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Z W Li

Publications and source records attributed to Z W Li.

At least 37 records · Page 2Linked to original sources
PubMed1999

Bis(7)-tacrine, a novel dimeric AChE inhibitor, is a potent GABA(A) receptor antagonist.

Heptylene-linked bis-(9-amino-1,2,3,4-tetrahydroacridine) (bis(7)-tacrine) is a potential palliative therapeutic agent for Alzheimer's disease (AD), on the basis of its superior acetylcholinesterase (AChE) inhibition and memory-enhancing potency relative to tacrine. In this study we report that bis(7)-tacrine exhibits a potentially complementary central nervous system action, antagonism of GABA(A) receptor function. Bis(7)-tacrine displaced [3H]muscimol from rat brain membranes with an apparent Ki of 6.0 microM; tacrine and physostigmine were shown to be 18 and 170 times less potent, respectively. In whole-cell patch-clamp recordings, bis(7)-tacrine inhibited GABA-induced inward current with an IC50 of 5.6 microM, and shifted the GABA concentration-response curve to the right in a parallel manner. These results suggest that bis(7)-tacrine is a competitive antagonist of the GABA(A) receptor.

Alzheimer Disease↗
PubMed1999

Enhancement of GABA-activated current by muscarine in rat dorsal root ganglion neurons.

The modulation of GABA-gated ion channel responses to GABA, pentobarbital and diazepam by muscarine was studied in freshly isolated rat dorsal root ganglion neurons using a whole-cell patch-clamp technique. Muscarine enhanced current activated by 5 microM GABA dose-dependently with an EC50 of 40 +/- 2 microM. This potentiation was not blocked by pirenzepine, gallamine and atropine, the specific and non-specific muscarinic receptor antagonists. Muscarine shifted the GABA dose-response curve to the left, with the GABA EC50 decreased from 45 +/- 2 to 13 +/- 2 microM. The maximal response to GABA was suppressed to 89.3 +/- 4.6% as compared with the control (100%) by 80 microM muscarine. Muscarine potentiated GABA (1-100 microM)-activated current in a voltage-independent manner. Muscarine shifted the dose-response curve for pentobarbital enhancement of GABA-activated current to the left, and the enhancement of GABA-activated current by muscarine was additive to that of pentobarbital over all pentobarbital concentrations. Muscarine shifted the dose-response curve for diazepam (1-100 nM) enhancement of GABA-activated current to the left. However, muscarine attenuated the facilitatory effect of saturating concentrations of diazepam (> 100 nM). The potentiating effect of muscarine was blocked by 1 nM ethyl-beta-carboline-3-carboxylate, the inverse agonist of benzodiazepine receptors. These results suggest that GABA-gated ion channel responses to GABA and pentobarbital were potentiated by muscarine and the binding site(s) for muscarine might be related to those for diazepam.

Acetylcholine↗
PubMed1999

JNK2 and IKKbeta are required for activating the innate response to viral infection.

Viral infection or double-stranded (ds) RNA induce interferons (IFN) and other cytokines. Transcription factors mediating IFN induction are known, but the signaling pathways that regulate them are less clear. We now describe two such pathways. The first pathway leading to NF-kappaB depends on the dsRNA-responsive protein kinase (PKR), which in turn activates IKB kinase (IKK) through the IKKbeta subunit. The second viral-and dsRNA-responsive pathway is PKR independent and involves Jun kinase (JNK) activation leading to stimulation of AP-1. Both IKKbeta and JNK2 are essential for efficient induction of type I IFN and other cytokines in response to viral infection or dsRNA. This study establishes a general role for these kinases in activation of innate immune responses.

3T3 Cells↗
PubMed1999

RINm5f cells express inactivating BK channels whereas HIT cells express noninactivating BK channels.

