Investigations on contribution of glial inwardly-rectifying K(+) current to membrane potential and ion flux: an experimental and theoretical study.

The inwardly rectifying K(+) current [IK(IR)] allows large inward K(+) currents at potentials negative to K(+) equilibrium potential (EK) and it becomes small outward K(+) currents at those positive to EK. How changes of such currents enriched in glial cells can influence the functions of glial cell, neurons, or both is not clearly defined, although mutations of Kir4.1 channels have been demonstrated to cause serious neurological disorders. In this study, we identified the presence of IK(IR) in human glioma cells (U373 and U87 cells). The amplitude of IK(IR) in U373 cells was subject to inhibition by amitriptyline, arecoline, or BaCl2. The activity of inwardly rectifying K(+) channels was also clearly detected, and single-channel conductance of these channels was calculated to be around 23 pS. Moreover, based on a simulation model derived from neuron-glial interaction mediated by ion flux, we further found out that incorporation of glial IK(IR) conductance into the model can significantly contribute to regulation of extracellular K(+) concentrations and glial resting potential, particularly during high-frequency stimulation. Glial cells and neurons can mutually modulate their expression of ion channels through K(+) ions released into the extracellular space. It is thus anticipated that glial IK(IR) may be a potential target utilized to influence the activity of neuronal and glial cells as well as their interaction.

The preconditioning pulmonary protective effect of volatile isoflurane in acute lung injury is mediated by activation of endogenous iNOS.

PURPOSE: There is still a lack of evidence to support the use of specific anesthetic agents during major operations that could affect the development of postoperative acute lung injury (ALI). This study determined the protective effect of inhaled isoflurane in a rat model of endotoxin-induced ALI. METHODS: Rats were exposed to volatile isoflurane (1.5 % in oxygen) or pure oxygen via a facemask for 2 h. After a 3-h recovery period, rats were reanesthetized and ALI was induced by intratracheal instillation of lipopolysaccharide (LPS, 1 mg/kg in 0.5 ml saline). In some animals, a specific inducible nitric oxide synthase (iNOS) inhibitor, 1400W, (10 mg/kg, i.p.) was administered before exposure to isoflurane. Animals were sacrificed 12 h later for analysis. Pulmonary artery vasomotor function and alveolocapillary permeability were assessed. Expression of iNOS and CD11b, and activity of myeloperoxidase in the lung were analyzed. RESULTS: The maximal relaxation response to acetylcholine was significantly potentiated in rats pretreated with isoflurane. Lung wet-to-dry ratio was reduced in the lung of isoflurane-treated animals. Expression of iNOS and CD11b were attenuated in the lung tissue obtained from rats receiving isoflurane. Furthermore, enzymatic activity of myeloperoxidase was also reduced in the lung preexposed to isoflurane. However, these pulmonary protective effects of isoflurane were significantly abolished by pretreatment with 1400W. CONCLUSION: Pretreatment with volatile isoflurane attenuated inflammatory process in the lung tissue of rats with LPS-induced ALI, and this preconditioning pulmonary protective effect was mainly mediated by activation of endogenous iNOS in the lung.

Contribution of non-inactivating Na+ current induced by oxidizing agents to the firing behavior of neuronal action potentials: experimental and theoretical studies from NG108-15 neuronal cells.

The effects of chemical injury with oxidizing agents on voltage-gated Na+ current (I(Na)) in differentiated NG108-15 neuronal cells were investigated in this study. In whole-cell patch-clamp recordings, the challenge of these cells with t-butyl hydroperoxide (t-BHP; 1 mM) decreased the peak amplitude of I(Na) with no modification in the current-voltage relationship. It caused a slowing of current inactivation, although there was no alteration in the activation time course of I(Na). Cell exposure to t-BHP also increased a non-inactivating I(Na) (I(Na(NI)) elicited by long-lasting ramp pulses. The t-BHP-induced increase of I(Na(NI)) was reversed by a further application of riluzole (10 microM) or oxcarbazepine (10 microM). When I(Na) was elicited by simulated waveforms of action potentials (APs), during exposure to t-BHP, the amplitude of this inward current was diminished, accompanied by a reduction in inactivation/deactivation rate and an increase in current fluctuations. Under current-clamp recordings, addition of t-BHP (0.3 mM) enhanced AP firing in combination with clustering-like activity and sub-threshold membrane oscillations. In the simulation study, when the fraction of non-inactivating Na(v) channels was elevated, the simulated window component of I(Na) in response to a long-lasting ramp pulse was reduced; however, the persistent I(Na) was markedly enhanced. Moreover, when simulated firing of APs was generated from a modeled neuron, changes of AP firing caused by the increased fraction of non-inactivating Na(v) channels used to mimic the t-BHP actions were similar to the experimental observations. Taken together, it is anticipated that the effects of oxidizing agents on I(Na(NI)) could be an important mechanism underlying their neurotoxic actions in neurons or neuroendocrine cells occurring in vivo.

