scholarly journals A novel ion conducting route besides the central pore in an inherited mutant of G-protein-gated inwardly rectifying K+ channel

2021 ◽  
Author(s):  
I-Shan Chen ◽  
Jodene Eldstrom ◽  
David Fedida ◽  
Yoshihiro Kubo
Keyword(s):  
G Protein ◽  
Structural Changes ◽  
Single Channel ◽  
Ion Selectivity ◽  
K Channel ◽  
Girk Channels ◽  
Electrode Voltage ◽  
Ion Conducting ◽  
Inwardly Rectifying ◽  
Better Than

G-protein-gated inwardly rectifying K+ (GIRK; Kir3.x) channels play important physiological roles in various organs. Some of the disease-associated mutations of GIRK channels are known to induce loss of K+ selectivity but their structural changes remain unclear. In this study, we investigated the mechanisms underlying the abnormal ion selectivity of inherited GIRK mutants. By the two-electrode voltage-clamp analysis of GIRK mutants heterologously expressed in Xenopus oocytes, we observed that Kir3.2 G156S permeates Li+ better than Rb+, while T154del or L173R of Kir3.2 and T158A of Kir3.4 permeate Rb+ better than Li+, suggesting a unique conformational change in the G156S mutant. Applications of blockers of the selectivity filter (SF) pathway, Ba2+ or Tertiapin-Q (TPN-Q), remarkably increased the Li+-selectivity of Kir3.2 G156S but did not alter those of the other mutants. In single-channel recordings of Kir3.2 G156S expressed in mouse fibroblasts, two types of events were observed, one attributable to a TPN-Q sensitive K+ current and the second a TPN-Q resistant Li+ current. The results show that a novel Li+ permeable and blocker-resistant pathway exists in G156S in addition to the SF pathway. Mutations in the pore helix (PH), S148F and T151A, also induced high Li+ permeation. Our results demonstrate that the mechanism underlying the loss of K+ selectivity of Kir3.2 G156S involves formation of a novel ion permeation pathway besides the SF pathway, which allows permeation of various species of cations.

scholarly journals A G-protein-activated inwardly rectifying K+ channel (GIRK4) from human hippocampus associates with other GIRK channels

1996 ◽  
Vol 16 (3) ◽  
pp. 930-938 ◽  
Author(s):  
A Spauschus ◽  
KU Lentes ◽  
E Wischmeyer ◽  
E Dissmann ◽  
C Karschin ◽  
...  
Keyword(s):  
G Protein ◽  
K Channel ◽  
Girk Channels ◽  
Human Hippocampus ◽  
Inwardly Rectifying

Single-channel properties of a G-protein-coupled inward rectifier potassium channel in brain neurons

1996 ◽  
Vol 75 (1) ◽  
pp. 318-328 ◽  
Author(s):  
J. J. Grigg ◽  
T. Kozasa ◽  
Y. Nakajima ◽  
S. Nakajima
Keyword(s):  
G Protein ◽  
Single Channel ◽  
Inward Rectifier ◽  
Equilibrium Potential ◽  
K Channel ◽  
Open Probability ◽  
K Concentration ◽  
Inwardly Rectifying ◽  
G Protein Coupled ◽  
Cytoplasmic Side

1. In cultured rat locus coeruleus neurons, somatostatin or met-enkephalin induces an inwardly rectifying K+ conductance. This inward rectifier was analyzed at the single-channel level. 2. Using the inside-out patch-clamp, guanosine 5'-triphosphate (GTP) application to the cytoplasmic side in the presence of somatostatin or met-enkephalin in the pipette produced a large increase in channel activity, which disappeared on switching from GTP to guanosine 5'-diphosphate. 3. The unitary conductance was approximately 30 pS at -95 mV with an extracellular K+ concentration of 156 mM and an intracellular K+ concentration of 124 mM at 23 degrees C. The channel showed burst behavior, and the closed time histogram was fit by two exponentials, with the fast time constant being 0.4 ms. The burst time histogram was also fit by two exponentials, with time constants of 0.24 and 2.0 ms (at 10 nM somatostatin). When the somatostatin concentration was changed from 500 to 1 nM, the kinetic behavior of the channel did not change, except that the open probability of the patch was decreased. 4. The current-voltage relation of the unitary channel current showed inward rectification. The reversal potential coincided with the K+ equilibrium potential, and it shifted according to a change in the K+ equilibrium potential. 5. In the presence of external somatostatin, the application of guanosine 5'-O-(3-thiotriphosphate) to the cytoplasmic side induced an irreversible activation of this channel. 6. These results indicate that this K+ channel is the microscopic counterpart of the somatostatin- or met-enkephalin-induced inwardly rectifying K+ current in whole cell recording, and that the channel is activated by a G protein without a diffusible second messenger. Thus this channel is identified as a neuronal G-protein-coupled inward rectifier K+ channel. 7. Analysis of the burst behavior, based on a close-close-open kinetic model, revealed that there are at least four states in the K+ channel, a short gap, a longer closing, a short opening, and a long opening, and that the neuronal inward rectifier is activated at faster rates than the atrial inward rectifier.

