Review: Evolutionary link between prokaryotic and eukaryotic K+ channels.

1998 ◽  
Vol 201 (20) ◽  
pp. 2791-2799
Author(s):  
C Derst ◽  
A Karschin
Keyword(s):  
Membrane Proteins ◽  
Plasma Membranes ◽  
Sequence Data ◽  
Reducing Power ◽  
Eukaryotic Cell ◽  
K Channel ◽  
K Channels ◽  
Coding Regions ◽  
Kv Channels ◽  
Voltage Dependent

Considering the importance of K+ channels in controlling the crucial K+ gradient across the plasma membranes of all living cells, it comes as no surprise that, besides being present in every eukaryotic cell, these integral membrane proteins have recently also been identified in prokaryotes. Today, approximately a dozen successfully completed and many more ongoing sequencing projects permit a search for genes related to K+ channels in the genomes of both eubacteria and archaea. The coding regions of homologues show a remarkable variety in primary structure. They predict membrane proteins with one, two, three and six hydrophobic segments surrounding a putative K+-selective pore (H5) and the presence or absence of a cytosolic putative NAD+-binding domain (PNBD) that probably senses the reducing power of the cell. The analysis of kinships on the basis of phylogenetic algorithms identifies sequences closely related to eukaryotic voltage-dependent Kv channels, but also defines members of a primordial class of prokaryotic K+ channel (containing the 2TMS/PNBD motif). Considering the unique mechanisms that may account for the assembly of modern proteins from different ancestral genes, and with more primary sequence data soon to appear, a scheme for the evolutionary origin of K+ channels comes within reach.

Ba2+, TEA+, and quinine effects on apical membrane K+ conductance and maxi K+ channels in gallbladder epithelium

1990 ◽  
Vol 259 (1) ◽  
pp. C56-C68 ◽  
Author(s):  
Y. Segal ◽  
L. Reuss
Keyword(s):  
Apical Membrane ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
K Channel ◽  
Dependent Manner ◽  
Gallbladder Epithelium ◽  
Concentration Dependent Manner ◽  
K Channels ◽  
Voltage Dependent ◽  
Channel Currents

The apical membrane of Necturus gallbladder epithelium contains a voltage-activated K+ conductance [Ga(V)]. Large-conductance (maxi) K+ channels underlie Ga(V) and account for 17% of the membrane conductance (Ga) under control conditions. We examined the Ba2+, tetraethylammonium (TEA+), and quinine sensitivities of Ga and single maxi K+ channels. Mucosal Ba2+ addition decreased resting Ga in a concentration-dependent manner (65% block at 5 mM) and decreased Ga(V) in a concentration- and voltage-dependent manner. Mucosal TEA+ addition also decreased control Ga (60% reduction at 5 mM). TEA+ block of Ga(V) was more potent and less voltage dependent that Ba2+ block. Maxi K+ channels were blocked by external Ba2+ at millimolar levels and by external TEA+ at submillimolar levels. At 0.3 mM, quinine (mucosal addition) hyperpolarized the cell membranes by 6 mV and reduced the fractional apical membrane resistance by 50%, suggesting activation of an apical membrane K+ conductance. At 1 mM, quinine both activated and blocked K(+)-conductive pathways. Quinine blocked maxi K+ channel currents at submillimolar concentrations. We conclude that 1) Ba2+ and TEA+ block maxi K+ channels and other K+ channels underlying resting Ga; 2) parallels between the Ba2+ and TEA+ sensitivities of Ga(V) and maxi K+ channels support a role for these channels in Ga(V); and 3) quinine has multiple effects on K(+)-conductive pathways in gallbladder epithelium, which are only partially explained by block of apical membrane maxi K+ channels.

scholarly journals Potassium channel types in arterial chemoreceptor cells and their selective modulation by oxygen.

