Biomedical subjects

S Y Lin-Shiau

Publications and source records attributed to S Y Lin-Shiau.

At least 73 records · Page 4Linked to original sources

PubMed1999

Involvement of heat-shock protein 70 and P53 proteins in attenuation of UVC-induced apoptosis by thermal stress in hepatocellular carcinoma cells.

Induction of apoptosis is a function of external stimuli and cellular gene expression. Many cells respond to DNA damage by the induction of apoptosis, which depends on a functional p53 protein and is signaled by elevation of p53 levels. In this study, we found that a prior exposure to mild stress (42 degrees C) can protect HepG2 (p53+/+) cells from a subsequent UVC-induced apoptosis determined by DNA fragmentation and ratio of sub-G1 peak, but no heat-enhanced protection was found in Hep3B (p53-/-) cells. Although a similar inductive pattern of HSP70 protein and mRNA was detected in the two cell lines under thermal stress, the effect of thermal stress on UVC-induced apoptosis in HepG2 and Hep3B cells was obviously different. Overexpression of HSP70 by transient transfection of HSP70 expression vector in HepG2 cells significantly inhibited UVC-induced cell death; however, this inhibitory effect did not occur in transfected-Hep3B cells. Treatment of HepG2 cells with p53-specific antisense oligonucleotide could effectively block the antiapoptotic effect of thermal stress on UVC-induced apoptosis and increase of intracellular wild-type p53 protein by transfecting wtp53 expression plasmid into Hep3B cells yielded more resistance to UVC irradiation after prior thermal stress exposure. The results reveal an involvement of p53 in the antiapoptotic effect of thermal stress on UVC irradiation. Finally, a p53 protein increase was detected in UVC-treated HepG2 cells and could be coimmunoprecipitated with HSP70 after a thermal stress treatment. Prolonged p53 binding activity and enhanced expression of p53-controlled genes such as G1 arrest and DNA damage 45 and wild-type p53 activation factor 1/Cdk-interacting protein 1 by thermal stress are also observed in UVC-irradiated HepG2 cells. Based on these results, we propose that the antiapoptotic effect of thermal stress is mediated by increasing HSP70 and modulating intracellular p53 function.

Apoptosis↗

PubMed1999

Altered intracellular calcium level in association with neuronal death induced by lithium chloride.

In this study, we examined the effects of lithium chloride (LiCl) on the intracellular calcium levels ([Ca2+]i), and the survival of immature and mature cultured cerebellar granule neurons (CGNs) grown in medium containing high (25 mmol/L) or normal (5 mmol/L) potassium (K+) levels. LiCl dramatically reduced [Ca2+]i in immature CGNs maintained in high K+ (HK) medium and in those switched to serum containing normal K+ (NK) medium for 1 to 2 days. This reduction in [Ca2+]i led to massive neuronal death of immature neurons developed in both HK and NK medium. In mature (cultured 5-8 days in vitro) CGNs, LiCl exhibited potent toxicity when cells were grown in HK medium, and led to increased [Ca2+]i. Exposing mature CGNs to serum deprivation and normal extracellular K+ concentrations decreased [Ca2+]i and induced cell death, while the addition of LiCl in these conditions further decreased [Ca2+]i but prevented cell death. The morphologic features revealed by Nomarski optics further confirmed these effects of LiCl on neuronal survival. Together, these findings indicate that the effects of LiCl on [Ca2+]i and neuronal death, and the association between [Ca2+]i and cell death, depend on the developmental stage of CGNs and the growth conditions to which they are subjected. These findings may help in understanding the mechanism of neurotoxicity of LiCl during therapy.

Animals↗

PubMed1999

Induction of apoptosis by apigenin and related flavonoids through cytochrome c release and activation of caspase-9 and caspase-3 in leukaemia HL-60 cells.

