Modulation of sodium current kinetics by chlorpromazine in freshly-isolated striatal neurones of the adult guinea-pig

Patterns of spontaneous magnetoencephalographic activity in patients with schizophrenia

Magnetoencephalography noninvasively measures the magnetic fields produced by the brain. Pertinent research articles from 1993 to 2009 that measured spontaneous, whole-head magnetoencephalography activity in patients with schizophrenia were reviewed. Data on localization of oscillatory activity and correlation of these findings with psychotic symptoms are summarized. Although the variety of measures used by different research groups makes a quantitative meta-analysis difficult, it appears that magnetoencephalography activity in patients may exhibit identifiable patterns, defined by topographic organization and frequency band. Specifically, 11 of the 12 studies showed increased theta (4-8 Hz) and delta (1-4 Hz) band oscillations in the temporal lobes of patients; of the 10 studies that examined the relationship between oscillatory activity and symptomatology, 8 found a positive correlation between temporal lobe theta activity and positive schizophrenic symptoms. Abnormally high frontal delta activity was not seen. These findings are analyzed in comparison with the electroencephalogram literature on schizophrenics, and possible confounds (e.g., medication effects) are discussed. In the future, magnetoencephalography might be used to assist in diagnosis or might be fruitfully used in conjunction with new neuroscience research approaches such as computational modeling, which may be able to link oscillatory activity and cellular-level pathology.

The voltage- and time-dependent blocking effect of trifluoperazine on T lymphocyte Kv1.3 channels

Phenothiazines are well-known calmodulin inhibitors that interact with many receptors and channels including a variety of potassium channels. In this study, we report a blocking effect of trifluoperazine (TFP) on voltage-gated Kv1.3 channels expressed in human T lymphocytes. Application of TFP in the concentration range from 1 to 20 microM reduced the current amplitude to about a half of the control value. The currents were blocked to less than 0.05 of the control value at 50 microM TFP concentration. The blocking effect was accompanied by a substantial increase in the current inactivation rate, whereas the activation rate and the steady-state activation and inactivation were not changed significantly. The blocking effect of TFP was voltage dependent being most potent at +60mV and least potent at -20mV. The blocking effect of TFP on the currents and the recovery from block was time dependent. Other calmodulin antagonists: tamoxifen (TMX) and thioridazine also inhibited the channels at micromolar concentrations. The effects exerted by TMX and thioridazine resembled the inhibitory effect of TFP. The blocking effect of thioridazine was time dependent and appeared to be more potent that the inhibition by TFP and TMX. TFP, TMX and thioridazine inhibited the activity of Kv1.3 channels only when applied extracellularly. The inhibitory effect of all the compounds was reversible. The possible physiological significance of the current inhibition is discussed.

Differential blockade of neuronal voltage-gated Na(+) and K(+) channels by antidepressant drugs

The effects of a range of antidepressants were investigated on neuronal voltage-gated Na(+) and K(+) channels. With the exception of phenelzine, all antidepressants inhibited batrachotoxin-stimulated 22Na(+) uptake, most likely via negative allosteric inhibition of batrachotoxin binding to neurotoxin receptor site-2 on the Na(+) channel. Imipramine also produced a differential action on macroscopic Na(+) and K(+) channel currents in acutely dissociated rat dorsal root ganglion neurons. Imipramine produced a use-dependent block of Na(+) channels. In addition, there was a hyperpolarizing shift in the voltage-dependence of steady-state Na(+) channel inactivation and slowed repriming kinetics consistent with imipramine having a higher affinity for the inactivated state of the Na(+) channel. At higher concentrations, imipramine also blocked delayed-rectifier and transient outward K(+) currents in the absence of alterations to the voltage-dependence of activation or the kinetics of inactivation. These actions on voltage-gated ion channels may underlie the therapeutic and toxic effects of these drugs.

