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Sex-specific I KAS activation in rabbit ventricles with drug-induced QT prolongation. Heart Rhythm 2020; 18:88-97. [PMID: 32707174 DOI: 10.1016/j.hrthm.2020.07.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2020] [Revised: 06/30/2020] [Accepted: 07/13/2020] [Indexed: 01/23/2023]
Abstract
BACKGROUND Female sex is a known risk factor for drug-induced long QT syndrome (diLQTS). We recently demonstrated a sex difference in apamin-sensitive small-conductance Ca2+-activated K+ current (IKAS) activation during β-adrenergic stimulation. OBJECTIVE The purpose of this study was to test the hypothesis that there is a sex difference in IKAS in the rabbit models of diLQTS. METHODS We evaluated the sex difference in ventricular repolarization in 15 male and 22 female Langendorff-perfused rabbit hearts with optical mapping techniques during atrial pacing. HMR1556 (slowly activating delayed rectifier K+ current [IKs] blocker), E4031 (rapidly activating delayed rectifier K+ current [IKr] blocker) and sea anemone toxin (ATX-II, late Na+ current [INaL] activator) were used to simulate types 1-3 long QT syndrome, respectively. Apamin, an IKAS blocker, was then added to determine the magnitude of further QT prolongation. RESULTS HMR1556, E4031, and ATX-II led to the prolongation of action potential duration at 80% repolarization (APD80) in both male and female ventricles at pacing cycle lengths of 300-400 ms. Apamin further prolonged APD80 (pacing cycle length 350 ms) from 187.8±4.3 to 206.9±7.1 (P=.014) in HMR1556-treated, from 209.9±7.8 to 224.9±7.8 (P=.003) in E4031-treated, and from 174.3±3.3 to 188.1±3.0 (P=.0002) in ATX-II-treated female hearts. Apamin did not further prolong the APD80 in male hearts. The Cai transient duration (CaiTD) was significantly longer in diLQTS than baseline but without sex differences. Apamin did not change CaiTD. CONCLUSION We conclude that IKAS is abundantly increased in female but not in male ventricles with diLQTS. Increased IKAS helps preserve the repolarization reserve in female ventricles treated with IKs and IKr blockers or INaL activators.
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Effects of ondansetron on apamin-sensitive small conductance calcium-activated potassium currents in pacing-induced failing rabbit hearts. Heart Rhythm 2019; 17:332-340. [PMID: 31513946 DOI: 10.1016/j.hrthm.2019.09.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Indexed: 12/16/2022]
Abstract
BACKGROUND Ondansetron, a widely prescribed antiemetic, has been implicated in drug-induced long QT syndrome. Recent patch clamp experiments have shown that ondansetron inhibits the apamin-sensitive small conductance calcium-activated potassium current (IKAS). OBJECTIVE The purpose of this study was to determine whether ondansetron causes action potential duration (APD) prolongation by IKAS inhibition. METHODS Optical mapping was performed in rabbit hearts with pacing-induced heart failure (HF) and in normal hearts before and after ondansetron (100 nM) infusion. APD at 80% repolarization (APD80) and arrhythmia inducibility were determined. Additional studies with ondansetron were performed in normal hearts perfused with hypokalemic Tyrode's (2.4 mM) solution before or after apamin administration. RESULTS The corrected QT interval in HF was 326 ms (95% confidence interval [CI] 306-347 ms) at baseline and 364 ms (95% CI 351-378 ms) after ondansetron infusion (P < .001). Ondansetron significantly prolonged APD80 in the HF group and promoted early afterdepolarizations, steepened the APD restitution curve, and increased ventricular vulnerability. Ventricular fibrillation was not inducible in HF ventricles at baseline, but after ondansetron infusion, ventricular fibrillation was induced in 5 of the 7 ventricles (P = .021). In hypokalemia, apamin prolonged APD80 from 163 ms (95% CI 146-180 ms) to 180 ms (95% CI 156-204 ms) (P = .018). Subsequent administration of ondansetron failed to further prolong APD80 (180 ms [95% CI 156-204 ms] vs 179 ms [95% CI 165-194 ms]; P = .789). The results were similar when ondansetron was administered first, followed by apamin. CONCLUSION Ondansetron is a specific IKAS blocker at therapeutic concentrations. Ondansetron may prolong the QT interval in HF by inhibiting small conductance calcium-activated potassium channels, which increases the vulnerability to ventricular arrhythmias.
