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Square Wave Pulses (square + wave_pulse)
Selected AbstractsAntiepileptogenic and antiictogenic effects of retigabine under conditions of rapid kindling: An ontogenic studyEPILEPSIA, Issue 10 2008Andréy Mazarati Summary Purpose:, To examine antiepileptogenic and antiictogenic potential of retigabine (RTG) under conditions of rapid kindling epileptogenesis during different stages of development. Methods:, The experiments were performed in postnatal day 14 (P14), P21, and P35 male Wistar rats. After stereotaxic implantation of hippocampal stimulating and recording electrodes, the effects of RTG on baseline afterdischarge (AD) properties were studied. Next, the animals underwent rapid kindling (sixty 10 s trains, bipolar 20 Hz square wave pulses delivered every 5 min). The progression of seizures (kindling acquisition), and responses to test stimulations after kindling (retention) were compared between RTG and vehicle-treated rats. Additionally, the effects of RTG on the severity of seizures in previously kindled animals were examined. Results:, When administered intraperitoneally in doses that induced only mild, or no motor deficits, RTG significantly dampened brain excitability, evident as the increase of AD threshold and shortening of AD duration. During kindling, RTG delayed the development of focal seizures in P14 rats, and prevented the occurrence of full limbic seizures at all three ages. At P14 and P21, but not at P35, pretreatment with RTG prevented the establishment of kindling-induced enhanced seizure susceptibility. Administration of RTG to kindled animals decreased the severity of seizures induced by test stimulation. The effect was most prominent at P14. Discussion:, RTG exerted both antiepileptogenic and antiictogenic effects under conditions of rapid kindling model. These effects were apparent during postneonatal, early childhood, and adolescent stages of development. [source] Inactivation of orange juice peroxidase by high-intensity pulsed electric fields as influenced by process parametersJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 1 2006Pedro Elez-Martínez Abstract The inactivation of orange juice peroxidase (POD) under high-intensity pulsed electric fields (HIPEF) was studied. The effects of HIPEF parameters (electric field strength, treatment time, pulse polarity, frequency and pulse width) were evaluated and compared with conventional heat pasteurization. Samples were exposed to electric field strengths from 5 to 35 kV cm,1 for up to 1500 µs using square wave pulses in mono- and bipolar mode. Effect of pulse frequency (50,450 Hz), pulse width (1,10 µs) and electric energy on POD inactivation by HIPEF were also studied. Temperature was always below 40 °C. POD was totally inactivated by HIPEF and the treatment was more effective than thermal processing in inactivating orange juice POD. The extent of POD inactivation depended on HIPEF processing parameters. Orange juice POD inhibition was greater when the electric field strength, the treatment time, the pulse frequency and the pulse width increased. Monopolar pulses were more effective than bipolar pulses. Orange juice POD activity decreased with electric energy density input. The Weibull distribution function adequately described orange juice POD inactivation as a function of the majority of HIPEF parameters. Moreover, reduction of POD activity related to the electric field strength could be well described by the Fermi model. Copyright © 2005 Society of Chemical Industry [source] Excitatory purinergic neurotransmission in smooth muscle of guniea-pig taenia caeciTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Yong Zhang Non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmission has been an area of intense interest in gut motor physiology, whereas excitatory NANC neurotransmission has received less attention. In order to further explore excitatory NANC neurotransmission, we performed conventional intracellular recordings from guinea-pig taenia caeci smooth muscle. Tissue was perfused with oxygenated Krebs solution at 35°C and nerve responses