The inhibitory effects of nano‐Ag on voltage‐gated potassium currents of hippocampal CA1 neurons

The application of the nano‐sized materials continues to grow at a rapid rate in the fields of medicine, biotechnology, and environmental technology. Voltage‐gated potassium currents play a key role in excitable cellular viability and function, especially in the central nervous system. The aim of this study was to investigate the actions of silver nano‐particles (nano‐Ag) on voltage‐activated potassium currents in hippocampal CA1 neurons using whole cell patch‐clamp technique. The hydrodynamic mean diameter of nano‐Ag (10^?5g mL^?1) was 223.9 nm in artificial cerebrospinal fluid (ACSF). Both types, transient potassium (I_A) and delayed rectifier potassium (I_K) current amplitudes were inhibited by the nano‐Ag (10^?5g mL^?1). The nano‐Ag particles produced a hyperpolarizing shift in the activation‐voltage curve of I_K and inactivation‐voltage curve of I_A and also delayed the recovery of I_A from inactivation. The results suggest that nano‐Ag may have potential to alter the excitability of neurons by depressing the potassium channels. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2010.     

Inhibitory effect of tungsten carbide nanoparticles on voltage-gated potassium currents of hippocampal CA1 neurons

The effects of tungsten carbide nanoparticles (nano-WC) on the properties of voltage-dependent potassium currents and evoked action potentials were studied in the hippocampal CA1 pyramidal neurons of rats at the ages of postnatal days 10-14 using the whole-cell patch-clamp technique. The results indicated that: (1) the amplitudes of transient outward potassium current (I_A) and delayed rectifier potassium current (I_K) were significantly decreased by 10⁻⁷ g/ml nano-WC, while the current-voltage curves of I_A and I_K were significantly decreased by nano-WC from +10 to +90 mV. (2) Nano-WC produced a depolarizing shift in the steady-state activation curve of I_A and I_K with increased slope factors, and delayed the recovery of I_A from inactivation, but no significant effects were found on the inactivation of I_A. (3) Nano-WC prolonged the evoked action potential duration and lowered the firing rate. These results suggest that 10⁻⁷ g/ml nano-WC can decrease the amplitudes of I_A and I_K currents by reducing the opening number of voltage-gated potassium channels and delaying the recovery of I_A from inactivation, which indicate that nano-WC has the potential neurotoxicity.     

Effects of Resibufogenin and Cinobufagin on voltage-gated potassium channels in primary cultures of rat hippocampal neurons

Outward delayed rectifier potassium channel and outward transient potassium channel have multiple important roles in maintaining the excitability of hippocampal neurons. The present study investigated the effects of two bufadienolides, Resibufogenin (RBG) and Cinobufagin (CBG), on the outward delayed rectifier potassium current (I_K) and outward transient potassium current (I_A) in rat hippocampal neurons. RBG and CBG have similar structures and both were isolated from the venom gland of toad skin. RBG inhibited both I_K and I_A, whereas CBG inhibited I_K without noticeable effect on I_A. Moreover, at 1 μM concentration both RBG and CBG could alter some channel kinetics and gating properties of I_K, such as steady-state activation and inactivation curves, open probability and time constants. These findings suggested that I_K is probably a target of bufadienolides, which may explain the mechanisms of bufadienolides’ pathological effects on central nervous system.     

Effects of Cd<Superscript>2+</Superscript> on transient outward and delayed rectifier potassium currents in acutely isolated rat hippocampal CA1 neurons

The effects of cadmium (Cd²⁺) on the transient outward potassium current (I _A) and delayed rectifier potassium current (I _K) were investigated in acutely dissociated rat hippocampal CA1 neurons using the whole-cell patch-clamp technique. The results showed that Cd²⁺ inhibited the amplitudes of I _A and I _K in a reversible and concentration-dependent manner, with half-maximal inhibitive concentration (IC₅₀) values of 546 ± 59 and 749 ± 53 μM, and the inhibitory effect of Cd²⁺ was voltage dependent. Cd²⁺ significantly shifted the steady-state activation and inactivation curve of I _A to more positive potentials. In contrast, Cd²⁺ caused a relatively less but still significant positive shift in the activation of I _K without effect on the inactivation curve. Cd²⁺ significantly slowed the recovery from inactivation of I _K but had no effect on the recovery time course of I _A. The results suggest that the modulation of I _A and I _K was most likely mediated by the interaction of Cd²⁺ with a specific site on the potassium-channel protein rather than by screening of bulk surface-negative charge. The effects of Cd²⁺ on the voltage-gated potassium currents may be a possible contributing mechanism for the Cd²⁺-induced neurotoxic damage. In addition, the effects of Cd²⁺ on the potassium currents at concentrations that overlap with its effects on calcium currents raise concerns about its use in pharmacological or physiological studies.     