1992 ◽  
Vol 100 (3) ◽  
pp. 401-426 ◽  
Author(s):  
M D Ganfornina ◽  
J López-Barneo
Keyword(s):  
Time Course ◽  
Single Channel ◽  
K Channel ◽  
Open Probability ◽  
K Channels ◽  
Glomus Cells ◽  
Control Value ◽  
Voltage Dependent ◽  
K Current ◽  
Chemoreceptor Cells

Single K+ channel currents were recorded in excised membrane patches from dispersed chemoreceptor cells of the rabbit carotid body under conditions that abolish current flow through Na+ and Ca2+ channels. We have found three classes of voltage-gated K+ channels that differ in their single-channel conductance (gamma), dependence on internal Ca2+ (Ca2+i), and sensitivity to changes in O2 tension (PO2). Ca(2+)-activated K+ channels (KCa channels) with gamma approximately 210 pS in symmetrical K+ solutions were observed when [Ca2+]i was greater than 0.1 microM. Small conductance channels with gamma = 16 pS were not affected by [Ca2+]i and they exhibited slow activation and inactivation time courses. In these two channel types open probability (P(open)) was unaffected when exposed to normoxic (PO2 = 140 mmHg) or hypoxic (PO2 approximately 5-10 mmHg) external solutions. A third channel type (referred to as KO2 channel), having an intermediate gamma(approximately 40 pS), was the most frequently recorded. KO2 channels are steeply voltage dependent and not affected by [Ca2+]i, they inactivate almost completely in less than 500 ms, and their P(open) reversibly decreases upon exposure to low PO2. The effect of low PO2 is voltage dependent, being more pronounced at moderately depolarized voltages. At 0 mV, for example, P(open) diminishes to approximately 40% of the control value. The time course of ensemble current averages of KO2 channels is remarkably similar to that of the O2-sensitive K+ current. In addition, ensemble average and macroscopic K+ currents are affected similarly by low PO2. These observations strongly suggest that KO2 channels are the main contributors to the macroscopic K+ current of glomus cells. The reversible inhibition of KO2 channel activity by low PO2 does not desensitize and is not related to the presence of F-, ATP, and GTP-gamma-S at the internal face of the membrane. These results indicate that KO2 channels confer upon glomus cells their unique chemoreceptor properties and that the O2-K+ channel interaction occurs either directly or through an O2 sensor intrinsic to the plasma membrane closely associated with the channel molecule.

Internal and external TEA block in single cloned K+ channels

1991 ◽  
Vol 261 (4) ◽  
pp. C583-C590 ◽  
Author(s):  
G. E. Kirsch ◽  
M. Taglialatela ◽  
A. M. Brown
Keyword(s):  
Single Channel ◽  
Channel Structure ◽  
K Channel ◽  
Cdna Clones ◽  
K Channels ◽  
Open Time ◽  
Voltage Dependent ◽  
Internal Site ◽  
Channel Open Time ◽  
Single Channel Currents

Tetraethylammonium (TEA) has been used recently to probe natural and mutational variants of voltage-dependent K+ channels encoded by cDNA clones. Its usefulness as a probe of channel structure prompted us to examine the molecular mechanism by which TEA blocks single-channel currents in Xenopus oocytes expressing the rat brain K+ channel, RCK2. TEA at the intracellular surface of membrane patches decreased channel open time and increased the duration of closed intervals. Tetrapentylammonium had similar but more potent effects. Extracellular application of TEA caused an apparent reduction of single-channel amplitude. Block was slower at the high-affinity internal site than at the low-affinity external site. Internal TEA selectively blocks open K+ channels, and the voltage dependence of the block indicates that the binding site lies within the membrane electric field at a point 25% of the distance from the cytoplasmic margin. External TEA also interacts with the open channel but is less sensitive to membrane potential. The results indicate that the internal and external TEA binding sites define the inner and outer margins of the aqueous pore.

scholarly journals Charybdotoxin block of single Ca2+-activated K+ channels. Effects of channel gating, voltage, and ionic strength.