scholarly journals Synergistic Activation of G Protein–Gated Inwardly Rectifying Potassium Channels by the βγ Subunits of G Proteins and Na+ and Mg2+ Ions

1999 ◽  
Vol 114 (5) ◽  
pp. 673-684 ◽  
Author(s):  
Jérôme Petit-Jacques ◽  
Jin Liang Sui ◽  
Diomedes E. Logothetis
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Single Channel ◽  
Local Environment ◽  
Girk Channels ◽  
Protein Activation ◽  
Synergistic Activation ◽  
Open Time ◽  
Rapid Amplification ◽  
Inwardly Rectifying

Native and recombinant G protein–gated inwardly rectifying potassium (GIRK) channels are directly activated by the βγ subunits of GTP-binding (G) proteins. The presence of phosphatidylinositol-bis-phosphate (PIP2) is required for G protein activation. Formation (via hydrolysis of ATP) of endogenous PIP2 or application of exogenous PIP2 increases the mean open time of GIRK channels and sensitizes them to gating by internal Na+ ions. In the present study, we show that the activity of ATP- or PIP2-modified channels could also be stimulated by intracellular Mg2+ ions. In addition, Mg2+ ions reduced the single-channel conductance of GIRK channels, independently of their gating ability. Both Na+ and Mg2+ ions exert their gating effects independently of each other or of the activation by the Gβγ subunits. At high levels of PIP2, synergistic interactions among Na+, Mg2+, and Gβγ subunits resulted in severalfold stimulated levels of channel activity. Changes in ionic concentrations and/or G protein subunits in the local environment of these K+ channels could provide a rapid amplification mechanism for generation of graded activity, thereby adjusting the level of excitability of the cells.

scholarly journals Familial Sinus Node Disease Caused by a Gain of GIRK (G-Protein Activated Inwardly Rectifying K + Channel) Channel Function

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Johanna Kuß ◽  
Birgit Stallmeyer ◽  
Matthias Goldstein ◽  
Susanne Rinné ◽  
Christiane Pees ◽  
...  
Keyword(s):  
G Protein ◽  
Sinus Node ◽  
K Channel ◽  
Channel Function ◽  
Node Disease ◽  
Sinus Node Disease ◽  
Inwardly Rectifying

Calcium-dependent inactivation of inwardly rectifying K+ channel in a tumor mast cell line

1992 ◽  
Vol 262 (1) ◽  
pp. C84-C90 ◽  
Author(s):  
M. Mukai ◽  
I. Kyogoku ◽  
M. Kuno
Keyword(s):  
Mast Cell ◽  
Cell Line ◽  
Single Channel ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Whole Cell ◽  
Mast Cell Line ◽  
Inwardly Rectifying ◽  
Inside Out

Antigenic stimulation of rat basophilic leukemia (RBL-2H3) cells, a tumor mast cell line, is associated with an increase in intracellular free Ca2+ concentrations ([Ca2+]i) and membrane polarization. We recorded whole cell and single-channel currents through the inwardly rectifying K+ channel, a major resting conductance of cells, using the patch-clamp technique, and we examined interactions between channel activity and [Ca2+]i. With 10 microM Ca2+ in the pipette, the amplitude of whole cell currents gradually declined within 5 min to 48 +/- 13% of that immediately after rupture of the patch membrane, in the presence of 1 mM ATP which minimized intrinsic rundown. In inside-out patches, activity of the channel was reduced by increasing the concentration of Ca2+ in the internal medium, both in the presence and absence of 1 mM ATP, with no apparent change in single-channel conductance. Time-averaged mean current activity in inside-out patches in the presence of 5 microM Ca2+ was less than 50% of that with Ca2+ of 100 nM or less. These results suggest that a rise in [Ca2+]i leads to a closure of the inwardly rectifying K+ channel. In some inside-out patches, inward currents characterized by burst composed of rapid transitions between open and closed states were observed (flickering currents). Single-channel properties of the flickering currents are similar to the inwardly rectifying K+ channel except for kinetics (single-channel conductance of 24.5 +/- 7.9 pS, inward rectification, and permeability to K+).(ABSTRACT TRUNCATED AT 250 WORDS)

Sign in / Sign up

Export Citation Format

Share Document