Multi-walled carbon nanotube increases the excitability of hippocampal CA1 neurons through inhibition of potassium channels in rat's brain slices

This study was to investigate the neurotoxicity of multi-walled carbon nanotube (MWCNT) by measuring neuronal excitability in rat hippocampal neurons and exploring the underlying mechanism. Whole cell patch-clamp technique was used. Action potential properties and the pattern of repetitive firing rate were assessed. Our data showed that spike half-width and repetitive firing rate were significantly increased in a concentration-dependent manner. Furthermore, voltage-activated potassium currents were recorded. It was found that MWCNT produced a concentration-dependent inhibition in amplitudes of I_A and I_K. In addition, MWCNT had effect on the activation kinetics of I_A and I_K with V_h being shifted to the negative potential at high concentration, while I_A inactivation curve was considerably shifted to the hyperpolarize potential with V_h being increased. However, no effect was found on the recovery from inactivation of I_A. The results suggest that MWCNT increases the excitability of hippocampal CA1 neurons by inhibiting voltage-gated potassium current.     

Effectiveness of nalbuphine,a κ-opioid receptor agonist and μ-opioid receptor antagonist,in the inhibition of INa,IK(M), and IK(erg) unlinked to interaction with opioid receptors

Nalbuphine (NAL) is recognized as a mixer with the κ-opioid receptor agonist and the μ-opioid receptor antagonist. However, whether this drug causes any modifications in neuronal ionic currents is unclear. The effects of NAL on ionic currents in mHippoE-14 hippocampal neurons were investigated. In the whole-cell current recordings, NAL suppressed the peak amplitude of voltage-gated Na⁺ current (I_Na) with an IC₅₀ value of 1.9 μM. It shifted the steady-state inactivation curve of peak I_Na to the hyperpolarized potential, suggesting that there is the voltage dependence of NAL-mediated inhibition of peak I_Na. In continued presence of NAL, subsequent application of either dynorphin A_1-13 (1 μM) or naloxone (30 μM) failed to modify its suppression of peak I_Na. Tefluthrin (Tef; 10 μM), a pyrethroid known to activate I_Na, increased peak I_Na with slowed current inactivation; however, further application of NAL suppressed Tef-mediated suppression of peak I_Na followed by an additional slowing of current inactivation. In addition, NAL suppressed the amplitude of M-type K⁺ current [I_K(M)] with an IC₅₀ value of 5.7 μM, while it slightly suppressed erg-mediated and delayed-rectifier K⁺ currents. In the inside-out current recordings, NAL failed to modify the activity of large-conductance Ca²⁺-activated K⁺ channels. In differentiated NG108-15 neuronal cells, NAL also suppressed the peak I_Na, and subsequent addition of Tef reversed NAL-induced suppression of I_Na. Our study highlights the evidence that in addition to modulate opioid receptors, NAL has the propensity to interfere with ionic currents including I_Na and I_K(M), thereby influencing the functional activities of central neurons.     

苄基四氢巴马汀对豚鼠心室肌细胞钾电流及钙、钠电流的作用

目的：研究苄基四氢巴马汀（BTHP）对心肌细胞的作用特点,以探讨其抗心律失常机制。方法：用全细胞膜片钳技术考察BTHP对心室肌细胞钾电流及钙、钠电流的作用。结果：BTHP 30 μmol.L^-1明显阻滞延迟整流钾电流（I_K包括：I_Kr及I_Ks）。可使I_Kr及I_Kr,tail的幅值下降,且对I_Kr阻滞作用呈频率依赖性;对I_Ks及I_Ks,tail幅值也有明显的抑制作用。BTHP 200　μmol.L^-1可明显阻滞I_Ca,L,使其电流幅值降低,但对I_K1,I_Ca,T,I_Na电流均无影响。结论：BTHP可明显阻滞心室肌细胞I_Kr,I_Ks,I_Ca,L电流,且对I_Kr阻滞作用呈频率依赖性。     