1988 ◽  
Vol 91 (3) ◽  
pp. 317-333 ◽  
Author(s):  
C S Anderson ◽  
R MacKinnon ◽  
C Smith ◽  
C Miller
Keyword(s):  
Ionic Strength ◽  
Plasma Membranes ◽  
Scorpion Venom ◽  
Dissociation Rate ◽  
K Channel ◽  
Single Channels ◽  
Association Rate ◽  
Open Probability ◽  
Apparent Dissociation Constant ◽  
K Channels

Charybdotoxin (CTX), a small, basic protein from scorpion venom, strongly inhibits the conduction of K ions through high-conductance, Ca2+-activated K+ channels. The interaction of CTX with Ca2+-activated K+ channels from rat skeletal muscle plasma membranes was studied by inserting single channels into uncharged planar phospholipid bilayers. CTX blocks K+ conduction by binding to the external side of the channel, with an apparent dissociation constant of approximately 10 nM at physiological ionic strength. The dwell-time distributions of both blocked and unblocked states are single-exponential. The toxin association rate varies linearly with the CTX concentration, and the dissociation rate is independent of it. CTX is competent to block both open and closed channels; the association rate is sevenfold faster for the open channel, while the dissociation rate is the same for both channel conformations. Membrane depolarization enhances the CTX dissociation rate e-fold/28 mV; if the channel's open probability is maintained constant as voltage varies, then the toxin association rate is voltage independent. Increasing the external solution ionic strength from 20 to 300 mM (with K+, Na+, or arginine+) reduces the association rate by two orders of magnitude, with little effect on the dissociation rate. We conclude that CTX binding to the Ca2+-activated K+ channel is a bimolecular process, and that the CTX interaction senses both voltage and the channel's conformational state. We further propose that a region of fixed negative charge exists near the channel's CTX-binding site.

Delayed activation of single mechanosensitive channels in Lymnaea neurons

1994 ◽  
Vol 267 (2) ◽  
pp. C598-C606 ◽  
Author(s):  
D. L. Small ◽  
C. E. Morris
Keyword(s):  
Dynamic Behavior ◽  
Abrupt Onset ◽  
Fundamental Difference ◽  
K Channel ◽  
Mechanosensitive Channels ◽  
Stretch Activation ◽  
Open Probability ◽  
K Channels ◽  
Voltage Dependent ◽  
Lymnaea Neurons

Some stretch-activated (SA) channels challenged with suction jumps exhibit adaptation, a dynamic behavior that can be overlooked because of its mechanical fragility. In previous studies of neuronal SA K channels, we detected no adaptation, but the protocols used were not designed to detect dynamics. Here, we reproduce the adaptation seen by others in Xenopus SA cationic (Cat) channels but show that, with the same protocol, no adaptation occurs with SA K channels. Instead, SA K channels exhibit a different dynamic behavior, delayed activation. Lymnaea SA K channels subjected to pressure jumps responded after a 1- to 4-s delay with a gradual, rather than abrupt, onset of activation. The delay was pressure dependent and was longer for patches from older cultured neurons. Delayed responses were fragile like SA Cat channel adaptation; they disappeared with repeated stimuli. Cytochalasin D decreased the delay and increased the stretch activation of SA K channels. Unlike SA Cat channel adaptation, which occurs only at hyperpolarized potentials, SA K channel delay was not voltage dependent. We note that once SA Cat and SA K channels are "stripped" of their fragile (cytoskeleton-dependent?) dynamics, however, their gating behaviors show little fundamental difference; both are stretch activatable and have a higher open probability at depolarized potentials.

scholarly journals Scanning the Intracellular S6 Activation Gate in the Shaker K+ Channel

2002 ◽  
Vol 119 (6) ◽  
pp. 521-531 ◽  
Author(s):  
David H. Hackos ◽  
Tsg-Hui Chang ◽  
Kenton J. Swartz
Keyword(s):  
Ionic Currents ◽  
K Channel ◽  
Dependent Manner ◽  
Kv Channel ◽  
Closed State ◽  
Kv Channels ◽  
Gate Structure ◽  
Activation Gate ◽  
Voltage Dependent ◽  
Gate Region