Evidence for aconitine-induced inhibition of delayed rectifier K(+) current in Jurkat T-lymphocytes.

Aconitine (ACO) is a highly toxic diterpenoid alkaloid and known to exert the immunomodulatory action. However, whether it has any effects on ion currents in immune cells remains unknown. The effects of ACO and other related compounds on ion currents in Jurkat T-lymphocytes were investigated in this study. ACO suppressed the amplitude of delayed-rectifier K(+) current (I(K(DR))) in a time- and concentration-dependent manner. Margatoxin (100 nM), a specific blocker of K(V)1.3-encoded current, decreased the I(K(DR)) amplitude in these cells and the ACO-induced inhibition of I(K(DR)) was not reversed by 1-ethyl-2-benzimidazolinone (30 µM) or nicotine (10 µM). The IC(50) value for ACO-mediated inhibition of I(K(DR)) was 5.6 µM. ACO accelerated the inactivation of I(K(DR)) with no change in the activation rate of this current. Increasing the ACO concentration not only reduced the I(K(DR)) amplitude, but also accelerated the inactivation time course of the current. With the aid of minimal binding scheme, the inhibitory action of ACO on I(K(DR)) was estimated with a dissociation constant of 6.8 µM. ACO also shifted the inactivation curve of I(K(DR)) to a hyperpolarized potential with no change in the slope factor. Cumulative inactivation for I(K(DR)) was enhanced in the presence of ACO. In Jurkat cells incubated with amiloride (30 µM), the ACO-induced inhibition of I(K(DR)) remained unaltered. In RAW 264.7 murine macrophages, ACO did not modify the kinetics of I(K(DR)), although it suppressed I(K(DR)) amplitude. Taken together, these effects can significantly contribute to its action on functional activity of immune cells if similar results are found in vivo.

Functional role of the activity of ATP-sensitive potassium channels in electrical behavior of hippocampal neurons: experimental and theoretical studies.

ATP-sensitive K(+) (K(ATP)) channels are distributed in a variety of cell types, including hippocampal neurons. These channels provide a link between electrical activity of cell membranes and cellular metabolism. The activity of K(ATP) channels in hippocampal H19-7 neurons treated with or without short interfering RNAs (siRNAs) directed against Kir6.2 mRNA was investigated in this study. In single-channel recordings, cell exposure to diazoxide (30 µM) significantly prolonged the mean open time of K(ATP) channels; however, neither closed-time kinetics nor the single-channel conductance of the channel was altered by this compound. However, in cells transfected with Kir6.2 siRNAs, diazoxide-stimulated activity of K(ATP) channels was abolished. Based on single-channel recordings, the activity of K(ATP) channels was mathematically constructed in a Markovian manner. The simulated activity of single K(ATP) channels was incorporated in a modeled hippocampal neuron to assess how any changes in K(ATP)-channel activity affect burst firing of action potentials (APs). The modeled neuron was adopted from the model of Xu and Clancy (2008). Specifically, to mimic the action of diazoxide, the baseline value of open time (τ(bas)) of K(ATP) channels was arbitrarily elevated, while varying number of active channels (N(O)) was set to simulate electrical behavior of Kir6.2 siRNAs-transfected cells. The increase of either N(O) or τ(bas) depressed membrane excitability of modeled neuron. Fast-slow analysis of AP bursting from this modeled neuron also revealed that the increased K(ATP)-channel activity shifted the voltage nullcline in an upward direction, thereby leading to a reduction of the repetitive spike regime. Taken together, it is anticipated that the increased activity of K(ATP) channels caused by increasing N(O) or τ(bas) contributes to or is responsible for burst firing of APs in hippocampal neurons if similar results occur in vivo.