苄基四氢巴马汀细胞内用药对豚鼠乳头状肌动作电位和心室肌细胞延迟整流钾电流的作用

目的　研究将苄基四氢巴马汀(BTHP)导入细胞内对豚鼠乳头状肌动作电位及单个心室肌细胞延迟整流钾电流的影响。方法　利用外加电压脉冲将药物导入乳头状肌细胞内，并用标准微电极方法测定动作电位；利用浓度差扩散方式使药物进入单个心室肌细胞内，采用全细胞膜片钳技术记录延迟整流钾电流（I_K）。结果　100 μmol.L^-1 BTHP使APD₂₀和APD₉₀分别延长13.5%和20.5%。30 μmol.L^-1 BTHP使I_K和I_K,tail分别从（14.1±2.2) pA.pF^-1和(4.0±0.6) pA.pF^-1降至(9.4±1.3) pA.pF^-1和(2.1±1.0) pA.pF^-1，下降率分别为33.2%和35.3%。 该药使I_K和I_K,tail的I-V曲线幅度降低，对曲线形状影响不明显。结论　BTHP入细胞内后可阻滞延迟整流钾电流和延长动作电位时程。     

慢性孵育β-淀粉样肽(25-35)对培养大鼠海马神经元外向钾电流的影响

目的　研究慢性孵育β-淀粉样肽_(25-35) (β-AP_25-35)对海马神经元上瞬时外向钾电流(I_A)和延迟整流钾电流(I_K)的影响。方法　在培养的大鼠海马神经元上用膜片钳全细胞记录钾通道电流。结果　β-AP_25-35 3μmol·L^-1 孵育细胞24h ,I_K 电流幅度增加(44.3±5.4)% ,电流密度由(30.4±6.4)pA·PF^-1 增加至(43.8±4.7)pA·PF^-1 ;β-AP_25-3510μmol·L^-1 孵育12h ,I_K 电流幅度增加(69.8±4.1) % ,电流密度增加至(51.6±7.9)pA·PF^-1,呈浓度依赖性;β-AP_25-35引起的I_K 增加对TEA 5mmol·L^-1 敏感;β-AP_25-35上调I_K 的作用主要发生在β-AP_25-355用药后48h内。β-AP_25-35对I_A无显著性影响。结论　β-AP_25-35选择性地增加海马神经元上I_K,这一作用可能与β-AP的神经毒性有关     

Effects of AN-132, a novel antiarrhythmic lidocaine analogue,and of lidocaine on membrane ionic currents of guinea-pig ventricular myocytes

Summary We studied the effects of AN-132 (10, 30 and 100 mol/1), an analogue of lidocaine, on membrane currents and action potentials of single guinea-pig ventricular cells using whole-cell clamp techniques. The effects of lidocaine, an authentic class I antiarrhythmic agent were used for comparative purposes. (1) AN-132 decreased the Na current (I _Na) in a concentration-dependent manner, with a greater efficacy than seen with lidocaine. The concentration of the half maximal inhibition on I _Na (K _d) was (31.7 mol/1), for AN-132 and 94.9 mol/l for lidocaine. (2) AN-132 also decreased the Ca current (I _Ca), concentration-dependently, while lidocaine had only a minor effect on I _Ca. The half maximal inhibition on I _Ca (K _d) was 23.1 mol/l and 27.4 mol/l for AN-132 and lidocaine, respectively. (3) AN-132 decreased the I _K1, in a concentration-dependent manner; lidocaine was without effect. (4) AN-132 increased the unspecified steady state outward current, at positive potentials and depressed the time- and voltage-dependent outward K current (I _K). Lidocaine had no effect on either current. (5) AN-132 shortened the action potential duration (APD), in a concentration-dependent manner, without altering the resting potential. From these findings, we conclude that apart from a potent inhibitory effect on I _Na, AN-132 had a variety of effects on other currents, properties not shared by lidocaine. Such multiple blocking effects on the membrane currents may relate to the alleged potent antiarrhythmic effect of AN-132. Send offprint requests to M. Arita at the above address     

Effect of methamphetamine on potassium and L-type calcium currents in rat ventricular myocytes

