Modulation by muscarinic receptor antagonists on negative chronotropic effects of tetrandrine.
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AIM: To investigate the influence of selective antagonist for muscarinic (M) receptor subtype on tetrandrine (Tet) reducing heart rate, inhibiting sinoatrial node (SAN) function, and its ionic mechanism. METHODS: Effects of reducing heart rate of Tet were maintained in isolated right atrium and pithed rats. Modification on action potentials (AP) of SAN cells and L-type calcium current (ICa-L) by Tet were recorded by means of standard microelectrode and patch-clamp whole cell recording techniques. RESULTS: Tet inhibited spontaneous beating rate of isolated right atrium (EC50, 23.7 mumol.L-1) and reduced heart rates in pithed rats in a concentration-dependent manner (EC50, 18.6 mg.kg-1). Automaticity of SAN was inhibited by Tet. AP upstroke velocity (Vmax), spontaneous depolarization rates in phase 4 (SP4) were decreased and sinus cycle length (SCL) was prolonged when treated with Tet. Tet (30 mumol.L-1) caused a reduction in peak value of ICa-L from (1275 +/- 190) pA to (498 +/- 94) pA in isolated single cardiomyocyte. Atropine and AF-DX 116 (M2 subtype selective antagonist) could attenuate such effects of Tet in a competitive mode. CONCLUSION: Negative chronotropic effects of Tet are due to its inhibition of ICa-L. Modification on ICa-L is the major mechanism of M receptor modulating Tet effects. (+info)
Inhibitory effects of dauricine on potassium currents in guinea pig ventricular myocytes.
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AIM: To study the effects of dauricine(Dau) on the rapidly activating component (IKr), the slowly activating component (IKs) of the delayed rectifier potassium current, and the inward rectifier potassium current (IKl) in guinea pig ventricular myocytes. METHODS: Single myocytes were dissociated by enzymatic dissociation method. The currents were recorded with the whole-cell configuration of the patch-clamp technique. RESULTS: (1) Dau 1, 3, 10, 30, and 100 mumol.L-1 blocked IKr and tail current (IKr-tail) in a concentration-dependent manner. The IC50 for block of IKr-tail was 16 (95% confidence limits: 13-22) mumol.L-1. The time constant of IKr-tail deactivation was (140 +/- 38) ms in the control and (130 +/- 26) ms in the presence of Dau 30 mumol.L-1 (n = 6 cells from 3 animals, P > 0.05). (2) Dau 1-100 mumol.L-1 produced concentration-dependent blocks of IKs and tail current (IKs-tail). The IC50 value for block of IKs-tail was 33 (95% confidence limits: 24-46) mumol.L-1. The time constant of IKs-tail deactivation was (92 +/- 18) ms in the control and (84 +/- 16) ms in the presence of Dau 30 mumol.L-1 (n = 8 cells from 4 animals, P > 0.05). (3) Addition of Dau 30 mumol.L-1 induced block of IKs and IKs-tail (n = 7 cells from 3 animals). The degree of block of IKs and IKs-tail depended on test potentials, increasing with more positive depolarizations. (4) Dau 20 mumol.L-1 blocked mainly inward component of IKl and reduced the reversal potential from -72 mV (control) to -78 mV (n = 6 cells from 3 animals). CONCLUSION: (1) Dau inhibited IKs, but not the process of IKs deactivation. (2) Dau blocked IKr, but not the process of deactivation. (3) Dau had a blocking effect on IKl. (+info)
Effect of tetrandrine on morphine dependence in isolated guinea pig ileum.