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Concomitant SK current activation and sodium current inhibition cause J wave syndrome. JCI Insight 2018; 3:122329. [PMID: 30429367 DOI: 10.1172/jci.insight.122329] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2018] [Accepted: 07/17/2018] [Indexed: 12/18/2022] Open
Abstract
The mechanisms of J wave syndrome (JWS) are incompletely understood. Here, we showed that the concomitant activation of small-conductance calcium-activated potassium (SK) current (IKAS) and inhibition of sodium current by cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA) recapitulate the phenotypes of JWS in Langendorff-perfused rabbit hearts. CyPPA induced significant J wave elevation and frequent spontaneous ventricular fibrillation (SVF), as well as sinus bradycardia, atrioventricular block, and intraventricular conduction delay. IKAS activation by CyPPA resulted in heterogeneous shortening of action potential (AP) duration (APD) and repolarization alternans. CyPPA inhibited cardiac sodium current (INa) and decelerated AP upstroke and intracellular calcium transient. SVFs were typically triggered by short-coupled premature ventricular contractions, initiated with phase 2 reentry and originated more frequently from the right than the left ventricles. Subsequent IKAS blockade by apamin reduced J wave elevation and eliminated SVF. β-Adrenergic stimulation was antiarrhythmic in CyPPA-induced electrical storm. Like CyPPA, hypothermia (32.0°C) also induced J wave elevation and SVF. It facilitated negative calcium-voltage coupling and phase 2 repolarization alternans with spatial and electromechanical discordance, which were ameliorated by apamin. These findings suggest that IKAS activation contributes to the development of JWS in rabbit ventricles.
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Phospholamban regulates nuclear Ca 2+ stores and inositol 1,4,5-trisphosphate mediated nuclear Ca 2+ cycling in cardiomyocytes. J Mol Cell Cardiol 2018; 123:185-197. [PMID: 30261161 DOI: 10.1016/j.yjmcc.2018.09.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 09/04/2018] [Accepted: 09/21/2018] [Indexed: 01/15/2023]
Abstract
AIMS Phospholamban (PLB) is the key regulator of the cardiac Ca2+ pump (SERCA2a)-mediated sarcoplasmic reticulum Ca2+ stores. We recently reported that PLB is highly concentrated in the nuclear envelope (NE) from where it can modulate perinuclear Ca2+ handling of the cardiomyocytes (CMs). Since inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) mediates nuclear Ca2+ release, we examined whether the nuclear pool of PLB regulates IP3-induced nuclear Ca2+ handling. METHODS AND RESULTS Fluo-4 based confocal Ca2+ imaging was performed to measure Ca2+ dynamics across both nucleus and cytosol in saponin-permeabilized CMs isolated from wild-type (WT) or PLB-knockout (PLB-KO) mice. At diastolic intracellular Ca2+ ([Ca2+]i = 100 nM), the Fab fragment of the monoclonal PLB antibody (anti-PLB Fab) facilitated the formation and increased the length of spontaneous Ca2+ waves (SCWs) originating from the nuclear region in CMs from WT but not from PLB-KO mice. We next examined nuclear Ca2+ activities at basal condition and after sequential addition of IP3, anti-PLB Fab, and the IP3R inhibitor 2-aminoethoxydiphenyl borate (2-APB) at a series of [Ca2+]i. In WT mice, at 10 nM [Ca2+]i where ryanodine receptor (RyR2) based spontaneous Ca2+ sparks rarely occurred, IP3 increased fluorescence amplitude (F/F0) of overall nuclear region to 1.19 ± 0.02. Subsequent addition of anti-PLB Fab significantly decreased F/F0 to 1.09 ± 0.02. At 50 nM [Ca2+]i, anti-PLB Fab not only decreased the overall nuclear F/F0 previously elevated by IP3, but also increased the amplitude and duration of spark-like nuclear Ca2+ release events. These nuclear Ca2+ releases were blocked by 2-APB. At 100 nM [Ca2+]i, IP3 induced short SCWs originating from nucleus. Anti-PLB Fab transformed those short waves into long SCWs with propagation from the nucleus into the cytosol. In contrast, neither nuclear nor cytosolic Ca2+ dynamics was affected by anti-PLB Fab in CMs from PLB-KO