Sodium currents in striatal neurons from dystonic dt(sz) hamsters: altered response to lamotrigine

Dystonic mutant dt(sz) hamsters are a model for paroxysmal dystonia. Handling/stress provoke the dystonic attacks. This phenomenon subsedes with maturation, but can be reinvoked when these animals receive sodium channel blockers such as lamotrigine, suggesting a dysfunction of striatal sodium channels. Voltage-gated fast sodium currents (I(Na(+))) were studied in acutely isolated striatal neurons from healthy and dt(sz) hamsters in whole-cell voltage clamp recordings. The action of lamotrigine was tested on (a) current/voltage relationship, (b) kinetics, and (c) steady-state inactivation and activation. Under control conditions, properties of I(Na(+)) were not different between healthy and dt(sz) neurons. With lamotrigine, however, (a) peak currents were significantly less depressed by the drug in neurons from dt(sz) hamsters as compared to healthy cells, and (b) the steady-state inactivation curve shift of I(Na(+)) was less pronounced in dt(sz) neurons. The results suggest that in dt(sz) hamsters, fast sodium currents in striatal neurons are more resistant to blockade. This sodium channel alteration might be causal for a functional imbalance between input and output structures of the basal ganglia under conditions of compromised I(+)(Na).

Inhibition of human alpha1E subunit-mediated ca2+ channels by the antipsychotic agent chlorpromazine

Chlorpromazine is a neuroleptic antipsychotic agent with a long history of clinical use. Its primary mode of action is thought to be through modulation of monoaminergic inter-neuronal communication; however, its side-effect profile indicates substantial activities in other systems. Recent work has begun to uncover actions of this compound on ion channels. In this light we have investigated the actions of chlorpromazine on the recombinant alpha1E subunit-encoded voltage-sensitive Ca2+ channel (VSCC) that is believed to encode drug-resistant R-type currents found in neurones and other cells. Chlorpromazine produced a dose-dependent antagonism of these channels that was reversed on drug removal. The mean IC50 was close to 10 microM. At this concentration, the level of antagonism observed was dependent on the membrane potential, with greater inhibition being observed at more negative test potentials. Furthermore, chlorpromazine induced substantial changes in the steady-state inactivation properties of alpha1Ebeta3-mediated currents, although it was not seen to elicit a corresponding change in inactivation kinetics. These results are discussed with regard to the possible clinical mechanisms of chlorpromazine actions.

Activation of sodium transport and intracellular sodium lowering by the neuroleptic drug chlorpromazine

Chlorpromazine (CPZ), a commonly used antipsychotic drug, at high concentration was found to reduce significantly the sodium content of both rat (Rattus norvegicus) and toad (Bufo marinus) liver cells. This reduction in intracellular sodium was demonstrated using 22Na+ flux and measurement of cell sodium content. The results suggest that the sodium-lowering effect of CPZ stemmed from a stimulation of sodium transport rather than from an inhibition of sodium influx (i.e., sodium channels), cell damage, or Na+:Na+ exchange. CPZ was found to interfere with the binding of ouabain to the sodium pump, although a simple reduction in sodium pump inhibition did not account for the sodium-lowering effect. CPZ was able to negate the effects of monensin, a sodium ionophore, suggesting a substantial capacity to activate sodium transport. The intracellular sodium-lowering action of CPZ through the activation of sodium transport represents a new property previously undescribed for this drug.

Block of potassium currents in rat isolated sympathetic neurones by tricyclic antidepressants and structurally related compounds

1. The block of K+ currents by the tricyclic antidepressants (TCAs), imipramine and amitriptyline and three structurally related compounds, chlorpromazine, tacrine and carbamazepine was investigated in rat isolated sympathetic neurones by whole-cell voltage-clamp recording. 2. At a concentration of 10 microM, imipramine, amitriptyline and chlorpromazine all blocked the delayed rectifier K+ current (IKv) by about the same extent, 54%, 47% and 53%. Tacrine was less effective (10%) while carbamazepine was ineffective at all concentrations tested. 3. The degree of block by the four effective compounds was relatively independent of the size of the voltage-step. Neither the activation nor the inactivation rates of IKv were altered by the blocking drugs. 4. Concentration-response relationships for imipramine and tacrine showed that imipramine was about 7 fold more potent than tacrine but that the maximum inhibition and the Hill slope were the same for both compounds. 5. Amitriptyline, chlorpromazine and imipramine (at 10 microM) were 2-3 fold more potent at inhibiting the sustained K+ current (mostly IKv) than the transient K+ current (mostly IA). Tacrine, however, was equally effective in blocking both components.