The aim of this study was to investigate the mechanism of flavonoid-induced apoptosis in HL-60 leukaemic cells. Thus, the effect of structurally related flavonoids on cell viability, DNA fragmentation and caspase activity was assessed. Loss of membrane potential and reactive oxygen species generation were also monitored by flow cytometry. The structurally related flavonoids, such as apigenin, quercetin, myricetin, and kaempferol were able to induce apoptosis in human leukaemia HL-60 cells. Treatment with flavonoids (60 microM) caused a rapid induction of caspase-3 activity and stimulated proteolytic cleavage of poly-(ADP-ribose) polymerase (PARP). Furthermore, these flavonoids induced loss of mitochondrial transmembrane potential, elevation of reactive oxygen species (ROS) production, release of mitochondrial cytochrome c into the cytosol, and subsequent induction of procaspase-9 processing. The potency of these flavonoids on these features of apoptosis were in the order of: apigenin > quercetin > myricetin > kaempferol in HL-60 cells treated with 60 microM flavonoids. These results suggest that flavonoid-induced apoptosis is stimulated by the release of cytochrome c to the cytosol, by procaspase-9 processing, and through a caspase-3-dependent mechanism. The induction of apoptosis by flavonoids may be attributed to their cancer chemopreventive activity. Furthermore, the potency of flavonoids for inducing apoptosis may be dependent on the numbers of hydroxyl groups in the 2-phenyl group and on the absence of the 3-hydroxyl group. This provides new information on the structure-activity relationship of flavonoids.

Apigenin↗

PubMed1998

Studies on curare-like action of the tripeptide carbobenzoxy-Gly-Gly-Arg-beta-naphthylamide in mouse diaphragm.

The effects of several protease substrates or protease inhibitors on neuromuscular transmission in the isolated mouse phrenic nerve-diaphragm were studied. N-Carbobenzoxy-Gly-Gly-Arg-beta-naphthylamide (Z-GGR-N) but none of the other agents inhibited the nerve-evoked muscle contractions. By means of electrophysiological studies, Z-GGR-N was found to inhibit the amplitudes of both end-plate potentials (epps) (IC50 approximately 50 microM) and miniature end-plate potentials (mepps) but to increase the frequencies of mepps. This tripeptide could protect the nicotinic acetylcholine receptor from the irreversible inhibitory action of alpha-bungarotoxin on the mouse diaphragm. Similar to D-tubocurarine, Z-GGR-N induced tetanic fading both of nerve-evoked muscle contractions and of the amplitude of epps. Furthermore, Z-GGR-N exhibited a greater depression of the amplitudes of train-epps than those of mepps, similar to that of hexamethonium and D-tubocurarine, indicating an effect on presynaptic autoreceptors. Suramin, which could competitively reverse the inhibitory effects of non-depolarizing relaxants, acted in this study as an antagonist of all the effects of Z-GGR-N, especially those at the presynaptic site. All of these findings suggest that Z-GGR-N is a novel tripeptide possessing curare-like actions at both presynaptic and postsynaptic sites and that these actions are independent of its protease substrate property.

Animals↗

PubMed1998

Involvement of reactive oxygen species and caspase 3 activation in arsenite-induced apoptosis.

Recent studies indicate that arsenic may generate reactive oxygen species to exert its toxicity. However, the mechanism is still unclear. In this study, we demonstrate that arsenite is able to induce apoptosis in a concentration- and time-dependent manner; however, arsenate is unable to do so. An increase of intracellular peroxide levels was accompanied with arsenite-induced apoptosis, as demonstrated by flow cytometry using DCFH-DA. N-Acetyl-L-cysteine (a thiol-containing antioxidant), diphenylene iodonium (an inhibitor of NADPH oxidase), 4,5-dihydro-1,3-benzene disulfonic acid (a selective scavenger of O2-), and catalase significantly inhibit arsenite-induced apoptosis and intracellular fluorescence intensity. In contrast, allopurinol (an inhibitor of xanthine oxidase), indomethacin (an inhibitor of cyclooxygenase), superoxide dismutase, or PDTC had no effect on arsenite-induced cell death. Activation of CPP32 activity, PARP (a DNA repair enzyme) degradation, and release of cytochrome c from mitochondria to the cytosol are involved in arsenite-induced apoptosis, and Bcl-2 antagonize arsenite-induced apoptosis by a mechanism that interferes in the activity of CPP32. These results lead to a working hypothesis that arsenite-induced apoptosis is triggered by the generation of hydrogen peroxide through activation of flavoprotein-dependent superoxide-producing enzymes (such as NADPH oxidase), and hydrogen peroxide might play a role as a mediator to induce apoptosis through release of cytochrome c to cytosol, activation of CPP32 protease, and PARP degradation.

