At 10 nM ouabain, action potential duration is prolonged. AP short-ening was observed only with ouabain … Author information: (1)Department of Medicine, Feinberg Cardiovascular Research Institute, Northwestern University Medical School, Chicago, IL 60611, USA. 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. 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 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. A similar anoxia sensitive negative potential was not produced by the application of ouabain in either the utricle or cochlea even though both potentials were reduced to negative values. They also help to understand the arrhythmogenic effects of high concentrations of digitalis. The systolic blood pressure (SBP) of 10 of the 12 rats in the EO group, designated as the EO-sensitive (OS) rats, began to increase from the fifth week of treatment and was significantly higher compared with that of the control group 6 weeks later (P 0.01). The inactivation of I to was measured Electrophysiological measurements demonstrated that moderate concentrations of glucagon exerted only a small effect in prolonging atrial and ventricular action potentials. 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). 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). Transmembrane potential, isometric tension, and K 42 content of sheep or calf myocardial bundles were recorded simultaneously during periods up to 30 hours. The threshold for decrease in ak, increase in aeK, and de-crease in membrane potential is 1 ,uM, at which con-centration … Its value depended on drug concentration. Effect of cardiac glycosides on action potential characteristics and contractility in cat ventricular myocytes: role of calcium overload. 4. After atrial action potentials disappeared, oscillatory potentials were recorded from an S-A nodal cell. Alpha iK was measured with single and double-barrel K-sensitive electrodes. The effects of EO on the myocardial action potential and transient potassium efflux (Ito) were measured by patch clamping. Ouabain therefore potentiated the effect of membrane potential on calcium influx. 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? Ouabain is a selective Na+/K+, -ATPase inhibitor, binds to α2 /α3 subunit with Ki of 41 nM/15 nM. This suggests that sodium/calcium exchange has little voltage dependence in this situation. 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. Rosen et al. Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 microM ouabain. 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. Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 microM ouabain. The potential would be above the resting state and can potentially lead to active depolarization. Objective: To study the effect and mechanism of tetrahydropalmatine (THP) ouabain-induced on delayed after depolarization (DAD) and anti-triggered ventricular arrhythmia in in-vivo rabbit heart. The mucosal to serosal flux of Na+ and the serosal to mucosal flux of Cl‐ were significantly decreased in the presence of ouabain. The negative inotropic effect of acetylcholine was reduced by treatment with ouabain.3. 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. These effects could explain the negative inotropic action of high concentrations of glycosides, as well as the action potential changes observed by several investigators. 31 and 33 min) of the atrium isolated from a rabbit (day 90). 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). 10. Effects of E-4031, KB-R7943 and ouabain on the rat pap-illary muscles Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 ,uM ouabain. 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. The purpose of this study was to evaluate the effects of aging on the LA electrophysiological heterogeneity and ouabain-induced arrhythmogenicity. The level of membrane potential was modulated by passing intracellular polarizing current. A prestep of 30 msec to -40 mV was used to inac-tivate sodium currents. Ouabain abolished both the p.d. The effect was reversible. Effects of ouabain on the PVs without spontaneous activity. The calcium current was blocked by adding 0.1 mM CdCl 2 to Tyrode's solution. both norepinephrine and isoproterenol produced positive inotropic effects … 6. 3. 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). Ouabain at 0.5 µmol/L increased LVSP-LVEDP, +dp/ Table 1. Ouabain at low concentrations (1.5 x 10-8 M/L) decreased intracellular K to a new steady level which was reached after several hours. The stimulatory effect of DBcAMP on H+ secretion was still present after pretreatment with cimetidine or atropine. (A) The tracings show an example of ouabain (1μM) induced PV firing in a PV without spontaneous activity. (1973) studied the toxic effect of ouabain on electrocar-diogram and transmembrane action potential in isolated canine Purkinje fibers. Adrenaline elevated the depressed plateau of the action potential from calf and sheep Purkinje fibres, but ouabain and glucagon were without effect. Predict the effect of the poison ouabain which blocks Na+/K+ pumps, on the neuronal action potential. (B) The superimposed tracings show the effects of ouabain (0.1, 1μM) on the AP configuration and contractile force. 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. six cardiac glycosides on action potential and contractile characteristics, and showed that digitoxin has a dose-related prolongation effect on action potential duration. Dihydro-ouabain or reduction of [K] o below 5.9 mM augment the positive inotropic effect of veratridine, while the interaction between veratridine and noradrenaline is additive. 90 ) resting state and can potentially lead to active depolarization six glycosides! 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