The steady-state potassium conductance of the ranvier node at various external K-concentrations

1977 ◽  
Vol 370 (2) ◽  
pp. 185-194 ◽  
Author(s):  
J. M. Dubois ◽  
C. Bergman
Keyword(s):  
Steady State ◽  
Potassium Conductance ◽  
Ranvier Node ◽  
External K

Inward rectification in rat nucleus accumbens neurons

1989 ◽  
Vol 62 (6) ◽  
pp. 1280-1286 ◽  
Author(s):  
N. Uchimura ◽  
E. Cherubini ◽  
R. A. North
Keyword(s):  
Steady State ◽  
Nucleus Accumbens ◽  
Time Course ◽  
Potassium Conductance ◽  
Resting Potential ◽  
Inward Rectification ◽  
Resting Membrane Potential ◽  
Potential Range ◽  
Inward Current ◽  
Rat Nucleus Accumbens

1. Intracellular recordings were made from neurons in slices cut from the rat nucleus accumbens septi. Membrane currents were measured with a single-electrode voltage-clamp amplifier in the potential range -50 to -140 mV. 2. In control conditions (2.5 mM potassium), the resting membrane potential of the neurons was -83.4 +/- 1.1 (SE) mV (n = 157). Steady state membrane conductance was voltage dependent, being 34.8 +/- 1.7 nS (n = 25) at -100 mV and 8.0 +/- 0.7 nS (n = 25) at -60 mV. 3. Barium (1 microM) markedly reduced the inward rectification and caused a small inward current (40.6 +/- 8.7 pA, n = 8) at the resting potential. These effects became larger with higher barium concentrations, and, in 100 microM barium, the current-voltage relation was straight. 4. The block of the inward current by barium (at -130 mV) occurred with an exponential time course; the time constant was approximately 1 s at 1 microM barium and less than 90 ms with 100 microM. Strontium had effects similar to those of barium, but 1000-fold higher concentrations were required. Cesium chloride (2 mM) and rubidium chloride (2 mM) also blocked the inward rectification; their action reached steady state within 50 ms. 5. It is concluded that the nucleus accumbens neurons have a potassium conductance with many features of a typical inward rectifier and that this contributes to the potassium conductance at the resting potential.

Potassium conductance in rabbit esophageal epithelium

1993 ◽  
Vol 265 (1) ◽  
pp. G28-G34 ◽  
Author(s):  
W. E. Khalbuss ◽  
R. Alkiek ◽  
C. G. Marousis ◽  
R. C. Orlando
Keyword(s):  
Steady State ◽  
Epithelial Cells ◽  
Short Circuit ◽  
Basolateral Membrane ◽  
Potassium Conductance ◽  
Short Circuit Current ◽  
Sodium Absorption ◽  
High K ◽  
Esophageal Epithelial Cells ◽  
Apical Membranes

K+ conductance in apical and basolateral cell membranes of rabbit esophageal epithelial cells was investigated within intact epithelium by impalement with conventional microelectrodes from luminal or serosal sides. Under steady-state conditions, K+ conductance was demonstrated in basolateral, but not apical, membranes by showing 1) membrane depolarization upon exposure to either solutions high in K+ (20-65 mM) or containing Ba2+, tetraethylammonium, or quinine, and 2) a resistance ratio that increased on exposure to high K+ solution and decreased on exposure to Ba2+, quinine, and tetraethylammonium. From exposures to high K+, the apparent K+ transference number and electromotive force generated at the basolateral membrane were calculated and found to be 0.42 +/- 0.01 and -83 +/- 3 mV, respectively. Furthermore, basolateral K+ conductance was shown to be important for maintaining resting net transepithelial Na+ absorption in that high K+ or barium inhibited the transepithelial potential difference and short-circuit current of Ussing-chambered epithelia. We conclude that under steady-state conditions the basolateral, but not apical, membranes of esophageal epithelial cells contain a K(+)-conductive pathway and that this pathway is important for active sodium absorption.

scholarly journals The Influence of External Potassium on the Inactivation of Sodium Currents in the Giant Axon of the Squid, Loligo pealei

1969 ◽  
Vol 53 (6) ◽  
pp. 685-703 ◽  
Author(s):  
William J. Adelman ◽  
Yoram Palti
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Membrane Conductance ◽  
Absolute Magnitude ◽  
Giant Axon ◽  
Membrane Potentials ◽  
Initial Transient ◽  
External Potassium ◽  
Loligo Pealei ◽  
External K

Isolated giant axons were voltage-clamped in seawater solutions having constant sodium concentrations of 230 mM and variable potassium concentrations of from zero to 210 mM. The inactivation of the initial transient membrane current normally carried by Na+ was studied by measuring the Hodgkin-Huxley h parameter as a function of time. It was found that h reaches a steady-state value within 30 msec in all solutions. The values of h∞, τh, αh,and ßh as functions of membrane potential were determined for various [Ko]. The steady-state values of the h parameter were found to be inversely related, while the time constant, τh, was directly related to external K+ concentration. While the absolute magnitude as well as the slopes of the h∞ vs. membrane potential curves were altered by varying external K+, only the magnitude and not the shape of the corresponding τh curves was altered. Values of the two rate constants, αh and ßh, were calculated from h∞ and τh values. αh is inversely related to [Ko] while ßh is directly related to [Ko] for hyperpolarizing membrane potentials and is independent of [Ko] for depolarizing membrane potentials. Hodgkin-Huxley equations relating αh and ßh to Em were rewritten so as to account for the observed effects of [Ko]. It is concluded that external potassium ions have an inactivating effect on the initial transient membrane conductance which cannot be explained solely on the basis of potassium membrane depolarization.

scholarly journals Cation transport in Escherichia coli. IX. Regulation of K transport.