The mechanisms of cardiac toxicity caused by methamphetamine (MA) are poorly understood at present. This study was designed to investigate the effects of MA on ionic currents in myocardial cells. The effects of MA on transient outward potassium current (I_to), inward rectifying potassium current (I_K1), and L-type calcium current (I_Ca-L) in isolated rat ventricular myocytes were studied using the whole-cell patch clamp technique. It was demonstrated that MA inhibited the I_to, I_K1, and I_Ca-L in the rat ventricular myocytes concentration-dependently. MA shifted left the I_to steady-state inactivation curve and shifted down the recovery curve, but had no influence on the steady-state activation curve. MA did not affect the I_Ca-L steady-state activation curve or steady-state inactivation curve, but shifted down the recovery curve. We concluded that MA had inhibitory effects on the I_to, I_K1, and I_Ca-L in ventricular myocytes, which might be one of the possible electrophysiological mechanisms of cardiac damage caused by MA.     

Effects of an extract of Ginkgo biloba On the action potential and associated transmembrane ionic currents in mammalian cardiac myocytes: Inhibition of isoproterenol-induced chloride current

Ventricular myocytes of guinea pig heart were used to examine the effects of an extract of Ginkgo biolba (EGb 761) on the action potential and individual transmembrane ionic currents. Elecrophysiological events were recorded using the “whole-cell” configuration of the patch-clamp technique. A systematic analysis of the data revealed that EGb 761 (5-50 μg/ml) did not affect the normal action potential or the various ionic currents involved in its generation; i.e., fast inward sodium current (I_Na), inward calcium currents (I_CaT and I_CaL), delayed outward potassium current (I_K), inward rectifying potassium current (I_K1), and ATP-senstive potassium current (I_K-ATP) evoked by 2,4-dinitrophenol (2,4-DNP). However, EGb 761 (≥5 μg/ml) elicited a pronouced concentration-dependent and reversible inhibiton of isoproternol-induced Cl^? current (I_Cl), the maximal effect being observed at 50 μg/ml. This current may be significantly involved in sympathetic hyperactivity, hypoxia, and ischemia, pathophysiological conditions for which EGb 761 offers therapeutic benefit. The basic mechanism(s) underlying the inhibitory effect of EGb 761 on I_Cl and the constituent(s) of EGb 761 responsible for this action remain to be identified, but it seems clear, from results which showed that neither ginkgolide B (50–500 ng/ml) nor biolobalide (150–1,500 ng/ml) influenced this current, that a terpenoid constituent of EGb 761 is probably not involved.     

Activation of voltage‐gated sodium current and inhibition of erg‐mediated potassium current caused by telmisartan,an antagonist of angiotensin II type‐1 receptor,in HL‐1 atrial cardiomyocytes

Telmisartan (TEL) is a non‐peptide blocker of angiotensin II type‐1 (AT₁) receptor. However, the mechanisms through which this drug interacts directly with ion currents in hearts remain largely unclear. Herein, we aim to investigate the effects of TEL the on ionic currents and membrane potential of murine HL‐1 cardiomyocytes. In whole‐cell recordings, addition of TEL stimulated the peak and late components of voltage‐gated Na⁺ currents (I_Na) with different potencies. The EC₅₀ values required to achieve the stimulatory effect of this drug on peak and late I_Na were 0.2 and 1.2 μmol/L, respectively, and the current‐voltage relationship of peak I_Na shifted toward less‐depolarized potentials during exposure to TEL. Telmisartan not only increased peak I_Na but also prolonged the inactivation time course of late I_Na. Amiodarone (Amio) or ranolazine (Ran), but not angiotensin II, could reverse TEL‐mediated effects. The drug enhanced the recovery rate of I_Na inactivation and exerted an inhibitory effect on erg‐mediated K⁺ and L‐type Ca²⁺ currents. In whole‐cell current‐clamp recordings, addition of the drug resulted in prolongation of the duration of action potentials (APs) in a dose‐dependent manner in HL‐1 cells; Amio or Ran could reverse this increase in AP durations. Telmisartan‐mediated prolongation of AP was attenuated in KCNH2 siRNA‐transfected HL‐1 cells. In cultured smooth muscle cells of the human coronary artery, TEL enhanced I_Na amplitudes and slowed current inactivation. Stimulation by TEL of I_Na in HL‐1 cells did not simply increase current magnitude but altered current kinetics, thereby suggesting state‐dependent activation. Telmisartan may have greater affinity to the open/inactivated state than to the resting state residing in Na_V channels. Collectively, TEL‐mediated stimulation of I_Na and inhibition of I_K(erg) could be an important ionic mechanism underlying the increased cell excitability of HL‐1 cells; these actions, however, cannot be entirely explained by its blockade of AT₁ receptor.     

