Intracellular protons inhibit inward rectifier K+ channel of guinea-pig ventricular cell membrane

1992 ◽  
Vol 422 (3) ◽  
pp. 280-286 ◽  
Author(s):  
Hiroyuki Ito ◽  
Johan Vereecke ◽  
Edward Carmeliet
Keyword(s):  
Cell Membrane ◽  
Guinea Pig ◽  
Inward Rectifier ◽  
K Channel ◽  
Ventricular Cell

scholarly journals Secretory modulation of basolateral membrane inwardly rectified K+ channel in guinea pig distal colonic crypts

2002 ◽  
Vol 282 (4) ◽  
pp. C719-C735 ◽  
Author(s):  
Yingjun Li ◽  
Dan R. Halm
Keyword(s):  
Guinea Pig ◽  
Basolateral Membrane ◽  
Inward Rectifier ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Prostaglandin E ◽  
Open Probability ◽  
Pipette Solution ◽  
Colonic Crypts ◽  
Activity Mode

Cell-attached recordings revealed K+ channel activity in basolateral membranes of guinea pig distal colonic crypts. Inwardly rectified currents were apparent with a pipette solution containing 140 mM K+. Single-channel conductance (γ) was 9 pS at the resting membrane potential. Another inward rectifier with γ of 19 pS was observed occasionally. At a holding potential of −80 mV, γ was 21 and 41 pS, respectively. Identity as K+ channels was confirmed after patch excision by changing the bath ion composition. From reversal potentials, relative permeability of Na+ over K+ ( P Na/ P K) was 0.02 ± 0.02, with P Rb/ P K = 1.1 and P Cl/ P K < 0.03. Spontaneous open probability ( P o) of the 9-pS inward rectifier (gpKir) was voltage independent in cell-attached patches. Both a low ( P o = 0.09 ± 0.01) and a moderate ( P o = 0.41 ± 0.01) activity mode were observed. Excision moved gpKir to the medium activity mode; P o ofgpKir was independent of bath Ca2+activity and bath acidification. Addition of Cl− and K+ secretagogues altered P o ofgpKir. Forskolin or carbachol (10 μM) activated the small-conductance gpKir in quiescent patches and increased P o in low-activity patches. K+ secretagogues, either epinephrine (5 μM) or prostaglandin E2 (100 nM), decreased P o of gpKir in active patches. This gpKir may be involved in electrogenic secretion of Cl− and K+ across the colonic epithelium, which requires a large basolateral membrane K+ conductance during maximal Cl− secretion and, presumably, a lower K+ conductance during primary electrogenic K+ secretion.

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.

Xenon Does Not Alter Cardiac Function or Major Cation Currents in Isolated Guinea Pig Hearts or Myocytes

2000 ◽  
Vol 92 (2) ◽  
pp. 516-516 ◽  
Author(s):  
David F. Stowe ◽  
Georg C. Rehmert ◽  
Wai-Meng Kwok ◽  
Henry U. Weigt ◽  
Michael Georgieff ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Guinea Pig ◽  
Salt Solution ◽  
Left Ventricular ◽  
Inward Rectifier ◽  
K Channel ◽  
Conduction Time ◽  
Patch Clamp Technique ◽  
Isolated Hearts ◽  
Major Cation

Background The noble gas xenon (Xe) has been used as an inhalational anesthetic agent in clinical trials with little or no physiologic side effects. Like nitrous oxide, Xe is believed to exert minimal unwanted cardiovascular effects, and like nitrous oxide, the vapor concentration to achieve 1 minimum alveolar concentration (MAC) for Xe in humans is high, i.e., 70-80%. In the current study, concentrations of up to 80% Xe were examined for possible myocardial effects in isolated, erythrocyte-perfused guinea pig hearts and for possible effects on altering major cation currents in isolated guinea pig cardiomyocytes. Methods Isolated guinea pigs hearts were perfused at 70 mm Hg via the Langendorff technique initially with a salt solution at 37 degrees C. Hearts were then perfused with fresh filtered (40-microm pore) and washed canine erythrocytes diluted in the salt solution equilibrated with 20% O2 in nitrogen (control), with 20% O2, 40% Xe, and 40% N2, (0.5 MAC), or with 20% O2 and 80% Xe (1 MAC), respectively. Hearts were perfused with 80% Xe for 15 min, and bradykinin was injected into the blood perfusate to test endothelium-dependent vasodilatory responses. Using the whole-cell patch-clamp technique, 80% Xe was tested for effects on the cardiac ion currents, the Na+, the L-type Ca2+, and the inward-rectifier K+ channel, in guinea pig myocytes suffused with a salt solution equilibrated with the same combinations of Xe, oxygen, and nitrogen as above. Results In isolated hearts, heart rate, atrioventricular conduction time, left ventricular pressure, coronary flow, oxygen extraction, oxygen consumption, cardiac efficiency, and flow responses to bradykinin were not significantly (repeated measures analysis of variance, P&gt;0.05) altered by 40% or 80% Xe compared with controls. In isolated cardiomyocytes, the amplitudes of the Na+, the L-type Ca2+, and the inward-rectifier K+ channel over a range of voltages also were not altered by 80% Xe compared with controls. Conclusions Unlike hydrocarbon-based gaseous anesthetics, Xe does not significantly alter any measured electrical, mechanical, or metabolic factors, or the nitric oxide-dependent flow response in isolated hearts, at least partly because Xe does not alter the major cation currents as shown here for cardiac myocytes. The authors' results indicate that Xe, at approximately 1 MAC for humans, has no physiologically important effects on the guinea pig heart.

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