In Kv channels, an activation gate is thought to be located near the intracellular entrance to the ion conduction pore. Although the COOH terminus of the S6 segment has been implicated in forming the gate structure, the residues positioned at the occluding part of the gate remain undetermined. We use a mutagenic scanning approach in the Shaker Kv channel, mutating each residue in the S6 gate region (T469-Y485) to alanine, tryptophan, and aspartate to identify positions that are insensitive to mutation and to find mutants that disrupt the gate. Most mutants open in a steeply voltage-dependent manner and close effectively at negative voltages, indicating that the gate structure can both support ion flux when open and prevent it when closed. We find several mutant channels where macroscopic ionic currents are either very small or undetectable, and one mutant that displays constitutive currents at negative voltages. Collective examination of the three types of substitutions support the notion that the intracellular portion of S6 forms an activation gate and identifies V478 and F481 as candidates for occlusion of the pore in the closed state.

scholarly journals Structure of a pore-blocking toxin in complex with a eukaryotic voltage-dependent K+ channel

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Anirban Banerjee ◽  
Alice Lee ◽  
Ernest Campbell ◽  
Roderick MacKinnon
Keyword(s):  
Electron Density ◽  
Selectivity Filter ◽  
K Channel ◽  
Wild Type ◽  
Kv Channel ◽  
Pore Blocking ◽  
Kv Channels ◽  
Filter Structure ◽  
Conduction Pathway ◽  
Voltage Dependent

Pore-blocking toxins inhibit voltage-dependent K+ channels (Kv channels) by plugging the ion-conduction pathway. We have solved the crystal structure of paddle chimera, a Kv channel in complex with charybdotoxin (CTX), a pore-blocking toxin. The toxin binds to the extracellular pore entryway without producing discernable alteration of the selectivity filter structure and is oriented to project its Lys27 into the pore. The most extracellular K+ binding site (S1) is devoid of K+ electron-density when wild-type CTX is bound, but K+ density is present to some extent in a Lys27Met mutant. In crystals with Cs+ replacing K+, S1 electron-density is present even in the presence of Lys27, a finding compatible with the differential effects of Cs+ vs K+ on CTX affinity for the channel. Together, these results show that CTX binds to a K+ channel in a lock and key manner and interacts directly with conducting ions inside the selectivity filter.

Ionic channels in epithelial cell membranes

1985 ◽  
Vol 65 (4) ◽  
pp. 833-903 ◽  
Author(s):  
W. Van Driessche ◽  
W. Zeiske
Keyword(s):  
Frog Skin ◽  
Plasma Membranes ◽  
Ionic Channels ◽  
K Channel ◽  
Na Channel ◽  
Na Channels ◽  
K Channels ◽  
Excitable Membranes ◽  
Tight Epithelia ◽  
Apical Membranes

This review focused on results obtained with methods that allow studies of ionic channels in situ, namely, patch clamping and current-noise analysis. We reported findings for ionic channels in apical and basolateral plasma membranes of various tight and leaky epithelia from a wide range of animal species and tissues. As for ionic channel "species," we restricted ourselves to the discussion of cation-specific (Na+ or K+), hybrid (Na+ and K+), and Cl- channels. For the K+-specific channels it can be said that their properties in conduction (multisite, single file), selectivity (only "K+-like" cations), and blocking behavior (Ba2+, Cs+, TEA) much resemble those observed for K+ channels in excitable membranes. This seems to include also the Ca2+-activated "maxi" K+ channel. Thus, K+ channels in excitable membranes and K+ channels in epithelia appear to be very closely related in their basic structural principles. This is, however, not at all unexpected, because K+ channels provide the dominant permeability characteristics of nearly all plasma membranes from symmetrical and epithelial cells. An exception is, of course, apical membranes of tight epithelia whose duty is Na+ absorption against large electrochemical gradients in a usually anisosmotic environment. Here, Na+ channels dominate, although a minor fraction of membrane permeability comes from K+ channels, as in frog skin, colon, or distal nephron. Epithelial Na+ channels are different from excitable Na+ channels in that they 1) are far more selective and 2) seem to be chemically rather than electrically gated. Furthermore, their specific blockers belong to very different chemical families, although a guanidinium/amidinium moiety is a common feature (TTX vs. amiloride). [For a more detailed summary of Na+ channel properties see sect. IV H.] Most interesting is the occurrence of relatively nonselective cationic (hybrid) channels in apical membranes of tight epithelia, like larval or adult frog skin. Here, not only the weak selectivity is astonishing but also the fact that these channels react with so-called K+-channel-specific (Ba2+, TEA) as well as with Na+-channel-specific (amiloride, BIG) compounds. Moreover, this cross-reactivity does not seem to be inhibitory but, on the contrary, stimulating. Clearly these channels may become a fascinating object with which to assess whether Na+ and K+ channels are not only structurally but also genetically related and whether they can somehow be converted into each other.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Cation permeation through the voltage-dependent potassium channel in the squid axon. Characteristics and mechanisms.

