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Y Uezono

Publications and source records attributed to Y Uezono.

At least 37 records · Page 2Linked to original sources
PubMed1999

Evidence that multiple P2X purinoceptors are functionally expressed in rat supraoptic neurones.

1. The expression, distribution and function of P2X purinoceptors in the supraoptic nucleus (SON) were investigated by reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and Ca2+-imaging and whole-cell patch-clamp techniques, respectively. 2. RT-PCR analysis of all seven known P2X receptor mRNAs in circular punches of the SON revealed that mRNAs for P2X2, P2X3, P2X4, P2X6 and P2X7 receptors were expressed in the SON, and mRNAs for P2X3, P2X4 and P2X7 were predominant. 3. In situ hybridization histochemistry for P2X3 and P2X4 receptor mRNAs showed that both mRNAs were expressed throughout the SON and in the paraventricular nucleus (PVN). 4. ATP caused an increase in [Ca2+]i in a dose-dependent manner with an ED50 of 1.7 x 10-5 M. The effects of ATP were mimicked by ATPgammaS and 2-methylthio ATP (2MeSATP), but not by AMP, adenosine, UTP or UDP. alphabeta-Methylene ATP (alphabetaMeATP) and ADP caused a small increase in [Ca2+]i in a subset of SON neurones. 5. The P2X7 agonist 2'- & 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) at 10-4 M increased [Ca2+]i, but the potency of BzATP was lower than that of ATP. In contrast, BzATP caused a more prominent [Ca2+]i increase than ATP in non-neuronal cells in the SON. 6. The effects of ATP were abolished by extracellular Ca2+ removal or by the P2 antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), and inhibited by extracellular Na+ replacement or another P2 antagonist, suramin, but were unaffected by the P2X7 antagonist oxidized ATP, and the inhibitor of Ca2+-ATPase in intracellular Ca2+ stores cyclopiazonic acid. 7. Two patterns of desensitization were observed in the [Ca2+]i response to repeated applications of ATP: some neurones showed little or moderate desensitization, while others showed strong desensitization. 8. Whole-cell patch-clamp analysis showed that ATP induced cationic currents with marked inward rectification. The ATP-induced currents exhibited two patterns of desensitization similar to those observed in the [Ca2+]i response. 9. The results suggest that multiple P2X receptors, including P2X3, are functionally expressed in SON neurones, and that activation of these receptors induces cationic currents and Ca2+ entry. Such ionic and Ca2+-signalling mechanisms triggered by ATP may play an important role in the regulation of SON neurosecretory cells.

Adenosine↗
PubMed1999

Involvement of PDGF in pressure-induced mesangial cell proliferation through PKC and tyrosine kinase pathways.

In glomerular hypertension, mesangial cells (MC) are subjected to at least two physical forces: mechanical stretch and high transmural pressure. Increased transmural pressure, as well as mechanical stretch, promotes MC proliferation, which may enhance glomerulosclerosis. The exact mechanism of this effect is not fully understood. We examined the effects of transmural pressure alone on cell proliferation and DNA synthesis and investigated the role of platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), candidates for mediation of glomerular diseases, in the pressure-induced events. Pressure was applied to cultured MC placed in a sealed chamber using compressed helium gas. Application of pressure resulted in a time-dependent ( approximately 2 h) and pressure level-dependent (approximately 80 mmHg) increase in cell number (1.4-fold) and [(3)H]thymidine incorporation (2.7-fold). Pressure-induced DNA synthesis was significantly suppressed by inhibitors of phospholipase C (2-nitro-4-carboxyphenyl-N, N-diphenylcarbamate), protein kinase C [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine and chelerythrine], or tyrosine kinases (genistein). Pressure caused a rapid but transient formation of inositol 1,4,5-trisphosphate, which was blocked by the phospholipase C inhibitor. Pressure also promoted a rapid increase in tyrosine kinase activity. Pressure increased mRNA levels of PDGF-B, with a peak at 6 h, but not those of PDGF-A or bFGF. Pressure-induced DNA synthesis was partially inhibited by a neutralizing anti-PDGF antibody but not by an antibody against bFGF or nonimmune IgG. Our results indicated that pressure by itself increases DNA synthesis and proliferation of cultured rat MC possibly through activation of protein kinase C and tyrosine kinases, and PDGF-B could be partially involved in these pathways.

Animals↗
PubMed1999

Adrenomedullin inhibits transmural pressure induced mesangial cell proliferation through activation of protein kinase A.