Large-conductance Ca2+- and voltage-activated BK-type K+ channels are expressed abundantly in normal rat pancreatic islet cells and in the clonal rat insulinoma tumor (RINm5f) and hamster insulinoma tumor (HIT) beta cell lines. Previous work has suggested that the Ca2+ sensitivity of BK channels in RIN cells is substantially less than that in HIT cells, perhaps contributing to differences between the cell lines in responsiveness to glucose in mediating insulin secretion. In both RIN cells and normal pancreatic beta cells, BK channels are thought to play a limited role in responses of beta cells to secretagogues and in the electrical activity of beta cells. Here we examine in detail the properties of BK channels in RIN and HIT cells using inside-out patches and whole cell recordings. BK channels in RIN cells exhibit rapid inactivation that results in an anomalous steady-state Ca2+ dependence of activation. In contrast, BK channels in HIT cells exhibit the more usual noninactivating behavior. When BK inactivation is taken into account, the Ca2+ and voltage dependence of activation of BK channels in RIN and HIT cells is essentially indistinguishable. The properties of BK channel inactivation in RIN cells are similar to those of inactivating BK channels (termed BKi channels) previously identified in rat chromaffin cells. Inactivation involves multiple, trypsin-sensitive cytosolic domains and exhibits a dependence on Ca2+ and voltage that appears to arise from coupling to channel activation. In addition, the rates of inactivation onset and recovery are similar to that of BKi channels in chromaffin cells. The charybdotoxin (CTX) sensitivity of BKi currents is somewhat less than that of the noninactivating BK variant. Action potential voltage-clamp waveforms indicate that BK current is activated only weakly by Ca2+ influx in RIN cells but more strongly activated in HIT cells even when Ca2+ current magnitude is comparable. Concentrations of CTX sufficient to block BKi current in RIN cells have no effect on action potential activity initiated by glucose or DC injection. Despite its abundant expression in RIN cells, BKi current appears to play little role in action potential activity initiated by glucose or DC injection in RIN cells, but BK current may play an important role in action potential repolarization in HIT cells.

Action Potentials↗
PubMed1999

Inhibition by baclofen of NMDA-activated current in rat dorsal root ganglion neurons.

AIM: To explore the modulatory effect of baclofen on NMDA-activated current in rat dorsal root ganglion (DRG) neurons. METHODS: Whole-cell patch-clamp technique was used to record NMDA-activated current in isolated DRG neurons. Drugs were applied by rapid solution exchange. RESULTS: Preapplication of baclofen 1-100 mumol.L-1 induced a concentration-dependent inhibition of the inward NMDA-activated current markedly. NMDA (100 mumol.L-1)-activated current was inhibited by 52% +/- 14% (n = 11, P < 0.01) by preapplication of baclofen 100 mumol.L-1. The inhibitory effect of baclofen was reversible, and was removed by saclofen 100 mumol.L-1, which was a selective antagonist of GABAB receptor. CONCLUSION: Preapplication of baclofen exerts an inhibitory effect on NMDA-activated current in the primary sensory neurons.

Animals↗
PubMed1998

Inactivating BK channels in rat chromaffin cells may arise from heteromultimeric assembly of distinct inactivation-competent and noninactivating subunits.

Inactivating and noninactivating variants of large-conductance, Ca2+-dependent, voltage-dependent BK-type channels are found in rat chromaffin cells and are largely segregated into different cells. Here we test the hypothesis that, within the population of cells that express inactivating BK current (BKi current), the BKi channels are largely heteromultimers composed of inactivation-competent subunits (bk(i)) and noninactivating subunits (bk(s)). Several independent types of evidence support this view. The gradual removal of inactivation by trypsin is consistent with the idea that in most cells and patches there are, on average, about two to three inactivation domains per channel. In addition, several aspects of blockade of BKi current by charybdotoxin (CTX) are consistent with the idea that BKi channels contain differing numbers (one to four) of relatively CTX-resistant bk(i) subunits. Finally, the frequency of occurrence of noninactivating BKs channels in patches with predominantly inactivating BKi channels is consistent with the binomial expectations of random, independent assembly of two distinct subunits, if most cells have, on average, about two to three bk(i) subunits per channel. These results suggest that the phenotypic properties of BKi currents and the resulting cellular electrical excitability may exhibit a continuum of behavior that arises simply from the differential expression of two distinct subunits.

