Magnesium shifts voltage dependence of activation of delayed rectifier I(K) in guinea pig ventricular myocytes

1997 ◽  
Vol 272 (3) ◽  
pp. H1292-H1301 ◽  
Author(s):  
B. A. Williams ◽  
G. N. Beatch
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Inward Rectification ◽  
Delayed Rectifier ◽  
Maximal Effect ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
K Current ◽  
Dose Dependent Decrease ◽  
20 Nm

The sensitivity of the delayed rectifier K+ current (I(K)) to intracellular Mg2+ was investigated in guinea pig ventricular myocytes using the whole cell patch-clamp technique. An increase in free intracellular Mg2+ concentration ([Mg2+]i) led to a dose-dependent decrease in I(K) with a half-maximal effect of approximately 20 nM. Activation of I(K) was shifted toward more positive voltages on increasing [Mg2+]i, but little effect was observed on activation and deactivation kinetics. Isoproterenol increased I(K) and was partially reversible in both control and 100 nM [Mg2+]i. The antiarrhythmic drug dofetilide was used to separate I(K) into its two components, rapidly activating (I(Kr)) and slowly activating (I(Ks)). The magnitude of both components decreased to a similar extent with an increase in [Mg2+]i. As [Mg2+]i was reduced, however, the number of experiments in which the dofetilide-sensitive current I(Kr) displayed inward rectification was reduced. In contrast to results previously reported for frog myocytes, it is unlikely that Mg2+ effects on guinea pig I(K) are mediated by a protein phosphatase.

Endothelin enhances delayed potassium current via phospholipase C in guinea pig ventricular myocytes

1992 ◽  
Vol 262 (2) ◽  
pp. H345-H354 ◽  
Author(s):  
Y. Habuchi ◽  
H. Tanaka ◽  
T. Furukawa ◽  
Y. Tsujimura ◽  
H. Takahashi ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Phospholipase C ◽  
Potassium Current ◽  
Ventricular Myocytes ◽  
Delayed Rectifier ◽  
Internal Solution ◽  
Kinase C ◽  
K Current ◽  
20 Nm ◽  
Pkc Activation

The effects of endothelin, a novel vasoconstrictive peptide, on the delayed rectifier K+ current (IK) were examined in single dialyzed cells from guinea pig ventricles. Either big endothelin or endothelin-1 enhanced IK at a dissociation constant of 2 nM with L-type Ca2+ current being unaffected. Under intracellular perfusion with pCa 7.6 solution, 3 nM big endothelin increased IK by 55 +/- 38.5%. Either pretreatment with 10 microM 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H 7) or a low Ca2+ [10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) and minus CaCl2] internal solution diminished the enhancement. Preceding stimulation of protein kinase C (PKC) by 10-20 nM 12-O-tetradecanoylphorbol-13-acetate also reduced the degree of enhancement. When Na+ was eliminated from the solutions, endothelin increased IK distinctively in cells internally dialyzed with a low Ca2+ solution. This enhancement was not abolished by either pretreatment with H 7 or by removal of Ca2+ from the external perfusate but by increasing the internal EGTA concentration to 40 mM. Preincubation with ryanodine or internal perfusion with heparin also reduced the IK enhancement under Na(+)-free conditions. Intracellular application of 200 microM guanosine 5'-O-(3-thiotriphosphate) effectively attenuated the effect of endothelin. It is concluded that endothelin enhances IK via phospholipase C-mediated PKC activation and intracellular Ca2+ mobilization. GTP-binding protein is involved in these reactions.

scholarly journals The Electrophysiological Effects of Qiliqiangxin on Cardiac Ventricular Myocytes of Rats

2013 ◽  
Vol 2013 ◽  
pp. 1-4 ◽  
Author(s):  
Yidong Wei ◽  
Xiaoyu Liu ◽  
Haidong Wei ◽  
Lei Hou ◽  
Wenliang Che ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Sodium Current ◽  
Chinese Herb ◽  
Antiarrhythmic Therapy ◽  
Delayed Rectifier ◽  
Ca Channel ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
K Current ◽  
Cardiac Ventricular Myocytes

