Fast and slow blockades of the inward-rectifier K+ channel by external divalent cations in guinea-pig cardiac myocytes

1993 ◽  
Vol 422 (5) ◽  
pp. 427-435 ◽  
Author(s):  
Takao Shioya ◽  
Hiroko Matsuda ◽  
Akinori Noma
Keyword(s):  
Guinea Pig ◽  
Cardiac Myocytes ◽  
Divalent Cations ◽  
Inward Rectifier ◽  
K Channel

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.

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.

Coenzyme Q10 attenuates cyanide-activation of the ATP-sensitive K+ channel current in single cardiac myocytes of the guinea-pig

1991 ◽  
Vol 344 (1) ◽  
Author(s):  
Hiroyuki Ito ◽  
Toshiaki Nakajima ◽  
Reiko Takikawa ◽  
Eiji Hamada ◽  
Mari Iguchi ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Cardiac Myocytes ◽  
Coenzyme Q10 ◽  
K Channel ◽  
Channel Current

ATP-dependent decay and recovery of K+ channels in guinea pig cardiac myocytes

1990 ◽  
Vol 258 (1) ◽  
pp. H45-H50 ◽  
Author(s):  
M. Takano ◽  
D. Y. Qin ◽  
A. Noma
Keyword(s):  
Cardiac Myocytes ◽  
Recovery Time ◽  
Inward Rectifier ◽  
Time Dependent ◽  
K Channel ◽  
Concentration Jump ◽  
Time Constants ◽  
K Channels ◽  
Inside Out ◽  
Single Exponential

ATP-dependent decay and recovery of the inward rectifier and ATP-sensitive K+ channels were investigated using inside-out patch recording in cardiac myocytes. The solution facing the inner side of the membrane was instantaneously changed with the oil-gate concentration jump method. Both channels were decayed by removing ATP and were recovered by reapplying ATP. The coexistence of Mg2+ was required for the recovery. 5'-Adenylylimidodiphosphate failed to reverse the ATP-dependent decay. The cumulative histograms of survival time and recovery time, obtained from the inward rectifier K+ channel, showed a single exponential distribution, time constants of which were 55 and 43 s, respectively. The time-dependent nature of decay and recovery was also confirmed in the ATP-sensitive K+ channel. The findings indicated that intracellular ATP is one of the factors that determines the activity of the K+ channels. It is most probable that phosphorylation of channel molecules is essential for maintaining the K+ channel in an operative state.

scholarly journals Ion selectivity and current saturation in inward-rectifier K+ channels

2012 ◽  
Vol 139 (2) ◽  
pp. 145-157 ◽  
Author(s):  
Lei Yang ◽  
Johan Edvinsson ◽  
Henry Sackin ◽  
Lawrence G. Palmer
Keyword(s):  
Divalent Cations ◽  
Ion Selectivity ◽  
Monovalent Cation ◽  
Inward Rectifier ◽  
Ion Concentration ◽  
K Channel ◽  
Cation Selectivity ◽  
Current Saturation ◽  
Lower Permeability ◽  
A Site

We investigated the features of the inward-rectifier K channel Kir1.1 (ROMK) that underlie the saturation of currents through these channels as a function of permeant ion concentration. We compared values of maximal currents and apparent Km for three permeant ions: K+, Rb+, and NH4+. Compared with K+ (imax = 4.6 pA and Km = 10 mM at −100 mV), Rb+ had a lower permeability, a lower imax (1.8 pA), and a higher Km (26 mM). For NH4+, the permeability was reduced more with smaller changes in imax (3.7 pA) and Km (16 mM). We assessed the role of a site near the outer mouth of channel in the saturation process. This site could be occupied by either permeant ions or low-affinity blocking ions such as Na+, Li+, Mg2+, and Ca2+ with similar voltage dependence (apparent valence, 0.15–0.20). It prefers Mg2+ over Ca2+ and has a monovalent cation selectivity, based on the ability to displace Mg2+, of K+ &gt; Li+ ∼ Na+ &gt; Rb+ ∼ NH4+. Conversely, in the presence of Mg2+, the Km for K+ conductance was substantially increased. The ability of Mg2+ to block the channels was reduced when four negatively charged amino acids in the extracellular domain of the channel were mutated to neutral residues. The apparent Km for K+ conduction was unchanged by these mutations under control conditions but became sensitive to the presence of external negative charges when residual divalent cations were chelated with EDTA. The results suggest that a binding site in the outer mouth of the pore controls current saturation. Permeability is more affected by interactions with other sites within the selectivity filter. Most features of permeation (and block) could be simulated by a five-state kinetic model of ion movement through the channel.

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