Adrenomedullin (AM), a hypotensive peptide isolated from human pheochromocytoma, inhibits the proliferation of mesangial cells (MC) induced by mitogens such as platelet-derived growth factor. Quite recently, we have demonstrated that transmural pressure applied to cultured MC increased DNA synthesis and cell proliferation through protein kinase C and tyrosine kinase pathways. However, the modulatory effect of AM on pressure-induced cell proliferation is as yet unknown. In the present study, we examined the effect of AM on transmural pressure-induced DNA synthesis in cultured rat MC. Pressure was applied to cells placed in a sealed chamber using compressed helium. Application of pressure resulted in an increase in [(3)H]thymidine incorporation (approximately 2.0-fold). AM clearly inhibited pressure-induced DNA synthesis in a concentration-dependent manner. This inhibition was paralleled by an increase in cellular cAMP levels evoked by AM. Forskolin and dibutyryl cAMP mimicked the inhibitory effect of AM. The protein kinase A inhibitor H-89 significantly attenuated the effect of AM. Human AM(22-52)-NH(2), a putative AM receptor antagonist, reversed the inhibitory effects of AM more potently than did human CGRP(8-37), a calcitonin gene related peptide receptor antagonist. Our results suggest that AM, by acting mainly on AM-sensitive receptors, inhibits pressure-induced DNA synthesis in cultured rat MC through activation of protein kinase A. AM may play a protective role against MC proliferation in certain pathological conditions.

Adrenomedullin↗
PubMed1999

Propofol inhibits muscarinic acetylcholine receptor-mediated signal transduction in Xenopus Oocytes expressing the rat M1 receptor.

The effects of propofol, 2,6-diisopropylphenol, an intravenous general anesthetic, on signal transduction mediated by the rat M1 muscarinic acetylcholine (ACh) receptor (M1 receptor) were examined in electrophysiological studies by analyzing receptor-stimulated, Ca2+-activated Cl--current responses in the Xenopus oocyte expression system. In oocytes expressing the M1 receptor, ACh induced the Ca2+-activated C1- current, in a dose-dependent manner (EC50= 114 nM). Propofol (5-50 microM) reversibly and dose-dependently inhibited induction of the Ca2+-activated Cl- current by ACh (100 nM) (IC50=5.6 microM). To determine a possible site affected by propofol in this signal transduction, we tested the effects of this anesthetic (10 microM) on the activation of current by injection of CaCl2 and aluminum fluoride (AlF4-). Propofol did not affect activation of the current by the intracellular injected Ca2+, or activation of the current by the intracellular injected AlF4-. These results indicate that propofol does not affect G protein, the inositol phosphate turnover, release of Ca2+ from Ca2+ store or the Ca2+-activated Cl- channel. Propofol apparently inhibits the M1 receptor-mediated signal transduction at the receptor site and/or the site of interaction between the receptor and associated G protein.

Acetylcholine↗
PubMed1999

Prostaglandin E2 induces Ca2+ release from ryanodine/caffeine-sensitive stores in bovine adrenal medullary cells via EP1-like receptors.

Prostaglandin E2 (PGE2) causes Ca2+ release from intracellular Ca2+ stores and stimulates phosphoinositide metabolism in bovine adrenal medullary cells. These results have been interpreted as PGE2 induces Ca2+ release from inositol trisphosphate (IP3)-sensitive stores. However, we have recently shown that pituitary adenylate cyclase-activating polypeptide (PACAP), bradykinin, and angiotensin II release Ca2+ from caffeine/ryanodine-sensitive stores, although they cause a concomitant increase of intracellular IP3. In light of these results, the mechanism of PGE2-induced Ca2+ release was investigated in the present study. PGE2 dose-dependently caused a transient but consistent Ca2+ release from internal Ca2+ stores. The PGE2-induced Ca2+ release was unaffected by cinnarizine, a blocker of IP3-induced Ca2+ release. By contrast, it was potently inhibited by prior application of caffeine and ryanodine. Although IP3 production in response to PGE2 was abolished by the phospholipase C inhibitor U-73122, Ca2+ release in response to PGE2 was unaffected by U-73122. The PGE2-induced Ca2+ release was unaffected by Rp-adenosine 3',5'-cyclic monophosphothioate, an inhibitor of protein kinase A, and forskolin, a cyclic AMP (cAMP)-elevating agent, did not cause Ca2+ release. The EP1 agonist 17-phenyl-trinorPGE2 and the EP1/EP3 agonist sulprostone mimicked the Ca(2+)-releasing effects of PGE2, whereas the EP2 agonist butaprost or the EP2/EP3 agonist misoprostol caused little or no Ca2+ release. The EP1 antagonist SC-51322 significantly suppressed the Ca2+ release response induced by PGE2, whereas the EP4 antagonist AH-23828B had little effect. These results suggest that PGE2, acting on EP1-like receptors, induces Ca2+ release from ryanodine/caffeine-sensitive stores through a mechanism independent of IP3 and cAMP and that PGE2 may share the same mechanism with PACAP and the other peptide ligands in causing Ca2+ release in bovine adrenal medullary cells.