mice in all these conditions. Furthermore, in WT CMs pretreated with RyR2 blocker tetracaine, IP3 and anti-PLB Fab still increased the magnitude of nuclear Ca2+ release but failed to regenerate SCWs. Finally, anti-PLB Fab increased low Ca2+ affinity mag-fluo 4 fluorescence intensity in the lumen of NE of nuclei isolated from WT but not in PLB-KO mice. CONCLUSION PLB regulates nuclear Ca2+ handling. By increasing Ca2+ uptake into lumen of the NE and perhaps other perinuclear membranes, the acute reversal of PLB inhibition decreases global Ca2+ concentration at rest in the nucleoplasm, and increases Ca2+ release into the nucleus, through mechanisms involving IP3R and RyR2 in the vicinity.
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Role of apamin-sensitive small conductance calcium-activated potassium currents in long-term cardiac memory in rabbits. Heart Rhythm 2018; 15:761-769. [PMID: 29325977 DOI: 10.1016/j.hrthm.2018.01.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Indexed: 12/13/2022]
Abstract
BACKGROUND Apamin-sensitive small conductance calcium-activated K current (IKAS) is up-regulated during ventricular pacing and masks short-term cardiac memory (CM). OBJECTIVE The purpose of this study was to determine the role of IKAS in long-term CM. METHODS CM was created with 3-5 weeks of ventricular pacing and defined by a flat or inverted T wave off pacing. Epicardial optical mapping was performed in both paced and normal ventricles. Action potential duration (APD80) was determined during right atrial pacing. Ventricular stability was tested before and after IKAS blockade. Four paced hearts and 4 normal hearts were used for western blotting and histology. RESULTS There were no significant differences in either echocardiographic parameters or fibrosis levels between groups. Apamin induced more APD80 prolongation in CM than in normal ventricles (mean [95% confidence interval]: 9.6% [8.8%-10.5%] vs 3.1% [1.9%-4.3%]; P <.001). Apamin significantly lengthened APD80 in the CM model at late activation sites, indicating significant IKAS up-regulation at those sites. The CM model also had altered Ca2+ handling, with the 50% Ca2+ transient duration and amplitude increased at distal sites compared to a proximal site (near the pacing site). After apamin, the CM model had increased ventricular fibrillation (VF) inducibility (paced vs control: 33/40 (82.5%) vs 7/20 (35%); P <.001) and longer VF durations (124 vs 26 seconds; P <.001). CONCLUSION Chronic ventricular pacing increases Ca2+ transients at late activation sites, which activates IKAS to maintain repolarization reserve. IKAS blockade increases VF vulnerability in chronically paced rabbit ventricles.
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The effect of green tea extract on the removal of sulfur-containing oral malodor volatiles in vitro and its potential application in chewing gum. J Breath Res 2010; 4:036005. [PMID: 21383482 DOI: 10.1088/1752-7155/4/3/036005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Increasing pH solution from 7.5 to 8.0 was found to significantly improve the effectiveness of green tea extract for methanethiol removal in vitro. Green tea extract was also found to remove hydrogen sulfide and its effectiveness was greatly improved under alkaline conditions. It was found that with green tea extract, maximum H₂S removal was achieved when the pH was between 8.1 and 8.4 at 37 °C for 5 min. Further increases in pH resulted in decrease of the extract effectiveness. Vegetable acetone powders which contain polyphenol oxidases or peroxidases were found to further enhance the effectiveness for the removal of thiols when used in combination with green tea extracts at body temperature under alkaline conditions. Adding 5% baking soda to green tea extract-containing chewing gum was found to buffer saliva pHs to 8.0 during 10 min of chewing. However, severe discoloration was observed and undesirable bitterness was perceived, most likely due to the polymerization of unencapsulated green tea polyphenols. Therefore, encapsulation of green tea extract is recommended for applications at elevated pHs.
