Calcium Current In Ventricular Myocytes Research Articles

Luteolin improves heart preservation through inhibiting hypoxia-dependent L-type calcium channels in cardiomyocytes.

The current study aimed to evaluate whether luteolin could improve long-term heart preservation; this was achieved by evaluating the heart following long-term storage in University of Wisconsin solution (the control group) and in solutions containing three luteolin concentrations. The effects of different preservation methods were evaluated with respect to cardiac function while hearts were in custom-made ex vivo Langendorff perfusion systems. Different preservation methods were evaluated with respect to the histology, ultrastructure and apoptosis rate of the hearts, and the function of cardiomyocytes. In the presence of luteolin, the rate pressure product of the left ventricle was increased within 60 min of reperfusion following a 12-h preservation, coronary flow was higher within 30 min of reperfusion, cardiac contractile function was higher throughout reperfusion following 12- and 18-h preservations, and the left ventricle peak systolic pressure was significantly higher compared with the control group (all P<0.05). The expression levels of apoptosis regulator Bax and apoptosis regulator Bcl-2 in the luteolin groups were significantly decreased and increased, respectively. Lactate dehydrogenase, creatine kinase and malondialdehyde enzymatic activity was increased following long-term storage, while the activity of superoxide dismutase was significantly decreased. Furthermore, luteolin inhibited L-type calcium currents in ventricular myocytes under hypoxia conditions. Thus, luteolin demonstrated protective effects during long-term heart preservation in what appeared to be a dose-dependent manner, which may be accomplished through inhibiting hypoxia-dependent L-type calcium channels.

The effect of allicin on the ventricular myocytes of rabbit with heart failure

Objective To observe the effect of allicin on the action potential duration (APD) and L-type calcium current (ICa, L) in the ventricular myocytes of rabbits with heart failure in order to explore the mechanisms of therapeutic effect of allicin on cardiac arrhythmias complicated with heart failure. Methods Forty-five New Zealand White male rabbits were randomly (random number) assigned to 3 groups (n=15 in each group): sham operated group (sham group), heart failure group (HF group), and heart failure treated with allicin group (HF+All group). The rabbit heart failure model was established by abdominal aortic constriction coupled with aortic regurgitation, the ventricular myocytes were obtained by enzyme double digestion, and the whole cell clamp was used to record action potential and calcium current.The action potential duration (APD), ICa, L and gating mechanism were observed during heart failure and allicin administered. Data were processed with pCLAMP version 10.2. Statistical analysis was performed using SPSS 17.0. Comparisons among groups were carried out using ANOVA, and SNK-q was used for multiple comparison as post-hoc. Results (1) Prolonged APD was found during heart failure, APD50 was prolonged from (93.4±4.7) ms in sham group to (115.5±6.2) ms in HF group(P<0.01). After administration of allicin 30 μmol/L, APD50 was shortened to (105.2±5.5) ms (P<0.05). (2) The density of ICa,L increased during heart failure, peak current density increased increased from (-8.4±0.6) pA/pF in sham group to (-15.1±1.1) pA/pF while 0 mV attained at depolarizations (P<0.01). After administration of allicin 30 μmol/L, the current density reduced to (-10.1±0.8) pA/pF ( P<0.01). The effect of allicin presented in both voltage dependent and consentration dependent manner. (3) According to the gating mechanism study, the main mechanism of lowering the density of ICa, L by allicin after heart failure was the acceleration of the steady inactivation of the channel, and the de-escalation of the recovery kinetic after the inactivation of the channel. Conclusions Allcin can be used to reduce the calcium current of ventricular myocytes in animal heart failure model, it has the potential of clinical use in treating cardiac arrhythmias during heart failure. Key words: Allicin; Heart failure; Rabbit; Ventricular myocytes; Action potential; L- calcium current

Eschewing ischemia or responding to it

This month’s installment of Generally Physiological considers the regulation of nitric oxide (NO) delivery to vascular smooth muscle cells, the effects of an increase in free intracellular magnesium (Mg2+i) on calcium current in ventricular myocytes during transient cardiac ischemia, and the

Effects of valsartan on L-type calcium current in ventricular myocytes of rabbits after myocardial infarction

Objective To determine the effects of valsartan, a specific angiotensin Ⅱ type 1 receptor blockade, on arrhythmia in rabbits after myocardial infarction and to discuss the mechanism. Method Twentyfour rabbits were randomly (random number) divided into sham operated (SO) group ( n = 8), myocardial infarction (MI) group ( n = 8) and valsartan (VAL) group ( n = 8). The rabbits of SO group were operated upon with median stemotomy without left ventricular coronary artery hgature. The rabbits of MI group and VAL group had median stemotomy with left ventricular coronary artery ligature. After MI, the rabbits of VAL group were fed with border zone of infracted left ventricular wall and the L-type calcium current was recorded by whole-cell patch clamp technique. Results Ventricular tachycardia or fibrillation (VT/VF) episodes were markedly decreased in VAL group than that in MI group [(3.2 ± 0. 6) vs. ( 11.7 ± 1.8)] after 12 weeks. The density of Ica-L current was higher in MI group than that in SO group and VAL group [( - 9.12 ± 0.73) pA/pF vs. ( - 6.29 ± 0.65) pA/pF and ( - 6.75 ± 0.64) pA/pF], ( P ＜ 0.05), however, there were no significant differences in Ica-L current between So group and VAL group ( P ＞ 0.05). Conclusions Valsartan reduces the VT/VF episodes in rabbits after MI. The effects of valsartan may be attributed to the inhibited electrical remodeling after MI. Key words: Myocardial infarction; Ventricular arrhythmias; L-type calcium current; Patch clamp; Valsartan; Rabbit