Adrenal Medulla↗
PubMed1999

Coupling of the expressed cannabinoid CB1 and CB2 receptors to phospholipase C and G protein-coupled inwardly rectifying K+ channels.

Signaling of the cannabinoid CB1 and CB2 receptors through phospholipase C (PLC) and G protein-coupled inwardly rectifying K+ channels (GIRK) was studied after their expression in COS7 cells and Xenopus oocytes. The CB1 or CB2 receptor was co-expressed with alpha subunits of the Galphaq family (Galphaq, Galpha11, Galpha14, Galpha15 and Galpha16) in COS7 cells. Receptor-dependent activation of PLC was observed after co-expressing the CB1 receptor with Galpha14, Galpha15 or Galpha16 but not with Galphaq or Galpha11. Co-expression of Gbeta1 and Ggamma2 abolished the activation, indicating that the activation was mediated by Galpha. PLC activation was not observed when the CB2 receptor was expressed alone or co-expressed with any of the above Galpha subunits. Coupling to GIRK was observed with both CB1 and CB2 receptors after expression in Xenopus oocytes. Significantly larger currents were induced when the receptor was co-expressed with both GIRK1 and GIRK4 than with either GIRK alone. Co-expression of Galpha transducin with the receptor significantly reduced the K+ currents, indicating that GIRK activation was mediated by Gbetagamma but not by Galpha. These findings suggest two new signaling pathways for the cannabinoid receptors.

Animals↗
PubMed1998

Cloning and tissue distribution of novel splice variants of the rat GABAB receptor.

We have identified two novel splice variants of the metabotropic gamma-aminobutyric acid receptor (GABABR1), designated GABABR1c and GABABR1d, when screening a rat cerebellum cDNA library. GABABR1c has an amino acid sequence identical to GABABR1b, a member of GABABR1 isoforms, and an additional 93-bp insertion that generates an additional 31-amino-acid sequence in the fifth transmembrane region of GABABR1b. Thus, GABABR1c may have a structural variation in the second extracellular loop and fifth transmembrane region. GABABR1d also has an amino acid sequence identical to GABABR1b and an additional insertion of 566 bp that generates a divergent amino acid sequence in the carboxylterminal end. Reverse-transcription polymerase chain reaction analysis showed that in various rat tissues GABABR1c mRNA was ubiquitously expressed and GABABR1d mRNA in forebrain, cerebellum, eye, kidney, and urinary bladder. GABABR1 isoforms may function not only in the central nervous system but also in various peripheral tissues.

Alternative Splicing↗
PubMed1998

Adrenomedullin increases intracellular Ca2+ and inositol 1,4,5-trisphosphate in human oligodendroglial cell line KG-1C.

The effects of adrenomedullin (AM), a hypotensive peptide, were investigated in cultured human oligodendroglial cell line KG-1C. Human AM increased the intracellular Ca2+ concentration ([Ca2+]i) at concentrations greater than 10(-7) M. Human calcitonin gene-related peptide (CGRP), a peptide structurally related to AM, also increased [Ca2+]i with a potency similar to that of AM. AM increased [Ca2+]i in the absence of extracellular Ca2+. Further, AM increased inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) level in a concentration-dependent manner similar to that of AM-induced [Ca2+]i, suggesting that AM-induced elevation of [Ca2+]i is due to Ca2+ release from Ins(1,4,5)P3-sensitive stores. AM (10(-9) to 10(-6) M) increased cAMP in a concentration-dependent manner. Forskolin also increased cAMP, but did not mimic the [Ca2+]i-raising effect of AM. These findings suggest that functional AM receptors are present in oligodendroglial KG-1C cells and that AM increases [Ca2+]i through a mechanism independent of cAMP.