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Abstract
Bioactive lysophospholipids (LPLs) are released by blood cells and can modulate many cellular activities such as angiogenesis and cell survival. In this study, the effects of sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA) on excitability and exocytosis in bovine chromaffin cells were investigated using the whole-cell configuration of the patch-clamp. Voltage-gated Ca(2+) current was inhibited by S1P and LPA pre-treatment in a concentration-dependent manner with IC(50)s of 0.46 and 0.79 mumol/L, respectively. Inhibition was mostly reversible upon washout and prevented by suramin, an inhibitor of G-protein signaling. Na(+) current was inhibited by S1P, but not by LPA. However, recovery of Na(+) channels from inactivation was slowed by both LPLs. The outward K(+) current was also significantly reduced by both LPLs. Chromaffin cells fired repetitive action potentials in response to minimal injections of depolarizing current. Repetitive activity was dramatically reduced by LPLs. Consistent with the reduction in Ca(2+) current, exocytosis elicited by a train of depolarizations and the ensuing endocytosis were both inhibited by LPL pre-treatments. These data demonstrate the interaction between immune and endocrine systems mediated by the inhibitory effects of LPLs on the excitability of adrenal chromaffin cells.
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Identification of two types of ATP-sensitive K+ channels in rat ventricular myocytes. Life Sci 2006; 80:378-87. [PMID: 17097686 DOI: 10.1016/j.lfs.2006.09.042] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2006] [Revised: 09/18/2006] [Accepted: 09/20/2006] [Indexed: 11/24/2022]
Abstract
The ATP-sensitive K(+) (K(ATP)) channels are known to provide a functional linkage between the electrical activity of the cell membrane and metabolism. Two types of inwardly rectifying K(+) channel subunits (i.e., Kir6.1 and Kir6.2) with which sulfonylurea receptors are associated were reported to constitute the K(ATP) channels. In this study, we provide evidence to show two types of K(ATP) channels with different biophysical properties functionally expressed in isolated rat ventricular myocytes. Using patch-clamp technique, we found that single-channel conductance for the different two types of K(ATP) channels in these cells was 57 and 21 pS. The kinetic properties, including mean open time and bursting kinetics, did not differ between these two types of K(ATP) channels. Diazoxide only activated the small-conductance K(ATP) channel, while pinacidil and dinitrophenol stimulated both channels. Both of these K(ATP) channels were sensitive to block by glibenclamide. Additionally, western blotting, immunochemistry, and RT-PCR revealed two types of Kir6.X channels, i.e., Kir6.1 and Kir6.2, in rat ventricular myocytes. Single-cell Ca(2+) imaging also revealed that similar to dinitrophenol, diazoxide reduced the concentration of intracellular Ca(2+). The present results suggest that these two types of K(ATP) channels may functionally be related to the activity of heart cells.
