Inhibitory effects of dauricine on early afterdepolarizations and L-type calcium current

2009 ◽  
Vol 87 (11) ◽  
pp. 954-962 ◽  
Author(s):  
Qiang-Ni Liu ◽  
Li Zhang ◽  
Pei-Li Gong ◽  
Xiao-Yan Yang ◽  
Fan-Dian Zeng
Keyword(s):  
Steady State ◽  
Calcium Current ◽  
Enzymatic Digestion ◽  
Papillary Muscles ◽  
Inhibitory Effects ◽  
Early Afterdepolarizations ◽  
Whole Cell Patch Clamp ◽  
Steady State Inactivation ◽  
The Right ◽  
Microelectrode Techniques

We have previously reported that dauricine exerted antiarrhythmic effects on various experimental arrhythmias. To further clarify its mechanism, the effects of dauricine on action potential duration (APD), early afterdepolarizations (EADs), triangulation, which is defined as the repolarization time from APD at 30% level (APD30) to APD at 90% level (APD90), and L-type calcium current (ICa-L) were studied using standard microelectrode techniques on rabbit papillary muscles and whole-cell patch clamp techniques on single myocytes isolated from rabbits by enzymatic digestion, respectively. Cardiac hypertrophy was induced by coarctating the abdominal aorta of rabbits. The results showed that in papillary muscles of hypertrophied rabbits, 1 µmol/L dofetilide, a selective IKr blocker, prolonged APD50 and APD90 and induced EADs (4/6, p < 0.01) with hypokalemia ([K+]o = 2.7 mmol/L). Dauricine inhibited EADs (p < 0.01) and shortened the prolonged APD (p < 0.01). In single myocytes, dauricine also inhibited EADs induced by dofetilide, hypokalemia, and hypomagnesaemia. Dauricine decreased the triangulation and reduced the peak amplitude of ICa-L at all potentials tested. Dauricine shifted the steady-state activation curves to the right and steady-state inactivation curves to the left and prolonged the τ value of the recovery curve. These results suggest that dauricine inhibits EADs and this effect may be associated with its blockade of ICa-L.

Daurisoline Suppressed Early Afterdepolarizations and Inhibited L-Type Calcium Current

2010 ◽  
Vol 38 (01) ◽  
pp. 37-49 ◽  
Author(s):  
Qiang-Ni Liu ◽  
Li Zhang ◽  
Pei-Li Gong ◽  
Xiao-Yan Yang ◽  
Fan-Dian Zeng
Keyword(s):  
Steady State ◽  
Calcium Current ◽  
Left Ventricular ◽  
Papillary Muscles ◽  
Early Afterdepolarizations ◽  
Whole Cell Patch Clamp ◽  
Ventricular Cells ◽  
Steady State Inactivation ◽  
The Right ◽  
Low K

Our previous studies have shown that daurisoline (DS) exerted antiarrhythmic effects on various experimental arrhythmias. In this study, the effects of DS on early afterdepolarizations (EADs) and its possible mechanisms have been investigated. Cardiac hypertrophy was induced in rabbits by coarctating the abdominal aorta. The effects of DS on action potential duration (APD) and the incidences of EADs were studied in hypertrophied papillary muscles of rabbits in the conditions of low external K + concentration ([ K +] o ) and dofetilide (dof) by using standard microelectrode technique. The whole-cell patch clamp was used to record the L-type calcium current ( ICa-L ) in isolated left ventricular cells of rabbits. The results showed that in hypertrophied papillary muscles of rabbits with low [ K +] o ([ K +]o = 2.7 mM ), 1 µM dof prolonged APD50 and APD90 markedly and the incidence of EADs was 66.7% (4/6, p < 0.01); when 15 µM DS was applied, the incidence of EADs was 0% (0/4, p < 0.01) and the prolonged APD was shortened (p < 0.01). In a single myocyte, DS could also inhibit EADs induced by dof, low [ K +] o and low external Mg 2+ concentration ([ Mg 2+] o ) ([ Mg 2+] o = 0.5 mM ). DS could decrease the triangulation. In a single myocyte, DS could make the I-V curve upward, shift the steady-state activation curves to the right and the steady-state inactivation curves to the left and prolong the τ value of recovery curve obviously. These results suggested that DS could inhibit EADs which may be associated with its blockade effects on ICa-L .

