scholarly journals Mode of regulation by G protein of the ATP-sensitive K+ channel in guinea-pig ventricular cell membrane.

1994 ◽  
Vol 478 (1) ◽  
pp. 101-107 ◽  
Author(s):  
H Ito ◽  
J Vereecke ◽  
E Carmeliet
Keyword(s):  
Cell Membrane ◽  
Guinea Pig ◽  
G Protein ◽  
K Channel ◽  
Ventricular Cell ◽  
Mode Of Regulation

scholarly journals On the mechanism of G protein beta gamma subunit activation of the muscarinic K+ channel in guinea pig atrial cell membrane. Comparison with the ATP-sensitive K+ channel.

1992 ◽  
Vol 99 (6) ◽  
pp. 961-983 ◽  
Author(s):  
H Ito ◽  
R T Tung ◽  
T Sugimoto ◽  
I Kobayashi ◽  
K Takahashi ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Guinea Pig ◽  
G Proteins ◽  
Katp Channel ◽  
K Channel ◽  
Channel Activation ◽  
Gamma Subunit ◽  
Internal Solution ◽  
Gamma S ◽  
Atrial Cell

The mechanism of G protein beta gamma subunit (G beta gamma)-induced activation of the muscarinic K+ channel (KACh) in the guinea pig atrial cell membrane was examined using the inside-out patch clamp technique. G beta gamma and GTP-gamma S-bound alpha subunits (G alpha *'s) of pertussis toxin (PT)-sensitive G proteins were purified from bovine brain. Either in the presence or absence of Mg2+, G beta gamma activated the KACh channel in a concentration-dependent fashion. 10 nM G beta gamma almost fully activated the channel in 132 of 134 patches (98.5%). The G beta gamma-induced maximal channel activity was equivalent to or sometimes larger than the GTP-gamma S-induced one. Half-maximal activation occurred at approximately 6 nM G beta gamma. Detergent (CHAPS) and boiled G beta gamma preparation could not activate the KACh channel. G beta gamma suspended by Lubrol PX instead of CHAPS also activated the channel. Even when G beta gamma was pretreated in Mg(2+)-free EDTA internal solution containing GDP analogues (24-48 h) to inactivate possibly contaminating G i alpha *'s, the G beta gamma activated the channel. Furthermore, G beta gamma preincubated with excessive GDP-bound G o alpha did not activate the channel. These results indicate that G beta gamma itself, but neither the detergent CHAPS nor contaminating G i alpha *, activates the KACh channel. Three different kinds of G i alpha * at 10 pM-10 nM could weakly activate the KACh channel. However, they were effective only in 40 of 124 patches (32.2%) and their maximal channel activation was approximately 20% of that induced by GTP-gamma S or G beta gamma. Thus, G i alpha * activation of the KACh channel may not be significant. On the other hand, G i alpha *'s effectively activated the ATP-sensitive K+ channel (KATP) in the ventricular cell membrane when the KATP channel was maintained phosphorylated by the internal solution containing 100 microM Mg.ATP. G beta gamma inhibited adenosine or mACh receptor-mediated, intracellular GTP-induced activation of the KATP channel. G i alpha *'s also activated the phosphorylated KATP channel in the atrial cell membrane, but did not affect the background KACh channel. G beta gamma subsequently applied to the same patch caused prominent KACh channel activation. The above results may indicate two distinct regulatory systems of cardiac K+ channels by PT-sensitive G proteins: G i alpha activation of the KATP channel and G beta gamma activation of the KACh channel.

scholarly journals Expression levels of RGS7 and RGS4 proteins determine the mode of regulation of the G protein-activated K+ channel and control regulation of RGS7 by Gβ5

FEBS Letters ◽  
2001 ◽  
Vol 492 (1-2) ◽  
pp. 20-28 ◽  
Author(s):  
Tal Keren-Raifman ◽  
Amal K. Bera ◽  
Dror Zveig ◽  
Sagit Peleg ◽  
D.Scott Witherow ◽  
...  
Keyword(s):  
G Protein ◽  
K Channel ◽  
Expression Levels ◽  
Control Regulation ◽  
And Control ◽  
Mode Of Regulation

scholarly journals On the mechanism of basal and agonist-induced activation of the G protein-gated muscarinic K+ channel in atrial myocytes of guinea pig heart.

1991 ◽  
Vol 98 (3) ◽  
pp. 517-533 ◽  
Author(s):  
H Ito ◽  
T Sugimoto ◽  
I Kobayashi ◽  
K Takahashi ◽  
T Katada ◽  
...  
Keyword(s):  
Guinea Pig ◽  
G Protein ◽  
K Channel ◽  
Dependent Manner ◽  
Atrial Myocytes ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Concentration Dependent Manner ◽  
Guinea Pig Heart ◽  
Gamma S

Using the patch clamp technique, we examined the agonist-free, basal interaction between the muscarinic acetylcholine (m-ACh) receptor and the G protein (GK)-gated muscarinic K+ channel (IK.ACh), and the modification of this interaction by ACh binding to the receptor in single atrial myocytes of guinea pig heart. In the whole cell clamp mode, guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma S) gradually increased the IK.ACh current in the absence of agonists (e.g., acetylcholine). This increase was inhibited in cells that were pretreated with islet-activating protein (IAP, pertussis toxin) or N-ethylmaleimide (NEM). In inside-out patches, even in the absence of agonists, intracellular GTP caused openings of IK.ACh in a concentration-dependent manner in approximately 80% of the patches. Channel activation by GTP in the absence of agonist was much less than that caused by GTP-gamma S. The agonist-independent, GTP-induced activation of IK.ACh was inhibited by the A promoter of IAP (with nicotinamide adenine dinucleotide) or NEM. As the ACh concentration was increased, the GTP-induced maximal open probability of IK.ACh was increased and the GTP concentration for the half-maximal activation of IK.ACh was decreased. Intracellular GDP inhibited the GTP-induced openings of IK.ACh in a concentration-dependent fashion. The half-inhibition of IK.ACh openings occurred at a much lower concentration of GDP in the absence of agonists than in the presence of ACh. From these results, we concluded (a) that the interaction between the m-ACh receptor and GK is essential for basal stimulation of IK.ACh, and (b) that ACh binding to the receptor accelerates the turnover of GK and increases GK's affinity to GTP analogues over GDP.

Regulation of G Protein-Gated K+ Channels

Physiology ◽  
1989 ◽  
Vol 4 (4) ◽  
pp. 158-161
Author(s):  
Y Kurachi
Keyword(s):  
Cell Membrane ◽  
G Protein ◽  
G Proteins ◽  
Binding Proteins ◽  
Membrane Receptors ◽  
K Channel ◽  
K Channels ◽  
Gtp Binding Proteins ◽  
Gtp Binding

GTP-binding proteins (G or N) transduce signals from various membrane receptors to effector systems in the cell membrane. Recently it was shown that G proteins couple a variety of receptors to a K+ channel.

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.

Sign in / Sign up

Export Citation Format

Share Document