3T3 Cells↗

PubMed1998

Effects of germanium oxide and other chemical compounds on phenylmercury acetate-induced genotoxicity in cultured human lymphocytes.

Phenylmercury acetate (PMA), which not only causes an elevation of sister chromatid exchanges (SCEs) but also induces high frequency of endoreduplication in human lymphocytes, may be genotoxic to humans. The major aim of our study was to investigate the effects of germanium oxide (GeO2), D-penicillamine (D-PA), dimercaprol (BAL), and diltiazem (DTM) on PMA-induced genotoxicity as quantified by SCEs. All concentrations of the four chemical compounds tested alone did not induce genotoxicity in cultured human lymphocytes. However, GeO2 significantly inhibited PMA-induced genotoxicity in a concentration-dependent manner. Similarly, D-PA at concentrations of 3 microM and 10 microM, and BAL at a concentration of 30 microM produced the antigenotoxic effects. In addition, GeO2 (1.5 microM) significantly reversed an increase of endoreduplication frequency caused by PMA. In a cell cycle kinetic study, GeO2 (0.5-5.0 microM) reversed the inhibition of PMA on the proliferating rate index (PRI) of lymphocytes. On the contrary, both D-PA and DTM at concentrations of 30-300 microM markedly potentiated PMA-induced inhibition of PRI. These findings show that GeO2, D-PA and BAL could antagonize PMA-induced genotoxicity, and GeO2 appears to be the most effective.

Adult↗

PubMed1998

Phorbol ester-induced contractions of mouse detrusor muscle are inhibited by nifedipine.

The effects of phorbol esters on contractions of detrusor strips isolated from mouse urinary bladder were studied. Beta-phorbol-12,13-dibutyrate (beta-PDBu, 10 nM) significantly enhances both the neurogenic and myogenic detrusor contractions to a similar extent. By contrast, an inactive isoform of protein kinase C (PKC) stimulation, alpha-phorbol-12,13-dibutyrate (100 nM) has no such enhancing effect on the muscle contraction. The effect of beta-PDBu was dependent on the extracellular Ca2+ concentration. Nifedipine (0.3 microM, a L-type Ca2+ channel blocker), staurosporine (1 microM) and bisindolylmaleimide I (microM, a selective PKC inhibitor) but not omega-conotoxin GVIA (an N-type Ca2+ channel blocker) abolished the enhancing effect of beta-PDBu. In other words, beta-PDBu failed to augment the nifedipine-insensitive component of the muscle contraction. Moreover, beta-PDBu not only enhances the muscle response induced by exogenous agonists (acetylcholine or ATP) and KCl but also increases the resting tone of detrusor muscle, an effect which is also inhibited by nifedipine and bisindolylmaleimide I. From these findings, it is concluded that the enhancing effect of beta-PDBu is due to activation of the L-type Ca2+ channel through phosphorylation by protein kinase C. This allows more Ca2+ influx from the extracellular medium, leading to an increase in the contractions of the mouse detrusor muscle.

Animals↗

PubMed1998

Involvement of nitric oxide in the potentiation of neurogenic contraction by manganese and nickel ions in mouse urinary bladder.

Repetitive electrical field stimulation evoked muscle contractions of the isolated mouse detrusor strips, which could be abolished by tetrodotoxin (TTX). Both Mn2+ and Ni2+ (0.01-0.06 mM) enhanced neurogenic detrusor contractions in high Ca2+ (5 mM) medium. The non-cholinergic component of the evoked detrusor contractions (in the presence of atropine) was specifically sensitive to this enhancing effect by either Mn2+ or Ni2+. In contrast, the cholinergic component in alpha,beta-methylene ATP-treated detrusors remained unaffected. As compared with Mn2+ and Ni2+, other metal ions, Cu2+, Co2+, Cd2+ and UO2(2+), failed to enhancing the non-cholinergic component of neurogenic detrusor contractions. Nitric oxide synthase (NOS) inhibitors, NG-nitro-L-arginine methyl ester and 7-nitroindazole (a selective neuronal NOS inhibitor) markedly inhibited the enhancing effect by either Mn2+ or Ni2+ on the neurogenic detrusor contractions. Moreover, Mn2+ and Ni2+ did not affect the contractions induced by either carbachol or alpha,beta-methylene ATP. It is concluded from these findings that the neuronal NOS-NO generation pathway is apparently involved in the enhancing effect of Mn2+ and Ni2+ on the muscle contractions elicited by excitatory non-cholinergic neurotransmission in the mouse detrusor strips.