Electrophysiological characteristics of antiarrhythmic potential of acrophyllidine,a furoquinoline alkaloid isolated from Acronychia halophylla

The antiarrhythmic potential of acrophyllidine, a natural furoquinoline alkaloid isolated from the plant, Acronychia halophylla, has been documented. In the present study, the electrophysiological effects of acrophyllidine in Langendorff‐perfused rat hearts and isolated cardiomyocytes were examined. In isolated rat heart (constant pressure), acrophyllidine suppressed ischemia/reperfusion‐induced polymorphic ventricular tachyarrhythmias with an EC₅₀ value of 4.4 μM. In the perfused whole‐heart model (constant flow), acrophyllidine increased the atrioventricular and His‐Purkinje system conduction intervals, ventricular repolarization time (VRT), and basic cycle length and also prolonged the refractory periods of the AV node, His‐Purkinje system and ventricle. In isolated rat ventricular myocytes, acrophyllidine prolonged the action potential duration (APD) and decreased both the maximal upstroke velocity of depolarization (V_max) and action potential amplitude in a concentration‐dependent manner. Whole‐cell voltage clamp studies show that acrophyllidine blocked the Na⁺ channel (IC₅₀ = 3.6 μM) with a negative‐shift of its voltage‐dependent steady‐state inactivation curve and slowing of its recovery from inactivation. Similarly, Ca²⁺ inward current (I_Ca) was inhibited but to a lesser extent. Acrophyllidine also suppressed the transient outward (I_to) (IC₅₀ equals; 4.5 μM) and the steady‐state outward K⁺ current (I_SS) (IC₅₀ = 3.4 μM). The inhibition of I_to was associated with an acceleration of its rate of inactivation. Additionally, acrophyllidine suppressed I_to in a time‐dependent manner and caused a negative‐shift of the steady‐state inactivation curve and a slowed rate of recovery from inactivation. It is concluded that acrophyllidine blocks Na^+, I_to and I_SS channels and in similar concentrations partly blocks Ca²⁺ channel. These changes alter the electrophysiological properties of the conduction system and may be responsible for the termination of the ischaemia/reperfusion induced ventricular arrhythmias. Drug Dev. Res. 50:170–185, 2000. © 2000 Wiley‐Liss, Inc.     

Effect of antipsychotic drug perphenazine on fast sodium current and transient outward potassium current in rat ventricular myocytes

Antipsychotic drug perphenazine belongs to the phenothiazine group commonly reported to induce ECG changes and tachyarrhythmias. Data about its effect on ionic membrane currents in cardiomyocytes are missing. We analyzed the effect of perphenazine (0.1–100 μM) on fast sodium current I _Na and transient outward potassium current I _to in enzymatically isolated rat right ventricular myocytes by the whole-cell patch-clamp technique at room temperature. Perphenazine reversibly blocked I _Na (reducing its amplitude; IC₅₀ = 1.24 ± 0.10 μM) and I _to (accelerating its apparent inactivation with a slight decrease of its amplitude; IC₅₀ = 38.2 ± 3.5 μM, evaluated from changes of the time integral). The fast time constant of I _to inactivation was significantly decreased in a concentration-dependent manner (IC₅₀ = 30.0 ± 6.6 μM). Both blocks were use and frequency dependent at 3.3 Hz. We conclude that perphenazine causes concentration-, use-, and frequency-dependent block of I _Na and I _to . Computer simulations suggest that perphenazine interacts preferentially with I _Na channels in inactivated states and with I _to channels in both open and open-inactivated states.     