Animals↗
PubMed1998

Hypersensitivity to seizures in beta-amyloid precursor protein deficient mice.

Secreted forms of the beta-amyloid precursor protein (beta-APP) have neuroprotective properties in vitro and may be involved in the containment of neuronal excitation. To test whether loss of secreted forms of beta-APP (sAPPs) may enhance excitotoxic responses, we injected mice homozygous for a targeted mutation of the beta-APP gene (beta-APPDelta/Delta) intraperitoneally with kainic acid. We found that in these mice, kainic acid induced seizures initiated earlier, and acute mortality was enhanced compared to isogenic wild-type mice independently from the callosal agenesis phenotype observed to occur at increased frequency in APP mutant mice. Expression of c-fos in cortex and cingulate gyrus was enhanced in beta-APPDelta/Delta mice, although the amount of structural damage and apoptosis in the hippocampal pyramidal cell layer and cortex was similar to that of controls. When cerebellar granule cell cultures and cortical neuronal cultures were challenged with glutamate receptor agonists, the rates of cell death and apoptosis of beta-APPDelta/Delta mice were indistinguishable from those of controls. Therefore, deficiency of sAPPs causes facilitation of seizure activity in the absence of enhanced cell death. Since enhanced seizures were observed also in mice homozygous for a deletion of the entire beta-APP gene, this phenotype results from a loss of APP rather than from a dominant effect of APPDelta.

Amyloid beta-Protein Precursor↗
PubMed1998

[Inhibitory effects of clonidine on GABA-activated currents in rat DRG neurons].

Whole-cell patch-clamp recordings were performed on neurons from freshly isolated rat dorsal root ganglion (DRG) to investigate modulatory effects of clonidine, an alpha 2-adrenoceptor agonist, on GABA-activated currents. In the majority of the neurons examined (72/75), GABA (10(-6)-10(-3) mol/L) induced a concentration-dependent inward current, which could be blocked by bicuculine (10(-4)-10(-5) mol/L). In 51 out of 72 cells, pretreatment with different dosages of clonidine (10(-8)-10(-4) mol/L) decreased the GABA (10(-4) mol/L)-activated current by 8.5%, 19.0%, 33.4%, 44.4% and 40.3%, respectively, while clonidine itself only induced a slight inward current in a few cells (12/72). The inhibitory action of clonidine blockable by yohimbine (10(-4) mol/L) was voltage-independent and did not change the membrane conductance during the activation of GABAA receptor. Unlike NA, (-)-isoproternol (10(-4)-10(-5) mol/L) exerted no effect on GABA-activated currents. Intracellular application of H-7 (10(-4) mol/L) via micropipette resulted in a significant blockade of clonidine inhibition (19/20) except one cell showing only a slight inhibition (11.2%). The results suggest that the inhibitory effect of clonidine on GABA-activated currents in DRG neurons might involve phosphorylation of GABAA receptor following activation of alpha 2-adrenoceptor through a mechanism of intracellular transduction.

Adrenergic alpha-Agonists↗
PubMed1998

[Modulation of bradykinin on ATP-activated currents in isolated rat DRG neurons].

