scholarly journals Voltage-clamp studies of transient inward current and mechanical oscillations induced by ouabain in ferret papillary muscle

1982 ◽  
Vol 327 (1) ◽  
pp. 255-271 ◽  
Author(s):  
Hrayr S. Karagueuzian ◽  
Bertram G. Katzung
Keyword(s):  
Voltage Clamp ◽  
Papillary Muscle ◽  
Inward Current ◽  
Mechanical Oscillations ◽  
Transient Inward Current

Voltage Sensitive Ca-Channels and the Transient Inward Current in Paramecium Tetraurelia

1979 ◽  
Vol 78 (1) ◽  
pp. 149-161 ◽  
Author(s):  
YOUKO SATOW ◽  
CHING KUNG
Keyword(s):  
Voltage Clamp ◽  
Resting Potential ◽  
Ca Channel ◽  
Paramecium Tetraurelia ◽  
Ca Channels ◽  
Action Current ◽  
Inward Current ◽  
Transient Inward Current ◽  
Inorganic Cation ◽  
Inward Currents

Transient inward currents across the membrane of P. tetraurelia are recorded upon step depolarizations with a voltage clamp in solutions where Ca2+ is the only added inorganic cation. It is shown that the current is normally carried by Ca2+ through the Ca-channels which activate and inactivate in time. The transient inward current is dependent on both the size of the depolarizing step and the holding level before the step. Maximum inward current (Imax) occurs when the membrane is first held at the resting level (- 30 mV), then stepped to 0 mV in a solution containing 0.91 mM-Ca2+. The Imax is smaller when the membrane is first held at depolarized level. This is due to the depolarization-sensitive inactivation of the Ca-channels. The Imax is also smaller when the membrane is first held at a hyperpolarized level. This may be explained by the activation of hyperpolarization-sensitive K-channels known to exist in the Paramecium membrane. I max increases with concentration of Ca2+ up to 0.9 mM. Further increase in the Ca2+ concentration does not affect Imax. This apparent saturation at 0.9 mM-Ca2+ may reflect a rate-limiting step of Ca2+ permeation. The increase in Ca2+ concentration shifts the V-Ipeak curve in the direction of less sensitivity. This result is best explained as the effect of bound Ca2+ on the surface potential of the Paramecium membrane. These results provide the first detailed description of the properties of the action current through the Ca-channel in Paramecium. They also define the conditions under which future voltage-clamp studies of wild-type and mutant membranes of P. tetraurelia should be performed, i.e. to maximize the resolution of the Ca-channel activity, the membrane should be held at or near the resting potential and there should be over 0.9 mM-Ca2+ in the test solutions. The behaviour of the Paramecium Ca-channel and small Imax in the presence of K+ are discussed.

Injection of inositol 1, 3, 4, 5-tetrakisphosphate into Xenopus oocytes generates a chloride current dependent upon intracellular calcium

1987 ◽  
Vol 232 (1266) ◽  
pp. 59-70 ◽  
Keyword(s):  
Intracellular Calcium ◽  
Chloride Channels ◽  
Surface Membrane ◽  
Chelating Agent ◽  
Threshold Current ◽  
Inward Current ◽  
Inositol 1 ◽  
Calcium Dependent ◽  
Transient Inward Current ◽  
The Mean