Animals↗

PubMed1998

Morphological changes induced by prostaglandin E in cultured rat osteoblasts.

Prostaglandin E (PGE)-induced morphological changes of osteoblasts and its possible mechanisms were investigated in cultured calvaria and isolated osteoblasts from long bone fragments of neonatal rats. The control osteoblasts, either on the calvaria or isolated from the long bone fragments, were flat, polygonal in shape, and arranged in a monolayer under scanning electron microscopy (SEM) or phase contrast microscopy. Treatment with 1 mumol/L of prostaglandin E2 (PGE2, 2 h) caused these bone cells to contract a soma, whereas 10 and 100 mumol/L PGE2 (2 h) caused 18%-30% of the bone cells to elongate and expose the undersurface. Incubation of the cultured osteoblasts with PGE2 at different time periods showed a bell-shaped pattern with the optimal response at 2 h of incubation. A similar reaction can be induced by treatment with prostaglandin E1 (PGE1) or dibutyryl cyclic adenosine monophosphate (DBcAMP) in combination with 3-isobutyl-1-methylxanthine (IBMX). Furthermore, we assessed the percentage of responsive isolated bone cells to investigate interactions with other agents. The morphological changes induced by PGEs were inhibited by H-8, a protein kinase inhibitor. On the other hand, elevated intracellular calcium enhanced the PGE-induced morphological changes. Fluorescence labeling showed that PGEs caused the breakdown of the actin microfilaments, but spared the microtubules and vimentin filaments in the isolated osteoblast-like cells. These results suggest that the morphological changes of osteoblasts induced by PGEs may be related to the intracellular cAMP and calcium levels.

1-Methyl-3-isobutylxanthine↗

PubMed1998

Oltipraz, a novel inhibitor of hepatitis B virus transcription through elevation of p53 protein.

Molecular epidemiological studies of populations at high risk for liver cancer have shown that hepatitis B virus (HBV) and aflatoxin B1 exposures are two major risk factors for this disease. Oltipraz is currently being considered for clinical trial to protect against aflatoxin B1-induced hepatocarcinogenesis based on its proven protective effect in many different animal models. In addition, oltipraz inhibits human immunodeficiency virus (HIV) replication. The inactivation of reverse transcriptase of HIV appears to be the antiviral mechanism. It has been demonstrated that a number of compounds that inhibit HIV replication also inhibit HBV replication in vitro. Therefore, we tested the possibility of oltipraz blocking HBV replication in 2.2.15 cells (clonal cells derived from HepG2 cells that were transfected with a plasmid containing HBV DNA) in vitro. Results of the experiments indicate that oltipraz has a dose-dependent inhibitory effect on HBV replication and specifically blocks HBV transcription in 2.2.15 cells. In addition, oltipraz induces endogenous wild-type p53 protein in a dose- and time-course-dependent manner. Taken together, we speculate that the effects of oltipraz against replication of HBV and specific blocking of HBV transcription may be through the induction of p53-mediated pathway in 2.2.15 cells. In addition to its known chemopreventive action on aflatoxin B1 hepatocarcinogenesis, oltipraz was shown here to inhibit HBV replication. These dual effects put oltipraz as the excellent candidate for the chemopreventive agent of human hepatocellular carcinoma.

Alleles↗

PubMed1998

Comparative studies on the induction of muscle contracture in mouse diaphragm and Ca2+ release from sarcoplasmic reticulum vesicles by organotin compounds.

