Molecular determinants of single-channel conductance and ion selectivity in the Cys-loop family: insights from the 5-HT3 receptor

2005 ◽  
Vol 26 (11) ◽  
pp. 587-594 ◽  
Author(s):  
John A. Peters ◽  
Tim G. Hales ◽  
Jeremy, J. Lambert
Keyword(s):  
Single Channel ◽  
Ion Selectivity ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Molecular Determinants

Novel structural determinants of single-channel conductance in nicotinic acetylcholine and 5-hydroxytryptamine type-3 receptors

2006 ◽  
Vol 34 (5) ◽  
pp. 882-886 ◽  
Author(s):  
J.A. Peters ◽  
J.E. Carland ◽  
M.A. Cooper ◽  
M.R. Livesey ◽  
T.Z. Deeb ◽  
...  
Keyword(s):  
Transmembrane Domain ◽  
Single Channel ◽  
Ion Selectivity ◽  
Atomic Scale ◽  
Scale Model ◽  
Amino Acid Residues ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Structural Determinants ◽  
Type 3

Nicotinic ACh (acetylcholine) and 5-HT3 (5-hydroxytryptamine type-3) receptors are cation-selective ion channels of the Cys-loop transmitter-gated ion channel superfamily. Numerous lines of evidence indicate that the channel lining domain of such receptors is formed by the α-helical M2 domain (second transmembrane domain) contributed by each of five subunits present within the receptor complex. Specific amino acid residues within the M2 domain have accordingly been demonstrated to influence both single-channel conductance (γ) and ion selectivity. However, it is now clear from work performed on the homomeric 5-HT3A receptor, heteromeric 5-HT3A/5-HT3B receptor and 5-HT3A/5-HT3B receptor subunit chimaeric constructs that an additional major determinant of γ resides within a cytoplasmic domain of the receptor termed the MA-stretch (membrane-associated stretch). The MA-stretch, within the M3–M4 loop, is not traditionally thought to be implicated in ion permeation and selection. Here, we describe how such observations extend to a representative neuronal nicotinic ACh receptor composed of α4 and β2 subunits and, by inference, probably other members of the Cys-loop family. In addition, we will attempt to interpret our results within the context of a recently developed atomic scale model of the nicotinic ACh receptor of Torpedo marmorata (marbled electric ray).

scholarly journals A superfamily of small potassium channel subunits: form and function of the MinK-related peptides (MiRPs)

1998 ◽  
Vol 31 (4) ◽  
pp. 357-398 ◽  
Author(s):  
GEOFFREY W. ABBOTT ◽  
STEVE A. N. GOLDSTEIN
Keyword(s):  
Membrane Proteins ◽  
Ion Channel ◽  
Single Channel ◽  
Ion Selectivity ◽  
Unique Function ◽  
Type I ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Channel Function ◽  
And Function

1. INTRODUCTION 3581.1 Summary 3581.2 Overview 3591.3 Four classes of pore-forming K+channel subunits – necessary and (sometimes) sufficient 3611.4 Soluble and peripheral membrane proteins that interact with P loop subunits to alter function 3621.5 Integral membrane proteins that interact with P loop subunits to alter function 3632. MinK DETERMINES THE FUNCTION OF MIXED CHANNEL COMPLEXES 3632.1 The KCNE1 gene product (MinK) gives rise to K+-selective currents and controversy 3632.2 MinK assembles with a P loop protein, KvLQT1, to form K+channels with unique function 3642.2.1 Single-channel conductance of KvLQT1 and MinK/KvLQT1 channels 3662.2.2 Other differences between KvLQT1 and MinK/KvLQT1 channels 3672.3 MinK assembles with HERG, another P loop subunit, to regulate channel activity 3682.4 MinK does not form chloride-selective ion channels 3683. EXPERIMENTAL AND NATURAL MinK MUTATIONS 3693.1 Site-directed mutations 3693.1.1 MinK mutation alters basic channel attributes and identifies key residues 3693.1.2 MinK is a Type I transmembrane peptide 3703.1.3 MinK is intimately associated with the IKspore 3703.1.4 The number of MinK subunits in IKschannel complexes 3723.2 KCNE1 mutations associated with arrhythmia and deafness alter IKschannel function 3733.3 Summary of MinK sites critical to IKschannel function 3744. MinK-RELATED PEPTIDES: AN EMERGING SUPERFAMILY 3744.1 KCNE2, 3 and 4 encode MinK-related peptides 1, 2 and 3 (MiRPs) 3744.2 MiRP1 assembles with a P loop protein, HERG, to form K+channels with unique function 3754.2.1 MiRP1 alters activation, deactivation and single-channel conductance 3764.2.2 MiRP1 alters regulation by K+ion and confers biphasic kinetics to channel blockade 3784.2.3 Stable association of MiRP1 and HERG subunits 3804.3 KCNE2 mutations are associated with arrhythmia and decreased K+flux 3834.4 Summary of the evidence that cardiac IKrchannels are MiRP1/HERG complexes 3855. MinK-RELATED PEPTIDES: COMMONALTIES AND IMPLICATIONS 3865.1 Genetics and structure 3865.2 Cell biology and function 3876. ANSWERS, SOME OUTSTANDING ISSUES, CONCLUSIONS 3877. ACKNOWLEDGEMENTS 3898. REFERENCES 389MinK and MinK-related peptide 1 (MiRP1) are integral membrane peptides with a single transmembrane span. These peptides are active only when co-assembled with pore-forming K+ channel subunits and yet their role in normal ion channel behaviour is obligatory. In the resultant complex the peptides establish key functional attributes: gating kinetics, single-channel conductance, ion selectivity, regulation and pharmacology. Co-assembly is required to reconstitute channel behaviours like those observed in native cells. Thus, MinK/KvLQT1 and MiRP1/HERG complexes reproduce the cardiac currents called IKs and IKr, respectively. Inherited mutations in KCNE1 (encoding MinK) and KCNE2 (encoding MiRP1) are associated with lethal cardiac arrhythmias. How these mutations change ion channel behaviour has shed light on peptide structure and function. Recently, KCNE3 and KCNE4 were isolated. In this review, we consider what is known and what remains controversial about this emerging superfamily.