Differential inhibition of a transient K+ current by chlorpromazine and 4-aminopyridine in neurones of the rat dorsal root ganglia

1. K+ currents were recorded from neurones of the newborn rat cultured dorsal root ganglia, by a whole cell variation of the patch-clamp technique. 2. Chlorpromazine (CPZ), a neuroleptic, reversibly reduced the amplitude of the transient K+ current (referred to as 'IT' hereafter) with a dissociation constant (Kd) of 4.5 microM. The inhibition of the delayed rectifier K+ current (IDR) was much less potent (Kd, 120 microM). CPZ (100 microM) had no effect on the inward rectifier K+ current. 3. The blocking action of CPZ on IT was about seven times more potent than that of 4-aminopyridine (4-AP) which had a Kd of 31 microM. The inhibition of IT followed one-to-one binding stoichiometry with both drugs. 4. The decay time course of IT was not affected by CPZ, whereas 4-AP markedly accelerated the decay phase of IT. 5. The steady-state inactivation curve of IT was shifted in the negative direction (about 5 mV) by CPZ, whereas the curve was shifted in the positive direction (about 13 mV) by 4-AP. 6. The recovery from inactivation as measured by a conventional double pulse protocol was described by two exponential components in the control solution. CPZ markedly reduced the first component and slowed down the recovery from inactivation. In contrast, in the presence of 4-AP, the peak amplitude of IT was rather increased by a preceding IT possibly through voltage-dependent unbinding of 4-AP molecules. 7. These results indicate that CPZ has a preferential blocking action on IT and the mechanism underlying this block is markedly different from the mechanism underlying the blocking action of 4-AP.

Kinetic analysis of two types of Na+ channels in rat dorsal root ganglia

1. The gating properties of two types of Na+ channels were studied in neurones isolated from rat dorsal root ganglia using the whole cell variation of the patch electrode voltage-clamp technique. 2. Two types of Na+ currents (INa) were identified on the basis of their sensitivity to tetrodotoxin (TTX). One type was insensitive to TTX (up to 0.1 mM), while the other type was blocked by 1 nM of TTX. Whereas they were both insensitive to 50 microM Cd2+, a high concentration (2 mM) of Co2+ selectively inhibited the TTX-insensitive type. 3. The activation thresholds were about -60 and -40 mV for the TTX-sensitive and the TTX-insensitive INa, respectively. Activation of the TTX-sensitive INa developed with a sigmoidal time course which was described by m3 kinetics, whereas the activation of the TTX-insensitive INa was described by a single exponential function. A deactivation process, as measured by the tail current upon repolarization, followed an exponential decay in either type of INa. 4. The rate constant of activation indicated that under comparable membrane potential conditions, the TTX-insensitive channels open 4-5 times slower than the TTX-sensitive ones upon depolarization. Likewise, the rate constant of inactivation indicated that the TTX-insensitive channels inactivate 3-7 times more slowly than the TTX-sensitive ones upon repolarization. 5. The steady-state activation curve for the TTX-insensitive INa was shifted about 20 mV in the positive direction from that for the TTX-sensitive INa. 6. The steady-state inactivation curve for the TTX-insensitive INa as obtained with a 0.5 s prepulse was shifted about 26 mV in the positive direction from that for the TTX-sensitive INa, indicating a greater availability for the TTX-insensitive INa in depolarized membrane. However, on increasing the duration of prepulse, the inactivation curve for the TTX-insensitive INa, but not for the TTX-sensitive INa, shifted in the negative direction due to an extremely slow inactivation process in the TTX-insensitive INa. Consequently, an overlap between the activation and inactivation curves which causes a steady influx of Na+ (window current) became progressively reduce. 7. The time course of INa decay was best described by a single exponential process in either the TTX-sensitive or TTX-insensitive INa, whereas the development of inactivation and the recovery from inactivation, which were measured by a conventional double-pulse protocol, followed a second order process in either channel type.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopamine receptor subtypes colocalize in rat striatonigral neurons

