Potential-dependent membrane sodium pump current in snail giant neurons

1976 ◽  
Vol 7 (4) ◽  
pp. 333-337
Author(s):  
N. I. Kononenko
Keyword(s):  
Sodium Pump ◽  
Pump Current ◽  
Sodium Pump Current

Sodium-pump potentials and currents in guinea-pig ventricular muscles and myocytes

1999 ◽  
Vol 77 (5) ◽  
pp. 339-349 ◽  
Author(s):  
Yuji Kasamaki ◽  
An Chi Guo ◽  
Lesya M Shuba ◽  
Toshitsugu Ogura ◽  
Terence F McDonald
Keyword(s):  
Guinea Pig ◽  
Voltage Clamp ◽  
Cardiac Glycosides ◽  
Sodium Pump ◽  
Pump Current ◽  
Papillary Muscles ◽  
Maximal Concentration ◽  
Sodium Pump Current ◽  
Reproducible Manner

When guinea-pig papillary muscles were depolarized to ca. -30 mV by superfusion with K+-free Tyrode's solution supplemented with Ba2+, Ni2+, and D600, addition of Cs+ transiently hyperpolarized the membrane in a reproducible manner. The size of the hyperpolarization (pump potential) depended on the duration of the preceding K+-free exposure; peak amplitudes (Epmax) elicited by 10 mM Cs+ after 5-, 10-, and 15-min K+-free exposures were 12.9, 17.7, and 23.2 mV, respectively. Pump potentials were unaffected by external Cl- but suppressed by cardiac glycosides, hyperosmotic conditions, and low-Na+ solution. Using Epmax as an indicator of Na+ pump activation, the half-maximal concentration for activation by Cs+ was 12-16.3 mM. At 6 mM, Cs+ was three times less potent than Rb+ or K+ and five times more potent than Li+. From these findings, and correlative voltage-clamp data from myocytes, we calculate that (i) a pump current of 7.8 nA/cm2 generates an Epmax of 1 mV and (ii) resting pump current in normally polarized muscle (~0.16 µA/cm2) is five times smaller than previously estimated.Key words: sodium pump, cesium, rubidium, sodium pump current.

Electric current generated by squid giant axon sodium pump: external K and internal ADP effects

1978 ◽  
Vol 235 (1) ◽  
pp. C63-C68 ◽  
Author(s):  
R. F. Abercrombie ◽  
P. de Weer
Keyword(s):  
Sodium Pump ◽  
Giant Axon ◽  
Pump Current ◽  
Membrane Resistance ◽  
Extracellular Potassium ◽  
Sodium Efflux ◽  
Steroid Sensitive ◽  
External Potassium ◽  
Loligo Pealei ◽  
External K

The operation of the sodium pump of giant axons of the squid, Loligo pealei, has been studied simultaneously in two independent ways: 1) by measuring sodium efflux with 22Na, and 2) by calculating the transmembrane current generated by the pump from measurements of membrane resistance and digitalis-sensitive membrane potential. In normal, untreated axons, the effect of increasing the external potassium concentration on both sodium efflux and pump current is similar, which suggests that Na:K pump stoichiometry remains relatively constant in the range of 0-20 mM external K. The data are compatible with a 3:2 Na:K ratio. In axons whose intracellular ADP level has been elevated by injection of L-arginine, a large, electrically silent, cardiotonic steroid-sensitive sodium efflux takes place in the absence of external potassium; this suggests that pump-mediated Na:Na exchange is 1:1 or electroneutral. Finally, elevation of external potassium levels causes the appearance, in high-ADP axons, of electrogenic pumping, with little effect on sodium efflux; hence, in contrast to what is seen in normal (low-ADP) axons, the charge translocated, per sodium ion extruded, increases sharply with increasing extracellular potassium levels.