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AIM: To evaluate the effects of tetrandrine (Tet) and nimodipine (Nim) on the morphine (Mor) withdrawal response in the isolated guinea pig ileum. METHODS: The withdrawal contracture was elicited by addition of naloxone (Nal) (1 mumol.L-1) to the isolated naive ileum incubated with Mor (3 mumol.L-1) at 37.5 degrees C for 4 h or to the ileum obtained from Mor-dependent guinea pig. RESULTS: When Nim (0.01, 0.05, and 0.1 mumol.L-1) or Tet (1, 10, and 50 mumol.L-1) was added 1 min before Nal in the naive ilea bathed in Krebs solution containing Mor, or when the ilea from Mor-dependent guinea pigs were incubated with Nim (0.01, 0.05, and 0.1 mumol.L-1) or Tet (1, 10, and 50 mumol.L-1) for 15 min, or when Nim (5 and 10 mg.kg-1, i.p.) or Tet (15 and 30 mg.kg-1, i.p.) was administered in vivo to Mor-dependent guinea pigs, the Nal-precipitated withdrawal contracture was significantly decreased in a dose-dependent manner. CONCLUSION: Tet and Nim, Ca2+ channel blockers, could inhibit the Nal-precipitated Mor withdrawal response in the isolated guinea pig ileum. (+info)
Effects of berbamine on intracellular calcium concentration in cultured HeLa cells.
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AIM: To study the involvement of Ca2+ signaling and the effects of berbamine (Ber) on intracellular calcium concentration ([Ca2+]i) elevated in cultured HeLa cells. METHODS: [Ca2+]i was measured by confocal microscopy in single HeLa cell loaded with Fluo 3-AM. The change of [Ca2+]i was represented by fluorescent intensity (FI). RESULTS: (1) In the presence of extracellular Ca2+ 1.3 mmol.L-1, the resting level of FI was 186 +/- 44, n = 49 cells from all control experiments, and KCl, NE, caffeine, and calcimycin (Cal) all induced [Ca2+]i elevations in cultured HeLa cells. (2) The resting level of FI was not affected by pretreatment with Ber. The FI increased by KCl 60 mmol.L-1, NE 100 micromol.L-1, and Cal 30 micromol.L-1 were attenuated (P < 0.05 or P < 0.01), the slope and the time to peak of FI increase were decreased and prolonged. (3) In the absence of extracellular Ca2+, caffeine 80 mmol.L-1-induced [Ca2+]i mobilization was not inhibited by Ber 100 micromol.L-1 pretreatment. (4) These effects of Ber were similar to those of verapamil (Ver) 10 mumol.L-1. CONCLUSION: Although it was derived from cervical cancer, the HeLa cells which were belong to the nonexcitable cell possessed the similar biological properties with excitable cells, and Ca2+ also played a crucial role in signal transduction processes. (+info)
Western and Chinese antirheumatic drug-induced T cell apoptotic DNA damage uses different caspase cascades and is independent of Fas/Fas ligand interaction.
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Spontaneous or therapeutic induction of T cell apoptosis plays a critical role in establishing transplantation tolerance and maintaining remission of autoimmune diseases. We investigated the mechanisms of apoptosis induced by Chinese and Western antirheumatic drugs (ARDs) in human T cells. We found that hydroxychloroquine, Tripterygium wilfordii hook F, and tetrandrine (Tet), but not methotrexate, at therapeutic concentrations can cause T cell death. In addition, Tet selectively killed T cells, especially activated T cells. Although ARD-induced cytotoxicity was mediated through apoptotic mechanisms, Fas/Fas ligand interaction was not required. We further demonstrated that the processes of phosphatidylserine externalization and DNA damage along the ARD-induced T cell apoptotic pathway could operate independently, and that selective inhibition of DNA damage by caspase inhibitors did not prevent T cells from undergoing cell death. Moreover, we found that Tet- and Tripterygium wilfordii hook F-induced T cell DNA damage required caspase-3 activity, and hydroxychloroquine-induced T cell DNA damage was mediated through a caspase-3- and caspase-8-independent, but Z-Asp-Glu-Val-Asp-fluomethyl ketone-sensitive, signaling pathway. Finally, the observation that ARD-induced activation of caspase-3 in both Fas-sensitive and Fas-resistant Jurkat T cells indicates that Fas/Fas ligand interaction plays no role in ARD-induced T cell apoptosis. Our observations provide new information about the complex apoptotic mechanisms of ARDs, and have implications for combining Western and Chinese ARDs that have different immunomodulatory mechanisms in the therapy of autoimmune diseases and transplantation rejection. (+info)
Reciprocal regulation of capacitative and arachidonate-regulated noncapacitative Ca2+ entry pathways.
