A prestep of 30 msec to -40 mV was used to inac-tivate sodium currents. Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 microM ouabain. Effect of cardiac glycosides on action potential characteristics and contractility in cat ventricular myocytes: role of calcium overload. mV in 10 mV increments for 250 msec. Ouabain / w ɑː ˈ b ɑː ɪ n / or / ˈ w ɑː b eɪ n, ˈ w æ-/ (from Somali waabaayo, "arrow poison" through French ouabaïo) also known as g-strophanthin, is a plant derived toxic substance that was traditionally used as an arrow poison in eastern Africa for both hunting and warfare. a holding potential of -80 mV to voltage steps from -40 to +60Figure 1. AP short-ening was observed only with ouabain … In contrast to ouabain. 31 and 33 min) of the atrium isolated from a rabbit (day 90). 10. Ouabain abolished both the p.d. (B) The superimposed tracings show the effects of ouabain (0.1, 1μM) on the AP configuration and contractile force. This suggests that sodium/calcium exchange has little voltage dependence in this situation. Ouabain (10(-6) g/ml) caused characteristic alterations in the tension-frequency relationship, enhancing the contractile tension at low but not high frequencies. The slow inward current and the maximum slow conductance also decreased under ouabain. The purpose of this study was to evaluate the effects of aging on the LA electrophysiological heterogeneity and ouabain-induced arrhythmogenicity. tiple sites of action, we studied changes in contractility and action potential (AP) configuration in cat ventricular myocytes produced by six cardiac glycosides (ouabain, ouabagenin, di-hydroouabain, actodigin, digoxin, and resibufogenin). Action potential durations were significantly influenced by alterations in frequency of contraction. Effects of ouabain on the PVs without spontaneous activity. To determine whether the responses of resting membrane potential (RMP) and hyperpolarization-activated current (IH) are altered by the application of ouabain, one of the Na+-K+ pump inhibitors, in neonatal rat small-diameter (<30microm) nodose ganglion (NG) neurons, we examined the effects of 1microM ouabain on those responses using perforated patch-clamp techniques. The threshold for decrease in ak, increase in aeK, and de-crease in membrane potential is 1 ,uM, at which con-centration … This review article focuses on the cardenolide ouabain and discusses its various in vitro and in vivo effects, its role as an endogenous compound, its mechanisms of action, and its potential use as a therapeutic agent; placing especial emphasis on our findings of ouabain as a pro-cystogenic agent in autosomal dominant polycystic kidney disease (ADPKD). Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 microM ouabain. What do you think would happen to the neuronal action potential if the concentration of sodium ions in the extracellular fluid decreased significantly, to the point of reversing the gradient? Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 ,uM ouabain. At 10 nM ouabain, action potential duration is prolonged. E-4031 at 3.0 µmol/L potentiated the positive inotropic effect of ouabain and shortened T75% (Table 3, Figs.1 and 3). The potential would be above the resting state and can potentially lead to active depolarization. At 10 nM ouabain, action potential duration is prolonged. (1973) studied the toxic effect of ouabain on electrocar-diogram and transmembrane action potential in isolated canine Purkinje fibers. The calcium current was blocked by adding 0.1 mM CdCl 2 to Tyrode's solution. We have studied the effect of hypoxia and ouabain on the muscle resting potential (RP) of the cockroach Periplaneta americana L. The experiments were done in insects reared either in normoxic or hypoxic conditions and treated, or not treated, with Methods: 14 rabbits were divided into two groups at random, control group and THP group. At 10 nM ouabain, action potential duration is prolonged. It was recently discovered that ouabain, long thought to be exclusively a plant product, is actually synthesized by animals, and secreted from the adrenal cortex to regulate body osmosis and cellular concentrations of sodium. The level of membrane potential was modulated by passing intracellular polarizing current. The mucosal to serosal flux of Na+ and the serosal to mucosal flux of Cl‐ were significantly decreased in the presence of ouabain. The inactivation of I to was measured These effects could explain the negative inotropic action of high concentrations of glycosides, as well as the action potential changes observed by several investigators. The effect on the transmembrane action potentials normally seen with ouabain (an acceleration of repolarization) was noted even in the face of a negative inotropic effect at low Ca ++ concentrations. bain, action potential duration is prolonged. Adrenaline elevated the depressed plateau of the action potential from calf and sheep Purkinje fibres, but ouabain and glucagon were without effect. In the presence of ouabain (5 × 10 −4 M ), the membrane potential depolarized to a constant level for 1‐4 hr, then hyperpolarized for 5‐7 hr after which it gradually depolarized again. They also help to understand the arrhythmogenic effects of high concentrations of digitalis. The inotropic effects of ouabain were retained even after pretreatment with saxitoxin (5 μmol/l) or changing the holding potential to −40 mV (to inactivate Na + current). The long‐term effects of ouabain on the membrane potential of the Anisodoris giant neurone (G cell) were examined in cells maintained for periods of up to 15 hr at 11–13° C. 2. Figure I Effects of ouabain on the action potential recorded from an atrial cell (up to 22 min) and an S-A nodal cell (26. The effect of membrane potential on the manifestations of ouabain-induced alterations in the electrical activity of shortened sheep cardiac Purkinje fibres was studied by a microelectrode technique. The effects of ouabain ... the duration of both the calcium-dependent action potential and the afterhyperpolarization following the action potential was prolonged by ouabain (≥10nM). The stimulatory effect of DBcAMP on H+ secretion was still present after pretreatment with cimetidine or atropine. To more fully define differences between agents indicative of multiple sites of action, we studied changes in contractility and action potential (AP) configuration in cat ventricular myocytes produced by six cardiac glycosides (ouabain, ouabagenin, dihydroouabain, actodigin, digoxin, and resibufogenin). Rosen et al. The effects of EO on the myocardial action potential and transient potassium efflux (Ito) were measured by patch clamping. Inclusion of 1×10 −3 M ouabain into the 1×10 −3 M Ethacrynic acid perilymph perfusate reduced the anoxia sensitive negative potential by 50 to 80% in the utricle and cochlea respectively. The positive inotropic effect of 1.6 μM veratridine declines progressively when the contraction frequency is reduced below 0.5 Hz; rested-state contractions (at 0.004 Hz) are not increased by 1.6 μM veratridine. 3. In four experiments, alpha ik and contractile force were measured in the same muscle. Author information: (1)Department of Medicine, Feinberg Cardiovascular Research Institute, Northwestern University Medical School, Chicago, IL 60611, USA. Ouabain at 0.5 µmol/L increased LVSP-LVEDP, +dp/ Table 1. (A) The tracings show an example of ouabain (1μM) induced PV firing in a PV without spontaneous activity. six cardiac glycosides on action potential and contractile characteristics, and showed that digitoxin has a dose-related prolongation effect on action potential duration. The image below represents its biosynthesis and … Its value depended on drug concentration. and ISC of the histamine‐stimulated gastric mucosa. Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 microM ouabain. 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