Reduced L-type calcium current in ventricular myocytes from pigs with hyperdynamic septic shock*

To hypothesize that reduced L-type calcium current with consequent shortening of cardiac repolarization is present in a clinically relevant porcine model of hyperdynamic septic shock. Myocardial depression is a well-recognized manifestation of sepsis and septic shock. Reduction of L-type calcium current was demonstrated to contribute to the myocardial depression in endotoxemic rodents. Laboratory animal experiments. Animal research laboratory at a university. Twenty-two domestic pigs of either gender. In anesthetized, mechanically ventilated, and instrumented pigs, sepsis was induced by bacteremia (central venous infusion of live Pseudomonas aeruginosa) and continued for 22 hrs. Electrocardiogram was recorded before and 22 hrs after induction of bacteremia. RR, QT, and QTc intervals were significantly shortened by sepsis. In vitro, action potentials were recorded in right ventricular trabeculae. Action potential durations were shortened in septic preparations. Tumor necrosis factor-alpha did not influence action potential durations. L-type calcium current was measured in isolated ventricular myocytes. Peak L-type calcium current density was reduced in myocytes from septic animals (8.3 +/- 0.4 pA/pF vs. 11.2 +/- 0.6 pA/pF in control). The voltage dependence of both L-type calcium current activation and inactivation was shifted to more negative potentials in myocytes from septic animals. Action potential-clamp experiments revealed that the contribution of L-type calcium current to the septic action potential was significantly diminished. In cardiac myocytes incubated with tumor necrosis factor-alpha, L-type calcium current was not further affected. In a clinically relevant porcine model, hyperdynamic septic shock induced shortening of ventricular repolarization and reduction of L-type calcium current. The contribution of L-type calcium current to the action potential in septic ventricular myocytes was significantly diminished. Tumor necrosis factor-alpha probably did not contribute to this effect.

Regional dispersion of L-type calcium current in ventricular myocytes of German shepherd dogs with lethal cardiac arrhythmias

The purpose of this study was to determine if regional differences in L-type Ca(2+) current (I(Ca,L)) are altered in a German shepherd model of sudden death. German shepherd dogs with inherited sudden cardiac death have reduced sympathetic innervation in the anteroseptal left ventricle that may contribute to arrhythmias in afflicted animals compared to control unafflicted animals. Differences in a number of repolarizing K(+) currents have been identified in this model, but I(Ca,L) has not been studied. We measured action potentials in intact tissue and I(Ca,L) in isolated myocytes from anteroseptal and anterobasal left ventricle. Action potential plateau level and I(Ca,L) density were significantly lower in unafflicted anteroseptal than in afflicted anteroseptal, afflicted anterobasal, or unafflicted anterobasal. Isoproterenol increased I(Ca,L) density more in the unafflicted anteroseptal group than in the other groups. Differences in I(Ca,L) between afflicted and control animals, combined with our earlier finding of regional reductions in I(Kr), provide a likely substrate for the occurrence of pause-dependent arrhythmias in afflicted animals and for the T-wave abnormalities characterizing them.

Characterization of nifedipine-resistant calcium current in neonatal rat ventricular cardiomyocytes.

Calcium current was recorded from ventricular cardiomyocytes of rats at various stages of postnatal development using the whole cell patch-clamp technique. In cultured 3-day-old neonatal cells, the current carried by Ca(2+) or Ba(2+) (5 mM) was not completely inhibited by 2 microM nifedipine. A residual current was activated in the same voltage range as the L-type, nifedipine-sensitive Ca(2+) current, but its steady-state inactivation was negatively shifted by 16 mV. This nifedipine-resistant calcium current was not further inhibited by other organic calcium current antagonists such as PN200-110, verapamil, and diltiazem nor by nickel, omega-conotoxin, or tetrodotoxin. It was completely blocked by cadmium and increased by isoproterenol and forskolin. This current was >20% of total calcium current in ventricular myocytes freshly isolated from neonatal rats, and it decreased during postnatal maturation, disappearing at the adult stage. This suggests that this current could be caused by an isoform of the L-type calcium channel expressed in a way that reflects the developmental stage of the rat heart.

Reduced L-type calcium current in ventricular myocytes from endotoxemic guinea pigs.

