiation compared to that by the individual anesthetics to 190%, 260% and 460%, respectively. Combination of thiopentone and pentobarbitone (50 microM) increased potentiation, compared to that by thiopentone alone. Binary combinations of propofol with either thiopentone or pentobarbitone showed more potentiation, compared to that observed with the individual anesthetics. Our results indicate that thiopentone, pentobarbitone and propofol all act as positive allosteric modulators at the alpha(1) glycine receptor. In contrast, methohexitone has no action alone but acts as a competitive antagonist to thiopentone, pentobarbitone and propofol. We suggest that, on the basis of these results, these four intravenous anaesthetics share a common site of action at the glycine receptor.     

Structure-activity relationships for the action of 11 pyrethroid insecticides on rat Na v 1.8 sodium channels expressed in Xenopus oocytes

Pyrethroid insecticides bind to voltage-sensitive sodium channels and modify their gating kinetics, thereby disrupting nerve function. This paper describes the action of 11 structurally diverse commercial pyrethroid insecticides on the rat Na v 1.8 sodium channel isoform, the principal carrier of the tetrodotoxin-resistant, pyrethroid-sensitive sodium current of sensory neurons, expressed in Xenopus laevis oocytes. All 11 compounds produced characteristic sodium tail currents following a depolarizing pulse that ranged from rapidly-decaying monoexponential currents (allethrin, cismethrin and permethrin) to persistent biexponential currents (cyfluthrin, cyhalothrin, cypermethrin and deltamethrin). Tail currents for the remaining compounds (bifenthrin, fenpropathrin, fenvalerate and tefluthrin) were monoexponential and decayed with kinetics intermediate between these extremes. Reconstruction of currents carried solely by the pyrethroid-modified subpopulation of channels revealed two types of pyrethroid-modified currents. The first type, found with cismethrin, allethrin, permethrin and tefluthrin, activated relatively rapidly and inactivated partially during a 40-ms depolarization. The second type, found with cypermethrin, cyfluthrin, cyhalothrin, deltamethrin, fenpropathrin and fenvalerate, activated more slowly and did not detectably inactivate during a 40-ms depolarization. Only bifenthrin did not produce modified currents that fit clearly into either of these categories. In all cases, the rate of activation of modified channels was strongly correlated with the rate of tail current decay following repolarization. Modification of Na v 1.8 sodium channels by cyfluthrin, cyhalothrin, cypermethrin and deltamethrin was enhanced 2.3- to 3.4-fold by repetitive stimulation; this effect appeared to result from the accumulation of persistently open channels rather than preferential binding to open channel states. Fenpropathrin was the most effective compound against Na v 1.8 sodium channels from the perspective of either resting or use-dependent modification. When use dependence is taken into account, cypermethrin, deltamethrin and tefluthrin approached the effectiveness of fenpropathrin. The selective expression of Na v 1.8 sodium channels in nociceptive neurons suggests that these channels may be important targets for pyrethroids in the production of paresthesia following dermal exposure.     

Effects of dextrorotatory morphinans on brain Na+ channels expressed in Xenopus oocytes

We previously demonstrated that dextromethorphan (DM; 3-methoxy-17-methylmorphinan) analogs have neuroprotective effects. Here, we investigated the effects of DM, three of its analogs (DF, 3-methyl-17-methylmorphinan; AM, 3-allyloxy-17-methoxymorphian; and CM, 3-cyclopropyl-17-methoxymorphinan) and one of its metabolites (HM; 3-methoxymorphinan), on Na(+) channel activity. We used the two-microelectrode voltage-clamp technique to test the effects of DM, DF, AM, CM and HM on Na(+) currents (I(Na)) in Xenopus oocytes expressing cRNAs encoding rat brain Nav1.2 alpha and beta1 or beta2 subunits. In oocytes expressing Na(+) channels, DM, DF, AM and CM, but not HM, induced tonic and use-dependent inhibitions of peak I(Na) following low- and high-frequency stimulations. The order of potency for the inhibition of peak I(Na) was AM-CM > DM=DF. The DM, DF, AM and CM-induced tonic inhibitions of peak I(Na) were voltage-dependent, dose-dependent and reversible. The IC(50) values for DM, DF, AM and CM were 116.7+/-14.9, 175.8+/-16.9, 38.6+/-15.5, and 42.5+/-8.5 microM, respectively. DM and its analogs did not affect the steady-state activation and inactivation voltages. AM and CM, but not DM and DF, inhibited the plateau I(Na) more effectively than the peak I(Na) in oocytes expressing inactivation-deficient I1485Q-F1486Q-M1487Q (IFMQ3) mutant channels; the IC(50) values for AM and CM in this system were 8.4+/-1.3 and 8.7+/-1.3 microM, respectively, for the plateau I(Na) and 43.7+/-5.9 and 32.6+/-7.8 microM, respectively, for the peak I(Na). These results collectively indicate that DM and its analogs could be novel Na(+) channel blockers acting on the resting and open states of brain Na(+) channels.     

