钾离子通道亚单位mRNA在犬左右心室中层心肌中的表达

目的研究犬左右室中层心肌短暂外向钾电流(Ito)、延迟整流钾电流缓慢激活成分(Iks)亚单位mRNA的表达情况,探讨左右室复极异质性的可能分子机制。方法应用逆转录-聚合酶链反应(RT-PCR)半定量分析犬左右室中层心肌Ito的α亚单位(Kv4.3)、β亚单位(KchIP2)、Iks的α亚单位(KvLQT1)mRNA的表达量(以β-actin为内参照)。结果Kv4.3 mRNA水平在左右室中层心肌中表达没有显著性差异(P>0.05),KchIP2 mRNA、Kv-LQT1 mRNA水平在右室中层心肌表达明显高于左室中层心肌(P<0.01或<0.05)。结论KchIP2、KvLQT1 mRNA水平在左右室中层心肌中表达上的差异可能是其离子流差异的分子基础。     

Inhibition of K+ currents by homocysteine in rat ventricular myocytes

INTRODUCTION: Clinical evidence suggests that increased blood levels of homocysteine may be an independent risk factor for the development of cardiovascular disease, but the functional effects of this sulfhydryl amino acid on the myocardium are poorly understood. The present study was conducted to determine the direct effects of homocysteine on the electrophysiologic properties of the heart. METHODS AND RESULTS: Whole-cell voltage-clamp recordings were made in ventricular myocytes isolated from normal rat hearts to analyze the Ca2+-independent, transient outward K+ current (I(to)), a major repolarizing current in these cells. Maximum I(to) density (measured at +60 mV) was decreased approximately 47% from baseline in the presence of 500 microM homocysteine (P < 0.05), but the amount of block varied in a frequency- and voltage-dependent manner. Decreased I(to) density was not accompanied by significant changes in voltage- or time-dependent properties of the current, nor was it affected by pretreating myocytes with the protein kinase inhibitor staurosporine. Because a portion of total extracellular homocysteine is oxidized, we examined the response to homocystine, the oxidized form of homocysteine. In myocytes superfused with 500 microM homocystine, maximum I(to) density was decreased by approximately 40% from baseline (P < 0.05). In contrast, the thiolactone form of homocysteine did not alter I(to) amplitude. CONCLUSION: These data suggest that homocysteine and its oxidized form homocystine acutely inhibit I(to) channels in ventricular myocytes by mechanisms involving the free thiol or disulfide moieties of these compounds. High homocysteine or homocystine levels may contribute to abnormal repolarization and arrhythmogenic conditions in the intact heart.     

Angiographic right and left ventricular function in arrhythmogenic right ventricular dysplasia

We prospectively documented right ventricular (RV) and left ventricular (LV) volumes and ejection fractions in a large series of patients with arrhythmogenic RV dysplasia/cardiomyopathy (ARVD/C). Eighty-five patients with ARVD/C and 11 controls underwent 2 successive orthogonal right and left monoplane x-ray-digitized cineangiographies. Volumes were calculated using the hemielliptical RV and ellipsoidal LV models. All controls and 58 of 85 patients (ARVD/C-I) had a RV ejection fraction > or =35% and 27 patients had a RV ejection fraction <35% (ARVD/C-II). Tricuspid annulus plane systolic excursion (TAPSE) was lower in ARVD/C-II than in ARVD/C-I patients (6 +/- 3 vs 14 +/- 3 mm) and controls (16 +/- 2 mm) (each p <0.001). In patients with ARVD/C, TAPSE was positively related to RV ejection fraction (r = 0.79) and to crista supraventricularis shortening (r = 0.81) (each p <0.001). Sensitivity and specificity of TAPSE <12 mm in identifying patients with RV ejection fraction <35% were 96% and 78%, respectively. LV ejection fraction was > or =50% in 68 patients, 40% to 49% in 10, and <40% in 7. Diffuse RV outflow tract aneurysm was observed in 9 patients, all belonging to ARVD/C-II, and this sign identified patients with LV ejection fraction <40% with 86% sensitivity and 96% specificity. In conclusion, 68% of ARVD/C patients had normal RV ejection fraction and RV volumes, and 80% of ARVD/C patients had normal LV ejection fraction. Decreased TAPSE <12 mm and a diffuse RV outflow tract aneurysm were sensitive and specific indicators of RV ejection fraction <35% and LV ejection fraction <40%, respectively.     