Effects of estrogens on Ca channels in myometrial cells isolated from pregnant rats

1995 ◽  
Vol 268 (1) ◽  
pp. C64-C69 ◽  
Author(s):  
T. Yamamoto
Keyword(s):  
Steady State ◽  
Ca Channel ◽  
Ca Channels ◽  
Inhibitory Effects ◽  
Inactivation Curve ◽  
Pregnant Rat ◽  
Negative Direction ◽  
Myometrial Cells ◽  
Steady State Inactivation ◽  
Channel Currents

Whole cell patch-clamp techniques were applied to cultured smooth muscle cells isolated from the longitudinal layer of the late pregnant rat myometrium. Effects of estrogens on Ca channels were examined. Inhibitory effects of beta-estradiol (1 microM) on Ca channel currents were recognized. The inhibitory effects of beta-estradiol depended on holding potentials. beta-Estradiol shifted the steady-state inactivation curve in the negative direction by 7 mV at mid potential (n = 9). Diethylstilbestrol, a synthetic estrogen, gave similar effects on Ca channel currents at lower concentration (2 microM) to those of beta-estradiol. Strong inhibitory effects on Ca channel currents were obtained by higher concentration (20 microM). Diethylstilbestrol shifted the steady-state inactivation curve in the negative direction by 7 mV at mid potential (n = 5). The results indicate that estrogens influence the voltage dependency and the whole cell conductance of Ca channels of pregnant rat myometrial cells. The acute effect of estrogens may cause both electrical and mechanical depression of myometrium.

scholarly journals The calcium-independent transient outward potassium current in isolated ferret right ventricular myocytes. II. Closed state reverse use-dependent block by 4-aminopyridine.

1993 ◽  
Vol 101 (4) ◽  
pp. 603-626 ◽  
Author(s):  
D L Campbell ◽  
Y Qu ◽  
R L Rasmusson ◽  
H C Strauss
Keyword(s):  
Steady State ◽  
Right Ventricular ◽  
Ventricular Myocytes ◽  
Patch Clamp Technique ◽  
Time Constants ◽  
Closed State ◽  
Whole Cell Patch Clamp ◽  
Dependent Behavior ◽  
Steady State Inactivation ◽  
K Current

Block of the calcium-independent transient outward K+ current, I(to), by 4-aminopyridine (4-AP) was studied in ferret right ventricular myocytes using the whole cell patch clamp technique. 4-AP reduces I(to) through a closed state blocking mechanism displaying "reverse use-dependent" behavior that was inferred from: (a) development of tonic block at hyperpolarized potentials; (b) inhibition of development of tonic block at depolarized potentials; (c) appearance of "crossover phenomena" in which the peak current is delayed in the presence of 4-AP at depolarized potentials; (d) relief of block at depolarized potentials which is concentration dependent and parallels steady-state inactivation for low 4-AP concentrations (V1/2 approximately -10 mV in 0.1 mM 4-AP) and steady-state activation at higher concentrations (V1/2 = +7 mV in 1 mM 4-AP, +15 mV in 10 mM 4-AP); and (e) reassociation of 4-AP at hyperpolarized potentials. No evidence for interaction of 4-AP with either the open or inactivated state of the I(to) channel was obtained from measurements of kinetics of recovery and deactivation in the presence of 0.5-1.0 mM 4-AP. At hyperpolarized potentials (-30 to -90 mV) 10 mM 4-AP associates slowly (time constants ranging from approximately 800 to 1,300 ms) with the closed states of the channel (apparent Kd approximately 0.2 mM). From -90 to -20 mV the affinity of the I(to) channel for 4-AP appears to be voltage insensitive; however, at depolarized potentials (+20 to +100 mV) 4-AP dissociates with time constants ranging from approximately 350 to 150 ms. Consequently, the properties of 4-AP binding to the I(to) channel undergo a transition in the range of potentials over which channel activation and inactivation occurs (-30 to +20 mV). We propose a closed state model of I(to) channel gating and 4-AP binding kinetics, in which 4-AP binds to three closed states. In this model 4-AP has a progressively lower affinity as the channel approaches the open state, but has no intrinsic voltage dependence of binding.

Abstract 1523: A Novel SCN5A Gain-of-Function Mutation M1875T Associated with Familial Atrial Fibrillation

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Takeru Makiyama ◽  
Masaharu Akao ◽  
Satoshi Shizuta ◽  
Takahiro Doi ◽  
Kei Nishiyama ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Mutational Analysis ◽  
Gain Of Function ◽  
Japanese Family ◽  
Function Type ◽  
Whole Cell Patch Clamp ◽  
Steady State Inactivation ◽  
Familial Atrial Fibrillation ◽  
The Right ◽  
Inherited Arrhythmias

