Dependence of Na+-K+ pump current-voltage relationship on intracellular Na+, K+, and Cs+ in rabbit cardiac myocytes

2002 ◽  
Vol 283 (5) ◽  
pp. C1511-C1521 ◽  
Author(s):  
Peter S. Hansen ◽  
Kerrie A. Buhagiar ◽  
Benjamin Y. Kong ◽  
Ronald J. Clarke ◽  
David F. Gray ◽  
...  
Keyword(s):  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Pump Current ◽  
Inhibitory Effect ◽  
Negative Slope ◽  
Current Voltage ◽  
Patch Pipette ◽  
Voltage Dependent ◽  
Current Voltage Relationship ◽  
Voltage Relationship

To examine effects of cytosolic Na+, K+, and Cs+ on the voltage dependence of the Na+-K+ pump, we measured Na+-K+ pump current ( I p) of ventricular myocytes voltage-clamped at potentials ( V m) from −100 to +60 mV. Superfusates were designed to eliminate voltage dependence at extracellular pump sites. The cytosolic compartment of myocytes was perfused with patch pipette solutions with a Na+ concentration ([Na]pip) of 80 mM and a K+ concentration from 0 to 80 mM or with solutions containing Na+ in concentrations from 0.1 to 100 mM and K+ in a concentration of either 0 or 80 mM. When [Na]pip was 80 mM, K+ in pipette solutions had a voltage-dependent inhibitory effect on I pand induced a negative slope of the I p- V m relationship. Cs+ in pipette solutions had an effect on I p qualitatively similar to that of K+. Increases in I p with increases in [Na]pip were voltage dependent. The dielectric coefficient derived from [Na]pip- I p relationships at the different test potentials was 0.15 when pipette solutions included 80 mM K+ and 0.06 when pipette solutions were K+free.

Simulation of Na/K Pump Current-Voltage Relationship

1992 ◽  
Vol 671 (1 Ion-Motive AT) ◽  
pp. 449-451 ◽  
Author(s):  
X.-Y. LIU ◽  
T. A. KINARD ◽  
J. R. STIMERS
Keyword(s):  
Pump Current ◽  
Current Voltage ◽  
Current Voltage Relationship ◽  
Voltage Relationship

scholarly journals Contributions of space-clamp errors to apparent time-dependent loss of Mg2+ block induced by NMDA

2017 ◽  
Vol 118 (1) ◽  
pp. 532-543
Author(s):  
Min-Yu Sun ◽  
Mariangela Chisari ◽  
Lawrence N. Eisenman ◽  
Charles F. Zorumski ◽  
Steven J. Mennerick
Keyword(s):  
Voltage Clamp ◽  
Hippocampal Neurons ◽  
Network Activity ◽  
Negative Slope ◽  
Secondary Currents ◽  
Current Voltage ◽  
Nmda Current ◽  
Current Voltage Relationship ◽  
Voltage Relationship ◽  
Juvenile Mouse

N-methyl-d-aspartate receptors (NMDARs) govern synaptic plasticity, development, and neuronal response to insult. Prolonged activation of NMDARs such as during an insult may activate secondary currents or modulate Mg2+ sensitivity, but the conditions under which these occur are not fully defined. We reexamined the effect of prolonged NMDAR activation in juvenile mouse hippocampal slices. NMDA (10 μM) elicited current with the expected negative-slope conductance in the presence of 1.2 mM Mg2+. However, several minutes of continued NMDA exposure elicited additional inward current at −70 mV. A higher concentration of NMDA (100 µM) elicited the current more rapidly. The additional current was not dependent on Ca2+, network activity, or metabotropic NMDAR function and did not persist on agonist removal. Voltage ramps revealed no alteration of either reversal potential or NMDA-elicited conductance between −30 mV and +50 mV. The result was a more linear NMDA current-voltage relationship. The current linearization was also induced in interneurons and in mature dentate granule neurons but not immature dentate granule cells, dissociated cultured hippocampal neurons, or nucleated patches excised from CA1 pyramidal neurons. Comparative simulations of NMDA application to a CA1 pyramidal neuron and to a cultured neuron revealed that linearization can be explained by space-clamp errors arising from gradual recruitment of distal dendritic NMDARs. We conclude that persistent secondary currents do not strongly contribute to NMDAR responses in juvenile mouse hippocampus and careful discernment is needed to exclude contributions of clamp artifacts to apparent secondary currents. NEW & NOTEWORTHY We report that upon sustained activation of NMDARs in juvenile mouse hippocampal neurons there is apparent loss of Mg2+ block at negative membrane potentials. However, the phenomenon is explained by loss of dendritic voltage clamp, leading to a linear current-voltage relationship. Our results give a specific example of how spatial voltage errors in voltage-clamp recordings can readily be misinterpreted as biological modulation.

scholarly journals Voltage-dependent block of cardiac inward-rectifying potassium current by monovalent cations.