Effect of melamine on potassium currents in rat hippocampal CA1 neurons

As an industrially synthesized chemical, melamine has been applied in a wide range of areas. However, many questions on the adverse effect and toxicity of melamine have been emerged, recently. In this investigation, the cytotoxicity of melamine on PC12 cells was evaluated. Furthermore, the effect of melamine on the transient outward potassium current (I_A) and the delayed rectifier potassium current (I_K) in hippocampal CA1 pyramidal neurons of rat was studied using whole-cell patch-clamp technique. The results showed that melamine-induced cell death in a concentration and time-dependent manner, and produced a concentration-dependent inhibition in amplitudes of I_A and I_K at any concentrations (5 × 10⁻⁴, 5 × 10⁻⁵, and 5 × 10⁻⁶ g/ml). Moreover, at higher concentration (5 × 10⁻⁴ g/ml), melamine had observable effects of the steady-state inactivation of I_A, that is melamine shifted inactivation curve of I_A towards hyperpolarization. The spontaneous firing frequency was increased as well. These results suggest that the regulation of I_A and I_K induced by melamine would make neurons display aberrant firing properties and abnormal neuronal discharge, which could be a possible underlying mechanism for the melamine-induced neurotoxicity.     

Effects of the class III antiarrhythmic drug ambasilide on outward currents in human atrial myocytes

We have studied the inhibitory influence of the class III antiarrhythmic drug ambasilide (LU 47110) on the transient outward current I _to1 and the sustained current T _so following inactivation of I _to1 in human atrial myocytes. The two currents are separated by a mathematical procedure based on the amplitudes and time constants of the biexponential inactivation of the total outward current. The frequency dependence, the recovery from inactivation and the kinetics of activation and inactivation are described. Ambasilide reversibly and concentration dependently inhibited I _to1, I _so and the sodium current I _Na. Concentration required for half maximal inhibition (IC₅₀) for the effects on I _to1 and I _so were 23.3 mol/l and 45.7 mol/l respectively, concentrations shown by others to be effective in terminating and preventing fibrillation in a dog atrial arrhythmia model. Ambasilide not only reduced the amplitude of I _to1 and I _so but also accelerated the time course of inactivation from 14.22 to 6.69 ms and from 202.3 to 87.9 ms respectively. The amplitude of I _to1 showed only a small dependence on stimulation frequency characteristic for human atrial myocytes, whereas I _so was reduced significantly at higher stimulation frequencies. Ambasilide did not change these relationships (0.1–4 Hz) and therefore did not show the reverse use-dependence known from other class III antiarrhythmic agents and which is an important property for a prospective antiarrhythmic drug. The lack of an effect of ambasilide on both steady-state activation and inactivation of I _to1, and the time constant of recovery from inactivation, suggests that ambasilide acts by changing conductance rather than by influencing the gating mechanism. The described characteristics make ambasilide an interesting substance in the group of class III antiarrhythmic drugs.     

Modulation of the delayed K+ current by histamine in guinea pig ventricular myocytes

Summary The effects of histamine on delayed K⁺ current (I_K) were investigated in patch-clamped single guinea pig ventricular myocytes. Histamine increased I_K with a maximal fractional response of 2.7 and a k_d of 9.4 × 10^–7 mol/l. At a concentration of 10^–8 mol/l, histamine did not increase I_K significantly, but increased I_Ca by 52% ± 12%. The voltage-dependence of I_K activation, the reversal potential and the time course of the I_K tail decay were not changed by histamine. Under pretreatment with 10^–4 mol/l of ranitidine, neither histamine (10^–6 mol/l) nor 2-pyridylethylamine (10^–4 mol/l) caused any sizable increase in I_K. When the cell was pretreated with a saturating dose of isoproterenol (10^–6 mol/l), histamine did not additively enhance I_K. The I_K enhancement by 3 × 10^–7 mol/l histamine was partially antagonized by concurrent exposure to 5 × 10^–6 mol/l carbachol. Whereas, use of a higher concentration of histamine (10^–6 mol/l) obscured the inhibitory effect of carbachol. It is concluded that histaminergic action of I_K is attributed exclusively to H₂ receptor-mediated reactions involving G_s protein and adenylate cyclase. Send offprint requests to Y. Habuchi at the above address     

莲心碱对心肌慢反应动作电位及慢内向电流的影响

莲心碱(Lien)10～100μmol/L可浓度依赖性地降低离体兔窦房结(SAN)起搏细胞慢反应动作电位幅度(APA)及零相最大上升速率(V_max),延长窦性周长(SCL),并可明显拮抗Bay K 8644增大SAN起搏细胞及高K⁺诱发的豚鼠乳头肌慢反应动作电位的APA和(V_max)作用。Lien 1～100 μmol/L还可浓度依赖性地抑制犬浦氏纤维慢内向电流(I_si),3和100μmol/L分别使I_si峰值下降14和88%。结果表明Lien具有抗钙作用。