Background: Mutations in the cardiac sodium (Na + ) channel gene, SCN5A , have been associated with a variety of inherited arrhythmias, but the gain-of-function type modulation in SCN5A is associated with only one phenotype, long-QT syndrome type3 (LQTS3). Methods and Results: We studied a Japanese family with autosomal dominant hereditary atrial fibrillation (AF), multiple members of which showed onset of AF or frequent premature atrial contractions at a young age. The 31-year-old proband received radio-frequency catheter ablation, during which time numerous ectopic firings and increased excitability throughout the right atrium were documented. Mutational analysis identified a novel missense mutation, M1875T, in SCN5A . Further investigations revealed the aggregation of this mutation in all of the affected individuals (Figure A ). Functional assays of the M1875T Na + channels using whole-cell patch-clamp demonstrated a distinct gain-of-function type modulation; a pronounced depolarized shift (+16.4 mV) in V 1/2 of the voltage dependence of steady-state inactivation (Figure B ), and no late Na + current which is a defining mechanism of LQTS3. These biophysical features of the mutant channels are potentially associated with increased atrial excitability and normal QT interval in all of the affected individuals. Conclusions: We identified a novel SCN5A mutation associated with familial AF. The mutant channels displayed a gain-of-function type modulation of cardiac Na + channels, which is a novel mechanism predisposing increased atrial excitability and familial AF. This is a new phenotype resulting from the SCN5A gain-of-function mutations and is distinct from LQTS3.

scholarly journals The calcium-independent transient outward potassium current in isolated ferret right ventricular myocytes. I. Basic characterization and kinetic analysis.

1993 ◽  
Vol 101 (4) ◽  
pp. 571-601 ◽  
Author(s):  
D L Campbell ◽  
R L Rasmusson ◽  
Y Qu ◽  
H C Strauss
Keyword(s):  
Steady State ◽  
Ventricular Myocytes ◽  
Nonlinear Least Squares ◽  
Patch Clamp Technique ◽  
Time Constants ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
K Current ◽  
Necessary And Sufficient

Enzymatically isolated myocytes from ferret right ventricles (12-16 wk, male) were studied using the whole cell patch clamp technique. The macroscopic properties of a transient outward K+ current I(to) were quantified. I(to) is selective for K+, with a PNa/PK of 0.082. Activation of I(to) is a voltage-dependent process, with both activation and inactivation being independent of Na+ or Ca2+ influx. Steady-state inactivation is well described by a single Boltzmann relationship (V1/2 = -13.5 mV; k = 5.6 mV). Substantial inactivation can occur during a subthreshold depolarization without any measurable macroscopic current. Both development of and recovery from inactivation are well described by single exponential processes. Ensemble averages of single I(to) channel currents recorded in cell-attached patches reproduce macroscopic I(to) and indicate that inactivation is complete at depolarized potentials. The overall inactivation/recovery time constant curve has a bell-shaped potential dependence that peaks between -10 and -20 mV, with time constants (22 degrees C) ranging from 23 ms (-90 mV) to 304 ms (-10 mV). Steady-state activation displays a sigmoidal dependence on membrane potential, with a net aggregate half-activation potential of +22.5 mV. Activation kinetics (0 to +70 mV, 22 degrees C) are rapid, with I(to) peaking in approximately 5-15 ms at +50 mV. Experiments conducted at reduced temperatures (12 degrees C) demonstrate that activation occurs with a time delay. A nonlinear least-squares analysis indicates that three closed kinetic states are necessary and sufficient to model activation. Derived time constants of activation (22 degrees C) ranged from 10 ms (+10 mV) to 2 ms (+70 mV). Within the framework of Hodgkin-Huxley formalism, Ito gating can be described using an a3i formulation.

scholarly journals K(+) currents in cultured neurones from a polyclad flatworm

2000 ◽  
Vol 203 (20) ◽  
pp. 3189-3198
Author(s):  
S.D. Buckingham ◽  
A.N. Spencer
Keyword(s):  
Steady State ◽  
Patch Clamp ◽  
K Channels ◽  
Type K ◽  
Whole Cell Patch Clamp ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
The Brain ◽  
K Currents ◽  
Cultured Neurones