Modulation of bradykinin (BK) on ATP-activated membrane currents in the isolated rat dorsal root ganglion (DRG) neurons was investigated using whole-cell patch-clamp technique. In 56 neurons examined, BK (10(-6)-10(-4) mol/L)-induced responses were as follows: (1) inward current (40/56); (2) outward current (7/56); (3) no responses (9/56). In the majority of the neurons examined, ATP (10(-6)-10(-3) mol/L) activated a concentration-dependent inward current with obvious desensitization. ATP-activated current was potentiated markedly by preapplication of BK. The enhancement of BK was dependent on the concentration of BK and ATP. It was found that BK potentiated the peak value of ATP-activated currents predominately while the steady state value was not affected obviously. The onset of BK potentiation of ATP-activated currents needed preincubation of BK at least for 30 s and the time of the enhancement lasted over 20 min. The results suggest that BK may play a role in the facilitation of the excitatory effect of ATP on primary sensory neurons.

Adenosine Triphosphate↗
PubMed1998

[Inhibition of GABA-activated currents in isolated rat DRG neurons by bradykinin].

In the present paper, the modulation of GABA-activated currents by bradykinin (BK) was studied in DRG neurons freshly isolated from rat using whole-cell patch-clamp techniques. Among the neurons (n = 34) responding to GABA, 27 were sensitive to BK. Pre-application of BK, eliciting an inward current alone, inhibited GABA-activated current markedly. For example, 10(-6) mol/L BK suppressed GABA-activated current by about 30%. BK shifted the GABA dose-response curve downward obviously and depressed the maximal response to GABA by 1/3 or more while the Kd value was unchanged. The results suggest that BK inhibits GABA-activated current noncompetitively in rat DRG neurons.

Animals↗
PubMed1998

[Inhibition by SKF38393 of GABA-activated currents in rat DRG neurons].

Experiments were performed on neurons freshly isolated from rat DRG using whole-cell patch-clamp techniques. The majority of the neurons examined were sensitive to GABA (60/70) in the concentration range from 10(-6) to 10(-3) mol/L, showing obvious desensitization. In the 60 GABA-sensitive cells, responses induced by selective agonist of dopamine D1 receptor SKF38393 [(+/-) SKF38393HCL] manifested three types: (1) outward current (7/60); (2) inward current (5/60) and (3) no detectable response (48/60). As compared with GABA-activated current, the amplitude of SKF38393-activated current are smaller and showed no apparent desensitization. When the neurons were treated with SKF38393 prior to application of GABA for 30 s, the GABA-activated current in majority of the cells (53/60) was inhibited, while the remaining six showed no effect. The effect of SKF38393 was dose dependent. That is, with SKF38393 at concentration of 10(-7), 10(-6), 10(-5) and 10(-4) mol/L, the GABA-activated current was inhibited by (24.8 +/- 2.6)% (n = 7), (26.8 +/- 1.5)% (n = 7), (35.6 +/- 1.2)% (n = 8) and (45.6 +/- 2.3)% (n = 8) respectively. By intracellular application of 10(-4) mol/L H-7, a potent inhibitor of protein kinase, the inhibitory effect of SKF38393 was abolished completely, a results suggesting that the inhibition by SKF38393 of the GABA-activated current might be a result of intracellular phosphorylation of GABAA receptor.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1997

Modulation by adenosine of GABA-activated current in rat dorsal root ganglion neurons.