Dopaminergic neurons of the substantia nigra provide one of the major neuromodulatory inputs to the neostriatum. Recent in situ hybridization experiments have suggested that postsynaptic dopamine receptors are segregated in striatonigral and striatopallidal neurons. We have tested this hypothesis in acutely isolated, retrogradely labeled striatonigral neurons by examining the neuromodulatory effects of selective dopaminergic agonists on Na currents and by probing single-cell antisense RNA populations with dopamine receptor cDNAs. In most of the neurons examined (20/31), the application of the D1 dopamine receptor agonist SKF 38393 reduced evoked whole-cell Na+ current. The D2 agonists quinpirole and bromocriptine had mixed effects; in most neurons (23/42), whole-cell Na+ currents were reduced, but in others (8/42), currents were increased. In cell-attached patch recordings, bath application of SKF 38393 decreased currents as in whole-cell recordings, whereas quinpirole consistently (6/10) enhanced currents--suggesting that D2-like receptors could act through membrane delimited and non-delimited pathways. Changes in evoked current were produced by modulation of peak conductance and modest shifts in the voltage dependence of steady-state inactivation. Antisense RNA probes of dopamine receptor cDNA Southern blots consistently (5/5) revealed the presence of D1, D2, and D3 receptor mRNA in single striatonigral neurons. These findings argue that, contrary to a strict receptor segregation hypothesis, many striatonigral neurons colocalize functional D1, D2, and D3 receptors.

Blockade by trifluoperazine of a Ca(2+)-activated K+ channel in rat hippocampal pyramidal neurons

The effects of trifluoperazine, a phenothiazine derivative, on the large-conductance Ca(2+)-activated K+ channel (BKCa) in dissociated rat hippocampal pyramidal neurons were examined using the inside-out configuration of the patch-clamp technique. The BKCa was activated by 12.6 microM Ca2+ on the internal surface of the membrane patch. The single channel conductance of the BKCa was 244 +/- 17.5 pS (n = 10) in symmetrical solutions of 150 mM K+. Trifluoperazine, applied on the internal surface of the membrane, decreased the open probability of the channel without changing the single channel conductance. The reduction in the open probability was well described by a block of the open state of the channel in a simple sequential model. The apparent dissociation constant (KD) for the reduction was calculated to be 1.4 microM and the Hill coefficient 0.69 at +20 mV. The inhibition was voltage dependent, being more pronounced at depolarized voltages. The voltage dependence enabled us to estimate that the binding site for the agent in the channel lies about half way across the membrane electrical field. It is concluded that trifluoperazine blocks the open state of the BKCa, which is known to provide an outward current for repolarization and afterhyperpolarization of the neuronal action potential. This may result in a decrease in spike intervals during burst firing of neurons.

Ontogenic development of the TTX-sensitive and TTX-insensitive Na+ channels in neurons of the rat dorsal root ganglia

Developmental changes in the sensitivity of neurons to tetrodotoxin (TTX) were studied in relation to the cell size in rat dorsal root ganglia (DRG). Na+ currents were recorded from neurons of various stages of development. Two types of Na+ channels were identified on the basis of their sensitivity to TTX. One type was insensitive to a very high concentration (0.1 mM) of TTX, while the other type was blocked by a low concentration (1 nM) of TTX. These two types of Na+ channels were observed throughout the developmental stages examined from day 17 of gestation and adulthood. Thus, both types of Na+ channels are already established at the early stage of neuronal development and appear to be retained throughout the life-span of the DRG neuron. The concentration-response relationships for the block of TTX-sensitive Na+ current by TTX did not appreciably change during development. Although two types of Na+ channels had strikingly different kinetic properties, the kinetic properties of each channel type were basically similar throughout development. The TTX-sensitive Na+ channels were mainly concentrated in cells with large cell diameters throughout developmental stages examined. These large cells appear to correspond to the 'large-light' cells. On the contrary, the TTX-insensitive Na+ channels were found in smaller diameter cells which may correspond to the 'small-dark' cells. Thus, it is concluded that there are heterogeneous categories of neurons which have Na+ channels with different physiological and pharmacological properties. Since Na+ channels play a pivotal role in the action potential generation, these heterogeneity of DRG neurons appear to be instrumental in integrating the sensory signals.

Primary culture of neurons derived from the adult mammalian brain

A method is described for the isolation and culture of neurons in the adult mammalian brain. The cell could be maintained in primary culture for more than several weeks. Whereas the neurons freshly dissociated from the adult brain did not respond to any of the neurotransmitter substances applied, the neurons regained the ability to respond to a variety of neurotransmitters when cultured. The cultured neurons of the adult mammalian brain may be an excellent model for physiological as well as pharmacological investigations of the central nervous system.