scholarly journals Sodium flux ratio in voltage-clamped squid giant axons.

1981 ◽  
Vol 77 (5) ◽  
pp. 489-502 ◽  
Author(s):  
T Begenisich ◽  
D Busath
Keyword(s):  
Sodium Channels ◽  
Binding Sites ◽  
Flux Ratio ◽  
Ion Binding ◽  
Ion Permeation ◽  
Giant Axons ◽  
Sodium Flux ◽  
Ion Binding Sites ◽  
Loligo Pealei ◽  
Ion Pore

The sodium flux ratio across the axolemma of internally perfused, voltage-clamped giant axons of Loligo pealei has been measured at various membrane potentials. The flux ratio exponent obtained from these measurements was about unity and independent of membrane voltage over the 50 mV range from about -20 to +30 mV. These results, combined with previous measurements of ion permeation through sodium channels, show that the sodium channel behaves like a multi-ion pore with two ion binding sites that are rarely simultaneously occupied by sodium.

scholarly journals Sodium Flux Ratio in Na/K Pump-Channels Opened by Palytoxin

2007 ◽  
Vol 130 (1) ◽  
pp. 41-54 ◽  
Author(s):  
R.F. Rakowski ◽  
Pablo Artigas ◽  
Francisco Palma ◽  
Miguel Holmgren ◽  
Paul De Weer ◽  
...  
Keyword(s):  
Binding Sites ◽  
Reversal Potential ◽  
Flux Ratio ◽  
Giant Fiber ◽  
Animal Cells ◽  
Giant Axons ◽  
Single File ◽  
Sodium Flux ◽  
Na Ions ◽  
Loligo Pealei

Palytoxin binds to Na+/K+ pumps in the plasma membrane of animal cells and opens an electrodiffusive cation pathway through the pumps. We investigated properties of the palytoxin-opened channels by recording macroscopic and microscopic currents in cell bodies of neurons from the giant fiber lobe, and by simultaneously measuring net current and 22Na+ efflux in voltage-clamped, internally dialyzed giant axons of the squid Loligo pealei. The conductance of single palytoxin-bound “pump-channels” in outside-out patches was ∼7 pS in symmetrical 500 mM [Na+], comparable to findings in other cells. In these high-[Na+], K+-free solutions, with 5 mM cytoplasmic [ATP], the K0.5 for palytoxin action was ∼70 pM. The pump-channels were ∼40–50 times less permeable to N-methyl-d-glucamine (NMG+) than to Na+. The reversal potential of palytoxin-elicited current under biionic conditions, with the same concentration of a different permeant cation on each side of the membrane, was independent of the concentration of those ions over the range 55–550 mM. In giant axons, the Ussing flux ratio exponent (n') for Na+ movements through palytoxin-bound pump-channels, over a 100–400 mM range of external [Na+] and 0 to −40 mV range of membrane potentials, averaged 1.05 ± 0.02 (n = 28). These findings are consistent with occupancy of palytoxin-bound Na+/K+ pump-channels either by a single Na+ ion or by two Na+ ions as might be anticipated from other work; idiosyncratic constraints are needed if the two Na+ ions occupy a single-file pore, but not if they occupy side-by-side binding sites, as observed in related structures, and if only one of the sites is readily accessible from both sides of the membrane.

scholarly journals Mechanism of Ion Permeation in Skeletal Muscle Chloride Channels

1997 ◽  
Vol 110 (5) ◽  
pp. 551-564 ◽  
Author(s):  
Christoph Fahlke ◽  
Christine Dürr ◽  
Alfred L. George
Keyword(s):  
Skeletal Muscle ◽  
Conformational Changes ◽  
Binding Sites ◽  
Chloride Channels ◽  
Ion Selectivity ◽  
Ion Binding ◽  
Ion Permeation ◽  
Conduction Pathway ◽  
Voltage Dependent ◽  
Ion Binding Sites

Voltage-gated Cl− channels belonging to the ClC family exhibit unique properties of ion permeation and gating. We functionally probed the conduction pathway of a recombinant human skeletal muscle Cl− channel (hClC-1) expressed both in Xenopus oocytes and in a mammalian cell line by investigating block by extracellular or intracellular I− and related anions. Extracellular and intracellular I− exert blocking actions on hClC-1 currents that are both concentration and voltage dependent. Similar actions were observed for a variety of other halide (Br−) and polyatomic (SCN−, NO3−, CH3SO3−) anions. In addition, I− block is accompanied by gating alterations that differ depending on which side of the membrane the blocker is applied. External I− causes a shift in the voltage-dependent probability that channels exist in three definable kinetic states (fast deactivating, slow deactivating, nondeactivating), while internal I− slows deactivation. These different effects on gating properties can be used to distinguish two functional ion binding sites within the hClC-1 pore. We determined KD values for I− block in three distinct kinetic states and found that binding of I− to hClC-1 is modulated by the gating state of the channel. Furthermore, estimates of electrical distance for I− binding suggest that conformational changes affecting the two ion binding sites occur during gating transitions. These results have implications for understanding mechanisms of ion selectivity in hClC-1, and for defining the intimate relationship between gating and permeation in ClC channels.

scholarly journals Synthesis and Photoregulated Metal Coordination of Azobenzene Polymer Having Ion Binding Sites

1991 ◽  
Vol 23 (2) ◽  
pp. 127-134 ◽  
Author(s):  
Masato Nanasawa ◽  
Takahiro Nishiyama ◽  
Hiroyoshi Kamogawa
Keyword(s):  
Binding Sites ◽  
Metal Coordination ◽  
Ion Binding ◽  
Azobenzene Polymer ◽  
Ion Binding Sites

The Effect Of Metal Ions On Human Factor IX Antigenicity

1981 ◽  
Author(s):  
R M Lewis ◽  
H M Reisner ◽  
B C Abels ◽  
H R Roberts
Keyword(s):  
Divalent Cation ◽  
Binding Sites ◽  
Human Factor ◽  
Antibody Binding ◽  
Factor Ix ◽  
Ion Binding ◽  
Human Factor Ix ◽  
Excess Mg ◽  
Ion Binding Sites ◽  
Two Populations

Affinity chromatography of an inhibitor to human factor IX (F.IX) separated the antibody into two populations. The ion dependent population of antibodies had an absolute divalent cation (Me++) binding requirement. The non-ion dependent population bound F.IX equally in the presence or absence of Me++. The concentration of Me++ required for ½ the maximum ion dependent antibody binding (½ max) was (in nM) Ca++ 0.40, Mn++ 0.05, Sr++ 0.70 and Mg++ 0.65.Ca++ potentiated the binding of antibody in the presence of excess Mg++. In addition, the ½ max for Ca++ was reduced about four fold. These observations are consistent with separate binding sites on the F.IX molecule for Ca++ and Mg++ and potentiation of Ca++ binding by Mg++. Scat- chard analysis of ion dependent antibody binding indicates about a 10 fold greater affinity of antibody in the presence of Ca++ than Mg++. In the presence of both cations, affinity was at least as high as in the presence of Ca++ alone supporting the presence of separate ion binding sites on the F.IX molecule.

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