Increased spontaneous unit activity and appearance of spontaneous negative potentials in the goldfish tectum during refinement of the optic projection.
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Spontaneous (not retinally driven) postsynaptic activity was examined during activity-dependent refinement of optic fibers in the goldfish tectum. Unit recordings in vivo and in vitro demonstrated that spontaneous tectal activity increased to 150% of normal during refinement at 1-2 months after optic nerve crush and subsequently returned to baseline over the next month. This increase was not mimicked by long-term denervation indicating an effect specifically influenced by regenerating fibers. Loss of optic input was also found to induce spontaneous negative potentials (SNPs) rapidly in the tectum. SNPs were negative, monophasic potentials of 70-120 msec duration and -0.15 to -1.5 mV amplitude. SNPs occurred with no apparent periodicity at a frequency of approximately 0.3-0.6 Hz. Multiple electrode recordings and depth analysis showed that SNPs were localized events occurring in columnar domains of tectum a few hundred micrometers wide. Cross-correlation analysis revealed that SNPs were strongly correlated with local unit bursting, suggesting SNPs are generated by the summed synaptic and spike currents of coactive cells in small regions of the tectum. SNPs were suppressed by a low concentration of APV indicating they were regulated by NMDA receptors. During regeneration, the number and size of SNPs reached a peak during refinement and subsequently decreased, eventually disappearing. This temporal association with refinement suggests that these patterns of postsynaptic activity may have functional relevance. It is hypothesized that SNPs or the underlying activity that produces them increases the excitability of target cells, allowing the weak, less-convergent input from regenerating axons to drive target groups of cells in the tectum during refinement. (+info)
Effects of berbamine on ATP-induced [Ca2+]i mobilization in cultured vascular smooth muscle cells and cardiomyocytes.
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AIM: To study the effects of berbamine (Ber) on [Ca2+]i homeostasis induced by adenosine triphosphate (ATP) in vascular smooth muscle cells (VSMC) of rabbits and cardiomyocytes of rats. METHODS: Both cell types were cultured and loaded with Fura 3-AM. [Ca2+]i was measured by fluorescent intensity (FI) in each cell with confocal microscopy. RESULTS: (1) ATP 30 mumol.L-1 elevated [Ca2+]i in VSMC and cardiomyocytes, FI values reached 660 +/- 258 and 1058 +/- 252 from 250 +/- 84 and 218 +/- 76 at 19 s +/- 5 s and 11.8 s +/- 2.4 s, but FI in nucleus was not changed in VSMC. (2) Ber 30 mumol.L-1 did not affect the resting FI in both cell types, but prolonged the time to peak (P < 0.01) and reduced the FI elevated by ATP (P < 0.01), but not completely inhibited even at 100 mumol.L-1. (3) In D-Hanks' solution or in the presence of egtazic acid (EGTA) 3 mmol.L-1, the inhibitory effect of Ber was not seen (P > 0.05). (4) All effects of Ber on ATP-induced [Ca2+]i mobilization were similar to those of Ver 10 mumol.L-1. CONCLUSION: In VSMC and cardiomyocytes, ATP-induced CA2+ influx was inhibited by Ber and Ver, while the Ca2+ release was not. (+info)
Effects of tetrandrine on changes of NMDA receptor channel in cortical neurons of rat induced by anoxia.
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AIM: To study the effects of tetrandrine (Tet) on the changes of NMDA receptor channels in cortical neurons induced by anoxia. METHODS: Cell-attached configuration of patch-clamp techniques. Anoxia was produced by perfused cells with 95% N2 + 5% CO2 gassed bath solution. RESULTS: During anoxia, the open time constant (tau 2), open probability (Po) of 35-pS and 100-pS channels increased. Tet 7.5 mumol.L-1 reduced the Po of 35-pS and 100-pS channels, 15 and 30 mumol.L-1 inhibited open of 100-pS channel fully, and changed the open time constant of 35-pS from two to single exponential distribution. CONCLUSION: Tet inhibition of the open of NMDA receptor channels induced by anoxia was one of its protective mechanisms. (+info)
Dauricine suppressed CsCl-induced early afterdepolarizations and triggered arrhythmias in rabbit heart in vivo.
