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

scholarly journals Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle

2014 ◽  
Vol 306 (5) ◽  
pp. C460-C470 ◽  
Author(s):  
Kiril L. Hristov ◽  
Amy C. Smith ◽  
Shankar P. Parajuli ◽  
John Malysz ◽  
Georgi V. Petkov
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Guinea Pig ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Channel Activity ◽  
Open Probability ◽  
Channel Regulation ◽  
Pkc Activation

Large-conductance voltage- and Ca2+-activated K+ (BK) channels are critical regulators of detrusor smooth muscle (DSM) excitability and contractility. PKC modulates the contraction of DSM and BK channel activity in non-DSM cells; however, the cellular mechanism regulating the PKC-BK channel interaction in DSM remains unknown. We provide a novel mechanistic insight into BK channel regulation by PKC in DSM. We used patch-clamp electrophysiology, live-cell Ca2+ imaging, and functional studies of DSM contractility to elucidate BK channel regulation by PKC at cellular and tissue levels. Voltage-clamp experiments showed that pharmacological activation of PKC with PMA inhibited the spontaneous transient BK currents in native freshly isolated guinea pig DSM cells. Current-clamp recordings revealed that PMA significantly depolarized DSM membrane potential and inhibited the spontaneous transient hyperpolarizations in DSM cells. The PMA inhibitory effects on DSM membrane potential were completely abolished by the selective BK channel inhibitor paxilline. Activation of PKC with PMA did not affect the amplitude of the voltage-step-induced whole cell steady-state BK current or the single BK channel open probability (recorded in cell-attached mode) upon inhibition of all major Ca2+ sources for BK channel activation with thapsigargin, ryanodine, and nifedipine. PKC activation with PMA elevated intracellular Ca2+ levels in DSM cells and increased spontaneous phasic and nerve-evoked contractions of DSM isolated strips. Our results support the concept that PKC activation leads to a reduction of BK channel activity in DSM via a Ca2+-dependent mechanism, thus increasing DSM contractility.

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.

scholarly journals Membrane-bound nucleoside diphosphate kinase activity in atrial cells of frog, guinea pig, and human.

1992 ◽  
Vol 71 (4) ◽  
pp. 808-820 ◽  
Author(s):  
H Heidbüchel ◽  
G Callewaert ◽  
J Vereecke ◽  
E Carmeliet
Keyword(s):  
Guinea Pig ◽  
Kinase Activity ◽  
Nucleoside Diphosphate Kinase ◽  
Atrial Cells ◽  
Membrane Bound

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-.

Acetylcholine-sensitive muscarinic K+ channels in mammalian ventricular myocytes

1994 ◽  
Vol 266 (5) ◽  
pp. H1812-H1821 ◽  
Author(s):  
S. Koumi ◽  
J. A. Wasserstrom
Keyword(s):  
Guinea Pig ◽  
Single Channel ◽  
Ventricular Myocytes ◽  
Inward Rectification ◽  
K Channel ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Current Voltage ◽  
S 100 ◽  
Relationship Of

Acetylcholine (ACh) is known to increase K+ conductance in the atrium and in pacemaker tissues in the heart. This effect has not been well defined in mammalian ventricular tissues. We have identified and characterized the ACh-sensitive muscarinic K+ channel [IK(ACh)] activity in isolated human, cat, and guinea pig ventricular myocytes using the patch-clamp technique. Application of ACh increased whole cell membrane current in human ventricular myocytes. Current-voltage relationship of the ACh-induced current in ventricle exhibited inward-rectification whose slope conductance was smaller than that in atrium. In single-channel recording from cell-attached patches, IK(ACh) activity was observed when ACh was included in the solution. The channel exhibited a slope conductance of 43 +/- 2 pS. Open times were distributed according to a single exponential function with mean open lifetime of 1.8 +/- 0.3 ms. The channel had conductance and kinetic characteristics similar to human atrial IK(ACh), which had a slope conductance of 43 +/- 3 pS and mean open lifetime of 1.6 +/- 0.3 ms. However, concentration of ACh at half-maximal stimulation (KD) of the channel in ventricle was greater (KD = 0.13 microM) than that in atrium (KD = 0.03 microM). Adenosine caused activation of the same K+ channel. After formation of an excised inside-out patch, channel activity disappeared. Application of GTP (100 microM) or GTP gamma S (100 microM) to the solution caused reactivation of the channel. When myocytes were preincubated with pertussis toxin (PTX), ACh failed to activate these channels, indicating that the PTX-sensitive G protein, Gi, is essential for activation of IK(ACh). IK(ACh) channel activity was also found in cat and guinea pig ventricular myocytes. We conclude that ACh directly activates the IK(ACh) in mammalian ventricular myocytes via Gi in a fashion almost identical to atrial myocytes.

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