Characterization of a high-conductance, voltage-dependent cation channel from the plasma membrane of rye roots in planar lipid bilayers

Planta ◽  
1993 ◽  
Vol 191 (4) ◽  
Author(s):  
PhilipJ. White
Keyword(s):  
Plasma Membrane ◽  
Lipid Bilayers ◽  
Cation Channel ◽  
Planar Lipid Bilayers ◽  
Voltage Dependent ◽  
High Conductance

scholarly journals Cation channel conductance and pH gating of the innate immunity factor APOL1 are governed by pore-lining residues within the C-terminal domain

2020 ◽  
Vol 295 (38) ◽  
pp. 13138-13149 ◽  
Author(s):  
Charles Schaub ◽  
Joseph Verdi ◽  
Penny Lee ◽  
Nada Terra ◽  
Gina Limon ◽  
...  
Keyword(s):  
Innate Immunity ◽  
Plasma Membrane ◽  
Lipid Bilayers ◽  
Cation Channel ◽  
Planar Lipid Bilayers ◽  
Channel Formation ◽  
Cation Selectivity ◽  
Terminal Domain ◽  
Immunity Factor ◽  
Pore Lining

The human innate immunity factor apolipoprotein L-I (APOL1) protects against infection by several protozoan parasites, including Trypanosoma brucei brucei. Endocytosis and acidification of high-density lipoprotein–associated APOL1 in trypanosome endosomes leads to eventual lysis of the parasite due to increased plasma membrane cation permeability, followed by colloid-osmotic swelling. It was previously shown that recombinant APOL1 inserts into planar lipid bilayers at acidic pH to form pH-gated nonselective cation channels that are opened upon pH neutralization. This corresponds to the pH changes encountered during endocytic recycling, suggesting APOL1 forms a cytotoxic cation channel in the parasite plasma membrane. Currently, the mechanism and domains required for channel formation have yet to be elucidated, although a predicted helix-loop-helix (H-L-H) was suggested to form pores by virtue of its similarity to bacterial pore-forming colicins. Here, we compare recombinant human and baboon APOL1 orthologs, along with interspecies chimeras and individual amino acid substitutions, to identify regions required for channel formation and pH gating in planar lipid bilayers. We found that whereas neutralization of glutamates within the H-L-H may be important for pH-dependent channel formation, there was no evidence of H-L-H involvement in either pH gating or ion selectivity. In contrast, we found two residues in the C-terminal domain, tyrosine 351 and glutamate 355, that influence pH gating properties, as well as a single residue, aspartate 348, that determines both cation selectivity and pH gating. These data point to the predicted transmembrane region closest to the APOL1 C terminus as the pore-lining segment of this novel channel-forming protein.

Cation channels from Tetrahymena cilia incorporated into planar lipid bilayers

1985 ◽  
Vol 249 (1) ◽  
pp. C177-C179 ◽  
Author(s):  
Y. Oosawa ◽  
M. Sokabe
Keyword(s):  
Lipid Bilayers ◽  
Single Channel ◽  
Cation Channel ◽  
Cation Channels ◽  
Planar Lipid Bilayers ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Ciliary Membrane ◽  
Voltage Dependent

A single cation channel from Tetrahymena cilia was incorporated into planar lipid bilayers. This channel selected for K+, Na+, and Li+ over Cl- and gluconate-, and its single channel conductance (at +25 mV) was 211 +/- 8 pS (mean +/- SE) in 100 mM K+-gluconate. The channel was not voltage dependent and may contribute to the resting K+ conductance of ciliary membrane.

Characterization of a voltage-dependent potassium channel in quid Schwann cells reconstituted in planar lipid bilayers

Glia ◽  
1995 ◽  
Vol 15 (1) ◽  
pp. 33-42 ◽  
Author(s):  
F. Noceti ◽  
A. N. Ramírez ◽  
L. D. Possani ◽  
G. Prestipino
Keyword(s):  
Potassium Channel ◽  
Schwann Cells ◽  
Lipid Bilayers ◽  
Planar Lipid Bilayers ◽  
Voltage Dependent

Calcium-activated potassium channels from coronary smooth muscle reconstituted in lipid bilayers

1991 ◽  
Vol 260 (6) ◽  
pp. H1779-H1789 ◽  
Author(s):  
L. Toro ◽  
L. Vaca ◽  
E. Stefani
Keyword(s):  
Smooth Muscle ◽  
Lipid Bilayers ◽  
Surface Membrane ◽  
Dependent Manner ◽  
Coronary Smooth Muscle ◽  
Voltage Sensors ◽  
Kca Channels ◽  
Voltage Dependent ◽  
Calcium Activated Potassium Channels

This work is the initial characterization of Ca(2+)-activated K+ (KCa) channels from coronary smooth muscle reconstituted into lipid bilayers. The channels were obtained from a surface membrane preparation of porcine coronary smooth muscle. KCa channels were the predominant K+ channels in this preparation. The conductance histogram (n = 137 channels) revealed two main populations of “maxi” KCa channels with conductances of 245 and 295 pS. Each population could be subdivided in two “isoforms” or “isochannels” with different functional properties (voltage and Ca2+ sensitivities and kinetics). The analysis of “burst” probability of opening showed that at pCa 4 the two isochannels of 245 pS (KCa-1 and KCa-1') had half-activation potentials (V1/2) of -80 and 6 mV, respectively. The isochannels of 295 pS (KCa-2 and KCa-2') had V1/2 of -28 and -66 mV, respectively. KCa-1 had the highest Ca2+ sensitivity; at -60 mV, the concentration of half-activation value for Ca2+ was 1.2 +/- 0.3 microM (n = 5). External tetraethylammonium reduced channel amplitude in a voltage-dependent manner; dissociation constant was 180 +/- 6 and 466 +/- 41 microM at -40 and +80 mV, respectively (n = 5). Charybdotoxin (5-50 nM) produced typical long closings. These effects were similar in all the channels. We conclude that coronary smooth muscle possesses isoforms of maxi KCa channels with Ca2+ and voltage sensors with different properties, which may confer to each channel a specific functional role.

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