1. The modulation by adenosine of GABA-activated current (IGADA) was studied in freshly isolated rat dorsal root ganglion (DRG) neurons using the whole-cell patch-clamp technique. 2. In most of the DRG neurons examined (68/90, 75.5%) adenosine (1-10 microM) suppressed IGABA, while in some neurons examined, it potentiated (16/90, 17.8%) IGABA. It exerted no effects on IGABA in a few cells (6/90, 6.7%). 3. Adenosine shifted the GABA concentration-response curve downward with no significant change of the EC50. The maximal response to GABA was suppressed by 29.6 +/- 2.6%. The adenosine-induced inhibition of IGABA showed no voltage dependence. 4. 8-Cyclopentyl-1,3-dimethylxanthine (DPCPX; 1 microM), a selective A1 adenosine receptor antagonist, partially reversed adenosine inhibition of IGABA and completely blocked N6-cyclo-hexyladenosine (CHA; an A1 adenosine receptor agonist) inhibition of IGABA. DPCPX (1 microM) also blocked the suppression of IGABA by 2-chloroadenosine (CADO). CGS21680, a selective A2A adenosine receptor agonist, did not inhibit IGABA and DMPX, a selective A2A adenosine receptor antagonist, did not prevent adenosine inhibition of IGABA. 5. Intracellular application of H-7 (20 microM; a protein kinase C inhibitor) reversed adenosine inhibition of IGABA while inclusion of cAMP (1 mM), H-9 (20 microM; a protein kinase A inhibitor) and BAPTA (10 mM; a chelator of calcium ions) in the recording pipette did not affect the depression of IGABA by adenosine. IGABA was also suppressed by internal perfusion of PMA, a protein kinase C activator. 6. The results suggest that adenosine, as a neuromodulator, exerts a modulatory effect on the GABA-induced presynaptic inhibition in primary sensory transmission.

Adenosine↗
PubMed1997

The cytosolic inactivation domains of BKi channels in rat chromaffin cells do not behave like simple, open-channel blockers.

Most BK-type voltage- and Ca(2+)-dependent K+ channels in rat chromaffin cells exhibit rapid inactivation. This inactivation is abolished by brief trypsin application to the cytosolic face of membrane patches. Here we examine the effects of cytosolic channel blockade and pore occupancy on this inactivation process, using inside-out patches and whole-cell recordings. Occupancy of a superficial pore-blocking site by cytosolic quaternary blockers does not slow inactivation. Occupancy of a deeper pore-blocking site by cytosolic application of Cs+ is also without effect on the onset of inactivation. Although the rate of inactivation is relatively unaffected by changes in extracellular K+, the rate of recovery from inactivation (at -80 and -140 mV with 10 microM Ca2+) is faster with increases in extracellular K+ but is unaffected by the impermeant ion, Na+. When tail currents are compared after repolarization, either while channels are open or after inactivation, no channel reopening is detectable during recovery from inactivation. BK inactivation appears to be mechanistically distinct from that of other inactivating voltage-dependent channels. Although involving a trypsin-sensitive cytosolic structure, the block to permeation does not appear to occur directly at the cytosolic mouth or inner half of the ion permeation pathway.

Adrenal Medulla↗
PubMed1997

Evidence for the existence of substance P autoreceptor in the membrane of rat dorsal root ganglion neurons.

Substance P, a putative peptide neurotransmitter contained in primary sensory neurons, is suggested to play a major role in nociceptive transmission. In the present study, the existence of substance P autoreceptor in dorsal root ganglion neurons was identified with a method we developed recently and substance P-activated inward current in the dorsal root ganglion neurons and its ionic mechanism were also explored preliminarily. The majority of the cells examined (68/76, 89.5%) were sensitive to external application of substance P (0.01-10 microM) with a concentration-dependent inward current. This current was found to result from the opening of nonselective ion channel, preferring the Na+ channel. The substance P-activated current can be suppressed by Cd2+ (0.05 microM), which suggested Ca2+ may also be involved. Soon after the neurons had been identified to be endowed with substance P receptor with whole-cell patch-clamp technique, 17 cells were chosen for immunocytochemical staining to detect substance P-immunoreactivity. Seven neurons which were classified into small and intermediate size were found to reveal substance P-immunoreactivity. Using this method we have identified the existence of substance P autoreceptor in rat DRG neurons.

Animals↗
PubMed1997

Inhibitory effect of baclofen on GABA-induced depolarization and GABA-activated current in primary sensory neurons.