Adrenomedullin↗
PubMed1998

Activation of inwardly rectifying K+ channels by GABA-B receptors expressed in Xenopus oocytes.

In Xenopus oocytes coinjected with poly(A)+ RNA derived from the rat cerebellum and cRNAs for the cloned G protein-gated inwardly rectifying K+ channel (GIRK), GIRK1 and GIRK2, the GABA-B agonist baclofen elicited inwardly rectifying K+ currents. The inward K+ currents elicited by baclofen were inhibited by the selective GABA-B antagonists 2-OH saclofen and CGP 35348, and by the GIRK inhibitor Ba2+. In contrast, baclofen caused no currents in oocytes injected with the cerebellar poly(A)+ RNA alone, the poly(A)+ RNA and cRNA for GIRK1 or GIRK2, or only cRNAs for GIRK1 and GIRK2. These findings indicate that GABA-B receptors in the rat cerebellum were functionally expressed in Xenopus oocytes and activated the cloned GIRKs composed of GIRK1 and GIRK2 as heteromultimers.

Animals↗
PubMed1998

Stimulatory effect of lymphocyte-derived factor on catecholamine efflux from cultured bovine adrenal medullary cells.

The effects of lymphocytes and their conditioned medium on catecholamine efflux and uptake were examined in cultured bovine adrenal medullary cells. Co-culture of adrenal medullary cells with lymphocytes for 3 days caused an increase in appearance of catecholamines in the culture medium. Treatment of adrenal medullary cells with a conditioned medium prepared from lymphocytes also enhanced the appearance of catecholamines in culture medium in time- (8-48 h) and concentration-dependent manners. Heat treatment of the conditioned medium at 60 and 100 degrees C for 10 min reduced its stimulatory effect to 59 and 20% of control, respectively. After gel filtration on a Sephadex G-25 column or dialysis (<8 kDa molecular mass cutoff), the stimulatory activity of the conditioned medium was found in a high molecular fraction. The conditioned medium had little effect on the activity of lactate dehydrogenase in the medium of cultured adrenal medullary cells and on desipramine-sensitive [3H]norepinephrine uptake by the cells. These findings suggest that lymphocytes release a heat-sensitive factor(s) (molecular mass of more than 8 kDa) which increases efflux of catecholamines from cultured adrenal medullary cells.

Adrenal Medulla↗
PubMed1998

Function of the rat calcitonin receptors, C1a and C1b, expressed in Xenopus oocytes.

The function of the cloned rat calcitonin receptors, C1a and C1b, was studied in Xenopus oocytes using the two-electrode voltage clamp method. In oocytes expressing the C1a receptors and the cystic fibrosis transmembrane conductance regulator (CFTR), C1a/ CFTR, application (30 sec) of either salmon calcitonin (sCT) or human calcitonin (hCT) activated currents through CFTR. In C1b/CFTR, sCT activated the currents, whereas hCT failed to elicit a response. The sCT induced currents in C1a/CFTR were similar in size to those in C1b/CFTR. Both the activation and the deactivation of sCT-induced currents were slower in C1a/ CFTR. In oocytes expressing C1a or C1b alone, application of relatively high concentrations of sCT induced small oscillatory inward currents. Application of hCT induced small inward currents in C1a alone, but failed to activate currents in C1b alone. These results demonstrate new insights into the signal transduction of calcitonin receptors.

Adenylyl Cyclases↗
PubMed1998

Transmural compression-induced proliferation and DNA synthesis through activation of a tyrosine kinase pathway in rat astrocytoma RCR-1 cells.

Gliosis results from abnormal proliferation of glial cells and often occurs in response to brain or spinal cord injury. There are many factors that trigger gliosis associated with such injuries, including ischemia, humoral factors produced by the injured tissue, and possibly mechanical compression itself. In the present study, the effects of mechanical compression on cell proliferation and DNA synthesis were examined in vitro with the rat astrocyte cell line RCR-1. Pressure was applied to cells by instilling compressed helium into sealed plates or flasks in which the partial pressure of oxygen were maintained constant. Compression resulted in time- and intensity-dependent increases in cell number and [3H]thymidine incorporation, with maximum effects apparent at 10 min and 120 mmHg. Compression-induced cell proliferation and DNA synthesis were not inhibited by gadolinium (Gd3+), a blocker of stretch-activated ion channels, or by inhibitors of protein kinase A, protein kinase C, or Ca2+/calmodulin-dependent protein kinases. However, the tyrosine kinase inhibitor genistein inhibited these effects of compression in a concentration-dependent manner. Conditioned medium from compressed cells also induced cell proliferation and DNA synthesis at atmospheric pressure in a genistein-sensitive manner. These results suggest that transmural compression triggers the release of a factor (or factors) that induces cell proliferation and DNA synthesis through a tyrosine kinase pathway in RCR-1 cells.