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AIM: To study the effect of dauricine on CsCl-induced early afterdepolarizations (EAD) and ventricular arrhythmias in rabbits. METHODS: Monophasic action potentials (MAP) of the left ventricle of the rabbit heart in situ were recorded with MAP recording technique. CsCl 1-2 mmol.kg-1 i.v. was used to induce EAD and ventricular arrhythmias. RESULTS: CsCl resulted in decrease of MAP amplitude (MAPA, P < 0.05) and prolongation of MAP duration at 90% repolarization (MAPD90, P < 0.01), QRS, and R-R duration (P < 0.05) compared with those before CsCl in the dauricine and control group. CsCl injection induced EAD that appeared within about 30 s and disappeared 5-15 min thereafter. EAD always preceded ventricular arrhythmias including ventricular premature beats and paroxysmal ventricular tachycardia. The EAD amplitude (EADA) in the dauricine group (26% +/- 9% of MAPA) was smaller than that in the control group (52% +/- 5% of MAPA, P < 0.05) and the incidence of arrhythmias in dauricine group (28%) was lower than that in control group (80%, P < 0.05). CONCLUSION: Dauricine exerted an antagonistic effect on EAD and suppressed triggered ventricular arrhythmias by decreasing EADA. (+info)
Dauricine inhibits redistribution of platelet membrane glycoprotein IV and release of intracellular alpha-granule thrombospondin induced by thrombin.
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AIM: To study the possibility of dauricine (Dau) inhibiting redistribution of platelet membrane glycoprotein IV (GPIV) and release of intracellular alpha-granule thrombospondin (TSP) on platelet activation. METHODS: Using the flow cytometric assay of washed platelet to record expression of GPIV and release of TSP induced by thrombin. RESULTS: Dau did not affect GPIV and TSP on resting platelet membrane but inhibited redistribution of GPIV to the platelet surface and TSP release on activated platelet. There was a marked positive correlation between changes of GPIV and TSP (r = 0.511, P < 0.01). The inhibitory effect of Dau appeared not to be Ca2+ concentration-dependent. CONCLUSION: Dau inhibited redistribution of GPIV and release of intracellular alpha-granule thrombospondin induced by thrombin. (+info)
Evidence for P(2)-purinoceptors contribution in H(2)O(2)-induced contraction of rat aorta in the absence of endothelium.
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OBJECTIVE: H(2)O(2) can contract many arteries, however the underlying mechanisms are not fully understood. This study aims to test whether H(2)O(2)-induced vasoconstriction could be functionally attributed to the activation of P(2)-purinoceptors in rat aorta and to explore its possible signaling mechanisms. METHODS: Isometric tension recording of H(2)O(2) and ATP-induced contractions of rat aortic rings were compared in the absence or presence of various pharmacological tools to identify their possible common signaling pathways. RESULTS: Both H(2)O(2) and ATP induced transient phasic contractions in a concentration-dependent manner (1-1000 microM). Removal of endothelium potentiated the contractile responses to H(2)O(2) and to ATP. H(2)O(2) (30 microM)-induced phasic contraction could be abolished by catalase (800 U/ml), but not affected by SOD (150 U/ml), DMSO (5 mM) and apyrase (5 U/ml), suggesting no involvement of O(2)(-), hydroxyl free radicals and ATP release. Also, several receptor antagonists including phentolamine, atropine, methysergide and chlorpheniramine (each 3 microM) were without effect on H(2)O(2) (30 microM)-induced phasic contraction, suggesting no involvement of typical neurotransmitter release. However, both H(2)O(2) (30 microM) and ATP (1 mM)-induced phasic contractions not only presented homologous desensitization, but also showed heterogeneous desensitization. Furthermore, the phasic contractions in response to H(2)O(2) (30 microM) or ATP (100 microM) could be inhibited or abolished in a concentration dependent manner by RB-2 and suramin (10-100 microM), two widely used P(2)-purinoceptor antagonists, with only partial inhibition by Evans blue (300 microM), a moderately selective P(2x) receptor blocker, or by alpha-beta-methylene-ATP (100 microM), a selective P(2x) receptor desensitizer. On the other hand, both H(2)O(2) (30 microM) and ATP (100 microM)-induced phasic contractions were also attenuated, to different degree, by inhibitors of several enzymes including PLC, PKC, PLA(2) and cyclooxygenase. Lastly, removal of extracellular Ca(2+) or pretreatment with procaine (10 mM) and dantrolene (30 microM), two putative intracellular Ca(2+) release blockers, or with Ni(2+) (100 microM) and tetrandrine (5 microM), two Ca(2+) channel blockers, all significantly inhibited H(2)O(2) and ATP-induced contractions. However, nifedipine (1 microM), a voltage-dependent L-type Ca(2+) channel blocker, was without effect. CONCLUSIONS: Our results demonstrate that H(2)O(2)-induced phasic contraction of rat aorta involves, at least in part, the activation of P(2)-purinoceptors in the aortic smooth muscle cells (+info)
Potent enhancement of the sensitivity of Plasmodium falciparum to chloroquine by the bisbenzylisoquinoline alkaloid cepharanthin.