1978 ◽  
Vol 72 (3) ◽  
pp. 283-295 ◽  
Author(s):  
D B Rhoads ◽  
W Epstein
Keyword(s):  
Escherichia Coli ◽  
Steady State ◽  
Cation Transport ◽  
Transport Systems ◽  
Energy Requirements ◽  
Protonmotive Force ◽  
K Uptake ◽  
Kinetics Of ◽  
K Transport ◽  
External K

Kinetics of K exchange in the steady state and of net K uptake after osmotic upshock are reported for the four K transport systems of Escherichia coli: Kdp, TrkA, TrkD, and TrkF. Energy requirements for K exchange are reported for the Kdp and TrkA systems. For each system, kinetics of these two modes of K transport differ from those for net K uptake by K-depleted cells (Rhoads, D. B. F.B. Walters, and W. Epstein. 1976. J. Gen. Physiol. 67:325-341). The TrkA and TrkD systems are inhibited by high intracellular K, the TrkF system is stimulated by intracellular K, whereas the Kdp system is inhibited by external K when intracellular K is high. All four systems mediate net K uptake in response to osmotic upshock. Exchange by the Kdp and TrkA systems requires ATP but is not dependent on the protonmotive force. Energy requirements for the Kdp system are thus identical whether measured as net K uptake or K exchange, whereas the TrkA system differs in that it is dependent on the protonmotive force only for net K uptake. We suggest that in both the Kpd and TrkA systems formation of a phosphorylated intermediate is necessary for all K transport, although exchange transport may not consume energy. The protonmotive-force dependence of the TrkA system is interpreted as a regulatory influence, limiting this system to exchange except when the protonmotive force is high.

scholarly journals Cat Heart Muscle in Vitro

1962 ◽  
Vol 46 (2) ◽  
pp. 189-199 ◽  
Author(s):  
Ernest Page
Keyword(s):  
Steady State ◽  
Heart Muscle ◽  
Potential Difference ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Papillary Muscles ◽  
K Concentration ◽  
Cat Heart ◽  
External K

The steady state transmembrane resting potential difference (Vm) has been measured in quiescent papillary muscles. Vm was determined as a function of the external K concentration in Cl and SO4 solutions and compared with the K equilibrium potential. Other measurements were made after replacement of external Na by choline, K by Rb and Cs, and Cl by SO4, CH3SO4, and NO3. Effects on Vm of albumin, temperature, and variation in internal K concentration are described.

scholarly journals Interaction of Tetraethylammonium Ion Derivatives with the Potassium Channels of Giant Axons

1971 ◽  
Vol 58 (4) ◽  
pp. 413-437 ◽  
Author(s):  
Clay M. Armstrong
Keyword(s):  
Potassium Conductance ◽  
Squid Axon ◽  
Ammonium Ions ◽  
K Channels ◽  
Fourth Group ◽  
Quaternary Ammonium Ions ◽  
Tetraethylammonium Ion ◽  
K Concentration ◽  
Peak Value ◽  
External K

A number of compounds related to TEA+ (tetraethylammoniumion) were injected into squid axons and their effects on gK (the potassium conductance) were determined. In most of these ions a quaternary nitrogen is surrounded by three ethyl groups and a fourth group that is very hydrophobic. Several of the ions cause inactivation of gK, a type of ionic gating that is not normally seen in squid axon; i.e., after depolarization gK increases and then spontaneously decreases to a small fraction of its peak value even though the depolarization is maintained. Observations on the mechanism of this gating show that (a) QA (quaternary ammonium) ions only enter K+ channels that have open activation gates (the normal permeability gates). (b) The activation gates of QA-occluded channels do not close readily. (c) Hyperpolarization helps to clear QA ions from the channels. (d) Raising the external K+ concentration also helps to clear QA ions from the channels. Observations (c) and (d) strongly suggest that K+ ions traverse the membrane by way of pores, and they cannot be explained by the usual type of carrier model. The data suggest that a K+ pore has two distinct parts: a wide inner mouth that can accept a hydrated K+ ion or a TEA+-like ion, and a narrower portion that can accept a dehydrated or partially dehydrated K+ ion, but not TEA+.

Effect of procaine on electrical properties of squid axon membrane

1959 ◽  
Vol 196 (5) ◽  
pp. 1071-1078 ◽  
Author(s):  
Robert E. Taylor
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Electrical Properties ◽  
Potassium Conductance ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Squid Axon ◽  
Voltage Step ◽  
Axon Membrane ◽  
Rate Of Development

Procaine (0.025–0.1%; pH 7.9) caused a reduction in the amount and rate of development of the early transient (sodium) and late steady state (potassium) currents which occur during a depolarizing voltage step applied to the excised, voltage clamped squid axon. Consistent results were obtained by holding the membrane potential at a hyperpolarized value prior to the applied step. No effect was seen on the resting potential, on the sodium equilibrium potential, or on the proportion of the sodium carrying system which was ‘inactive’ at any membrane potential. The blocking action of procaine is a result of the inhibition by the drug of the sodium carrying system. The effect of procaine on the potassium conductance is such as to oppose the blocking action.

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.

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