Inhibitory action of methadone and its metabolites on erg-mediated K+ current in GH3 pituitary tumor cells.

Methadone (Mtd) is a widely used opioid drug associated with the side effect of hyperprolactinemia. The mechanism of how Mtd induces prolactin secretion remains unclear. The effects of Mtd and its two main metabolites (EDDP: (±)-2-ethyl-1,5-dimethyl-3,3-diphenylpyrrolinium percholarate and EMDP: 2-ethyl-5-methyl-3,3-dipnehyl-1-pyrroline) on ion currents were investigated in GH3 pituitary tumor cells. Hyperpolarization-elicited K+ currents in GH3 cells bathed in a high-K(+), Ca(2+)-free solution were studied to evaluate the effects of Mtd and other related compounds on the ether-à-go-go-related-gene (erg) K(+) current (I(K(erg))). Mtd suppressed the amplitude of I(K(erg)) in a concentration-dependent manner with an IC(50) value of 10.4 µM. With the aid of a minimal binding scheme, the inhibitory action of Mtd on I(K(erg)) was estimated with a dissociation constant of 8.2 µM. Mtd tended to increase the rate of I(K(erg)) deactivation in a voltage-dependent fashion. EDDP (10 µM) had no effect on I(K(erg)), while EMDP (10µM) slightly suppressed it. In GH3 cells incubated with naloxone (30 µM), the Mtd-induced inhibition of I(K(erg)) remained unaltered. Under cell-attached voltage-clamp recordings, Mtd increased the frequency of spontaneous action currents with no change in current amplitude. Similarly, Mtd can suppress I(K(erg)) in differentiated NG108-15 cells; dynorphin A(1-13) did not reverse Mtd-induced inhibition of I(K(erg)). This study shows that Mtd has a depressant effect on I(K(erg)), and suggests its ability to affect membrane excitability and prolactin secretion. The cyclization of Mtd, in which EDDP and EMDP are formed, tends to be critical in removal of the Mtd binding to erg K+ channel.

Effects of transient receptor potential-like current on the firing pattern of action potentials in the Hodgkin-Huxley neuron during exposure to sinusoidal external voltage.

Transient receptor potential vanilloid-1 (TRPV1) channels play a role in several inflammatory and nociceptive processes. Previous work showed that magnetic electrical field-induced antinociceptive [corrected] action is mediated by activation of capsaicin-sensitive sensory afferents. In this study, a modified Hodgkin-Huxley model, in which TRP-like current (ITRP) was incorporated, was implemented to predict the firing behavior of action potentials (APs), as the model neuron was exposed to sinusoidal changes in externally-applied voltage. When model neuron is exposed to low-frequency sinusoidal voltage, increased maximal conductance of ITRP can enhance repetitive bursts of APs accompanied by a shortening of inter-spike interval (ISI) in AP firing. The change in ISIs with number of interval is periodic with the phase-locking. In addition, increased maximal conductance of ITRP can abolish chaotic pattern of AP firing in model neuron during exposure to high-frequency voltage. The ISI pattern is converted from irregular to constant, as maximal conductance of ITRP is increased under such high-frequency voltage. Our simulation results suggest that modulation of TRP-like channels functionally expressed in small-diameter peripheral sensory neurons should be an important mechanism through which it can contribute to the firing pattern of APs.

Effects of ranolazine, a novel anti-anginal drug, on ion currents and membrane potential in pituitary tumor GH(3) cells and NG108-15 neuronal cells.

Ranolazine, a piperazine derivative, is currently approved for the treatment of chronic angina. However, its ionic mechanisms in other types of cells remain unclear, although it is thought to be a selective blocker of late Na(+) current. This study was conducted to evaluate the possible effects of ranolazine on Na(+) current (I(Na)), L-type Ca(2+) current (I(Ca,L)), inwardly rectifying K(+) current (I(K(IR))), delayed-rectifier K(+) current (I(K(DR))), and Ca(2+)-activated K(+) current (I(K(Ca))) in pituitary tumor (GH(3)) cells. Ranolazine depressed the transient and late components of I(Na) with different potencies. This drug exerted an inhibitory effect on I(K(IR)) with an IC(50) value of 0.92 microM, while it slightly inhibited I(K(DR)) and I(K(Ca)). It shifted the steady-state activation curve of I(K(IR)) to more positive potentials with no change in the gating charge of the channel. Ranolazine (30 microM) also reduced the activity of large-conductance Ca(2+)-activated K(+) channels in HEK293T cells expressing alpha-hSlo. Under current-clamp conditions, low concentrations (e.g., 1 microM) of ranolazine increased the firing of action potentials, while at high concentrations (>or=10 microM), it diminished the firing discharge. The exposure to ranolazine also suppressed I(Na) and I(K(IR)) effectively in NG108-15 neuronal cells. Our study provides evidence that ranolazine could block multiple ion currents such as I(Na) and I(K(IR)) and suggests that these actions may contribute to some of the functional activities of neurons and endocrine or neuroendocrine cells in vivo.