Animals↗
PubMed1998

An active metabolite of carbamazepine, carbamazepine-10,11-epoxide, inhibits ion channel-mediated catecholamine secretion in cultured bovine adrenal medullary cells.

We have recently reported inhibitory effects of carbamazepine (CBZ) on ion channel-mediated secretion of catecholamines in bovine adrenal medullary cells. Here, we report the effects of carbamazepine-10,11-epoxide (CBZ-E), an active metabolite of CBZ, and carbamazepine-10,11-diol (CBZ-D), a non-active metabolite, on 22Na+ influx, 45Ca2+ influx and catecholamine secretion in cultured adrenal medullary cells. CBZ-E, but not CBZ-D inhibited 22Na+ influx, 45Ca2+ influx and catecholamine secretion induced by carbachol or veratridine with a half-maximal inhibitory concentration (IC50) of 0.26 or 0.68 microg/ml, respectively. CBZ-E also inhibited high K+-evoked 45Ca2+ influx and catecholamine secretion (IC50 = 0.3 microg/ml), but CBZ-D did not. These findings suggest that CBZ-E, but not CBZ-D, attenuates catecholamine secretion by inhibiting nicotinic acetylcholine receptor-associated ion channels, voltage-dependent Na+ channels and voltage-dependent Ca2+ channels in the cells. This inhibition of CBZ-E as well as CBZ may be related to the clinical effects in neuropsychiatric disorders.

Adrenal Medulla↗
PubMed1998

Down-regulation of the noradrenaline transporter by interferon-alpha in cultured bovine adrenal medullary cells.

The aim of this study was to investigate the effect of long-term treatment with interferon (IFN)-alpha on the noradrenaline transporter of bovine adrenal medullary cells. Treatment of cultured adrenal medullary cells with IFN-alpha caused a decrease in uptake of [3H]noradrenaline by the cells in time (4-48 h)- and concentration (300-1,000 U/ml)-dependent manners. IFN-beta also inhibited [3H]noradrenaline uptake to a lesser extent than did IFN-alpha, whereas IFN-gamma had little effect. An anti-IFN-alpha antibody reduced the effect of IFN-alpha on [3H]noradrenaline uptake. Saturation analysis of [3H]noradrenaline uptake showed that the inhibitory effect of IFN-alpha was due to a reduction in the maximal uptake velocity (Vmax) values without altering apparent Michaelis constant (Km) values. Incubation of cells with IFN-alpha caused a translocation of protein kinase C from the soluble to the particulate fraction in the cells. The effect of IFN-alpha on [3H]noradrenaline uptake was diminished in protein kinase C-down-regulated cells. Incubation of cells with IFN-alpha for 48 h significantly reduced the specific binding of [3H]desipramine to crude plasma membranes isolated from cells. Scatchard analysis of [3H]desipramine binding revealed that IFN-alpha decreased the maximal binding (Bmax) values without any change in the dissociation constant (K(D)) values. These findings suggest that IFN-alpha suppresses the function of noradrenaline transporter by reducing the density of the transporter in cell membranes through, at least in part, a protein kinase C pathway.

Adrenal Medulla↗
PubMed1998

Pituitary adenylate cyclase-activating polypeptide causes Ca2+ release from ryanodine/caffeine stores through a novel pathway independent of both inositol trisphosphates and cyclic AMP in bovine adrenal medullary cells.