evoked by either oral or aboral nerve stimulation (NS) (4 square wave pulses, 0.3 ms duration, 20 Hz). Electrical activity was characterized by slow waves upon which one to three action potentials were superimposed. Oral NS evoked an inhibitory junction potential (IJP) at either the valley or peak of the slow wave. Application of nifedipine (1 ,m) abolished slow waves and action potentials, but membrane potential flunctuations (1,3 mV) and IJPs remained unaffected. Concomitant application of apamin (300 nm), a small-conductance Ca2+ -activated K+ channel blocker, converted the IJP to an EJP that was followed by slow IJP. Further administration of NG -nitro- l -arginine methyl ester (l -NAME, 200 ,m), a nitric oxide synthase inhibitor, abolished the slow IJP without affecting the EJP, implying that the slow IJP is due to nitrergic innervation. The EJP was abolished by tetrodotoxin (1 ,m), but was not significantly affected by atropine (3 ,m) and guanethidine (3 ,m) or hexamethonium (500 ,m). Substance P (SP, 1 ,m) desensitization caused slight attenuation of the EJP, but the EJP was abolished by desensitization with ,,,-methylene ATP (50 ,m), a P2 purinoceptor agonist that is more potent than ATP at the P2X receptor subtype, suramin (100 ,m), a non-selective P2 purinoceptor antagonist, and pyridoxal-phosphate-6-azophenyl-2,,4,-disulphonic acid (PPADS, 100 ,m), a selective P2X purinoceptor antagonist. In contrast, the EJP was unaffected by MRS-2179 (2 ,m), a selective P2Y1 receptor antagonist. Aboral NS evoked an apamin- and l -NAME-sensitive IJP, but virtually no NANC EJP. These data suggest the presence of polarized excitatory purinergic neurotransmission in guinea-pig taenia caeci, which appears to be mediated by P2X purinoceptors, most likely the P2X1 subtype. [source] Role of sarcoplasmic reticulum in control of membrane potential and nitrergic response in opossum lower esophageal sphincterBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2003Yong Zhang We previously demonstrated that a balance of Ca2+ -activated Cl, current (ICl(Ca)) and K+ current activity sets the resting membrane potential of opossum lower esophageal sphincter (LES) circular smooth muscle at ,,41 mV, which leads to continuous spike-like action potentials and the generation of basal tone. Ionic mechanisms underlying this basal ICl(Ca) activity and its nitrergic regulation remain unclear. Recent studies suggest that spontaneous Ca2+ release from sarcoplasmic reticulum (SR) and myosin light chain kinase (MLCK) play important roles. The current study investigated this possibility. Conventional intracellular recordings were performed on circular smooth muscle of opossum LES. Nerve responses were evoked by electrical square wave pulses of 0.5 ms duration at 20 Hz. In the presence of nifedipine (1 ,M), substance P (1 ,M), atropine (3 ,M) and guanethidine (3 ,M), intracellular recordings demonstrated a resting membrane potential (MP) of ,38.1±0.7 mV (n=25) with spontaneous membrane potential fluctuations (MPfs) of 1,3 mV. Four pulses of nerve stimulation induced slow inhibitory junction potentials (sIJPs) with an amplitude of 6.1±0.3 mV and a half-amplitude duration of 1926±147 ms (n=25). 1H -[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a specific guanylyl cyclase inhibitor, abolished sIJPs, but had no effects on MPfs. Caffeine, a ryanodine receptor agonist, hyperpolarized MP and abolished sIJPs and MPfs. Ryanodine (20 ,M) inhibited the sIJP and induced biphasic effects on MP, an initial small hyperpolarization followed by a large depolarization. sIJPs and MPfs were also inhibited by cyclopiazonic acid, an SR Ca2+ ATPase inhibitor. Specific ICl(Ca) and MLCK inhibitors hyperpolarized the MP and inhibited MPfs and sIJPs. These data suggest that (1) spontaneous release of Ca2+ from the SR activates ICl(Ca), which in turn contributes to resting membrane potential; (2) MLCK is involved in activation of ICl(Ca); (3) inhibition of ICl(Ca) is likely to underlie sIJPs induced by nitrergic innervation. British Journal of Pharmacology (2003) 140, 1097,1107. doi:10.1038/sj.bjp.0705537 [source] | ||||||||||