The mechanism of the actions of oxaliplatin on ion currents and action potentials in differentiated NG108-15 neuronal cells.

Oxaliplatin (OXAL) is a platinum-based chemotherapeutic agent which is effective against advanced or metastatic gastrointestinal cancer. However, the mechanisms responsible for the development of the neuropathy induced by this agent remain unclear. In this study, we attempted to evaluate the possible effects of OXAL on ion currents and action potentials (APs) in NG108-15 cells differentiated with dibutyryl cyclic-AMP. Application of OXAL decreased the peak amplitude of voltage-gated Na(+) current (I(Na)) with no change in the overall current-voltage relations of the currents. This agent also produced a concentration-dependent slowing of I(Na) inactivation. A further application of ranolazine reversed OXAL-induced slowing of I(Na) inactivation. Unlike ranolazine or riluzole, OXAL had no effect on persistent I(Na) elicited by long ramp pulses. OXAL (100 microM) also had little or no effect on the peak amplitude of L-type Ca(2+) currents in NG108-15 cells, while it suppressed delayed-rectifier K(+) current. In current-clamp recordings, OXAL alone reduced the amplitude of APs; however, it did not alter the duration of APs. However, after application of tefluthrin, OXAL did increase the duration of APs. Moreover, OXAL decreased the peak amplitude of I(Na) with a concomitant reduction of current inactivation in HEK293T cells expressing SCN5A. The effects of OXAL on ion currents presented here may contribute to its neurotoxic actions in vivo.

Analytical studies of rapidly inactivating and noninactivating sodium currents in differentiated NG108-15 neuronal cells.

The rapidly inactivating (I(Naf)) and noninactivating Na(+) currents (I(Na)(()(NI)())) were characterized in NG108-15 neuronal cells differentiated with dibutyryl cyclic AMP in this study. Standard activation and inactivation protocols were used to evaluate the steady-state and kinetic properties of the I(Naf) present in these cells. The voltage protocols with a slowly depolarizing ramp were implemented to examine the properties of I(Na)(()(NI)()). Based on experimental data and computer simulations, a window component of the rapidly inactivating sodium current (I(Naf)(()(W)())) was also generated in response to the slowly depolarizing ramp. The I(Naf)(()(W)()) was subtracted from I(Na)(()(NI)()) to yield the persistent Na(+) current (I(Na)(()(P)())). Our results demonstrate the presence of I(Na)(()(P)()) in these cells. In addition to modifying the steady-state inactivation of I(Naf), ranolazine or riluzloe could be effective in blocking I(Naf)(()(W)()) and I(Na)(()(P)()). The ability of ranolazine and riluzole to suppress I(Na)(()(P)()) was greater than their ability to inhibit I(Naf)(()(W)()). In current-clamp recordings, current-induced voltage oscillations were applied to elicit action potentials (APs) through a gradual transition between spontaneous depolarization and upstroke. Ranolazine or riluzole at a concentration of 3 microM then effectively suppressed the AP firing generated by oscillatory changes in membrane current. The data suggest that a small rise in I(Na)(()(NI)()) facilitates neuronal hyper-excitability due the decreased threshold of AP initiation. The underlying mechanism of the inhibitory actions of ranolazine or riluzole on membrane potential in neurons or neuroendocrine cells in vivo may thus be associated with their blocking of I(Na)(()(NI)()).

Underlying mechanism of actions of tefluthrin, a pyrethroid insecticide, on voltage-gated ion currents and on action currents in pituitary tumor (GH3) cells and GnRH-secreting (GT1-7) neurons.