1989 ◽  
Vol 94 (2) ◽  
pp. 349-361 ◽  
Author(s):  
R D Harvey ◽  
R E Ten Eick
Keyword(s):  
Ventricular Myocytes ◽  
Negative Slope ◽  
Voltage Sensitivity ◽  
Dependent Manner ◽  
Inward Current ◽  
Current Voltage ◽  
Steady State Current ◽  
Voltage Dependent ◽  
Current Block ◽  
K Current

The inward-rectifying K+ current (IK1) in cat ventricular myocytes, like inward-rectifying K+ currents in many other preparations, exhibited a negative slope conductance region at hyperpolarized membrane potentials that was time-dependent. This was evident as an inactivation of inward current elicited by hyperpolarizing voltage-clamp pulses resulting in a negative slope region of the steady-state current-voltage relationship at potentials negative to -140 mV. Removing extracellular Na+ prevented the development of the negative slope in this voltage region, suggesting that Na+ can block IK1 channels in a time- and voltage-dependent manner. The time and voltage dependence of Cs+-induced block of IK1 was also examined. Cs+ blocked inward current in a manner similar to that of Na+, but the former was much more potent. The fraction of current blocked by Cs+ in the presence of Na+ was reduced in a time- and voltage-dependent manner, which suggested that these blocking ions compete for a common or at least similar site of action. In the absence of Na+, inactivation of IK1 could also be induced by both Cs+ and Li+. However, Li+ was less potent than Na+ in this respect. Calculation of the voltage sensitivity of current block by each of these ions suggests that the mechanism of block by each is similar.

scholarly journals Steady-state current-voltage relationship of the Na/K pump in guinea pig ventricular myocytes.

1989 ◽  
Vol 94 (3) ◽  
pp. 511-537 ◽  
Author(s):  
D C Gadsby ◽  
M Nakao
Keyword(s):  
Steady State ◽  
Guinea Pig ◽  
Rate Constants ◽  
Ventricular Myocytes ◽  
Pump Current ◽  
Membrane Current ◽  
Negative Slope ◽  
Current Voltage ◽  
State Cycle ◽  
External K

Whole-cell currents were recorded in guinea pig ventricular myocytes at approximately 36 degrees C before, during, and after exposure to maximally effective concentrations of strophanthidin, a cardiotonic steroid and specific inhibitor of the Na/K pump. Wide-tipped pipettes, in combination with a device for exchanging the solution inside the pipette, afforded reasonable control of the ionic composition of the intracellular solution and of the membrane potential. Internal and external solutions were designed to minimize channel currents and Na/Ca exchange current while sustaining vigorous forward Na/K transport, monitored as strophanthidin-sensitive current. 100-ms voltage pulses from the -40 mV holding potential were used to determine steady-state levels of membrane current between -140 and +60 mV. Control experiments demonstrated that if the Na/K pump cycle were first arrested, e.g., by withdrawal of external K, or of both internal and external Na, then neither strophanthidin nor its vehicle, dimethylsulfoxide, had any discernible effect on steady-state membrane current. Further controls showed that, with the Na/K pump inhibited by strophanthidin, membrane current was insensitive to changes of external [K] between 5.4 and 0 mM and was little altered by changing the pipette [Na] from 0 to 50 mM. Strophanthidin-sensitive current therefore closely approximated Na/K pump current, and was virtually free of contamination by current components altered by the changes in extracellular [K] and intracellular [Na] expected to accompany pump inhibition. The steady-state Na/K pump current-voltage (I-V) relationship, with the pump strongly activated by 5.4 mM external K and 50 mM internal Na (and 10 mM ATP), was sigmoid in shape with a steep positive slope between about 0 and -100 mV, a less steep slope at more negative potentials, and an extremely shallow slope at positive potentials; no region of negative slope was found. That shape of I-V relationship can be generated by a two-state cycle with one pair of voltage-sensitive rate constants and one pair of voltage-insensitive rate constants: such a two-state scheme is a valid steady-state representation of a multi-state cycle that includes only a single voltage-sensitive step.

scholarly journals [Na] and [K] dependence of the Na/K pump current-voltage relationship in guinea pig ventricular myocytes.

1989 ◽  
Vol 94 (3) ◽  
pp. 539-565 ◽  
Author(s):  
M Nakao ◽  
D C Gadsby
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Pump Current ◽  
Hill Coefficient ◽  
Independent Manner ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Scale Down ◽  
Na Ions ◽  
The Right