Injection of inositol 1, 3, 4, 5-tetrakisphosphate (Ins(1, 3, 4, 5)P 4 ) into voltage-clamped oocytes of Xenopus laevis elicited an oscillatory chloride membrane current. This response did not depend upon extracellular calcium, because it could be produced in calcium-free solution and after addition of cobalt to block calcium channels in the surface membrane. However, it was abolished after intracellular loading with the calcium chelating agent EGTA, indicating a dependence upon intracellular calcium. The mean dose of Ins(1, 3, 4, 5)P 4 required to elicit a threshold current was 4 x 10 -14 mol. In comparison, inositol 1, 4, 5-trisphosphate (Ins(1, 4, 5)P 3 ) gave a similar oscillatory current with doses of about one twentieth as big. Hyperpolarization of the oocyte membrane during activation by Ins(1, 3, 4, 5)P 4 elicited a transient inward current, as a result of the opening of calcium-dependent chloride channels subsequent to the entry of external calcium. In some oocytes the injection of Ins(1, 3, 4, 5)P 4 was itself sufficient to allow the generation of the transient inward current, whereas in others a prior injection of Ins(1, 4, 5)P 3 was required. We conclude that Ins(1, 3, 4, 5)P 4 causes the release of intra­cellular calcium from stores in the oocyte, albeit with less potency than Ins(1, 4, 5)P 3 . In addition, Ins(1, 3, 4, 5)P 4 activates voltage-sensitive cal­cium channels in the surface membrane, via a process that may require ‘priming’ by Ins(1, 4, 5)P 3 .

Abstract 17193: Inhibiting Late Sodium Current Attenuates Isoproterenol-Induced Transient Inward Current and Delayed Afterdepolarizations in Ventricular Myocytes

Circulation ◽  
2015 ◽  
Vol 132 (suppl_3) ◽  
Author(s):  
Yejia Song ◽  
Nesrine El-Bizri ◽  
Sridharan Rajamani ◽  
Luiz Belardinelli
Keyword(s):  
Ventricular Myocytes ◽  
Sodium Current ◽  
Selective Inhibition ◽  
Adrenergic Stimulation ◽  
Patch Clamp Technique ◽  
Cardiac Tissues ◽  
Inward Current ◽  
Transient Inward Current ◽  
Whole Cell Patch Clamp ◽  
Series Of Experiments

Introduction: The β-adrenergic agonist isoproterenol (ISO) is known to induce the arrhythmogenic transient inward current (I Ti ) and delayed afterdepolarization (DAD) via a stimulation of L-type Ca 2+ current. Recent studies found that ISO-induced DADs in cardiac tissues are inhibited by GS967, a selective blocker of the late Na + current (I NaL ). Thus, we hypothesize that I NaL contributes to the actions of ISO, and selective inhibition of this current will reduce ISO-induced I Ti and DADs. Methods: Transmembrane currents and action potentials of rabbit and guinea pig (GP) ventricular myocytes were recorded using the whole-cell patch-clamp technique. ISO (0.1 μM), GS967 (1 μM) and the Na + channel blocker tetrodotoxin (TTX, 3 μM) were used in the experiments. Results: In rabbit myocytes, application of ISO caused an increase in the amplitude of I NaL from -0.10±0.03 to -0.32±0.04 pA/pF (n = 17, p < 0.05). The ISO-stimulated I NaL was inhibited by GS967 and TTX. In one series of experiments, ISO increased the I NaL from -0.14±0.04 to -0.35±0.06 pA/pF, and GS967 applied in the presence of ISO reduced the current to -0.14±0.03 pA/pF (n = 9, p < 0.05). In another series of experiments, the amplitude of I NaL was increased by ISO from -0.17±0.08 to -0.41±0.09 pA/pF, and was decreased to -0.09±0.08 pA/pF when TTX was applied with ISO (n = 5, p < 0.05). Application of ISO also induced I Ti and DADs. GS967 applied in the presence of ISO inhibited the amplitude of I Ti by 52±6%, from -1.79±0.30 to -0.87±0.16 pA/pF (n = 8, p < 0.05). Consistent with the inhibition of I Ti , GS967 suppressed the amplitude of ISO-induced DADs by 56±12%, from 6.54±1.59 to 3.22±1.27 mV (n = 5, p < 0.05). Similarly, in GP myocytes ISO-induced I Ti and DADs were decreased by GS967 from -1.14±0.21 to -0.73±0.16 pA/pF (n = 7, p < 0.05) and from 7.16±0.59 to 4.67±0.24 mV (n = 5, p < 0.05), respectively. Conclusions: An increased I NaL is likely to contribute to the proarrhythmic effects of ISO in cardiac myocytes. GS967 significantly attenuated ISO-induced I NaL , I Ti and DADs, suggesting that inhibiting this current could be an effective strategy to antagonize the arrhythmogenic actions of β-adrenergic stimulation.