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Cepharanthin is a proprietary extract of Stephania cepharantha, widely used in Japan for the treatment of inflammatory diseases. Cephranthin, its component alkaloids, and the standard resistance modulator verapamil were tested against Plasmodium falciparum for capacity to modulate sensitivity to chloroquine. Cepharanthin enhanced the activity of chloroquine against resistant clones by a factor of 15 at a concentration of only 200 nM (1.2 ng/ml). It is 50 times more potent than verapamil and 3 times more potent than the sum of its individual alkaloids. Combinations of component alkaloids acted synergistically to sensitize the parasite to chloroquine, possibly explaining the enhanced potency of Cepharanthin. Cepharanthin differed from verapamil in that it further sensitized clones that are considered to be fully susceptible, improving the baseline activity of chloroquine. Potent sensitization of parasites to chloroquine in vitro coupled with low toxicity suggests that coadministration of Cepharanthin might extend the clinical utility of chloroquine. (+info)
Effects of tetrandrine on calcium transport, protein fluorescences and membrane fluidity of sarcoplasmic reticulum.
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To understand whether the molecular mechanism of Tetrandrine (Tet)'s pharmacological effects is concerned with sarcoplasmic reticulum calcium transport so as to be involved in myocardial contractility, we observed the effects of Tet on calcium transport and membrane structure of rabbit skeletal muscle sarcoplasmic reticulum vesicles (SR) and rat cardiac sarcoplasmic reticulum vesicles (CSR). Calcium uptake was monitored with a dual-wavelength spectrophotometer. Protein conformation and fluorescence polarization were measured by fluospectrophotometric method and membrane lipids labelled with fluorescence probes for SR, respectively. 128 micromol l(-1) Tet reduced the initial rate of calcium uptake to 59% of control 6 min after reaction. Tet un-competitively inhibited SR Ca(2+), Mg(2+)-ATPase activity, causing the stoichiometric ratio of SR Ca(2+)/ATP to decrease to 1.43 from 2.0 of control. Inhibitory rates on SR Ca(2+),Mg(2+)-ATPase by Tet were reduced from 60% in the absence of phosphate to 50% in the presence of phosphate and reduced from 92% in 1 mmol l(-1) ATP to 60% in 5 mmol l(-1) ATP. Tet markedly reduced SR intrinsic protein fluorescence, while it slightly decreased the thiol(SH)-modified protein fluorescence of SR labelled with N-(3-pyrene)-maleimide. Tet slightly increased fluorescence polarization in the middle and deep layers of SR membrane lipids labelled with 7- or 12-(9-anthroyloxy) stearic acid (AS) probes, whereas it did not change that of SR labelled with 1, 6-diphenyl-1,3,5-hexatrine (DPH). These results revealed that prevention of SR calcium uptake by Tet was due to inhibition of the SR calcium pump Ca(2+),Mg(2+)-ATPase, changes in spatial conformation of the pumps protein molecules and a decrease in the extent of motion of membrane lipid molecules, thus altering the regulation of [Ca(2+)](i) and myocardial contractility. (+info)