The circulatory response to gram-negative sepsis and its experimental counterpart, endotoxemia, includes a profound dysfunction in myocardial contractility that is resident to the myocyte and associated with reduced systolic free intracellular Ca2+ concentration ([Ca2+]i). We explored the possibility that decreased systolic [Ca2+]i in endotoxemic myocytes is correlated with reduced L-type Ca2+ current (ICa,L). Ventricular myocytes were isolated from guinea pigs 4 h after an intraperitoneal injection of Escherichia coli lipopolysaccharide (LPS; 4 mg/kg). Membrane potentials and Ca2+ currents were measured using whole cell patch-clamp methods. The action potential duration of endotoxemic myocytes was significantly shorter than control values (time to 50% repolarization: LPS, 314 +/- 23 ms; control, 519 +/- 36 ms, P < 0.05). Correspondingly, endotoxemic myocytes demonstrated significantly reduced peak ICa,L density (3.5 +/- 0.2 pA/pF) and Ba2+ current (IBa) density (7.3 +/- 0.5 pA/pF) compared with respective values of control myocytes (ICa,L) density 6.1 +/- 0.3 pA/pF, IBa density 11.3 +/- 0.8 pA/pF; P < 0.05). Endotoxemia-induced reduction in peak ICa,L could not be attributed to alterations in current-voltage relationships, steady-state activation and inactivation, or recovery from inactivation. The beta-adrenoceptor agonist isoproterenol, but not the Ca2+ channel activator BAY K 8644, reversed the LPS-induced reduction in peak ICa,L, cell contraction, and systolic [Ca2+]i. These data demonstrate that part of the host response to endotoxemia involves diminished sarcolemmal ICa,L of ventricular myocytes.

Calcium currents in ventricular myocytes of prehypertrophic cardiomyopathic hamsters.

Possible changes in Ca2+ currents (ICa), which might contribute to Ca2+ overload in young (70- to 100-day-old) cardiomyopathic (CM) hamster hearts, were determined in isolated ventricular myocytes with conventional recording and discontinuous single-electrode voltage-clamp techniques. Action potential duration at 90% repolarization (APD90) was significantly longer in CM myocytes compared with normal cells (APD90 = 120.3 +/- 4.5 vs. 98.2 +/- 5.9 ms, P < 0.01). Input resistance, membrane time constant, and membrane capacitance were similar in normal and CM myocytes. Current-voltage (I-V) relations for peak ICa were depressed in CM cells compared with normal cells; this difference was statistically significant at the peak of the I-V curve. Activation and inactivation relations for ICa and recovery from inactivation were similar in myocytes from normal and CM hearts. These changes occurred in myocytes from young CM animals before development of heart failure. Results indicate that increased Ca2+ influx through L-type Ca2+ channels does not account for the longer APD in cardiomyopathy and is not involved in the development of Ca2+ overload in cardiomyopathy.

Asymmetric charge movement and calcium currents in ventricular myocytes of neonatal rat.

1. Calcium and sodium currents and non-linear capacitive currents were recorded from isolated ventricular cells from neonatal rats, using the whole-cell patch-clamp technique, usually with a holding potential of -100 mV. 2. When recording with internal and external solutions designed to suppress virtually all ionic currents except the calcium current, careful subtraction of all linear capacitive and ionic currents revealed that depolarizations elicited a small transient outward current which preceded the inward calcium current. This outward current was discernible just below the threshold potential for the calcium current and increased with larger depolarizations to a maximum for potentials of about +30 mV and above. 3. Elimination of the calcium current revealed that at each potential the transient outward current was accompanied by a roughly equal transient inward current upon repolarization. The properties of these currents indicate that they are non-linear capacitive currents. Best-fit Boltzmann curves of the 'on' charge (integral of the transient outward current) gave values for qmax, V and k of 3.9 nC/microF, -29.3 mV and 15.5 mV with internal Cs+. The maximum 'on' charge is similar to that found with calcium currents (4.3 nC/microF). Similar values were obtained with internal TEA+. 4. Boltzmann fits of conductance vs. voltage for the calcium channel gave mean values of -15.5 and 13.3 mV for V and k (with internal Cs+); the corresponding values for the sodium channel were -49.9 and 5.4 mV. 5. Pre-pulses (20 ms) to -60 mV inactivated 77% of the peak sodium current, but only inactivated about 10% of the peak calcium current and reduced the maximum 'on' charge (moved at potentials positive to -60 mV) by 19%. 6. With a holding potential of -100 mV, 10 microM-nifedipine blocked 89% of the calcium current, but had little effect on the amount of 'on' charge. The 'off' charge appeared to be slower in the presence of nifedipine. 7. These results and consideration of the number of calcium channels and high-affinity binding sites for dihydropyridines (DHP), suggest that a large part of the charge movement may be related to DHP binding sites and involved with gating calcium channels. Comparison with skeletal muscle suggests similarities in the mechanisms involved in excitation-contraction coupling.