A voltage-clamp analysis of currents underlying cyclic AMP-induced membrane modulation in isolated peptidergic neurons of Aplysia

1984 ◽  
Vol 52 (2) ◽  
pp. 340-349 ◽  
Author(s):  
L. K. Kaczmarek ◽  
F. Strumwasser
Keyword(s):  
Cell Culture ◽  
Cyclic Amp ◽  
Voltage Clamp ◽  
Cultured Cells ◽  
Sodium Current ◽  
Negative Slope ◽  
Spontaneous Discharge ◽  
Inward Current ◽  
Outward Currents ◽  
Bag Cell Neurons

A variety of chemical and electrophysiological evidence indicates that the onset of afterdischarge and the subsequent profound enhancement of spike broadening that occur in the bag cell neurons of Aplysia are related to an increase in adenosine 3',5'-monophosphate-(cAMP) dependent protein phosphorylation. We have now used a two-electrode voltage clamp to study the properties of isolated bag cell neurons in cell culture and their response to 8 benzylthio-cAMP (8BTcAMP) and N6-n-butyl 8BTcAMP. These membrane-permeant and phosphodiesterase-resistant cAMP analogs induce spontaneous discharge and spike broadening in both the intact bag cell cluster and isolated bag cell neurons in cell culture. The dominant inward current in these cultured cells was found to be the calcium current, Ica, which was abolished by Co2+ (20 mM) or Ni2+ (10 mM) and could be observed in Na+-free media. In a minority of cells (2 of 12), in normal ionic media, a transient inward current was observed that was unaffected by Co2+ and Ni2+ and probably represents a sodium current. The three characterized potassium currents, the delayed rectifying current IK, the calcium-dependent current IC, and the early transient current IA, distinguished by their differing pharmacological and voltage-activation properties, were present in all healthy cells. Three effects of the cyclic AMP analogs (0.5 mM) on the electrical properties of these cells were 1) the emergence of a region of negative slope resistance in the steady-state I-V relations, 2) a depression of the net sustained outward currents due to depolarizing commands, and 3) a marked reduction in IA. When outward currents had been largely suppressed using high concentrations of tetraethylammonium (TEA) ions (100-460 mM) no effects of the cyclic AMP analogs could be observed on peak inward currents using NA+ and Ca2+ or Ba2+ as carriers of inward current. At least part of these electrical effects of the cyclic AMP analogs could be accounted for by a depression of a delayed potassium current and the A current.

The toxic effects of ouabain: A voltage-clamp study

1982 ◽  
Vol 60 (9) ◽  
pp. 1153-1159 ◽  
Author(s):  
Y. Deslauriers ◽  
E. Ruiz-Ceretti ◽  
O. F. Schanne ◽  
M. D. Payet
Keyword(s):  
Action Potential ◽  
Voltage Clamp ◽  
Sodium Current ◽  
Negative Inotropic Effect ◽  
Slow Inward Current ◽  
Inward Current ◽  
Toxic Concentration ◽  
Voltage Curve ◽  
Current Voltage Curve ◽  
High Concentrations

The electrophysiologic effects of a toxic concentration of ouabain (10−5 M) were studied in frog atrial trabeculae. The toxic concentration was determined by the appearance of a negative inotropic effect and an increase in basal tension. Current- and voltage-clamp measurements were performed. Ouabain did not alter the passive electrical properties of the preparation. Under current-clamp conditions the membrane depolarized and the action potential amplitude as well as its maximum rate of rise decreased. The current–voltage curve for the fast inward current was shifted toward more positive potentials and the maximum sodium current decreased. The maximum sodium conductance was also reduced. The process of reactivation of the fast inward current was accelerated. The slow inward current and the maximum slow conductance also decreased under ouabain. These effects could explain the negative inotropic action of high concentrations of glycosides, as well as the action potential changes observed by several investigators. They also help to understand the arrhythmogenic effects of high concentrations of digitalis.

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