Qiliqiangxin, a Chinese herb, represents the affection in Ca channel function of cardiac myocytes. It is unknown whether Qiliqiangxin has an effect on Na current and K current because the pharmacological actions of this herb’s compound are very complex. We investigated the rational usage of Qiliqiangxin on cardiac ventricular myocytes of rats. Ventricular myocytes were exposed acutely to 1, 10, and 50 mg/L Qiliqiangxin, and whole cell patch-clamp technique was used to study the acute effects of Qiliqiangxin on Sodium current (INa), outward currents delayed rectifier outward K+current (IK), slowly activating delayed rectifier outward K+current (IKs), transient outward K+current (Ito), and inward rectifier K+current (IK1). Qiliqiangxin can decreaseINaby28.53%±5.98%, and its IC50was 9.2 mg/L. 10 and 50 mg/L Qiliqiangxin decreased by37.2%±6.4%and55.9%±5.5%summit current density ofIto. 10 and 50 mg/L Qiliqiangxin decreasedIKsby15.51%±4.03%and21.6%±5.6%. Qiliqiangxin represented a multifaceted pharmacological profile. The effects of Qiliqiangxin on Na and K currents of ventricular myocytes were more profitable in antiarrhythmic therapy in the clinic. We concluded that the relative efficacy of Qiliqiangxin was another choice for the existing antiarrhythmic therapy.

Permeability of time-dependent K+ channel in guinea pig ventricular myocytes to Cs+, Na+, NH4+, and Rb+

1990 ◽  
Vol 259 (5) ◽  
pp. H1448-H1454 ◽  
Author(s):  
R. W. Hadley ◽  
J. R. Hume
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Reversal Potential ◽  
Outward Current ◽  
Time Dependent ◽  
K Channel ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Outward Currents

Currents through time-dependent K+ channels (also referred to as IK or the delayed rectifier) were studied with the whole cell patch-clamp technique in isolated guinea pig ventricular myocytes. IK measurements were restricted to the examination of deactivation tail currents. Substitution of various monovalent cations for external K+ produced shifts of the reversal potential of IK. These shifts were used to calculate permeability ratios relative to K+. The permeability sequence for the IK channels was K+ = Rb+ greater than NH4+ = Cs+ greater than Na+. Time-dependent outward currents were also examined when the myocytes were dialyzed with Cs+ instead of K+. A sizeable time-dependent outward current, quite similar to that seen with K+ dialysis, was demonstrated. This current was primarily carried by intracellular Cs+, as the reversal potential of the current shifted 46 mV per 10-fold change of external Cs+ concentration. The significance of Cs+ permeation through IK channels is discussed with respect to the common use of Cs+ in isolating other currents.

Dual effects of external magnesium on action potential duration in guinea pig ventricular myocytes

1995 ◽  
Vol 268 (6) ◽  
pp. H2321-H2328 ◽  
Author(s):  
S. Zhang ◽  
T. Sawanobori ◽  
H. Adaniya ◽  
Y. Hirano ◽  
M. Hiraoka
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Decay Time ◽  
Action Potential Duration ◽  
Time Course ◽  
Ventricular Myocytes ◽  
Membrane Surface ◽  
Surface Charges ◽  
Whole Cell Patch Clamp ◽  
K Current

Effects of extracellular magnesium (Mg2+) on action potential duration (APD) and underlying membrane currents in guinea pig ventricular myocytes were studied by using the whole cell patch-clamp method. Increasing external Mg2+ concentration [Mg2+]o) from 0.5 to 3 mM produced a prolongation of APD at 90% repolarization (APD90), whereas 5 and 10 mM Mg2+ shortened it. [Mg2+]o, at 3 mM or higher, suppressed the delayed outward K+ current and the inward rectifier K+ current. Increases in [Mg2+]o depressed the peak amplitude and delayed the decay time course of the Ca2+ current (ICa), the latter effect is probably due to the decrease in Ca(2+)-induced inactivation. Thus 3 mM Mg2+ suppressed the peak ICa but increased the late ICa amplitude at the end of a 200-ms depolarization pulse, whereas 10 mM Mg2+ suppressed both components. Application of 10 mM Mg2+ shifted the voltage-dependent activation and inactivation by approximately 10 mV to more positive voltage due to screening the membrane surface charges. Application of manganese (1-5 mM) also caused dual effects on APD90, similar to those of Mg2+, and suppressed the peak ICa with slowed decay. These results suggest that the dual effects of Mg2+ on APD in guinea pig ventricular myocytes can be, at least in part, explained by its action on ICa with slowed decay time course in addition to suppressive effects on K+ currents.

scholarly journals The effect of C-type natriuretic peptide on delayed rectifier potassium currents in gastric antral circular myocytes of the guinea-pig