Chromanol 293B inhibits slowly activating delayed rectifier and transient outward currents in canine left ventricular myocytes

INTRODUCTION: Drugs that selectively inhibit the slowly activating component of the delayed rectifier potassium current (I(Ks)) are being considered as possible antiarrhythmic agents, because they produce more prolongation of action potential duration at fast rates with less transmural dispersion of repolarization compared with blockers of the rapidly activating component (I(Kr)). Although the chromanol derivative chromanol 293B has been shown to be relatively selective in blocking I(Ks) in some species, its selectivity is far from established. METHODS AND RESULTS: The present study uses whole-cell, patch-clamp technique to examine the selectivity of this compound for inhibition of I(Ks) in comparison with other repolarizing ionic currents, such as I(Kr), inward rectifier potassium current (I(Kl)), transient outward current (I(to)), and L-type calcium current (I(Ca-L)) in canine left ventricular mid-myocardial and endocardial cells. Chromanol 293B blocked I(Ks) with an IC50 of 1.8 microM and I(to) with an IC50 of 38 microM. Concentrations as high as 30 microM did not affect I(Kl), I(Kr), or I(Ca-L). Higher concentrations of chromanol 293B (100 microM) caused a slight, but statistically insignificant, inhibition of I(Kr). CONCLUSION: Our results indicate that chromanol 293B is a relatively selective blocker of I(Ks) in canine left ventricular myocytes.     

急性低氧对家兔心室肌细胞钙、钾通道电流的影响

目的:研究急性低氧对单个家兔心室肌细胞L-型钙通道电流(L-Ica)、ATP敏感性钾通道电流(Ik(ATP)以及短暂外向钾电流(Ito)的影响,以探讨急性低氧导致动作电位时程(APD)缩短的机制。方法:应用膜片钳全细胞记录方法。结果:低氧15分钟后心室肌细胞APD明显缩短(由491±57ms降至287±53ms,P<0.01);L-Ica峰值降低(由1.57±0.29 nA降至0.83士0.15 nA,P<0.01),电流-电压曲线上移;IK(ATP)通道开放,短暂外向钾电流(Ito)峰值增大(由4.76士0.43nA升至5.41±0.53hA,P<0.05);复氧2分钟后,IK(ATP)受到抑制(由2.98±0.37nA降至610.9±42.IPA,P<0.01)。结论:急性低氧时APD的缩短是L-Ica、IK(ATP)以及Ito变化综合作用的结果。     

Alpha1-adrenoceptor-mediated breakdown of phosphatidylinositol 4,5-bisphosphate inhibits pinacidil-activated ATP-sensitive K+ currents in rat ventricular myocytes

Phosphatidylinositol 4,5-bisphosphate (PIP2) stimulates ATP-sensitive K+ (K(ATP)) channel activity. Because phospholipase C (PLC) hydrolyzes membrane-bound PIP2, which in turn may potentially decrease K(ATP) channel activity, we investigated the effects of the alpha1-adrenoceptor-G(q)-PLC signal transduction axis on pinacidil-activated K(ATP) channel activity in adult rat and neonatal mouse ventricular myocytes. The alpha1-adrenoceptor agonist methoxamine (MTX) reversibly inhibited the pinacidil-activated K(ATP) current in a concentration-dependent manner (IC50 20.9+/-6.6 micromol/L). This inhibition did not occur when the specific alpha1-adrenoceptor antagonist, prazosin, was present. An involvement of G proteins is suggested by the ability of GDPbetaS to prevent this response. Blockade of PLC by U-73122 (2 micromol/L) or neomycin (2 mmol/L) attenuated the MTX-induced inhibition of K(ATP) channel activity. In contrast, the MTX response was unaffected by protein kinase C inhibition or stimulation by H-7 (100 micro mol/L) or phorbol 12,13-didecanoate. The MTX-induced inhibition became irreversible in the presence of wortmannin (20 micro mol/L), an inhibitor of phosphatidylinositol-4 kinase, which is expected to prevent membrane PIP2 replenishment. In excised inside-out patch membranes, pinacidil induced a significantly rightward shift of ATP sensitivity of the channel. This phenomenon was reversed by pretreatment of myocytes with MTX. Direct visualization of PIP2 subcellular distribution using a PLCdelta pleckstrin homology domain-green fluorescent protein fusion constructs revealed reversible translocation of green fluorescent protein fluorescence from the membrane to the cytosol after alpha1-adrenoceptor stimulation. Our data demonstrate that alpha1-adrenoceptor stimulation reduces the membrane PIP2 level, which in turn inhibits pinacidil-activated K(ATP) channels.     