It has been established that GABAA and GABAB receptors can exist separately and/or co-exist in the membrane of dorsal root ganglion neurons. In our previous investigation it has been shown that co-existence of these two kinds of receptors is about 80% of the neurons examined (20/25). The present study was aimed to explore whether the activation of these two kinds of receptors could interact with each other using intracellular and whole-cell patch-clamp recordings. Baclofen, a specific GABAB receptor agonist, was found to exert negative modulatory effects on the responses mediated by GABAA receptor. In experiments with intracellular recording, GABA (0.3-1000 microM)- and muscimol (100-1000 microM)-induced depolarization was attenuated markedly and reversibly by preapplication of baclofen (100 microM) (15/21 and 17/21, respectively). In whole-cell patch-clamp recordings GABA (100 microM) and two specific GABAA receptor agonists, muscimol (10 microM) and isoguvacine (50 microM), activated currents were inhibited markedly by preapplication of baclofen 30 s or more and the inhibition was concentration dependent (1-100 microM baclofen) and reversible. The possible mechanisms underlying the inhibition by baclofen of the responses mediated by GABAA receptor and the physiological significance implicated are discussed.

Animals↗
PubMed1997

Modulation of nicotinic ACh-, GABAA- and 5-HT3-receptor functions by external H-7, a protein kinase inhibitor, in rat sensory neurones.

1. The effects of external H-7, a potent protein kinase inhibitor, on the responses mediated by gamma-aminobutyric acid A type (GABAA)-, nicotinic acetylcholine (nicotinic ACh)-, ionotropic 5-hydroxytryptamine (5-HT3)-, adenosine 5'-triphosphate (ATP)-, N-methyl-D-aspartate (NMDA)- and kainate (KA)-receptors were studied in freshly dissociated rat dorsal root ganglion neurone by use of whole cell patch-clamp technique. 2. External H-7 (1-1000 microM) produced a reversible, dose-dependent inhibition of whole cell currents activated by GABA, ACh and 5-HT. 3. Whole-cell currents evoked by ATP, 2-methylthio-ATP, NMDA and KA were insensitive to external H-7. 4. External H-7 shifted the dose-response curve of GABA-activated currents downward without changing the EC50 significantly (from 15.0 +/- 4.0 microM to 18.0 +/- 5.0 microM). The maximum response to GABA was depressed by 34.0 +/- 5.3%. This inhibitory action of H-7 was voltage-independent. 5. Intracellular application of H-7 (20 microM), cyclic AMP (1 mM) and BAPTA (10 mM) could not reverse the H-7 inhibition of GABA-activated currents. 6. The results suggest that external H-7 selectively and allosterically modulates the functions of GABAA-, nicotine ACh- and 5-HT3 receptors via a common conserved site in the external domain of these receptors.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1996

Substance P potentiates ATP-activated currents in rat primary sensory neurons.

The aim of this study was to explore whether substance P could modulate the response mediated by ATP receptor. Experiments were carried out on rat dorsal root ganglion (DRG) neurons isolated acutely with enzymatic and mechanical treatment. The ATP-activated inward currents were recorded using the whole-cell patch-clamp technique. The majority of the neurons examined (82/85, 96.5%) were sensitive to ATP (1-1000 microM). Application of substance P (0.01-100 microM) also caused an inward current. Several differences between these two kinds of currents were observed. 0.01, 0.1 and 1 microM substance P increased the ATP (10 microM)-activated current to 113.7 +/- 3.1%, (n = 8); 127.2 +/- 6.7%, (n = 12) and 154.7 +/- 14.4% (n = 6) (means +/- S.E.M.), respectively. This potentiating effect can be blocked by spantide, an NK1 receptor antagonist, and intracellular application of H7 (which is a potent inhibitor of PKC) could also block this kind of potentiation of SP on ATP-activated current. Since the substance P receptor and ATP receptor can coexist in rat DRG neurons and activation of substance P receptor can modulate the response mediated by ATP receptor, it suggests that they may cooperate with each other in activating peripheral nociceptive endings of sensory neurons, especially during tissue damage and/or inflammation.

Adenosine Triphosphate↗