Na/K pump current was determined between -140 and +60 mV as steady-state, strophanthidin-sensitive, whole-cell current in guinea pig ventricular myocytes, voltage-clamped and internally dialyzed via wide-tipped pipettes. Solutions were designed to minimize all other components of membrane current. A device for exchanging the solution inside the pipette permitted investigation of Na/K pump current-voltage (I-V) relationships at several levels of pipette [Na] [( Na]pip) in a single cell; the effects of changes in external [Na] [( Na]o) or external [K] [( K]o) were also studied. At 50 mM [Na]pip, 5.4 mM [K]o, and approximately 150 mM [Na]o, Na/K pump current was steeply voltage dependent at negative potentials but was approximately constant at positive potentials. Under those conditions, reduction of [Na]o enhanced pump current at negative potentials but had little effect at positive potentials: at zero [Na]o, pump current was only weakly voltage dependent. At 5.4 mM [K]o and approximately 150 mM [Na]o, reduction of [Na]pip from 50 mM scaled down the sigmoid pump I-V relationship and shifted it slightly to the right (toward more positive potentials). Pump current at 0 mV was activated by [Na]pip according to the Hill equation with best-fit K0.5 approximately equal to 11 mM and Hill coefficient nH approximately equal to 1.4. At zero [Na]o, reduction of [Na]pip seemed to simply scale down the relatively flat pump I-V relationship: Hill fit parameters for pump activation by [Na]pip at 0 mV were K0.5 approximately equal to 10 mM, nH approximately equal to 1.4. At 50 mM [Na]pip and high [Na]o, reduction of [K]o from 5.4 mM scaled down the sigmoid I-V relationship and shifted it slightly to the right: at 0 mV, K0.5 approximately equal to 1.5 mM and nH approximately equal to 1.0. At zero [Na]o, lowering [K]o simply scaled down the flat pump I-V relationships yielding, at 0 mV, K0.5 approximately equal to 0.2 mM, nH approximately equal to 1.1. The voltage-independent activation of Na/K pump current by both intracellular Na ions and extracellular K ions, at zero [Na]o, suggests that neither ion binds within the membrane field. Extracellular Na ions, however, seem to have both a voltage-dependent and a voltage-independent influence on the Na/K pump: they inhibit outward Na/K pump current in a strongly voltage-dependent fashion, with higher apparent affinity at more negative potentials (K0.5 approximately equal to 90 mM at -120 mV, and approximately 170 mM at -80 mV), and they compete with extracellular K ions in a seemingly voltage-independent manner.(ABSTRACT TRUNCATED AT 400 WORDS)

1S,3R-ACPD Induces a Region of Negative Slope Conductance in the Steady-State Current-Voltage Relationship of Hippocampal Pyramidal Cells

1997 ◽  
Vol 77 (1) ◽  
pp. 221-228 ◽  
Author(s):  
Anita Lüthi ◽  
Beat H. Gähwiler ◽  
Urs Gerber
Keyword(s):  
Steady State ◽  
Reversal Potential ◽  
Pyramidal Cells ◽  
Resting Potential ◽  
Negative Slope ◽  
Inward Current ◽  
Current Voltage ◽  
Steady State Current ◽  
Current Voltage Relationship ◽  
Voltage Relationship

Lüthi, Anita, Beat H. Gähwiler, and Urs Gerber. 1 S,3 R-ACPD induces a region of negative slope conductance in the steady-state current-voltage relationship of hippocampal pyramidal cells. J. Neurophysiol. 77: 221–228, 1997. Synaptic responses mediated by metabotropic glutamate receptors (mGluRs) display a marked voltage-dependent increase in amplitude when neurons are moderately depolarized beyond membrane potential. We have investigated the basis for this apparent nonlinear behavior by activatingmGluRs with 1 S,3 R-1-aminocyclopentane-1,3-dicarboxylate(1 S,3 R-ACPD; 10 μM) in CA3 pyramidal cells from rat hippocampal slice cultures with the use of the single-electrode voltage-clamp technique. Under control conditions, cells depolarized from resting potential by 10–20 mV responded with delayed outwardly rectifying currents due to activation of voltage- and Ca2+-dependent K+ conductances. In contrast, in the continuous presence of 1 S,3 R-ACPD, small depolarizations (10–20 mV) induced a delayed inward current. The steady-state current-voltage relationship for this response displayed a region of negative slope conductance at potentials between −55 and −40 mV. The reversal potential of the corresponding 1 S,3 R-ACPD-sensitive tail currents (−93.0 ± 2.2 mV, mean ± SE) was close to the potassium reversal potential, consistent with an mGluR-mediated suppression of K+ current. When external K+ concentration was increased to 8 mM, there was a positive shift in reversal potential to −76.9 ± 5.1 mV. The depolarization-induced inward current in the presence of 1 S,3 R-ACPD was blocked by Ba2+ (1 mM). The response was not dependent on changes in intracellular Ca2+ concentration and was insensitive to bath-applied Cs+ (1 mM), ruling out a contribution of Ca2+-dependent currents or the inward rectifier I Q. Furthermore, the effect of 1 S,3 R-ACPD was not mimicked by inhibiting afterhyperpolarizing current and M current with low-Ca2+ saline (0.5 mM Ca2+, 10 mM Mg2+) containing 10 mM tetraethylammonium chloride. A comparison of the responses induced by 1 S,3 R-ACPD and N-methyl-d-aspartate showed that both induce an inward current with small depolarizations from resting potential but with different kinetics and Mg2+ sensitivity. These results indicate that the suppression of K+ currents in response to activation of mGluRs is markedly voltage dependent, increasing at depolarized potentials and decreasing at hyperpolarized potentials. The negative slope conductance at membrane voltages positive to resting potential may underlie the amplification of mGluR-mediated responses when the membrane potential approaches action potential threshold.

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