Paradoxical cellular Ca2+ signaling in severe but compensated canine left ventricular hypertrophy

In conscious dogs with severe left ventricular (LV) hypertrophy (H) (doubling of LV/body weight), which developed gradually over 1 to 2 years after aortic banding, baseline LV function was well compensated. The LV was able to generate twice the LV systolic pressure without an increase in LV end-diastolic pressure, or decrease in LV dP/dt or LV wall thickening. However, LV myocytes isolated from LVH dogs exhibited impaired contraction at baseline and in response to Ca2+. There was no change in L-type Ca2+ channel current (ICa) density but the ability of ICa to trigger Ca2+ release from the sarcoplasmic reticulum (SR) was reduced. Immunoblot analysis revealed a 68% decrease in SERCA2a, and a 35% decrease in the number of ryanodine receptors (RyR2), with no changes in protein level of calsequestrin, Na+/Ca2+ exchanger or phospholamban (PLB), but with both RyR2 and PLB hyperphosphorylated. Spontaneous Ca2+ sparks in LVH cells were found to have prolonged duration but similar intensities despite the reduced SR Ca2+ load. A higher Ca2+ spark rate was observed in LVH cells, but this is inconsistent with the reduced SR Ca2+ content. However, Ca2+ waves were found to be less frequent, slower and were more likely to be aborted in Ca2+-challenged LVH cells. These paradoxical observations could be accounted for by a nonuniform SR Ca2+ distribution, RyR2 hyperphosphorylation in the presence of decreased global SR Ca2+ load. We conclude that severe LVH with compensation masks cellular and subcellular Ca2+ defects that remain likely contributors to the limited contractile reserve of LVH.     

Further evidence that Whorfian effects are stronger in the right visual field than the left

The Whorf hypothesis holds that differences between languages induce differences in perception and/or cognition in their speakers. Much of the experimental work pursuing this idea has focused on the domain of color and has centered on the issue of whether linguistically coded color categories influence color discrimination. A new perspective has been cast on the debate by recent results that suggest that language influences color discrimination strongly in the right visual field but not in the left visual field (LVF). This asymmetry is likely related to the contralateral projection of visual fields to cerebral hemispheres and the specialization of the left hemisphere for language. The current study presents three independent experiments that replicate and extend these earlier results by using different tasks and testing across different color category boundaries. Our results differ in one respect: although we find that Whorfian effects on color are stronger for stimuli in the right visual field than in the LVF, we find that there are significant category effects in the LVF as well. The origin of the significant category effect in the LVF is considered, and two factors that might account for the pattern of results are proposed.     

Evolution of left ventricular involvement in arrhythmogenic right ventricular cardiomyopathy

Left ventricular (LV) involvement in arrhythmogenic right ventricular cardiomyopathy (ARVC) is fairly well known, but the evolution of LV involvement during long-term follow-up has not been well documented. We describe such evolution in a patient followed for 9 years. Evolution was confirmed by a progressive perfusion defect of the LV wall in myocardial scintigrams and by the development of LV asynergy with ventricular aneurysm formation in left ventriculograms. As the right ventricle progressively enlarged, we concluded that ARVC is a diffuse and progressive myocardial disease that affects both ventricles.     

Similar left and right ventricular sarcomere structure after support with a left ventricular assist device suggests the utility of right ventricular biopsies to monitor left ventricular reverse remodeling

BACKGROUND: To evaluate whether the morphology of the contractile filaments in cardiomyocytes of patients with end-stage heart failure, treated with a left ventricular assist device (LVAD), is identical in the left- and right ventricle (LV, RV) and in the interventricular septum (IVS) and can be monitored by biopsies taken with a bioptome. The application of an LVAD as a bridge to recovery of cardiac function requires monitoring of myocyte recovery. The use of RV biopsies for this purpose might be feasible, if morphologic findings in the RV coincide with those in the LV. METHODS AND RESULTS: At the time of heart transplantation, myocardial biopsies of LV, RV and IVS from 13 patients after LVAD support were compared using immunohistochemistry with monoclonal antibodies against contractile proteins. Additionally, in five of these patients, small biopsies obtained with a diagnostic bioptome were compared with large transmural biopsies of the same region. Hemodynamic monitoring was performed when the patients were fully recovered from the implantation, to rule out persistent RV failure. The staining pattern of actin, myosin, tropomyosin, troponin T and C was identical in the biopsies of LV, RV and IVS. Small biopsies taken with a bioptome appeared to be representative for the larger biopsies. Hemodynamic monitoring showed absence of RV failure in our study group. CONCLUSION: In the absence of RV failure, morphology of the contractile myofilaments after LVAD support for 215+/-143 days is identical in LV, RV and IVS. This may allow monitoring of the possible occurrence of LV reverse remodeling by RV biopsies.     