2008 ◽  
pp. 55-62
Author(s):  
HY Xu ◽  
X Huang ◽  
M Yang ◽  
J-B Sun ◽  
L-H Piao ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Phosphodiesterase Inhibitor ◽  
Potassium Currents ◽  
Inhibitory Effect ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Dependent Protein ◽  
Gastric Myocytes

C-type natriuretic peptides (CNP) play an inhibitory role in smooth muscle motility of the gastrointestinal tract, but the effect of CNP on delayed rectifier potassium currents is still unclear. This study was designed to investigate the effect of CNP on delayed rectifier potassium currents and its mechanism by using conventional whole-cell patch-clamp technique in guinea-pig gastric myocytes isolated by collagenase. CNP significantly inhibited delayed rectifier potassium currents [I(K (V))] in dose-dependent manner, and CNP inhibited the peak current elicited by depolarized step pulse to 86.1+/-1.6 % (n=7, P<0.05), 78.4+/-2.6 % (n=10, P<0.01) and 67.7+/-2.3 % (n=14, P<0.01), at concentrations of 0.01 micromol/l, 0.1 micromol/l and 1 micromol/l, respectively, at +60 mV. When the cells were preincubated with 0.1 micromol/l LY83583, a guanylate cyclase inhibitor, the 1 ?micromol/l CNP-induced inhibition of I(K (V)) was significantly impaired but when the cells were preincubated with 0.1 micromol/l zaprinast, a cGMP-sensitive phosphodiesterase inhibitor, the 0.01 micromol/l CNP-induced inhibition of I(K (V)) was significantly potentiated. 8-Br-cGMP, a membrane permeable cGMP analogue mimicked inhibitory effect of CNP on I(K (V)). CNP-induced inhibition of I(K (V)) was completely blocked by KT5823, an inhibitor of cGMP-dependent protein kinase (PKG). The results suggest that CNP inhibits the delayed rectifier potassium currents via cGMP-PKG signal pathway in the gastric antral circular myocytes of the guinea-pig.

Outward currents in normal and hypertrophied feline ventricular myocytes

1989 ◽  
Vol 256 (5) ◽  
pp. H1450-H1461 ◽  
Author(s):  
R. B. Kleiman ◽  
S. R. Houser
Keyword(s):  
Time Course ◽  
Ventricular Myocytes ◽  
Pressure Overload ◽  
Negative Slope ◽  
Inward Rectification ◽  
Delayed Rectifier ◽  
Outward Currents ◽  
K Current ◽  
Prolongation Of Action Potential ◽  
The Right

The properties of the inward rectifier K current (IK1) and the delayed rectifier K current (IK) were studied in single feline myocytes isolated from the right ventricle of normal cats and cats with experimentally induced right ventricular hypertrophy (RVH). IK1 demonstrated time-dependent decay during hyperpolarizations and showed inward rectification with a prominent negative-slope region between -30 and -10 mV. Both IK1 and IK was carried primarily by K ions. The activation of IK during depolarizations followed a monoexponential time course, whereas the deactivation of IK tail currents was either mono- or biexponential depending on the repolarization potential. IK showed marked rectification at positive potentials. A comparison of these currents in normal and hypertrophy myocytes revealed that in RVH the magnitude of IK1 is increased, whereas the magnitude of IK is decreased. IK showed steeper rectification, had slower activation, and had more rapid deactivation in RVH. These abnormalities of the IK may contribute to the prolongation of action potential duration, which characterizes pressure-overload cardiac hypertrophy.

Force measurements from voltage-clamped guinea pig ventricular myocytes

1990 ◽  
Vol 258 (2) ◽  
pp. H452-H459 ◽  
Author(s):  
N. Shepherd ◽  
M. Vornanen ◽  
G. Isenberg
Keyword(s):  
Guinea Pig ◽  
Time Course ◽  
Ventricular Myocytes ◽  
Isometric Force ◽  
Contractile Force ◽  
Patch Clamp Technique ◽  
Thin Glass ◽  
Tonic Component ◽  
Time To Peak ◽  
Whole Cell Patch Clamp