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MESH Headings
- Animals
- Blotting, Western
- Calcium/metabolism
- Diazoxide/pharmacology
- Dinitrophenols/pharmacology
- Dose-Response Relationship, Drug
- Fluorescent Antibody Technique, Direct
- Gene Expression/drug effects
- Glyburide/pharmacology
- Heart Ventricles/drug effects
- Heart Ventricles/metabolism
- Heart Ventricles/pathology
- KATP Channels
- Male
- Membrane Potentials/drug effects
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/pathology
- Patch-Clamp Techniques
- Pinacidil/pharmacology
- Potassium Channels, Inwardly Rectifying/drug effects
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/metabolism
- RNA, Messenger/metabolism
- Rats
- Rats, Sprague-Dawley
- Reverse Transcriptase Polymerase Chain Reaction
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Abstract
The gating of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channel is primarily controlled by intracellular Ca(2+) and/or membrane depolarization. These channels play a role in the coupling of excitation-contraction and stimulus-secretion. A variety of structurally distinct compounds may influence the activity of these channels. Squamocin, an Annonaceous acetogenin, could interact with the BK(Ca) channel to increase the amplitude of Ca(2+)-activated K(+) current in coronary smooth muscle cells. Its stimulatory effect is related to intracellular Ca(2+) concentrations. In inside-out patches, application of ceramide to the bath suppressed the activity of BK(Ca) channels recorded from pituitary GH(3) cells and from retinal pigment epithelial cells. ICI-182,780, an estrogen receptor antagonist, was found to modulate BK(Ca)-channel activity in cultured endothelial cells and smooth muscle cells in a mechanism unlinked to the inhibition of estrogen receptors. Caffeic acid phenethyl ester (CAPE) and its analogy, cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate, could directly increase the activity of BK(Ca) channels in GH(3) cells. CAPE also reduced the frequency and amplitude of intracellular Ca(2+) oscillations in these cells. The CAPE-stimulated activity in BK(Ca) channels is thought to be unassociated with its inhibition of NF-kappaB activation. Cilostazol, an inhibitor of cyclic nucleotide phosphodiesterase, could stimulate BK(Ca) channel-activity and reduce the firing of action currents simultaneously in GH(3) cells. Therefore, the regulation by these compounds of BK(Ca) channels may in part be responsible for their regulatory actions on cell functions.
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Changes in membrane cholesterol of pituitary tumor (GH3) cells regulate the activity of large-conductance Ca2+-activated K+ channels. CHINESE J PHYSIOL 2006; 49:1-13. [PMID: 16900700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023] Open
Abstract
The effects of changes in membrane cholesterol on ion currents were investigated in pituitary GH3 cells. Depletion of membrane cholesterol by exposing cells to methyl-beta-cyclodextrin (MbetaCD), an oligosaccharide, resulted in an increase in the density of Ca2+-activated K+ current (IK(Ca)). However, no significant change in IK(Ca) density was demonstrated in GH3 cells treated with a mixture of MbetaCD and cholesterol. Cholesterol depletion with MbetaCD (1.5 mg/ml) slightly suppressed the density of voltage-dependent L-type Ca2+ current. In inside-out patches recorded from MbetaCD-treated cells, the activity of large-conductance Ca2+-activated K+ (BK(Ca)) channels was enhanced with no change in single-channel conductance. In MbetaCD-treated cells, voltage-sensitivity of BK(Ca) channels was increased; however, no change in Ca2+-sensitivity could be demonstrated. A negative correlation between adjacent closed and open times in BK(Ca) channels was observed in MbetaCD-treated cells. In inside-out patches from MbetaCD-treated cells, dexamethasone (30 microM) applied to the intracellular surface did not increase BK(Ca)-channel activity, although caffeic acid phenethyl ester and cilostazol still opened its probability effectively. However, no modification in the activity of ATP-sensitive K+ channels could be seen in MbetaCD-treated cells. Current-clamp recordings demonstrated that the cholesterol depletion maneuver with MbetaCD reduced the firing of action potentials. Therefore, the increase in BK(Ca)-channel activity induced by membrane depletion may influence the functional activities of neurons or neuroendocrine cells if similar results occur in vivo.