Mutation of a conserved proline residue in the beta-subunit ectodomain prevents Na(+)-K(+)-ATPase oligomerization

1993 ◽  
Vol 265 (4) ◽  
pp. C1169-C1174 ◽  
Author(s):  
K. Geering ◽  
P. Jaunin ◽  
F. Jaisser ◽  
A. M. Merillat ◽  
J. D. Horisberger ◽  
...  
Keyword(s):  
Sodium Pump ◽  
Critical Role ◽  
Pump Current ◽  
Beta Subunit ◽  
Sequence Motif ◽  
Wild Type ◽  
Ouabain Binding ◽  
Conserved Sequence ◽  
External Potassium ◽  
And Function

A highly conserved sequence motif (4 tyrosines and 1 proline: YYPYY) of the Na(+)-K(+)-adenosinetriphosphatase (ATPase) beta 1-subunit ectodomain has been mutagenized to study its possible role in alpha/beta-assembly and sodium pump function. Single as well as double tyrosine mutants (tyrosine to phenylalanine: Y to F) of Xenopus laevis beta 1-subunits are able to associate with alpha 1-subunits and form functional Na-K pumps at the plasma membrane that are indistinguishable from wild-type alpha 1, beta 1-Na-K pumps (as assessed by measurements of ouabain binding, 86Rb flux, Na-K pump current, and activation by external potassium). In contrast, a single proline mutation (proline to glycine: P244G) reduced by > 90% the proper assembly and function of Na(+)-K(+)-ATPase, despite a normal rate of synthesis and core glycosylation. Our data indicate that proline-244 plays a critical role in the proper folding of the beta-subunit and its ability to associate efficiently with the alpha 1-subunit in the endoplasmic reticulum.

scholarly journals Voltage Dependence of the Apparent Affinity for External Na+ of the Backward-Running Sodium Pump

2001 ◽  
Vol 117 (4) ◽  
pp. 315-328 ◽  
Author(s):  
Paul De Weer ◽  
David C. Gadsby ◽  
R.F. Rakowski
Keyword(s):  
Steady State ◽  
Sodium Pump ◽  
Channel Model ◽  
Pump Current ◽  
Hill Coefficient ◽  
Access Channel ◽  
Electrogenic Sodium Pump ◽  
The Difference ◽  
Loligo Pealei ◽  
The Hill

The steady-state voltage and [Na+]o dependence of the electrogenic sodium pump was investigated in voltage-clamped internally dialyzed giant axons of the squid, Loligo pealei, under conditions that promote the backward-running mode (K+-free seawater; ATP- and Na+-free internal solution containing ADP and orthophosphate). The ratio of pump-mediated 42K+ efflux to reverse pump current, Ipump (both defined by sensitivity to dihydrodigitoxigenin, H2DTG), scaled by Faraday's constant, was −1.5 ± 0.4 (n = 5; expected ratio for 2 K+/3 Na+ stoichiometry is −2.0). Steady-state reverse pump current-voltage (Ipump-V) relationships were obtained either from the shifts in holding current after repeated exposures of an axon clamped at various Vm to H2DTG or from the difference between membrane I-V relationships obtained by imposing Vm staircases in the presence or absence of H2DTG. With the second method, we also investigated the influence of [Na+]o (up to 800 mM, for which hypertonic solutions were used) on the steady-state reverse Ipump-V relationship. The reverse Ipump-V relationship is sigmoid, Ipump saturating at large negative Vm, and each doubling of [Na+]o causes a fixed (29 mV) rightward parallel shift along the voltage axis of this Boltzmann partition function (apparent valence z = 0.80). These characteristics mirror those of steady-state 22Na+ efflux during electroneutral Na+/Na+ exchange, and follow without additional postulates from the same simple high field access channel model (Gadsby, D.C., R.F. Rakowski, and P. De Weer, 1993. Science. 260:100–103). This model predicts valence z = nλ, where n (1.33 ± 0.05) is the Hill coefficient of Na binding, and λ (0.61 ± 0.03) is the fraction of the membrane electric field traversed by Na ions reaching their binding site. More elaborate alternative models can accommodate all the steady-state features of the reverse pumping and electroneutral Na+/Na+ exchange modes only with additional assumptions that render them less likely.

Sign in / Sign up

Export Citation Format

Share Document