Calcium and potassium currents in cells from adult and aged canine right atria

BACKGROUND: Action potential (AP) contours vary considerably between normal adult and aged right atrial fibers. The ionic bases for these differences remain unknown. Therefore we studied Ca(2+) and K(+) currents in cells from adult and aged canine right atria (RA). METHODS AND RESULTS: We used whole cell patch clamp recording techniques to measure L-type Ca(2+) currents (I(CaL)) with either Ca(2+) or Ba(2+) (3 mM) as the charge carrier, and both the transient outward (I(to)) and sustained potassium currents (I(sus)) in cells dispersed from normal adult (Adult, 2-5 years) and older dogs (Aged, >8 years). There is a significant reduction in peak I(CaL) (47%) and I(BaL) (43%) in Aged cells, yet differences in I(BaL) disappear with maximal beta adrenergic stimulation (isoproterenol, 1 microM). Composite I(to) and I(sus) densities were significantly increased in the Aged versus Adult cell group (by 31 and 27% at +50 mV, respectively). I(to) decay during a maintained depolarization was slowed in Aged cells. Furthermore, I(to) steady-state inactivation curve was shifted positively in Aged cells. Finally, composite I(to) and I(sus) currents of Aged cells were more sensitive to tetraethylammonium chloride (TEA), a specific inhibitor of some types of K(+) currents. In the presence of TEA (5 mM), I(to) in Aged cells was significantly greater than that in Adult cells. CONCLUSIONS: Ionic currents differ in Aged versus Adult right atrial cells, such that a reduced Ca(2+) current and augmented outward currents could contribute significantly to the altered AP contour of the Aged RA cell. Adrenergic stimulation appears to restore Ba(2+) currents in Aged cells. Finally, an augmented TEA sensitive current plays a role in changes of I(sus) in Aged right atrial cells.     

Increased Na+ concentration and altered Na/K pump activity in hypertrophied canine ventricular cells

OBJECTIVE: To investigate whether hypertrophy in the dog with chronic atrioventricular block (CAVB) alters [Na+]i and Na/K-pump function of ventricular myocytes. METHODS: We measured the [Na+]i dependence of the Na/K pump current, I(p). This relation was used as a calibration curve for [Na+]i based on I(p). We measured I(p) at the time of access and extrapolated [Na+] at the pump sites, i.e. subsarcolemmal [Na+], [Na+](subs), from the calibration curve. RESULTS: The extrapolated [Na+](subs) was significantly higher in CAVB (7.9 vs. 3.2 mM in control). The [Na+]i dependence of I(p) in CAVB myocytes was shifted to the right (range of [Na+](i): 0-20 mM). In resting cells, the I(p), i.e. steady state Na+ efflux, which matches Na+ influx, was higher in CAVB (0.25+/-0.02 vs. 0.47+/-0.06 pA/pF, P<0.05). Maximal I(p) density was not different, and DHO sensitivity was not altered. CONCLUSIONS: Hypertrophy in CAVB cells is associated with increased [Na+](subs). This results from an increase in Na+ influx, and a decreased sensitivity of I(p) for Na+ in the range of [Na+]i studied. There is no evidence for a decrease in total pump capacity or for a functional Na/K-ATPase isoform shift. The rise in Na+ contributes to the contractile adaptation and preservation of sarcoplasmic reticulum Ca2+ content at the low heart rates of the dog with CAVB.     