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Inhibitory action of L-type Ca2+ current by paeoniflorin, a major constituent of peony root, in NG108-15 neuronal cells. Eur J Pharmacol 2005; 523:16-24. [PMID: 16243310 DOI: 10.1016/j.ejphar.2005.08.042] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2005] [Revised: 08/18/2005] [Accepted: 08/29/2005] [Indexed: 11/17/2022]
Abstract
The effects of paeoniflorin, a glycoside isolated from the root of Paeonia lactiflora, on ion currents in a mouse neuroblastoma and rat glioma hybrid cell line, NG108-15 were investigated. Paeoniflorin (1-300 microM) reversibly produced an inhibition of L-type voltage-dependent Ca2+ current (I(Ca,L)) in a concentration-dependent manner. Paeoniflorin caused no change in the overall shape of the current-voltage relationship of I(Ca,L). The IC50 value of paeoniflorin-induced inhibition of I(Ca,L) was 14 microM. However, neither adenosine deaminase (1 U/ml) nor 8-cyclopentyl-1, 3-dipropylxanthine (10 microM) could reverse the inhibition by paeoniflorin of I(Ca,L). Paeoniflorin (30 microM) shifted the steady-state inactivation curve of I(Ca,L) to more negative membrane potentials by approximately -10 mV. It also prolonged the recovery of I(Ca,L). The inhibitory effect of paeoniflorin on I(Ca,L) exhibited tonic and use-dependent characteristics. Paeoniflorin could effectively suppress I(Ca,L) evoked by action potential waveforms. Paeoniflorin at a concentration of 30 microM produce a slight inhibition of voltage-dependent Na+ current and delayed rectifier K+ current. Under current-clamp configuration, unlike adenosine, this compound decreased the firing of action potentials. Taken together, this study indicates that paeoniflorin can block L-type Ca2+ channels in NG108-15 cells in a mechanism unlinked to the binding to adenosine receptors. The effects of paeoniflorin on ion currents may partly, if not entirely, contribute to the underlying mechanisms through which it affects neuronal or neuroendocrine function.
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[Production of herbicide-resistant rice with transforming heterogene]. YI CHUAN XUE BAO = ACTA GENETICA SINICA 2001; 27:992-8. [PMID: 11209693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Abstract
Using pAHC20 (containing Bar gene), pWRG1515 (containing GUS gene and hygromycin phosphotransferase gene), and pCAMBIA3300 RG with Bar gene and snowdrop lectin (GNA) gene as donor DNA, the micro-adventitious shoots and the calli induced from mature embryos of Oryza sativa 87203, Eyi105, Shangnong aromatic glutinous rice as recipients were transformed with particle bombardment and Agrobacterium tumefaciens strain LBA4404 containing pAL4404, respectively. After chosen with phosphinothricin and antibiotic, GUS detection and PCR analysis, The results showed that the foreign genes had been transformed microprojectile-mediated to Oryza sativa Eyi105, the regeneration plants were obtained, and, 5 transgenic calli of Oryza sativa Eyi105 were obtained with Agrobacterium-mediated transformation.
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GATA-1 and GATA-4 transactivate inhibin/activin beta-B-subunit gene transcription in testicular cells. Mol Endocrinol 2000; 14:1820-35. [PMID: 11075815 DOI: 10.1210/mend.14.11.0549] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
We have recently demonstrated that a testicular GATA-binding protein, GATA-1, up-regulates the transcription of inhibin alpha-subunit gene through interaction with GATA motifs in the promoter region in MA-10, a mouse Leydig tumor cell line. In this study, we showed that both GATA-1 and GATA-4 also transactivated the transcription from the promoter for the 4.8-kb inhibin/activin beta-B-subunit gene transcripts, beta-B(4.8)-subunit promoter, in two testicular cell lines, MA-10 and MSC-1, which is a mouse Sertoli cell line. The abilities of GATA-1 and GATA-4 interacting with GATA and/or GATA-like sequences to transactivate the beta-B(4.8)-subunit promoter were next examined by mutation analysis. Mutations of GATA or GATA-like sequences caused no apparent effect or only a small decrease in the basal transcriptional activity of this promoter. However, mutation of the GATA motif at -65 markedly decreased 60-70% of the effect of GATA-1 on the transactivation of beta-B(4.8)-subunit promoter in both MA-10 and MSC-1 cells. In addition, mutation of the GATA motif in MSC-1 cells also reduced 40-50% of the effect of GATA-4 to transactivate this promoter. Interestingly, mutation of GATT at -42 caused a 70-90% increase in the transactivation of beta-B(4.8)-subunit promoter by GATA-1 or GATA-4. No significant change in the promoter activity was observed when GATT at -177 or GATC at -201 was mutated. Electrophoretic mobility shift assay confirmed the above observations that these GATA-binding proteins interacted with the GATA motif at -65 and GATT at -42, but not with GATC at -201 or GATT at -177. Serial deletion from the 5'-end of the basal promoter, from -226 to -90, markedly decreased the basal transcription, but increased the effect of GATA-1 on transactivation of the beta-B(4.8)-subunit promoter. In summary, our observations suggest that the two GATA-binding proteins transactivate the beta-B(4.8)-subunit promoter in testicular cells via complicated mechanisms. Both GATA-1 and GATA-4 factors act through the GATA motif at -65 and GATT at -42 to positively and negatively regulate the transcription from this promoter, respectively. Furthermore, GATA-1 may also interact directly or indirectly with DNA sequences at -180 to -90 to regulate the beta-B(4.8)-subunit promoter.