GABA受体Poly(A)~+mRNA在卵母细胞体内的翻译及其移植受体的生化药理特性

采用SDS/氯仿/苯酚法和oligo(dT)纤维素亲和层析法从胚鸡脑中提取的poly(A)~+mRNA注射到非州爪蟾卵母细胞体内可以成功地被翻译为具有结合功能的GABA受体,并首次用生化方法,包括[~sH]GABA配体结合试验及药物竞争性结合试验证明了卵母细胞膜上移植GABA受体的存在。蛋白质翻译抑制剂三尖杉酯碱可以完全阻断GABA受体的翻译过程。DNA转录抑制剂放线菌素D对这一过程无影响。移植GABA受体具有受体与配体结合的饱和特性,移植GABA受体与[~sH]GABA的结合可以被调变蛋白、蝇蕈醇、双可可碱及异丙基双环磷酸酯所抑制。移植GABA受体与天然鸡脑GABA受体的生化药理学性质基本一致。     

Pharmacological re-evaluation of a GABA(B) receptor antagonist CGP 47332A in rat brain

In rat neocortical slices maintained in Mg(2+)-free Krebs medium, the gamma-aminobutyric acid (GABA(B)) receptor agonist baclofen concentration-dependently depressed the frequency of spontaneous discharges (EC(50)=12 microM). This was reversibly antagonised by (R, S)-3-amino-2-hydroxy-propyl-P-n-butyl-phosphinic acid (CGP 47332A) (25, 100, 300 microM) which produced rightwards shifts of the baclofen concentration-response curves (pA(2) value=4.8+/-0.1). In electrically stimulated slices preloaded with [3H]GABA, CGP 47332A increased its release (EC(150)=100 microM) through antagonism of GABA(B) autoreceptors. Although CGP 47332A was some six times weaker on GABA(B) auto- than on heteroreceptors, yet its congener lacking the beta-hydroxy substituent displays equal potency in both binding (IC(50)=38 microM) and GABA(B) autoreceptor functional studies (EC(150)=38 microM) as previously reported [Froestl, W., Mickel, S.J. , Von Sprecher, G., Diel, P.J., Hall, R.G., Maier, L., Strub, D., Melillo, V., Baumann, P.A., Bernasconi, R., Gentsch, C., Hauser, K., Jaekel, J., Karlsson, G., Klebs, K., Maitre, L., Marescaux, C., Pozza, M.F., Schmutz, M., Steinmann, M.W., Van Riezen, H., Vassout, A., Mondadori, C., Olpe, H.R., Waldmeier, P.C., Bittiger, H., Phosphinic acid analogues of GABA: 2. Selective, orally active GABA(B) antagonists. J. Med. Chem. 38 (1995) 3313-3331.].     

Studies on the transmembrane signalling mechanism of the brain using Xenopus oocytes

Xenopus oocytes have been used as an efficient and convenient expression system of messenger ribonucleic acid (mRNA) exogeneously injected. The transmembrane signalling mechanism of acetylcholine (ACh)- and serotonin (5-HT)-evoked inward current and properties of voltage-sensitive Ca channel (VSCC) current were studied using the oocytes injected with rat brain mRNA. M1 ACh or 5-HT1C receptor stimulation causes Cl- current via G-protein activation, inositol phosphate formation, an increase of free Ca2+ and finally gating of Cl channels via Ca2(+)-calmodulin. Protein kinase C seems to modulate the responses negatively. In addition, N type VSCC was also expressed and regulated by both protein kinases A and C. Limitations of the expression system as well as advantages are discussed.