L-364,373 (R-L3) enantiomers have opposite modulating effects on IKs in mammalian ventricular myocytes

2013 ◽  
Vol 91 (8) ◽  
pp. 586-592 ◽  
Author(s):  
Claudia Corici ◽  
Zsófia Kohajda ◽  
Attila Kristóf ◽  
András Horváth ◽  
László Virág ◽  
...  
Keyword(s):  
Patch Clamp ◽  
Guinea Pig ◽  
Action Potential ◽  
Right Ventricular ◽  
Action Potential Duration ◽  
Action Potentials ◽  
Ventricular Arrhythmias ◽  
Ventricular Myocytes ◽  
Delayed Rectifier ◽  
Whole Cell Patch Clamp

Activators of the slow delayed rectifier K+ current (IKs) have been suggested as promising tools for suppressing ventricular arrhythmias due to prolongation of repolarization. Recently, L-364,373 (R-L3) was nominated to activate IKs in myocytes from several species; however, in some studies, it failed to activate IKs. One later study suggested opposite modulating effects from the R-L3 enantiomers as a possible explanation for this discrepancy. Therefore, we analyzed the effect of the RL-3 enantiomers on IKs in ventricular mammalian myocytes, by applying standard microelectrode and whole-cell patch-clamp techniques at 37 °C. We synthesized 2 substances, ZS_1270B (right) and ZS_1271B (left), the 2 enantiomers of R-L3. In rabbit myocytes, ZS_1270B enhanced the IKs tail current by approximately 30%, whereas ZS_1271B reduced IKs tails by 45%. In guinea pig right ventricular preparations, ZS_1270B shortened APD90 (action potential duration measured at 90% repolarization) by 12%, whereas ZS_1271B lengthened it by approximately 15%. We concluded that R-L3 enantiomers in the same concentration range indeed have opposite modulating effects on IKs, which may explain why the racemic drug R-L3 previously failed to activate IKs. ZS_1270B is a potent IKs activator, therefore, this substance is appropriate to test whether IKs activators are ideal tools to suppress ventricular arrhythmias originating from prolongation of action potentials.

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.

Effects of estrogen on action potential and membrane currents in guinea pig ventricular myocytes

1999 ◽  
Vol 277 (2) ◽  
pp. H826-H833 ◽  
Author(s):  
Seiko Tanabe ◽  
Toshio Hata ◽  
Masayasu Hiraoka
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Action Potentials ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Membrane Currents ◽  
Patch Clamp Technique ◽  
17Β Estradiol ◽  
Electrophysiological Effects ◽  
Ionic Basis

To explore a possible ionic basis for the prolonged Q-T interval in women compared with that in men, we investigated the electrophysiological effects of estrogen in isolated guinea pig ventricular myocytes. Action potentials and membrane currents were recorded using the whole cell configuration of the patch-clamp technique. Application of 17β-estradiol (10–30 μM) significantly prolonged the action potential duration (APD) at 20% (APD20) and 90% repolarization (APD90) at stimulation rates of 0.1–2.0 Hz. In the presence of 30 μM 17β-estradiol, APD20 and APD90 at 0.1 Hz were prolonged by 46.2 ± 17.1 and 63.4 ± 11.7% of the control ( n = 5), respectively. In the presence of 30 μM 17β-estradiol the peak inward Ca2+ current ( I CaL) was decreased to 80.1 ± 2.5% of the control ( n = 4) without a shift in its voltage dependence. Application of 30 μM 17β-estradiol decreased the rapidly activating component of the delayed outward K+ current ( I Kr) to 63.4 ± 8% and the slowly activating component ( I Ks) to 65.8 ± 8.7% with respect to the control; the inward rectifier K+ current was barely affected. The results suggest that 17β-estradiol prolonged APD mainly by inhibiting the I Kcomponents I Krand I Ks.

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.

scholarly journals Propagation of Action Potentials From the Soma to Individual Dendrite of Cultured Rat Amacrine Cells Is Regulated by Local GABA Input

2002 ◽  
Vol 87 (6) ◽  
pp. 2858-2866 ◽  
Author(s):  
Yoshitake Yamada ◽  
Amane Koizumi ◽  
Eisuke Iwasaki ◽  
Shu-Ichi Watanabe ◽  
Akimichi Kaneko
Keyword(s):  
Patch Clamp ◽  
Action Potential ◽  
Lateral Inhibition ◽  
Action Potentials ◽  
Amacrine Cell ◽  
Amacrine Cells ◽  
Inner Plexiform Layer ◽  
Whole Cell ◽  
Cell Patch Clamp ◽  
Whole Cell Patch Clamp