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Testicular GATA-1 factor up-regulates the promoter activity of rat inhibin alpha-subunit gene in MA-10 Leydig tumor cells. Mol Endocrinol 1998; 12:378-90. [PMID: 9514155 DOI: 10.1210/mend.12.3.0079] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We have previously demonstrated that the basal transcription of rat inhibin alpha-subunit gene in a mouse testicular Leydig tumor cell line, MA-10, depends upon a 67-bp DNA fragment at the position of -163 to -97. Within this promoter region two GATA motifs were observed. In this study, we investigated the possible role of GATA-binding proteins in the regulation of inhibin alpha-subunit gene transcription in testicular cells. Northern blot and RT-PCR analyses showed that mRNAs encoding GATA-binding proteins, GATA-1 and GATA-4, were detected in mouse and rat testis and in MA-10 and rat Sertoli cells. Testis-specific GATA-1 mRNA, which is transcribed from a promoter 8 kb upstream to the erythroid exon I of mouse GATA-1 gene, was also identified in MA-10 cells. Mutations of GATA sequences in alpha-subunit promoter markedly decreased the transcriptional activity of alpha-subunit gene when measured by their ability of transient expression of a bacterial reporter gene, chloramphenicol acetyltransferase (CAT), in MA-10 cells. Cotransfection of alphaCAT chimeric construct with cDNA expression plasmid coding for mouse GATA-1 or GATA-4 protein revealed that GATA-1 but not GATA-4 can transactivate alpha-subunit promoter in a dose-dependent manner. The transactivation by GATA-1 was inhibited if GATA sequences in alpha-subunit promoter were mutated. Furthermore, electrophoretic mobility shift assay demonstrated that GATA-binding proteins present in nuclear extracts of MA-10 cells and rat testis interacted with the GATA motifs in alpha-subunit promoter, and the GATA-1 in these nuclear extracts formed a supershifted immunocomplex with antibody raised against mouse GATA-1 protein. We therefore concluded that the basal transcription of inhibin alpha-subunit gene in testicular MA-10 cells is up-regulated by testicular GATA-1 but not GATA-4 through its interaction with the GATA motifs in alpha-subunit promoter. In summary, we have provided the first evidence of the functional role of a GATA-binding protein in the regulation of testicular gene expression.