We describe the first observations of isolated mammalian guinea pig ventricular myocytes that combine measurements of contractile force with the voltage-clamp method. The myocytes were attached by poly-L-lysine to the beveled ends of a pair of thin glass rods having a compliance of 0.76 m/N. The contractile force of a cell caused a 1- to 3-microm displacement of the rods; the motion of which was converted to an output voltage by phototransistors. By the use of the whole cell patch-clamp technique, the cells were depolarized at 1 Hz with 200-ms-long clamp pulses from -45 to +5 mV (35 degrees C, 3.6 mM CaCl2). Isometric force began after a latency of 7 +/- 2 ms, peaked at 93 +/- 21 ms, and relaxed (90%) at 235 +/- 63 ms. The time course of force was always faster than that of isotonic shortening (time to peak 154 +/- 18 ms). With 400-ms-long depolarizations, a tonic component was recorded as either sustained force or sustained shortening that decayed on repolarization. Substitution of Ca by Sr in the bath increased the inward current through Ca channels but slowed down the time course of force development. The results are consistent with the hypothesis that activator calcium derives mainly from internal stores and that Ca release needs Ca entry through channels.

PKC regulation of cardiac CFTR Cl− channel function in guinea pig ventricular myocytes

1998 ◽  
Vol 275 (1) ◽  
pp. C293-C302 ◽  
Author(s):  
Lisa M. Middleton ◽  
Robert D. Harvey
Keyword(s):  
Protein Kinase ◽  
Patch Clamp ◽  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Patch Clamp Technique ◽  
Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Perforated Patch Clamp

The role of protein kinase C (PKC) in regulating the protein kinase A (PKA)-activated Cl− current conducted by the cardiac isoform of the cystic fibrosis transmembrane conductance regulator (cCFTR) was studied in guinea pig ventricular myocytes using the whole cell patch-clamp technique. Although stimulation of endogenous PKC with phorbol 12,13-dibutyrate (PDBu) alone did not activate this Cl− current, even when intracellular dialysis was limited with the perforated patch-clamp technique, activation of PKC did elicit a significant response in the presence of PKA-dependent activation of the current by the β-adrenergic receptor agonist isoproterenol. PDBu increased the magnitude of the Cl− conductance activated by a supramaximally stimulating concentration of isoproterenol by 21 ± 3.3% ( n = 9) when added after isoproterenol and by 36 ± 16% ( n= 14) when introduced before isoproterenol. 4α-Phorbol 12,13-didecanoate, a phorbol ester that does not activate PKC, did not mimic these effects. Preexposure to chelerythrine or bisindolylmaleimide, two highly selective inhibitors of PKC, significantly reduced the magnitude of the isoproterenol-activated Cl− current by 79 ± 7.7% ( n = 11) and 52 ± 10% ( n = 8), respectively. Our results suggest that although acute activation of endogenous PKC alone does not significantly regulate cCFTR Cl− channel activity in native myocytes, it does potentiate PKA-dependent responses, perhaps most dramatically demonstrated by basal PKC activity, which may play a pivotal role in modulating the function of these channels.

Delayed-rectifier potassium channel activity in isolated membrane patches of guinea pig ventricular myocytes

1991 ◽  
Vol 260 (4) ◽  
pp. H1390-H1393 ◽  
Author(s):  
K. B. Walsh ◽  
J. P. Arena ◽  
W. M. Kwok ◽  
L. Freeman ◽  
R. S. Kass
Keyword(s):  
Guinea Pig ◽  
Single Channel ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Time Dependent ◽  
Delayed Rectifier ◽  
Potential Range ◽  
Ammonium Compound ◽  
Channel Activity ◽  
Patch Clamp Technique

When the patch-clamp technique was used, a slowly activating, time-dependent outward current was identified in both cell-attached and excised membrane patches obtained from guinea pig ventricular myocytes. This macroscopic patch current was present in approximately 50% of patches studied and could be observed both in the presence and absence of unitary single channel activity (i.e., ATP-sensitive K+ channels). The time course of activation of the patch current resembled that of the whole cell delayed-rectifier K+ current (IK) recorded under similar ionic conditions, and the patch current and IK were activated over a similar membrane potential range. The time-dependent patch current could be eliminated when the Nernst potential for K+ equaled that of the pulse voltage. The patch current was inhibited by external addition of the tertiary ammonium compound LY 97241 (50 microM) and was augmented after internal application of the catalytic subunit of adenosine 3',5'-cyclic monophosphate-dependent protein kinase (500 nM). Deactivating tail currents with kinetics similar to those of IK could be recorded to cell-attached and excised patches. Unitary single channel events underlying the time-dependent patch current could not be resolved despite various attempts to increase single channel conductance. Thus our results suggest that a major component of delayed rectification in guinea pig ventricular cells is due to the activity of a high-density, extremely low conductance K+ channel.

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