1987 ◽  
Vol 90 (2) ◽  
pp. 261-290 ◽  
Author(s):  
P K Wagoner ◽  
G S Oxford
Keyword(s):  
Binding Energies ◽  
Ion Concentration ◽  
K Channel ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
K Channels ◽  
Energy Profiles ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Ion Binding Sites

Characteristics of cation permeation through voltage-dependent delayed rectifier K channels in squid giant axons were examined. Axial wire voltage-clamp measurements and internal perfusion were used to determine conductance and permeability properties. These K channels exhibit conductance saturation and decline with increases in symmetrical K+ concentrations to 3 M. They also produce ion- and concentration-dependent current-voltage shapes. K channel permeability ratios obtained with substitutions of internal Rb+ or NH+4 for K+ are higher than for external substitution of these ions. Furthermore, conductance and permeability ratios of NH+4 or Rb+ to K+ are functions of ion concentration. Conductance measurements also reveal the presence of an anomalous mole fraction effect for NH+4, Rb+, or Tl+ to K+. Finally, internal Cs+ blocks these K channels in a voltage-dependent manner, with relief of block by elevations in external K+ but not external NH+4 or Cs+. Energy profiles for K+, NH+4, Rb+, Tl+, and Cs+ incorporating three barriers and two ion-binding sites are fitted to the data. The profiles are asymmetric with respect to the center of the electric field, have different binding energies and electrical positions for each ion, and (for K+) exhibit concentration-dependent barrier positions.

scholarly journals Apical K+ channels in Necturus taste cells. Modulation by intracellular factors and taste stimuli.

1992 ◽  
Vol 99 (4) ◽  
pp. 591-613 ◽  
Author(s):  
T A Cummings ◽  
S C Kinnamon
Keyword(s):  
Apical Membrane ◽  
Basolateral Membrane ◽  
Taste Receptor ◽  
K Channel ◽  
Patch Clamp Recording ◽  
Open Probability ◽  
K Channels ◽  
Voltage Dependent ◽  
Whole Cell Recordings ◽  
Inside Out

The apically restricted, voltage-dependent K+ conductance of Necturus taste receptor cells was studied using cell-attached, inside-out and outside-out configurations of the patch-clamp recording technique. Patches from the apical membrane typically contained many channels with unitary conductances ranging from 30 to 175 pS in symmetrical K+ solutions. Channel density was so high that unitary currents could be resolved only at negative voltages; at positive voltages patch recordings resembled whole-cell recordings. These multi-channel patches had a small but significant resting conductance that was strongly activated by depolarization. Patch current was highly K+ selective, with a PK/PNa ratio of 28. Patches containing single K+ channels were obtained by allowing the apical membrane to redistribute into the basolateral membrane with time. Two types of K+ channels were observed in isolation. Ca(2+)-dependent channels of large conductance (135-175 pS) were activated in cell-attached patches by strong depolarization, with a half-activation voltage of approximately -10 mV. An ATP-blocked K+ channel of 100 pS was activated in cell-attached patches by weak depolarization, with a half-activation voltage of approximately -47 mV. All apical K+ channels were blocked by the sour taste stimulus citric acid directly applied to outside-out and perfused cell-attached patches. The bitter stimulus quinine also blocked all channels when applied directly by altering channel gating to reduce the open probability. When quinine was applied extracellularly only to the membrane outside the patch pipette and also to inside-out patches, it produced a flickery block. Thus, sour and bitter taste stimuli appear to block the same apical K+ channels via different mechanisms to produce depolarizing receptor potentials.

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