Pituitary adenylate cyclase-activating polypeptide (PACAP) causes both Ca2+ release and Ca2+ influx in bovine adrenal chromaffin cells. To elucidate the mechanisms of PACAP-induced Ca2+ release, we investigated expression of PACAP receptors and measured inositol trisphosphates (IP3), cyclic AMP, and the intracellular Ca2+ concentration in bovine adrenal medullary cells maintained in primary culture. RT-PCR analysis revealed that bovine adrenal medullary cells express the PACAP receptor hop, which is known to couple with both IP3 and cyclic AMP pathways. The two naturally occurring forms of PACAP, PACAP38 and PACAP27, both increased cyclic AMP and IP3, and PACAP38 was more potent than PACAP27 in both effects. Despite the effects of PACAP on IP3 production, the Ca2+ release induced by PA-CAP38 or by PACAP27 was unaffected by cinnarizine, a blocker of IP3 channels. The potencies of the peptides to cause Ca2+ release in the presence of cinnarizine were similar. The Ca2+ release induced by PACAP38 or by PACAP27 was strongly inhibited by ryanodine and caffeine. In the presence of ryanodine and caffeine, PACAP38 was more potent than PACAP27. PACAP-induced Ca2+ release was unaffected by Rp-adenosine 3',5'-cyclic monophosphothioate, an inhibitor of protein kinase A. Ca2+ release induced by bradykinin and angiotensin II was also inhibited by ryanodine and caffeine, but unaffected by cinnarizine. Although IP3 production stimulated by PACAP38 or bradykinin was abolished by the phospholipase C inhibitor, U-73122, Ca2+ release in response to the peptides was unaffected by U-73122. These results suggest that PACAP induces Ca2+ release from ryanodine/caffeine stores through a novel intracellular mechanism independent of both IP3 and cyclic AMP and that the mechanism may be the common pathway through which peptides release Ca2+ in adrenal chromaffin cells.

Adrenal Medulla↗
PubMed1998

Carbamazepine-induced up-regulation of voltage-dependent Na+ channels in bovine adrenal medullary cells in culture.

Treatment of cultured bovine adrenal medullary cells with carbamazepine (CBZ) for 5 days caused an increase in catecholamine secretion induced by veratridine, an activator of voltage-dependent Na+ channels. However, no increase was stimulated by carbachol, an agonist of nicotinic receptors, or by 56 mM K+, a depolarizing agent that activates voltage-dependent Ca++ channels. CBZ (30 microg/ml) treatment enhanced veratridine-induced catecholamine secretion in a time-dependent manner (increases of 25%, 65% and 70% for 3, 5 and 7 days of treatment, respectively). CBZ treatment (5 days) increased veratridine-induced catecholamine secretion in a concentration-dependent manner (increases of 27%, 36%, 45% and 55% at 10, 15, 20 and 30 microgram/ml of CBZ, respectively). CBZ treatment also increased 22Na+ influx and 45Ca++ influx stimulated by veratridine. The stimulatory effect of CBZ treatment on catecholamine secretion was blocked by either actinomycin D or cycloheximide, an inhibitor of protein synthesis. Additive responses of catecholamine secretion and 22Na+ influx induced by veratridine were associated with combined exposure of the cells to CBZ and dibutyryl cyclic AMP. CBZ treatment (30 microg/ml, 5 days) significantly increased the specific binding of [3H]saxitoxin to cell membranes. A Scatchard analysis of [3H]saxitoxin binding revealed that CBZ increased the Bmax value without any change in the dissociation constant. These findings suggest that CBZ up-regulates the density and activity of voltage-dependent Na+ channels.

Adrenal Medulla↗
PubMed1997

Enhancement by baclofen of the Gs-coupled receptor-mediated cAMP production in Xenopus oocytes expressing rat brain cortex poly (A)+ RNA: a role of G-protein beta gamma subunits.

We investigated the mechanism by which GABA-B receptors enhance the Gs-coupled receptor-mediated cAMP production in Xenopus oocytes expressing poly (A)+ RNA derived from rat brain cortex. We expressed the cystic fibrosis transmembrane conductance regulator gene (CFTR) as a reporter for cAMP changes in oocytes. The GABA-B agonist (-)baclofen enhanced the adrenergic beta 2 agonist isoproterenol- or vasoactive intestinal peptide (VIP)-induced CFTR currents, whereas (-)baclofen alone did not cause any currents. The (-)baclofen-enhanced currents were inhibited by the GABA-B antagonist 2-OH saclofen. The enhancement by (-)baclofen was further augmented by coexpressing adenylyl cyclase (AC) type II, an isotype activated by G beta gamma and G alpha s, but not by coexpressing AC type III, an isotype insensitive to G beta gamma. Moreover, pretreatment of the oocytes with pertussis toxin (PTX) abolished the enhanced effect of (-)baclofen. These results indicate that upon GABA-B activation, the G beta gamma released from PTX-sensitive G-proteins activates the AC type II (or IV), and this process requires the G alpha s activation by Gs-coupled receptors.

Adrenergic beta-Agonists↗