Effects of organotins, including triethyltin and tributyltin, on skeletal muscle were studied with diaphragm and isolated sarcoplasmic reticulum membrane vesicles. Triethyltin induced muscle contracture in mouse diaphragm while tributyltin had comparatively less potency and efficacy in inducing the muscle contracture. The contracture induced by tributyltin was inhibited when the diaphragm was pretreated with low Ca2+ medium or caffeine while the contracture induced by triethyltin persisted in the Ca2+-free medium but was inhibited by pretreatment of caffeine. Pretreatment of dithiothreitol blocked the contracture induced by tributyltin but not that by triethyltin. Triethyltin dose-dependently induced Ca2+ release from sarcoplasmic reticulum vesicles and inhibited the Ca2+-ATPase activity. These results suggested that triethyltin induced contracture in mouse diaphragm was mainly by induction of Ca2+ release and inhibition of Ca2+ uptake of the internal Ca2+ storage site the sarcoplasmic reticulum, while the tributyltin induced contracture might be due to enhancement of extracellular Ca2+ influx which further induce the release of internal Ca2+ through the Ca2+-induced Ca2+ release mechanism.

Animals↗

PubMed1997

The in vivo effect of lipopolysaccharide on neuromuscular transmission in the mouse.

The in vivo effect of lipopolysaccharide (endotoxin) on nerve-evoked muscle contractions and neuromuscular transmission was studied in the mouse phrenic nerve-diaphragm preparations. In lipopolysaccharide-treated mouse diaphragms it was observed that indirectly induced twitch tension was unchanged while tetanic tension significantly decreased. Neostigmine (50 nM) increased the amplitude of nerve evoked muscle contractions, while it caused partial fade of tetanic contractions (Wedensky inhibition) and accelerated the run-down of end-plate potentials (e.p.ps) evoked by repetitive nerve stimulation, in the diaphragm of saline-control mice, but not of lipopolysaccharide-treated mice. These effects of neostigmine could be abolished by ouabain (5 microM). Measurement of the quantal contents of e.p.ps revealed that ouabain (5 microM) significantly increased it in the diaphragm of saline-control mice to an extent similar to that in diaphragm of lipopolysaccharide-treated mice. Moreover, ouabain-sensitive Na+, K(+)-ATPase activity in the sciatic nerve of lipopolysaccharide-treated mice was markedly decreased. The alterations in neuromuscular transmission of the diaphragm during endotoxemia could be reversed by the administration of polymyxin B (a lipopolysaccharide neutralizer) and NG-nitro-L-arginine (a nitric oxide (NO) synthase inhibitor), suggesting that NO is involved in these lipopolysaccharide-induced alterations of neuromuscular transmission mediated by an impairment of ouabain-sensitive Na+, K(+)-ATPase activity in mouse motor nerves.

Animals↗

PubMed1997

Distinct genotoxicity of phenylmercury acetate in human lymphocytes as compared with other mercury compounds.

In the present study, the frequency of sister chromatid exchanges (SCEs) was assayed to evaluate the genotoxic effects of mercury nitrate (Hg2+), methylmercury chloride (CH3HgCl and phenylmercury acetate (PMA) on human lymphocytes. The free radical scavengers, catalase (CA) and superoxide dismutase (SOD) were tested for their antigenotoxic effects toward PMA. PMA (1-30 microM) increased SCE frequency in a concentration-dependent manner. However, CH3HgCl significantly increased SCE frequency only at a concentration of 20 microM, and all concentrations treated with Hg2+ did not induce a positive effect. On the other hand, we first reported that 30 microM Hg2+, 20 microM CH3HgCl and (3-30 microM) PMA significantly increased the frequency of endoreduplicated mitosis. PMA was about 3- or 5-fold more effective in inducing endoreduplication than CH3HgCl or Hg2+ at equivalent toxic concentrations, respectively. However, neither CA nor SOD in concentrations of 75 and 150 microg/ml showed antagonistic action on the genotoxic effects of PMA. The results suggest that the mechanism of PMA-induced genotoxicity is not mediated by superoxide anion nor H2O2. It is concluded that PMA, which was more effective in inducing the elevation of both SCEs and endoreduplication, may be especially hazardous of the three mercury compounds tested.

Adult↗

PubMed1997

Capacitative Ca2+ influx in glial cells is inhibited by glycolytic inhibitors.

