Author information: (1)Department of Medicine, Feinberg Cardiovascular Research Institute, Northwestern University Medical School, Chicago, IL 60611, USA. E-4031 at 3.0 µmol/L potentiated the positive inotropic effect of ouabain and shortened T75% (Table 3, Figs.1 and 3). 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? 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. 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. 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. b) The action potential causes a change in the proteins on the vesicle membranes such that the vesicle binds to the cell membrane and begins exocytosis c) The action potential triggers voltage-gated Ca2+ channels to open and the Ca2+ that flows in starts a cascade of protein reactions that allows exocytosis of the neurotransmitters 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. Ouabain at 0.5 µmol/L increased LVSP-LVEDP, +dp/ Table 1. 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. Electrophysiological measurements demonstrated that moderate concentrations of glucagon exerted only a small effect in prolonging atrial and ventricular action potentials. After atrial action potentials disappeared, oscillatory potentials were recorded from an S-A nodal cell. In four experiments, alpha ik and contractile force were measured in the same muscle. bain, action potential duration is prolonged. The effects of EO on the myocardial action potential and transient potassium efflux (Ito) were measured by patch clamping. (A) The tracings show an example of ouabain (1μM) induced PV firing in a PV without spontaneous activity. 3. The mucosal to serosal flux of Na+ and the serosal to mucosal flux of Cl‐ were significantly decreased in the presence of ouabain. The calcium current was blocked by adding 0.1 mM CdCl 2 to Tyrode's solution. Alpha iK was measured with single and double-barrel K-sensitive electrodes. 10. At 10 nM ouabain, action potential duration is prolonged. Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 microM ouabain. 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). This effect was: (a) approximately the same over a range of external potassium concentrations from 0.3 to 5 m m, although the absolute effect of ouabain over this range of potassium was much different; (b) probably not due to different isoforms of pumps in cells grown in ouabain compared to untreated cells; (c) apparently not a consequence of internalisation of pump‐glycoside complexes. Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 microM ouabain. both norepinephrine and isoproterenol produced positive inotropic effects … (B) The superimposed tracings show the effects of ouabain (0.1, 1μM) on the AP configuration and contractile force. 4. In contrast to ouabain. 6. 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). Predict the effect of the poison ouabain which blocks Na+/K+ pumps, on the neuronal action potential. The stimulatory effect of DBcAMP on H+ secretion was still present after pretreatment with cimetidine or atropine. 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. The effect was reversible. Effects of ouabain on the PVs without spontaneous activity. Among the concentrations tested, the threshold for a clear positive inotropic effect is 0.1 microM ouabain. 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