Tefluthrin is a synthetic pyrethroid and involved in acute neurotoxic effects. How this compound affects ion currents in endocrine or neuroendocrine cells remains unclear. Its effects on membrane ion currents in pituitary tumor (GH3) cells and in hypothalamic (GT1-7) neurons were investigated. Application of Tef (10 microM) increased the amplitude of voltage-gated Na+ current (INa), along with a slowing in current inactivation and deactivation in GH3 cells. The current-voltage relationship of INa was shifted to more negative potentials in the presence of this compound. Tef increased INa with an EC50 value of 3.2 +/- 0.8 microM. It also increased the amplitude of persistent INa. Tef reduced the amplitude of L-type Ca2+ current. This agent slightly inhibited K+ outward current; however, it had no effect on the activity of large-conductance Ca2+-activated K+ channels. Under cell-attached voltage-clamp recordings, Tef (10 microM) increased amplitude and frequency of spontaneous action currents, along with appearance of oscillatory inward currents. Tef-induced inward currents were suppressed after further application of tetrodotoxin, riluzole or ranolazine. In GT1-7 cells, Tef also increased the amplitude and frequency of action currents. Taken together, the effects of Tef and its structural related pyrethroids on ion currents can contribute to the underlying mechanisms through which they affect endocrine or neuroendocrine function in vivo.

Propofol alone versus propofol in combination with meperidine for sedation during colonoscopy.

BACKGROUND: Despite the increasing popularity of propofol for sedation in colonoscopy, the optimal regimen is still controversial. Both propofol alone and propofol in combination with meperidine are frequently used during colonoscopy, but the impact of adding meperidine has not been evaluated. This study aimed to investigate if adding meperidine to propofol offers any advantage in terms of patient tolerance, recovery time, and postcolonoscopy discomforts. METHOD: Consecutive patients admitted to the physical checkup department of our hospital were randomized to receive either meperidine plus propofol (combination group, n=100) or propofol alone (propofol group, n=100) for sedated colonoscopy. The patients' tolerance and postcolonoscopy discomforts (pain, bloating, dizziness, and nausea/vomiting) were assessed with a 0-10 visual analog scale. The recovery times were assessed with 5-minute and 10-minute Aldrete scores. RESULTS: The dose of propofol was less in the combination group than the propofol group (129.80+/-37.93 mg vs. 147.90+/-47.85, mean+/-SD, P=0.003). The endoscopists, anesthetists, and nurses all rated patients' tolerance in favor of the combination group than the propofol group (mean+/-SD, endoscopists, 9.17+/-1.23 vs. 8.49+/-1.60, P=0.001; anesthetists, 9.21+/-1.08 vs. 8.63+/-1.37, P=0.001; nurses, 9.18+/-1.34 vs. 8.71+/-1.47, P=0.019, respectively). Patients in the combination group recovered earlier than the placebo group (5-min Aldrete scores: 9.48+/-1.09 vs. 9.05+/-1.32, mean+/-SD, P=0.013; short intervals to speak: 4.29+/-4.05 min vs. 6.30+/-5.22 min, P=0.003; and departure: 18.62+/-5.28 min vs. 20.28+/-5.68 min, P=0.034). There was also less abdominal bloating in the combination group after colonoscopy (1.23+/-1.79 vs. 2.19+/-2.12, mean+/-SD, P=0.004). Incidences of hypoxemia, hypotension, and overall satisfaction scores were comparable between the 2 groups. CONCLUSIONS: For sedated colonoscopy, propofol in combination with meperidine is better than propofol alone in improving patients' tolerance and recovery.

Potent activation of large-conductance Ca2+-activated K+ channels by the diphenylurea 1,3-bis-[2-hydroxy-5-(trifluoromethyl)phenyl]urea (NS1643) in pituitary tumor (GH3) cells.