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Characterization and regulation of two testicular inhibin/activin beta B-subunit messenger ribonucleic acids that are transcribed from alternate initiation sites. Endocrinology 1995; 136:947-55. [PMID: 7867604 DOI: 10.1210/endo.136.3.7867604] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We and others have shown that the inhibin/activin beta B-subunit gene is expressed differently in the gonads. Two species of 4.8- and 3.7-kilobase (kb) beta B-subunit messenger RNA (mRNA) with equal concentrations were identified in the testis, whereas 1 predominant 4.8-kb and a minor 3.7-kb mRNA were observed in the ovary. In this study, we analyzed the structures of these 2 mRNAs in rat testis and showed that both 4.8- and 3.7-kb beta B-subunit mRNAs were terminated at the region proximal to 2.2 kb down-stream from the translation stop codon. However, only 4.8-kb mRNA could be detected when RNA probes prepared from the 5'-region 1 kb up-stream from the translation start site were used for Northern blot analysis. Our observations suggested that the 2 heterogeneously sized beta B-subunit mRNAs are transcribed from different initiation sites. Transcription of the 4.8-kb mRNA was initiated at 3 adjacent nucleotides, GGA, 1.1 kb up-stream from the translation start codon ATG, whereas multiple transcription initiation sites spreading over 150 nucleotides upstream from the ATG codon were previously identified for 3.7-kb mRNA. Neither of the 2 transcripts contained TATA and CAAT boxes in their promoters. The 5'-flanking DNAs required for transcription of the 4.8- and 3.7-kb mRNA were examined by their ability to induce transient expression of the chloramphenicol acetyltransferase (CAT) gene in MA-10 Leydig tumor cells. A marked increase in CAT activity was detected when the 5'-flanking DNA for the 4.8- or 3.7-kb transcript was progressively shortened from its 5'-end. Maximal CAT activity was observed when -409 and -139 basepair beta B-subunit DNA up-stream from the 4.8- and 3.7-kb transcription initiation site, respectively, were fused to the CAT gene, suggesting the presence of a negative regulatory element(s) at the up-stream regions of these promoters. Although putative AP-2 sites were identified, treatment of the transfected cells with cAMP and/or phorbol 12-myristate 13-acetate did not apparently change CAT activity driven by either the 4.8- or 3.7-kb promoter. Our results concluded that 1) the two inhibin/activin beta B-subunit mRNAs were transcribed from different initiation sites; 2) both promoters may be controlled by up-stream negative regulatory elements; and 3) neither of these promoters is responsive to cAMP and/or phorbol esters under the conditions employed.
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The protein subunits of the double-stranded RNA dependent RNA polymerase and methyltransferase of the cytoplasmic polyhedrosis virus of silkworm, Bombyx mori. SCIENTIA SINICA. SERIES B, CHEMICAL, BIOLOGICAL, AGRICULTURAL, MEDICAL & EARTH SCIENCES 1986; 29:1267-72. [PMID: 3299695] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The particles of CPV of silkworm contain double-stranded RNA polymerase and methyltransferase. It was reported in a previous paper that the genome-enzyme complex could be isolated. The genome-enzyme complex shows high enzyme activity of RNA polymerase and methyltransferase in spite of the fact that it consists of only 5 percent of the protein. In order to clarify the protein subunits of the RNA polymerase and methyltransferase, two methods were adopted. The SDS-polyacrylamide gel electrophoretogram showed that the 125I-labeled genome-enzyme complex of CPV contained three protein components in molecular weight of 33 K, 67 K and 142 K daltons respectively and each protein component of them consisted of more than two protein subunits with different isoelectric points in 2-dimensional electrophoretogram. The antibody to the five protein components (P1, P2, P3, P4, P5) was prepared and used to inhibit the enzyme activities of RNA polymerase and methyltransferase. It showed that the RNA polymerase was inhibited by the antibody to proteins P1, P2 and P4, whereas the methyltransferase was mainly inhibited by the antibody to protein P1.
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[3H-Methyl]-methionine as possible methyl donor for formation of 5'-terminus of in vitro synthesized mRNA of cytoplasmic polyhedrosis virus of silkworm Bombyx mori. SCIENTIA SINICA 1981; 24:1737-42. [PMID: 7038870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The mRNA of the cytoplasmic polyhedrosis virus of silkworm Bombyx mori could be synthesized in vitro through the action of the virion associated RNA-polymerase in the presence of [3H-methyl]-methionine instead of S-adenosyl-L-methionine. The 3H-mRNA is isolated from the reaction mixture through a column of DEAE-Sephadex A-25 and digested with nuclease p1 and snake venom phosphodiesterase. The results of paper electrophoresis show that the methyl group of methionine is incorporated into the 5'-terminus of CPV mRNA. Even in the presence of S-adenosyl-L-methionine the [3H-methyl]-methionine could still function as a methyl donor for the formation of the 5'-caps of the mRNA of CPV.
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