Heterologous Multimeric Assembly Is Essential for K+ Channel Activity of Neuronal and Cardiac G-Protein-Activated Inward Rectifiers

1995 ◽  
Vol 212 (2) ◽  
pp. 657-663 ◽  
Author(s):  
F. Duprat ◽  
F. Lesage ◽  
E. Guillemare ◽  
M. Fink ◽  
J.P. Hugnot ◽  
...  
Keyword(s):  
G Protein ◽  
K Channel ◽  
Channel Activity ◽  
Inward Rectifiers

Different properties of the atrial G protein-gated K+ channels activated by extracellular ATP and adenosine

1995 ◽  
Vol 269 (4) ◽  
pp. H1349-H1358 ◽  
Author(s):  
C. Fu ◽  
A. Pleumsamran ◽  
U. Oh ◽  
D. Kim
Keyword(s):  
G Protein ◽  
Single Channel ◽  
Extracellular Atp ◽  
K Channel ◽  
Affinity Constant ◽  
Channel Activity ◽  
K Channels ◽  
Atrial Cells ◽  
K Current ◽  
Inside Out

Extracellular ATP (ATPo) and adenosine activate G protein-gated inwardly rectifying K+ currents in atrial cells. Earlier studies have suggested that the two agonists may use separate pathways to activate the K+ current. Therefore, we examined whether the K+ channels activated by the two agonists have different properties under identical ionic conditions. In cell-attached patches, K+ channels activated by 100 microM ATP in the pipette had a single-channel conductance and mean open time of 32.0 +/- 0.2 pS and 0.5 +/- 0.1 ms, respectively, compared with 31.3 +/- 0.3 pS and 0.9 +/- 0.1 ms for the K+ channels activated by adenosine (140 mM KCl). With ATPo as the agonist, the K+ channel activity in cell-attached patches was approximately threefold lower than that in inside-out patches with 100 microM GTP in the bath. Applying ATP to the cytoplasmic side of the membrane (ATPi) produced a biphasic concentration-dependent effect on channel activity: an increase at low [mean affinity constant (K0.5) = 190 microM] and a decrease at high (K0.5 = 1.3 mM) concentrations. In contrast, with adenosine as the agonist, K+ channel activity in cell-attached patches was approximately fourfold greater than that in inside-out patches with 100 microM GTP in the bath. In inside-out patches, ATPi only augmented the K+ channel activity (K0.5 = 32 microM). These results show that although both ATPo and adenosine activate kinetically similar K+ channels in atrial cells, the channels are regulated differently by intracellular nucleotides.

Muscarine-gated K+ channel: subunit stoichiometry and structural domains essential for G protein stimulation

1996 ◽  
Vol 271 (1) ◽  
pp. H379-H385 ◽  
Author(s):  
S. J. Tucker ◽  
M. Pessia ◽  
J. P. Adelman
Keyword(s):  
G Protein ◽  
Xenopus Oocytes ◽  
K Channel ◽  
Channel Activity ◽  
Atrial Myocytes ◽  
Structural Domains ◽  
Maximal Stimulation ◽  
Subunit Stoichiometry ◽  
K Current ◽  
Inwardly Rectifying

Coexpression in Xenopus oocytes of the cloned cardiac inward rectifier subunits Kir 3.1 and Kir 3.4 results in G protein-stimulated channel activity closely resembling the muscarinic channel underlying the inwardly rectifying K+ current in atrial myocytes. To determine the stoichiometry and relative subunit positions within the channel, Kir 3.1 and Kir 3.4 were coexpressed in varying ratios with cloned G beta 1 gamma 2 subunits and also as tandemly linked tetramers with different relative subunit positions. The results reveal that the most efficient channel comprises two subunits of each type in an alternating array within the tetramer. To localize regions important for subunit coassembly and G protein sensitivity, chimeric subunits containing domains from either Kir 3.1, Kir 3.4, or the G protein-insensitive subunit Kir 4.1 were expressed. The results demonstrate that the transmembrane domains dictate the potentiation of the coassembled channels and that, although the NH4- or COOH-termini of both subunits alone can confer G protein sensitivity, both termini are required for maximal stimulation by G beta 1 gamma 2.

scholarly journals Effects of anions on the G protein-mediated activation of the muscarinic K+ channel in the cardiac atrial cell membrane. Intracellular chloride inhibition of the GTPase activity of GK.