Cells from the brain of the polyclad flatworm Notoplana atomata were dispersed and maintained in primary culture for up to 3 weeks. Whole-cell patch-clamp of presumed neurones revealed outwardly directed K(+) currents that comprised, in varying proportions, a rapidly activating (time constant tau =0.94+/−0.79 ms; N=15) and inactivating (tau =26.1+/−1.9 ms; N=22) current and a second current that also activated rapidly (tau =1.1+/−0.2 ms; N=9) (means +/− s.e.m.) but did not inactivate within 100 ms. Both current types activated over similar voltage ranges. Activation and steady-state inactivation overlap and are markedly rightward-shifted compared with most Shaker-like currents (half-activation of 16.9+/−1. 9 mV, N=7, half-inactivation of −35.4+/−3.0 mV, N=5). Recovery from inactivation was rapid (50+/−2.5 ms at −90 mV). Both currents were unaffected by tetraethylammonium (25 mmol l(−1)), whereas 4-aminopyridine (10 mmol l(−1)) selectively blocked the inactivating current. The rapidly inactivating current, like cloned K(+) channels from cnidarians and certain cloned K(+) channels from molluscs and the Kv3 family of vertebrate channels, differed from most A-type K(+) currents reported to date. These findings suggest that K(+) currents in Notoplana atomata play novel roles in shaping excitability properties.

Cyclic AMP selectively reduces the N-type calcium current component of mouse sensory neurons in culture by enhancing inactivation

1989 ◽  
Vol 61 (1) ◽  
pp. 97-105 ◽  
Author(s):  
R. A. Gross ◽  
R. L. Macdonald
Keyword(s):  
Steady State ◽  
Cyclic Amp ◽  
Cholera Toxin ◽  
Calcium Current ◽  
Calcium Currents ◽  
Resting Membrane Potential ◽  
High Threshold ◽  
Drg Neurons ◽  
Inactivation Curve ◽  
Steady State Inactivation

1. The single-electrode voltage-clamp technique was used to assess the effect of elevated intracellular cyclic AMP levels on the three calcium current components of mouse dorsal root ganglion (DRG) neurons in culture. 2. Neither forskolin, cholera toxin, nor 8-Br-cyclic AMP affected the isolated transient low-threshold (T) calcium current. 3. When calcium currents were evoked at clamp potentials (Vc) positive to -20 mV from holding potentials (Vh) near the resting membrane potential, the calcium current consisted primarily of the transient high-threshold (N) and the slowly inactivating high-threshold (L) calcium current components. Under these conditions forskolin, cholera toxin, and 8-Br-cyclic AMP reduced the peak calcium current but had little or no effect on the late (greater than or equal to 300 ms) calcium current. When calcium currents were evoked from very negative Vh, however, there was no effect of these compounds. 4. Forskolin had no effect on the voltage-dependence of the current-voltage relation, nor on the rate of recovery of the calcium current from inactivation. 5. In other experiments, current traces were fitted using a multiexponential curve-fitting program that determined the amplitudes and inactivation time constants (tau i) of the three calcium current components. Forskolin selectively reduced the magnitude of the (curve-fitted) N current, and reduced its tau i. 6. Forskolin also enhanced steady-state inactivation of the N current, producing a -7.5 mV shift in the steady-state inactivation curve. 7. Cholera toxin, forskolin, and 8-Br-cyclic AMP had similar effects on calcium currents in mouse DRG neurons in culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging-associated changes in whole cell K+ and L-type Ca2+ currents in rat ventricular myocytes

2000 ◽  
Vol 279 (3) ◽  
pp. H889-H900 ◽  
Author(s):  
Shi J. Liu ◽  
Richard P. Wyeth ◽  
Russell B. Melchert ◽  
Richard H. Kennedy
Keyword(s):  
Steady State ◽  
Young Adult ◽  
Action Potential ◽  
Action Potential Duration ◽  
Ventricular Myocytes ◽  
Inactivation Kinetics ◽  
Whole Cell ◽  
Rat Ventricular Myocytes ◽  
Whole Cell Patch Clamp ◽  
Steady State Inactivation

The effect of aging on cardiac membrane currents remains unclear. This study examined the inward rectifier K+ current ( I K1), the transient outward K+current ( I to), and the L-type Ca2+ channel current ( I Ca,L) in ventricular myocytes isolated from young adult (6 mo) and aged (>27 mo) Fischer 344 rats using whole cell patch-clamp techniques. Along with an increase in the cell size and membrane capacitance, aged myocytes had the same magnitude of peak I K1 with a greater slope conductance but displayed smaller steady-state I K1. Aged myocytes also had a greater I to with an increased rate of activation, but the I to inactivation kinetics, steady-state inactivation, and responsiveness to l-phenylephrine, an α1-adrenergic agonist, were unaltered. The magnitude of peak I Ca,L in aged myocytes was decreased and accompanied by a slower inactivation, but the I Ca,L steady-state inactivation was unaltered. Action potential duration in aged myocytes was prolonged only at 90% of full repolarization (APD90) when compared with the action potential duration of young adult myocytes. Aged myocytes from Long-Evans rats showed similar changes in I toand I Ca,L but an increased I K1. These results demonstrate aging-associated changes in action potential, in morphology, and in I K1, I to, and I Ca,L of rat ventricular myocytes that possibly contribute to the decreased cardiac function of aged hearts.