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Receptor-activated Ca(2+) entry is usually thought to occur via capacitative or store-operated Ca(2+) channels. However, at physiological levels of stimulation, where Ca(2+) store depletion is only transient and/or partial, evidence has suggested that an arachidonic acid-dependent noncapacitative Ca(2+) entry is responsible. Recently, we have described a novel arachidonate-regulated Ca(2+)-selective (ARC) conductance that is entirely distinct from store-operated conductances in the same cell. We now show that these ARC channels are indeed specifically activated by low agonist concentrations and provide the predominant route of Ca(2+) entry under these conditions. We further demonstrate that sustained elevations in cytosolic Ca(2+), such as those resulting from activation of store-operated Ca(2+) entry by high agonist concentrations, inhibit the ARC channels. This explains earlier failures to detect the presence of this noncapacitative pathway in experiments where store-operated entry had already been fully activated. The result is that the respective activities of ARC and store-operated Ca(2+) channels display a unique reciprocal regulation that is related to the specific nature of the [Ca(2+)](i) signals generated at different agonist concentrations. Importantly, these data show that at physiologically relevant levels of stimulation, it is the noncapacitative ARC channels that provide the predominant route for the agonist-activated entry of Ca(2+). (+info)
Differential role of cytosolic phospholipase A2 in the invasion of brain microvascular endothelial cells by Escherichia coli and Listeria monocytogenes.
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Invasion of brain microvascular endothelial cells (BMECs) is a key step in the pathogenesis of meningitis due to Escherichia coli and Listeria monocytogenes. Although host cell actin cytoskeletal rearrangements are essential in BMEC invasion by E. coli K1 and L. monocytogenes, the underlying signaling mechanisms remain unclear. This study demonstrates that host cell cytosolic phospholipase A2 (cPLA2) contributes to E. coli K1 invasion of BMECs but not to L. monocytogenes invasion of BMECs. This difference was observed with 4-bromophenacyl bromide, a nonselective PLA2 inhibitor, and arachidonyl trifluoromethyl ketone, a selective cPLA2 inhibitor, and was confirmed with BMEC derived from cPLA2 knockout mice. Activation of cPLA2 leads to generation of intracellular arachidonic acid, which is metabolized via cyclooxygenase (COX) and lipo-oxygenase (LOX) pathways into eicosanoids. COX and LOX inhibitors also significantly inhibit E. coli K1 invasion of BMECs. (+info)
Cardiovascular actions of Radix Stephaniae Tetrandrae: a comparison with its main component, tetrandrine.
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A comparison of the cardiovascular actions of the extract of Radix Stephaniae Tetrandrae (RST), the root of a Chinese hero Stephania tetrandra S Moore, in rats with those of tetrandrine (Tet), the best known active component of RST was reviewed. The RST extract inhibits Ca2+ influx into the myocyte and reduces protein release during reperfusion with a Ca2+ containing solution following perfusion with a Ca2+ free solution (Ca2+ paradox), and arrhythmia during reperfusion in the isolated perfused heart. It also reduces the infarct size induced by ischemia/reperfusion in vitro and in vivo. In addition, the RST extract suppresses elevation of arterial blood pressure in DOCA-salt hypertensive rats. It does not further reduce the heart rate and coronary flow significantly during myocardial ischemia. The effects are similar to those of Tet. When compared with the same doses of Tet alone, the RST extract, of which 9% is Tet, produces equally potent effects on infarction, arrhythmias, coronary flow and heart rate, and has a greater inhibitory effect on protein release during Ca2+ paradox. The combination at 1:1 ratio of Tet and fangchinoline (Fan), another main component, which constitutes 6% of the RST extract and has no significant effects on the heart, produces comparable effects on protein release during Ca2+ paradox as Tet alone. The observations suggest that the efficacy of the RST extract cannot be accounted for by Tet alone. Some of the effects may be due to an interaction between the components of the extract. The RST extract also produces similar effects as verapamil, a prototype Ca2+ channel antagonist widely used in the treatment of ischemic heart diseases and hypertension, except that verapamil, at 1 mumol/L, a concentration that produces similar cardiac effects as the RST extract, further reduces heart rate significantly during ischemia. So the RST extract may be a therapeutically better agent in the treatment of ischemic heart diseases and hypertension than Ca2+ channel antagonists because of the absence of the inhibitory effect on heart rate during myocardial ischemia. (+info)