1992 ◽  
Vol 99 (5) ◽  
pp. 665-682 ◽  
Author(s):  
T Nakajima ◽  
T Sugimoto ◽  
Y Kurachi
Keyword(s):  
G Protein ◽  
Nucleoside Diphosphate Kinase ◽  
Hill Coefficient ◽  
K Channel ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Turn On ◽  
Patch Configuration ◽  
The Hill ◽  
The Relationship

The effects of various intracellular anions on the G protein (GK)-mediated activation of the muscarinic K+ (KACh) channel were examined in single atrial myocytes isolated from guinea pig hearts. The patch clamp technique was used in the inside-out patch configuration. With acetylcholine (ACh, 0.5 microM) in the pipette, 1 microM GTP caused different magnitudes of KACh channel activation in internal solutions containing different anions. The order of potency of anions to induce the KACh channel activity at 0.5 microM ACh and 1 microM GTP was Cl- greater than or equal to Br- greater than 1-. In the SO4(2-) or aspartic acid internal solution, no channel openings were induced by 1 microM GTP with 0.5 microM ACh. In both the Cl- and SO4(2-) internal solutions (with 0.5 microM ACh) the relationship between the concentration of GTP and the channel activity was fit by the Hill equation with a Hill coefficient of approximately 3-4. However, the concentration of GTP at the half-maximal activation (Kd) was 0.2 microM in the Cl- and 10 microM in the SO4(2-) solution. On the other hand, the quasi-steady-state relationship between the concentration of guanosine-5'-o-(3-thiotriphosphate) and the channel activity did not differ significantly between the Cl- and SO4(2-) solutions; i.e., the Hill coefficient was approximately 3-4 and the Kd was approximately 0.06-0.08 microM in both solutions. The decay of channel activity after washout of GTP in the Cl- solution was much slower than that in the SO4(2-) solution. These results suggest that intracellular Cl- does not affect the turn-on reaction but slows the turn-off reaction of GK, resulting in higher sensitivity of the KACh channel for GTP. In the Cl- solution, even in the absence of agonists, GTP (greater than 1 microM) or ATP (greater than 1 mM) alone caused activation of the KACh channel, while neither occurred in the SO4(2-) solution. These observations suggest that the activation of the KACh channel by the basal turn-on reaction of GK or by phosphate transfer to GK by nucleoside diphosphate-kinase may depend at least partly on the intracellular concentration of Cl-.

Effects of ginsenoside on G protein-coupled inwardly rectifying K+ channel activity expressed in Xenopus oocytes

2003 ◽  
Vol 468 (2) ◽  
pp. 83-92 ◽  
Author(s):  
Seok Choi ◽  
Jun-Ho Lee ◽  
Yang In Kim ◽  
Man-Jong Kang ◽  
Hyewon Rhim ◽  
...  
Keyword(s):  
G Protein ◽  
Xenopus Oocytes ◽  
K Channel ◽  
Channel Activity ◽  
Inwardly Rectifying ◽  
G Protein Coupled

scholarly journals Specific Regions of Heteromeric Subunits Involved in Enhancement of G Protein-gated K+Channel Activity

1997 ◽  
Vol 272 (10) ◽  
pp. 6548-6555 ◽  
Author(s):  
Kim W. Chan ◽  
Jin L. Sui ◽  
Michel Vivaudou ◽  
Diomedes E. Logothetis
Keyword(s):  
G Protein ◽  
K Channel ◽  
Channel Activity

scholarly journals A functional model for G protein activation of the muscarinic K+ channel in guinea pig atrial myocytes. Spectral analysis of the effect of GTP on single-channel kinetics.

1996 ◽  
Vol 108 (6) ◽  
pp. 485-495 ◽  
Author(s):  
Y Hosoya ◽  
M Yamada ◽  
H Ito ◽  
Y Kurachi
Keyword(s):  
Spectral Analysis ◽  
Guinea Pig ◽  
G Protein ◽  
Functional Model ◽  
K Channel ◽  
Channel Activity ◽  
Atrial Myocytes ◽  
Protein Activation ◽  
G Protein Activation ◽  
Active Channels

To elucidate the functional interaction between the active G protein subunit (GK*) and the cardiac muscarinic K+ (KACh) channel, the effect of intracellular GTP on the channel current fluctuation in the presence of 0.5 microM extracellular acetylcholine was examined in inside-out patches from guinea pig atrial myocytes using spectral analysis technique. The power density spectra of current fluctuations induced at various concentrations of GTP ([GTP]) were well fitted by the sum of two Lorentzian functions. Because the channel has one open state, the open-close transitions of the channel gate represented by the spectra could be described as C2<-->C1<-->O. As [GTP] was raised, the channel activity increased in a positive cooperative manner. The powers of the two Lorentzian components concomitantly increased, while the corner frequencies and the ratio of the powers at 0 Hz remained almost constant. This indicates that G protein activation did not affect the gating of each channel but mainly increased the number of functionally active channels in the patch to enhance the channel activity. Regulation of the number of functionally active channels could be described by a slow transition of the channel states, U (unavailable)<-->A (available), which is independent of the gating. The equilibrium of this slow transition was shifted by GTP from U to A. Monod-Wyman-Changeux's allosteric model for the channel state transition(U<-->A) could well describe the positive cooperative increase in the channel availability by GTP, assuming that, in the presence of saturating concentrations of ACh, [GK*] linearly increased as [GTP] was raised in our experimental range. The model indicates that the cardiac KACh channel could be described as a multimer composed of four or more functionally identical subunits, to each of which one GK* binds.

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