In non-excitable cells, stimulation of phosphoinositide (PI) turnover and inhibition of the endoplasmic reticulum (ER) Ca2+-ATPase are methods commonly used to deplete calcium stores, resulting in a capacitative Ca2+ influx (i.e., Ca2+ release-activated Ca2+ influx). Since this Ca2+ influx in glial cells has not been thoroughly investigated, we have used C6 glioma cells as a glial cell model to study this phenomenon. On adding cyclopiazonic acid (CPA) or thapsigargin (TG) (two ER Ca2+-ATPase inhibitors) in Ca2+-free medium, only a small transient increase in intracellular Ca2+ was seen. After depletion of the stored Ca2+, a marked Ca2+ influx, followed by a prolonged plateau, was seen on re-addition of extracellular Ca2+ ions (2 mM), i.e., capacitative Ca2+ influx. A similar effect was seen on adding ATP, known to deplete the inositol triphosphate (IP3)-sensitive Ca2+ store in C6 cells. After various degrees of store depletion, the amplitude of the capacitative Ca2+ influx was found to be highly dependent on the amount of Ca2+ remaining in the store. This Ca2+ influx was markedly inhibited by (1) La3+ and Ni2+, (2) SK&F 96365, econazole, and miconazole, and (3) membrane depolarization, clearly showing that this Ca2+ influx after store depletion in C6 cells is a capacitative mechanism. Interestingly, the capacitative Ca2+ influx can be inhibited by a reduction in intracellular ATP (ATPi) levels in glial cells. The role of ATPi in the capacitative Ca2+ influx is discussed.

Adenosine Triphosphate↗

PubMed1997

Decrease in myocardial Na(+)-K(+)-ATPase activity and ouabain binding sites in hypercholesterolemic rabbits.

OBJECTIVES: The purpose of this study was to explore the effect of high dietary cholesterol on the lipid composition, Na(+)-K(+)-ATPase activity and ouabain receptor property of the myocardial sarcolemma. METHODS: Male New Zealand white rabbits were fed with standard chow or standard chow supplemented with 0.5% (w/w) cholesterol and 10% (w/w) coconut oil to induce hypercholesterolemia. After 8 weeks, the rabbits were sacrificed; a myocardial sarcolemma fraction was then prepared from the left ventricular myocardium and analyzed for lipid composition. Assay of Na(+)-K(+)-ATPase activity and 3H-ouabain binding studies were performed in the myocardial sarcolemma from the control and cholesterol-fed rabbits. RESULTS: The cholesterol content, but not the phospholipid content, of the sarcolemma was significantly greater in the cholesterol-fed group, thus, resulting in an increased cholesterol/phospholipid molar ratio in the cholesterol-fed group. In addition, a decrease in Na(+)-K(+)-ATPase activity was also found in this group. The decrease in Na(+)-K(+)-ATPase activity was selective, since the Mg(++)-ATPase and 5'-nucleotidase activities remained unchanged. In the 3H-ouabain binding study, a decrease in the number of maximum binding sites, but not the binding affinity, for 3H-ouabain was found in the cholesterol-fed group. CONCLUSIONS: High dietary cholesterol induces higher levels of cholesterol not only in the plasma, but also in the myocardial sarcolemma. These changes result in decreased myocardial Na(+)-K(+)-ATPase activity mediated by a reduction in the maximum number of binding sites for ouabain but not a change in binding affinity.

5'-Nucleotidase↗

PubMed1997

Involvement of nitric oxide in the in vivo effects of lipopolysaccharide on the contractile and electrical properties of mouse diaphragm.

The contractile and electrical properties of the mouse diaphragm during endotoxemia were studied, and the possible role of nitric oxide (NO) on these changes was investigated. The mice were injected intraperitoneally with E. coli. lipopolysaccharide (endotoxin, LPS) at various times before isolation of the diaphragm to induce endotoxemia. It was observed that direct twitch tension was slightly increased, and that there was a significant increase in tetanic tension when compared with controls. The potentiation of direct twitch tension induced by a Cl--channel blocker (9-anthracene carboxylic acid), but not the potentiation by a Na+-channel activator (veratridine) or by K+-channel blockers (uranyl ion, 4-aminopyridine and tetraethylammonium ion), was attenuated in the diaphragm of LPS-treated mice. Moreover, the resting membrane potential was significantly reduced and the membrane input resistance was significantly increased, largely due to a decrease in Cl--conductance. However, the membrane K+-conductance remained unaltered. These results imply that the sarcolemmal Cl--channel is markedly affected in the mouse diaphragm during endotoxemia. These changes of contractile and electrical characteristics of the mouse diaphragm during endotoxemia could be reversed by treatment with dexamethasone and N(G)-nitro-L-arginine (NO synthase inhibitors). On the other hand, in in vitro studies, LPS (20 microg/ml), by itself, applied directly to the diaphragm, did not alter the muscle contractions or the membrane potentials. A NO donor, added to the diaphragm bath, increased the tetanus/twitch ratio and induced a transient depolarization. All of these findings suggest that LPS may, at least in part, affect the sarcolemmal electrical properties and muscle contractions during endotoxemia through the L-arginine:NO pathway.