Resynchronization of the left ventricular contraction by tailored programming of right and left ventricular pacing

Aims: The prerequisite and the rationale for the benefit of cardiacresynchronization therapy (CRT) is that it is able to resynchronizeleft ventricular (LV) walls that have a delayed activation. Methods and results: In 69 consecutive patients who underwent biventricular (BIV)pacemaker implantation, we assessed the magnitude of intraventricularresynchronization achieved by means of simultaneous (BIV 0)and sequential BIV pacing (with an individually optimized VVinterval value among +80 ms and –80 ms) using pulsed-wavetissue Doppler imaging techniques and in particular the measurementof the intra-LV electromechanical delay. The intra-LV delaywas defined as the difference between the longest and the shortestactivation time in the six basal segments of the LV. An abnormalintra-LV delay was defined as a value >41 ms. The intra-LVdelay was 63 ± 28 ms baseline, decreased to 44 ±26 ms with BIV 0 and to 26 ± 15 ms with optimized BIV(P = 0.001). BIV 0 determined the shortest delay in 28 (41%)patients (23 ± 12 ms). In 41 (59%) patients, a betterresynchronization was achieved with optimized VV intervals (LVfirst in 32 and RV first in 5) or single-chamber pacing (LVin 3 and RV in 1). With BIV 0, the intra-LV delay remained abnormalin 41% and was longer than baseline in 30% of patients comparedwith 9 and 12% with optimized BIV, respectively (P = 0.001). Conclusion: A sub-optimal resynchronization is achieved with simultaneousBIV pacing in most patients. A tailored programming of the relativecontribution of RV and LV pacing forms the prerequisite forimproving CRT results.     

Temporal patterns of electrical remodeling in canine ventricular hypertrophy: focus on IKs downregulation and blunted beta-adrenergic activation

OBJECTIVES: Electrical remodeling in cardiac hypertrophy often involves the downregulation of K+ currents, including beta-adrenergic (beta-A)-sensitive IKs. Temporal patterns of ion-channel downregulation are poorly resolved. In dogs with complete atrioventricular block (AVB), we examined (1) the time course of molecular alterations underlying IKs downregulation from acute to chronic hypertrophy; and (2) concomitant changing responses of repolarization to beta-adrenergic receptor (beta-AR) stimulation. METHODS AND RESULTS: Serial left-ventricular (LV) biopsies were collected from anesthetized dogs during sinus rhythm (SR; control) and at 3, 7 and 30 days of AVB. KCNQ1 mRNA and protein decreased within 3 days (protein expression 58 +/- 10% of control), remaining low thereafter. beta1-AR mRNA and protein decreased more gradually to 53 +/- 8% at 7 days. In chronic-AVB LV myocytes, IKs -tail density was reduced: 1.4 +/- 0.3 pA/pF versus 2.6 +/- 0.4 pA/pF in controls. beta-A enhancement of IKs was reduced. Isoproterenol shortened action-potential duration in control cells, while causing heterogeneous repolarization responses in chronic AVB. beta-A early afterdepolarizations were induced in 4 of 13 chronic-AVB cells, but not in controls. In intact conscious dogs, isoproterenol shortened QTc at SR (by -8 +/- 3% from 295 ms), left it unaltered at 3 days AVB (+1 +/- 3% from 325 ms) and prolonged QTc at 30 days (+6 +/- 3% from 365 ms). CONCLUSIONS: Profound decrease of KCNQ1 occurs within days after AVB induction and is followed by a more gradual decrease of beta1-AR expression. Downregulation and blunted beta-A activation of IKs contribute to the loss of beta-A-induced shortening of ventricular repolarization, favoring proarrhythmia. Provocation testing with isoproterenol identifies repolarization instability based on acquired channelopathy.     

Developmental changes in membrane Ca2+ and K+ currents in fetal, neonatal, and adult rabbit ventricular myocytes.

Whole-cell calcium current (ICa) and inwardly rectifying potassium current (IK1) were studied in 21-day fetal, 28-day fetal (total gestation, 31 days), 2-5-day neonatal, and adult rabbit ventricular myocytes isolated by enzymatic dissociation. Whole-cell peak ICa and IK1 at -100 mV increased significantly after birth. Cell size approximated from cell membrane capacitance also increased with age, with the most significant increase occurring after birth. When normalized to cell surface area, peak ICa density increased from day 21 of gestation to the neonate and then increased again from neonate to adult. In all age groups, peak ICa occurred at a test potential of +10 mV, and the shape of the Ca2+ current-voltage relation did not change with age. These findings suggest that there are no significant developmental changes in the voltage dependence of ICa. Therefore, the measured age-related increase in Ca2+ current density may result from increased channel expression. IK1 also exhibited a pattern of increasing current density with age. For IK1, the increase in current density was most rapid between day 21 and the perinatal period and much slower after birth. These results demonstrate that ICa and IK1 undergo significant changes during late fetal and postnatal development.