scholarly journals Lack of negative slope in I-V plots for BK channels at positive potentials in the absence of intracellular blockers

2013 ◽  
Vol 141 (4) ◽  
pp. 493-497 ◽  
Author(s):  
Yanyan Geng ◽  
Xiaoyu Wang ◽  
Karl L. Magleby
Keyword(s):  
Single Channel ◽  
Bk Channels ◽  
Negative Slope ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Linear Current ◽  
Joint Application ◽  
Current Voltage ◽  
Α Subunits

Large-conductance, voltage- and Ca2+-activated K+ (BK) channels display near linear current–voltage (I-V) plots for voltages between −100 and +100 mV, with an increasing sublinearity for more positive potentials. As is the case for many types of channels, BK channels are blocked at positive potentials by intracellular Ca2+ and Mg2+. This fast block progressively reduces single-channel conductance with increasing voltage, giving rise to a negative slope in the I-V plots beyond about +120 mV, depending on the concentration of the blockers. In contrast to these observations of pronounced differences in the magnitudes and shapes of I-V plots in the absence and presence of intracellular blockers, Schroeder and Hansen (2007. J. Gen. Physiol. http://dx.doi.org/10.1085/jgp.200709802) have reported identical I-V plots in the absence and presence of blockers for BK channels, with both plots having reduced conductance and negative slopes, as expected for blockers. Schroeder and Hansen included both Ca2+ and Mg2+ in the intracellular solution rather than a single blocker, and they also studied BK channels expressed from α plus β1 subunits, whereas most previous studies used only α subunits. Although it seems unlikely that these experimental differences would account for the differences in findings between previous studies and those of Schroeder and Hansen, we repeated the experiments using BK channels comprised of α plus β1 subunits with joint application of 2.5 mM Ca2+ plus 2.5 mM Mg2+, as Schroeder and Hansen did. In contrast to the findings of Schroeder and Hansen of identical I-V plots, we found marked differences in the single-channel I-V plots in the absence and presence of blockers. Consistent with previous studies, we found near linear I-V plots in the absence of blockers and greatly reduced currents and negative slopes in the presence of blockers. Hence, studies of conductance mechanisms for BK channels should exclude intracellular Ca2+/Mg2+, as they can reduce conductance and induce negative slopes.

ATP-sensitive K(+)-selective channels of inner medullary collecting duct cells

1994 ◽  
Vol 267 (3) ◽  
pp. F489-F496 ◽  
Author(s):  
S. C. Sansom ◽  
T. Mougouris ◽  
S. Ono ◽  
T. D. DuBose
Keyword(s):  
Single Channel ◽  
Collecting Duct ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Inner Medullary Collecting Duct ◽  
Outward Currents ◽  
Inward Currents ◽  
Excised Patches ◽  
Medullary Collecting Duct

The inner medullary collecting duct (IMCD) in vivo has the capacity to either secrete or reabsorb K+. However, a selective K+ conductance has not been described previously in the IMCD. In the present study, the patch-clamp method was used to determine the presence and properties of K(+)-selective channels in the apical membrane of the inner medullary collecting duct cell line, mIMCD-3. Two types of K(+)-selective channels were observed in both cell-attached and excised patches. The most predominant K+ channel, a smaller conductance K+ channel (SK), was present in cell-attached patches with 140 mM KCl (high bath K+) but not with 135 mM NaCl plus 5 mM KCl (low bath K+) in the bathing solution. The single-channel conductance of SK was 36 pS with inward currents and 29 pS with outward currents in symmetrical 140 mM KCl. SK was insensitive to both voltage and Ca2+. However, SK was inhibited significantly by millimolar concentrations of ATP in excised patches. A second K(+)-selective channel [a larger K+ channel (BK)] displayed a single-channel conductance equal to 132 pS with inward currents and 90 pS with outward currents in symmetrical 140 mM KCl solutions. BK was intermittently activated in excised inside-out patches by Mg(2+)-ATP in concentrations from 1 to 5 mM. With complete removal of Mg2+, BK was insensitive to ATP. BK was also insensitive to potential and Ca2+ and was observed in cell-attached patches with 140 mM KCl in the bath solution. Both channels were blocked reversibly by 1 mM Ba2+ from the intracellular surface but not by external Ba2+.(ABSTRACT TRUNCATED AT 250 WORDS)

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