scholarly journals Inactivation of the Sodium Current in Myxicola Giant Axons

1972 ◽  
Vol 59 (6) ◽  
pp. 659-675 ◽  
Author(s):  
L. Goldman ◽  
C. L. Schauf
Keyword(s):  
Steady State ◽  
Sodium Current ◽  
Voltage Characteristic ◽  
Current Voltage Characteristic ◽  
Inactivation Curve ◽  
Giant Axons ◽  
Sodium Conductance ◽  
Current Voltage ◽  
Steady State Inactivation ◽  
The Right

Experiments were conducted on Myxicola giant axons to determine if the sodium activation and inactivation processes are coupled or independent. The main experimental approach was to examine the effects of changing test pulses on steady-state inactivation curves. Arguments were presented to show that in the presence of a residual uncompensated series resistance the interpretation of the results depends critically on the manner of conducting the experiment. Analytical and numerical calculations were presented to show that as long as test pulses are confined to an approximately linear negative conductance region of the sodium current-voltage characteristic, unambiguous interpretations can be made. When examined in the manner of Hodgkin and Huxley, inactivation in Myxicola is quantitatively similar to that described by the h variable in squid axons. However, when test pulses were increased along the linear negative region of the sodium current-voltage characteristic, steady-state inactivation curves translate to the right along the voltage axis. The shift in the inactivation curve is a linear function of the ratio of the sodium, conductance of the test pulses, showing a 5.8 mv shift for a twofold increase in conductance. An independent line of evidence indicated that the early rate of development of inactivation is a function of the rise of the sodium conductance.

Transient Voltage-Dependent Potassium Currents Are Reduced in NTS Neurons Isolated From Renal Wrap Hypertensive Rats

2005 ◽  
Vol 94 (6) ◽  
pp. 3849-3859 ◽  
Author(s):  
Sergei Belugin ◽  
Steve Mifflin
Keyword(s):  
Steady State ◽  
Voltage Dependence ◽  
Fluorescent Tracer ◽  
Activation Kinetics ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Afferent Inputs ◽  
Made In

Whole cell patch-clamp measurements were made in neurons enzymatically dispersed from the nucleus of the solitary tract (NTS) to determine if alterations occur in voltage-dependent potassium channels from rats made hypertensive (HT) by unilateral nephrectomy/renal wrap for 4 wk. Some rats had the fluorescent tracer DiA applied to the aortic nerve before the experiment to identify NTS neurons receiving monosynaptic baroreceptor afferent inputs. Mean arterial pressure (MAP) was greater in 4-wk HT (165 ± 5 mmHg, n = 26, P < 0.001) rats compared with normotensive (NT) rats (109 ± 3 mmHg measured in 10 of 69 rats). Transient outward currents (TOCs) were observed in 67–82% of NTS neurons from NT and HT rats. At activation voltages from −10 to +10 mV, TOCs were significantly less in HT neurons compared with those observed in NT neurons ( P < 0.001). There were no differences in the voltage-dependent activation kinetics, the voltage dependence of steady-state inactivation, and the rise and decay time constants of the TOCs comparing neurons isolated from NT and HT rats. The 4-aminopyridine–sensitive component of the TOC was significantly less in neurons from HT compared with NT rats ( P < 0.001), whereas steady-state outward currents, whether or not sensitive to 4-aminopyridine or tetraethylammonium, were not different. Delayed excitation, studied under current clamp, was observed in 60–80% of NTS neurons from NT and HT rats and was not different comparing neurons from NT and HT rats. However, examination of the subset of NTS neurons exhibiting somatic DiA fluorescence revealed that DiA-labeled neurons from HT rats had a significantly shorter duration delayed excitation ( n = 8 cells, P = 0.022) than DiA-labeled neurons from NT rats ( n = 7 cells). Neurons with delayed excitation from HT rats had a significantly broader first action potential (AP) and a slower maximal downstroke velocity of repolarization compared with NT neurons with delayed excitation ( P = 0.016 and P = 0.014, respectively). The number of APs in the first 200 ms of a sustained depolarization was greater in HT than NT neurons ( P = 0.012). These results suggest that HT of 4-wk duration reduces TOCs in NTS neurons, and this contributes to reduced delayed excitation and increased AP responses to depolarizing inputs. Such changes could alter baroreflex function in hypertension.

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