1,3-Bis-[2-hydroxy-5-(trifluoromethyl)phenyl]urea (NS1643) is reported to be an activator of human ether-à-go-go-related gene current. However, it remains unknown whether it has any effects on other types of ion channels. The effects of NS1643 on ion currents and membrane potential were investigated in this study. NS1643 stimulated Ca(2+)-activated K(+) current [I(K(Ca))] in a concentration-dependent manner with an EC(50) value of 1.8 microM in pituitary tumor (GH(3)) cells. In inside-out recordings, this compound applied to the intracellular side of the detached channels stimulated large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels with no change in single-channel conductance. It shifted the activation curve of BK(Ca) channels to less depolarized voltages without altering the gating charge of the channels. NS1643-stimulated channel activity depended on intracellular Ca(2+), and mean closed time during exposure to NS1643 was reduced. NS1643 (3 microM) had little or no effect on peak amplitude of ether-à-go-go-related gene-mediated K(+) current evoked by membrane hyperpolarization, although it increased the amplitude of late-sustained components of K(+) inward current, which was suppressed by paxilline but not by azimilide. NS1643 (3 microM) had no effect on L-type Ca(2+) current. This compound reduced repetitive firing of action potentials, and further application of paxilline attenuated its decrease in firing rate. In addition, NS1643 enhanced BK(Ca)-channel activity in human embryonic kidney 293T cells expressing alpha-hSlo. In summary, we clearly show that NS1643 interacts directly with the BK(Ca) channel to increase the amplitude of I(K(Ca)) in pituitary tumor (GH(3)) cells. The alpha-subunit of the channel may be a target for the action of this small compound.

Time-dependent block of ultrarapid-delayed rectifier K+ currents by aconitine, a potent cardiotoxin, in heart-derived H9c2 myoblasts and in neonatal rat ventricular myocytes.

Aconitine (ACO), a highly toxic diterpenoid alkaloid, is recognized to have effects on cardiac voltage-gated Na(+) channels. However, it remains unknown whether it has any effects on K(+) currents. The effects of ACO on ion currents in differentiated clonal cardiac (H9c2) cells and in cultured neonatal rat ventricular myocytes were investigated in this study. In H9c2 cells, ACO suppressed ultrarapid-delayed rectifier K(+) current (I(Kur)) in a time- and concentration-dependent fashion. The IC(50) value for ACO-induced inhibition of I(Kur) was 1.4 microM. ACO could accelerate the inactivation of I(Kur) with no change in the activation time constant of this current. Steady-state inactivation curve of I(Kur) during exposure to ACO could be demonstrated. Recovery from block by ACO was fitted by a single-exponential function. The inhibition of I(Kur) by ACO could still be observed in H9c2 cells preincubated with ruthenium red (30 microM). Intracellular dialysis with ACO (30 microM) had no effects on I(Kur). I(Kur) elicited by simulated action potential (AP) waveforms was sensitive to block by ACO. Single-cell Ca(2+) imaging revealed that ACO (10 microM) alone did not affect intracellular Ca(2+) in H9c2 cells. In cultured neonatal rat ventricular myocytes, ACO also blocked I(Kur) and prolonged AP along with appearance of early afterdepolarizations. Multielectrode recordings on neonatal rat ventricular tissues also suggested that ACO-induced electrocardiographic changes could be associated with inhibition of I(Kur). This study provides the evidence that ACO can produce a depressant action on I(Kur) in cardiac myocytes.

Contribution of slowly inactivating potassium current to delayed firing of action potentials in NG108-15 neuronal cells: experimental and theoretical studies.

The properties of slowly inactivating delayed-rectifier K+ current (I(K)(dr)) were investigated in NG108-15 neuronal cells differentiated with long-term exposure to dibutyryl cyclic AMP. Slowly inactivating I(K)(dr) could be elicited by prolonged depolarizations from -50 to +50 mV. These outward K+ currents were found to decay at potentials above -20 mV, and the decay became faster with greater depolarization. Cell exposure to aconitine resulted in the reduction of I(K)(dr) amplitude along with an accelerated decay of current inactivation. Under current-clamp recordings, a delay in the initiation of action potentials (APs) in response to prolonged current stimuli was observed in these cells. Application of aconitine shortened the AP initiation in combination with an increase in both width of spike discharge and firing frequency. The computer model, in which state-dependent inactivation of I(K)(dr) was incorporated, was also implemented to predict the firing behavior present in NG108-15 cells. As the inactivation rate constant of I(K)(dr) was elevated, the firing frequency was progressively increased along with a shortening of the latency for AP appearance. Our theoretical work and the experimental results led us to propose a pivotal role of slowly inactivating I(K)(dr) in delayed firing of APs in NG108-15 cells. The results also suggest that aconitine modulation of I(K)(dr) gating is an important molecular mechanism through which it can contribute to neuronal firing.