scholarly journals Activation of the muscarinic K+ channel by P2-purinoceptors via pertussis toxin-sensitive G proteins in guinea-pig atrial cells.

1996 ◽  
Vol 490 (3) ◽  
pp. 659-671 ◽  
Author(s):  
H Matsuura ◽  
M Sakaguchi ◽  
Y Tsuruhara ◽  
T Ehara
Keyword(s):  
Guinea Pig ◽  
G Proteins ◽  
Pertussis Toxin ◽  
K Channel ◽  
Atrial Cells ◽  
P2 Purinoceptors

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 Development of muscarinic-cholinergic stimulation of inositol phosphate production in cultured embryonic chick atrial cells. Evidence for a switch in guanine-nucleotide-binding protein coupling

1990 ◽  
Vol 271 (2) ◽  
pp. 443-448 ◽  
Author(s):  
J V Barnett ◽  
S M Shamah ◽  
B Lassegue ◽  
K K Griendling ◽  
J B Galper
Keyword(s):  
Phospholipase C ◽  
G Proteins ◽  
Pertussis Toxin ◽  
Inositol Phosphate ◽  
In Ovo ◽  
Atrial Cells ◽  
Muscarinic Stimulation ◽  
Inositol Phosphate Production ◽  
Guanine Nucleotide Binding ◽  
Stimulation Of

We have demonstrated that muscarinic stimulation of inositol phosphate production in cultured atrial cells from chicks at 14 days in ovo is partially sensitive to inhibition by pertussis toxin. In these cells, muscarinic agonist binding is coupled to phospholipase C activity via at least two guanine-nucleotide-binding proteins (G-proteins), one sensitive to pertussis toxin and the other (Gp) insensitive to pertussis toxin [Barnett, Shamah, Lassegue, Griendling & Galper (1990) Biochem. J. 271, 437-442]. In the current study we demonstrate that during embryonic development of the chick heart, muscarinic stimulation of inositol phosphate production decreases by 50% between days 5 and 14 in ovo in cells cultured from both atrium and ventricle. In atrial cells, however, pertussis toxin-sensitive muscarinic stimulation of inositol phosphate production increased from undetectable levels at day 5 in ovo to 40% of total stimulation at day 12 in ovo. Muscarinic stimulation of inositol phosphate production in the ventricle did not become sensitive to pertussis toxin at any age studied. In permeabilized atrial cells from embryonic chicks at 5 days in ovo, guanosine 5′-[gamma-thio]triphosphate (GTP[S]) stimulated InsP1 levels by 40 +/- 10% (mean +/- S.E.M., n = 3), InsP2 levels by 117 +/- 18% and InsP3 levels by 51 +/- 8%, suggesting that at day 5 in ovo all of the muscarinic-stimulated inositol phosphate production was coupled to phospholipase C via Gp. H.p.l.c. analysis demonstrated that, in spite of these changes in coupling of phospholipase C to different G-proteins, no changes could be demonstrated in the isomers of InsP3 produced in response to carbamylcholine at both days 5 and 14 in ovo. These data demonstrate that embryonic development of the chick atrium is associated with a switch in coupling of muscarinic receptors to phospholipase C from Gp to a pertussis toxin substrate. This developmental switch in coupling of G-proteins may be related to possible developmental switches in levels of muscarinic receptor isoforms or switches in the subtype of phospholipase C.

Acetylcholine-mediated K+ channel activity in guinea-pig atrial cells is supported by nucleoside diphosphate kinase

1993 ◽  
Vol 422 (4) ◽  
pp. 316-324 ◽  
Author(s):  
Hein Heidb�chel ◽  
Geert Callewaert ◽  
Johan Vereecke ◽  
Edward Carmeliet
Keyword(s):  
Guinea Pig ◽  
Nucleoside Diphosphate Kinase ◽  
K Channel ◽  
Channel Activity ◽  
Atrial Cells

Acetylcholine activation of K+ channels in cell-free membrane of atrial cells

1986 ◽  
Vol 251 (3) ◽  
pp. H681-H684 ◽  
Author(s):  
Y. Kurachi ◽  
T. Nakajima ◽  
T. Sugimoto
Keyword(s):  
Pertussis Toxin ◽  
Binding Proteins ◽  
K Channel ◽  
K Channels ◽  
Gtp Binding Proteins ◽  
Gtp Binding ◽  
Atrial Cells ◽  
Activation Mechanisms ◽  
Free Membrane ◽  
Ach Receptors

The activation mechanisms of K+ channels by muscarinic acetylcholine (m-ACh) receptors were examined in isolated atrial cells by use of patch-recording technique. In "cell-attached" patch recordings, ACh, present in the pipette, activated an inwardly rectifying K+ channel. In "inside-out" patches, activation of the K+ channel by ACh diminished with time following excision of the patch, but it resumed when GTP was present in the solution bathing the intracellular side of the membrane. The A protomer of pertussis toxin, together with NAD, inhibited the channel activation in the presence of GTP. Since pertussis toxin specifically ADP-ribosylates GTP-binding proteins Ni and No, which can interact with m-ACh receptors, and inhibits their functions, it was concluded that m-ACh receptors communicate with the K+ channel via GTP-binding proteins, probably Ni and/or No, in atrial cell membrane.

The alpha subunit of the GTP binding protein activates muscarinic potassium channels of the atrium

Science ◽  
1988 ◽  
Vol 240 (4860) ◽  
pp. 1782-1783 ◽  
Author(s):  
E Cerbai ◽  
U Klockner ◽  
G Isenberg
Keyword(s):  
Guinea Pig ◽  
G Proteins ◽  
Bovine Brain ◽  
Alpha Subunit ◽  
Guanine Nucleotide ◽  
Guanosine Triphosphate ◽  
Gtp Binding ◽  
Atrial Cells ◽  
Gamma Subunits ◽  
Guanine Nucleotide Binding

It has been debated whether the potassium channel of the atrium is activated by the alpha subunit or by the beta gamma subunits of guanine nucleotide binding (G) proteins, which dissociate on activation with guanosine triphosphate (GTP). Therefore, the channel-activating effectiveness of these subunits on isolated guinea pig atrial cells was tested. The activated alpha K subunit from human erythrocytes activated the channel in subpicomolar concentrations. The beta gamma dimer from bovine brain activated the channel in nanomolar concentrations. These results support the view that, physiologically, the alpha subunit activates the channel.

FUNCTIONAL INTERACTIONS OF PERTUSSIS TOXIN-SENSITIVE G-PROTEINS WITH THE TRANSFECTED μ-OPIOID RECEPTOR IN RAT 1 FIBROBLASTS

Analgesia ◽  
1995 ◽  
Vol 1 (4) ◽  
pp. 438-441
Author(s):  
Zafiroula Georgoussi ◽  
Ian Mullaney ◽  
Alan Wise ◽  
Craig Carr ◽  
Graeme Milligan
Keyword(s):  
G Proteins ◽  
Opioid Receptor ◽  
Pertussis Toxin ◽  
Functional Interactions ◽  
Μ Opioid Receptor
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