Retinal amacrine cells are interneurons that make lateral and vertical connections in the inner plexiform layer of the retina. Amacrine cells do not possess a long axon, and this morphological feature is the origin of their naming. Their dendrites function as both presynaptic and postsynaptic sites. Half of all amacrine cells are GABAergic inhibitory neurons that mediate lateral inhibition, and their light-evoked response consists of graded voltage changes and regenerative action potentials. There is evidence that the amount of neurotransmitter release from presynaptic sites is increased by spike propagation into the dendrite. Thus understanding of how action potentials propagate in dendrites is important to elucidating the extent and strength of lateral inhibition. In the present study, we used the dual whole cell patch-clamp technique on the soma and the dendrite of cultured rat amacrine cells and directly demonstrated that the action potentials propagate into the dendrites. The action potential in the dendrite was TTX sensitive and was affected by the local membrane potential of the dendrite. Propagation of the action potential was suppressed by local application of GABA to the dendrite. Dual dendrite whole cell patch-clamp recordings showed that GABA suppresses the propagation of action potentials in one dendrite of an amacrine cell, while the action potentials propagate in the other dendrites. It is likely that the action potentials in the dendrites are susceptible to various external factors resulting in the nonuniform propagation of the action potential from the soma of an amacrine cell.

scholarly journals Diverse Ionic Currents and Electrical Activity of Cultured Myenteric Neurons From the Guinea Pig Proximal Colon

2000 ◽  
Vol 83 (3) ◽  
pp. 1253-1263 ◽  
Author(s):  
Fivos Vogalis ◽  
Kirk Hillsley ◽  
Terence K. Smith
Keyword(s):  
Patch Clamp ◽  
Guinea Pig ◽  
Action Potential ◽  
Action Potentials ◽  
Outward Current ◽  
Proximal Colon ◽  
Equilibrium Potential ◽  
Transient Outward Current ◽  
Myenteric Neurons ◽  
Fast Transient

The aim of this study was to perform a patch-clamp analysis of myenteric neurons from the guinea pig proximal colon. Neurons were enzymatically dispersed, cultured for 2–7 days, and recorded from using whole cell patch clamp. The majority of cells fired phasically, whereas about one-quarter of the neurons fired in a tonic manner. Neurons were divided into three types based on the currents activated. The majority of tonically firing neurons lacked an A-type current, but generated a large fast transient outward current that was associated with the rapid repolarizing phase of an action potential. The fast transient outward current was dependent on calcium entry and was blocked by tetraethylammonium. Cells that expressed both an A-type current and a fast transient outward current were mostly phasic. Depolarization of these cells to suprathreshold potentials from less than −60 mV failed to trigger action potentials, or action potentials were only triggered after a delay of >50 ms. However, depolarizations from more positive potentials triggered action potentials with minimal latency. Neurons that expressed neither the A-type current or the fast transient outward current were all phasic. Sixteen percent of neurons were similar to AH/type II neurons in that they generated a prolonged afterhyperpolarization following an action potential. The current underlying the prolonged afterhyperpolarization showed weak inward rectification and had a reversal potential near the potassium equilibrium potential. Thus cultured isolated myenteric neurons of the guinea pig proximal colon retain many of the diverse properties of intact neurons. This preparation is suitable for further biophysical and molecular characterization of channels expressed in colonic myenteric neurons.

Mechanisms underlying the modulation of arrhythmogenic events by components of ischemia in guinea pig cardiac myocytes

1994 ◽  
Vol 72 (4) ◽  
pp. 382-393 ◽  
Author(s):  
Qi-Ying Liu ◽  
Mario Vassalle
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Voltage Clamp ◽  
Action Potentials ◽  
Ventricular Myocytes ◽  
Resting Potential ◽  
Spontaneous Discharge ◽  
High K ◽  
Voltage Dependent ◽  
Dependent Mechanism

The effects of some components of ischemia on the oscillatory (Vos) and nonoscillatory (Vex) potentials and respective currents (Ios and Iex), as well as their mechanisms, were studied in guinea pig isolated ventricular myocytes by means of a single-microelectrode, discontinuous voltage clamp method. Repetitive activations induced not only Vos and Ios, but also Vex and Iex. A small decrease in resting potential caused an immediate increase in Vos followed by a gradual increase due to the longer action potential. Immediate and gradual increases in Ios also occurred during voltage clamp steps. A small depolarization increased Vos and Vex, and facilitated the induction of spontaneous discharge by fast drive. At Vh where INa is inactivated, depolarizing steps induced larger Ios and Iex, indicating the importance of the Na-independent Ca loading. High [K]odecreased the resting potential, but also Vos, Vex, Ios, Iex, and ICa. In high [K]o, depolarization still increased Vos and Vex. Norepinephrine (NE) enhanced Vos and Vex, and also Ios and Iex, during voltage clamp steps. High [K]o antagonized NE effects, and NE those of high [K]o. In conclusion, on depolarization, Vos and Ios immediately increase through a voltage-dependent mechanism; and then Vos and Ios gradually increase, apparently through an increased Ca load related to the longer action potentials and the Na–Ca exchange. The depolarization induced by Vex may contribute to increase Vos size. Vos and Vex are similarly influenced by different procedures that modify Ca load. The arrhythmogenic events are enhanced by the simultaneous presence of depolarization, faster rate, or NE. Instead, high [K]o decreases Vos and Vex by decreasing ICa and opposes the effects of NE. The voltage clamp results show that potentiation and antagonism between different components of ischemia are due primarily to changes in Ca loading and not to changes in action potential configuration.Key words: ischemia, arrhythmias, oscillatory and nonoscillatory potentials and currents, norepinephrine, potassium.

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