Animals↗

PubMed1997

Enhancement by nitric oxide of neurogenic contraction in the mouse urinary bladder.

In isolated detrusor strips from the mouse urinary bladder, contractile responses to electrical field stimulation were mostly mediated by neurally released acetylcholine and ATP. The aim of this study is to investigate the possible role of nitric oxide (NO) involved in the neurogenic detrusor contraction. Repetitive electrical field stimulation evoked muscle contractions of the isolated mouse detrusor strips, which could be abolished by tetrodotoxin (TTX). NO donors including sodium nitroprusside (SNP) and S-nitroso-N-acetyl-penicillamine (SNAP) as well as exogenous NO increased, while hemoglobin and NO synthase inhibitor N(G)-nitro-L-arginine decreased the neurogenic detrusor contractions. The addition of L-arginine reversed the inhibitory effect of N(G)-nitro-L-arginine. SNP failed to affect the contractions induced by carbachol and alpha,beta-methylene ATP. These findings suggest that NO potentiated the excitatory neuromuscular transmission in electrically stimulated detrusor strips from the mouse.

Animals↗

PubMed1997

Multiple types of Ca2+ channels in mouse motor nerve terminals.

We measured neurotransmitter release and motor nerve terminal currents in mouse phrenic nerve-diaphragm and triangularis sterni preparations, to evaluate the role of Ca2+-channel subtypes in regulating transmitter release. Saturated concentrations of either omega-agatoxin IVA [omega-Aga-IVA (0.3 microM), a blocker of P-type Ca2+ channels] or omega-conotoxin MVIIC [omega-CTx-MVIIC (2 microM), a P- and Q-type Ca2+-channel blocker], inhibited nerve-evoked muscle contractions and the amplitude of endplate potentials respectively. In contrast, combined treatment with nifedipine (50 microM, a blocker of L-type Ca2+ channels) plus omega-conotoxin GVIA [omega-CTx-GVIA (2 microM), a blocker of N-type Ca2+ channels] did not elicit inhibitory effects on nerve-evoked muscle contractions, endplate potentials or nerve terminal waveforms. Because of the non-linear relationship between endplate potentials and Ca2+ signals, a small decrease in presynaptic Ca2+ entry can significantly reduce the amplitude of the endplate potential. Thus, we applied 3,4-diaminopyridine (3,4-DAP, a K+-channel blocker) or high Ca2+ (10 mM) to accelerate and amplify the endplate potentials and Ca2+ currents. The endplate potentials amplified by 3,4-DAP or by high Ca2+ correspondingly proved to be quite resistant to both omega-Aga-IVA and omgea-CTx-MVIIC; omega-Aga-IVA exerted only a partial inhibitory effect on endplate potentials, and the omega-Aga-IVA-resistant component was further inhibited by omega-CTx-MVIIC. The component that was resistant to the two toxins could be completely blocked by the non-selective Ca2+ channel blocker Cd2+ (300 microM). A combination of the two toxins had no significant effects on either spontaneous transmitter release or postsynaptic resting membrane potentials of the diaphragm preparation and the Na+ and K+ waveforms of the triangularis sterni preparations. This finding suggests a preferential inhibitory effect at a presynaptic site. Measuring the Ca2+ currents in the triangularis sterni also revealed partial inhibition by omega-CTx-MVIIC with further incomplete inhibition by omega-Aga-IVA. Cd2+ (300 microM) abolished the toxin-resistant component of the Ca2+ current. In contrast, a combination of nifedipine (50 microM) with omega-CTx-GVIA (2 microM) was without inhibitory effect. We conclude that multiple types of Ca2+ channels, i.e. omega-Aga-IVA-sensitive, omega-CTx-MVIIC-sensitive and toxin-resistant Ca2+ channels, coexist in mouse motor nerve terminals.

Animals↗