Absence seizures occur in several types of human epilepsy and result from widespread, synchronous... more Absence seizures occur in several types of human epilepsy and result from widespread, synchronous feedback between the cortex and thalamus that produces brief episodes of loss of consciousness. Genetic rodent models have been invaluable for investigating the pathophysiological basis of these seizures. Here, we identify tetratricopeptide-containing Rab8binteracting protein (TRIP8b) knockout mice as a new model of absence epilepsy, featuring spontaneous spike-wave discharges on electroencephalography (EEG) that are the electrographic hallmark of absence seizures. TRIP8b is an auxiliary subunit of the hyperpolarization-activated
Serotonin 5-HT has been shown to phase shift circadian rhythms in mammals and to affect responses... more Serotonin 5-HT has been shown to phase shift circadian rhythms in mammals and to affect responses of the circadian system to light, but it is not clear which receptors are involved in these actions. We found that drugs which act as 5-HT receptor agonists suppressed 1A photic responses of hamster SCN cells, but these drugs also exhibit high affinity for the recently cloned 5-HT receptor. We therefore 7 studied the effects of 5-HT agonists and antagonists with differential affinities for 5-HT and 5-HT receptors on responses of hamster 7 1 A SCN cells to retinal illumination. We confirmed that the 5-HT receptor agonists 5-HT, 8-OH-DPAT and 5-CT, dose-dependently reduced photic activation of SCN cells. These effects could be blocked by co-application of antagonists with high affinities for 5-HT receptors: 7 ritanserin or clozapine. The 5-HT antagonist, cyanopindolol, which is inactive at 5-HT receptors, did not antagonize the actions 1ArBrD 7 of 8-OH-DPAT. Selective 5-HT antagonists, WAY100635 and p-MPPI, had weak or no antagonist effects on the responses to 1A 8-OH-DPAT in the SCN, but they effectively antagonized the actions of 8-OH-DPAT in the hippocampus. In the cerebellar cortex where few 5-HT receptors are present, ritanserin failed to antagonize the effects of 8-OH-DPAT. Our results indicate that the 5-HT receptor 7 7 subtype plays a major role in mediating the effects of 5-HT on photic responses of SCN cells in the hamster.
Propofol is a widely used intravenous general anesthetic. Propofol-induced unconsciousness in hum... more Propofol is a widely used intravenous general anesthetic. Propofol-induced unconsciousness in humans is associated with inhibition of thalamic activity evoked by somatosensory stimuli. However, the cellular mechanisms underlying the effects of propofol in thalamic circuits are largely unknown. We investigated the influence of propofol on synaptic responsiveness of thalamocortical relay neurons in the ventrobasal complex (VB) to excitatory input in mouse brain slices, using both current-and voltage-clamp recording techniques. Excitatory responses including EPSP temporal summation and action potential firing were evoked in VB neurons by electrical stimulation of corticothalamic fibers or pharmacological activation of glutamate receptors. Propofol (0.6 -3 µM) suppressed temporal summation and spike firing in a concentration-dependent manner. The thalamocortical suppression was accompanied by a marked decrease in both EPSP amplitude and input resistance, indicating that a shunting mechanism was involved. The propofol-mediated thalamocortical suppression could be blocked by a GABA A receptor antagonist or chloride channel blocker, suggesting that postsynaptic GABA A receptors in VB neurons were involved in the shunting inhibition. GABA A receptor-mediated inhibitory postsynaptic currents (IPSCs) were evoked in VB neurons by electrical stimulation of the reticular thalamic nucleus. Propofol markedly increased amplitude, decay time, and charge transfer of GABA A IPSCs. The results demonstrated that shunting inhibition of thalamic somatosensory relay neurons by propofol at clinically relevant concentrations is primarily mediated through the potentiation of the GABA A receptor chloride channel-mediated conductance, and such inhibition may contribute to the impaired thalamic responses to sensory stimuli seen during propofol-induced anesthesia.
Background: Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels generate the pace... more Background: Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels generate the pacemaking current, I h , which regulates neuronal excitability, burst firing activity, rhythmogenesis, and synaptic integration. The physiological consequence of HCN activation depends on regulation of channel gating by endogenous modulators and stabilization of the channel complex formed by principal and ancillary subunits. KCNE2 is a voltage-gated potassium channel ancillary subunit that also regulates heterologously expressed HCN channels; whether KCNE2 regulates neuronal HCN channel function is unknown. Methodology/Principal Findings: We investigated the effects of Kcne2 gene deletion on I h properties and excitability in ventrobasal (VB) and cortical layer 6 pyramidal neurons using brain slices prepared from Kcne2 +/+ and Kcne2 2/2 mice. Kcne2 deletion shifted the voltage-dependence of I h activation to more hyperpolarized potentials, slowed gating kinetics, and decreased I h density. Kcne2 deletion was associated with a reduction in whole-brain expression of both HCN1 and HCN2 (but not HCN4), although co-immunoprecipitation from whole-brain lysates failed to detect interaction of KCNE2 with HCN1 or 2. Kcne2 deletion also increased input resistance and temporal summation of subthreshold voltage responses; this increased intrinsic excitability enhanced burst firing in response to 4-aminopyridine. Burst duration increased in corticothalamic, but not thalamocortical, neurons, suggesting enhanced cortical excitatory input to the thalamus; such augmented excitability did not result from changes in glutamate release machinery since miniature EPSC frequency was unaltered in Kcne2 2/2 neurons. Conclusions/Significance: Loss of KCNE2 leads to downregulation of HCN channel function associated with increased excitability in neurons in the cortico-thalamo-cortical loop. Such findings further our understanding of the normal physiology of brain circuitry critically involved in cognition and have implications for our understanding of various disorders of consciousness.
GABAergic neurons in the reticular thalamic nucleus (RTN) synapse onto thalamocortical neurons in... more GABAergic neurons in the reticular thalamic nucleus (RTN) synapse onto thalamocortical neurons in the ventrobasal (VB) thalamus, and this reticulo-thalamocortical pathway is considered an anatomic target for general anesthetic-induced unconsciousness. A mutant mouse was engineered to harbor two amino acid substitutions (S270H, L277A) in the GABA A receptor (GABA A -R) α1 subunit; this mutation abolished sensitivity to the volatile anesthetic isoflurane in recombinant GABA A -Rs, and reduced in vivo sensitivity to isoflurane in the loss-of-righting-reflex assay. We examined the effects of the double mutation on GABA A -R-mediated synaptic currents and isoflurane sensitivity by recording from thalamic neurons in brain slices. The double mutation accelerated the decay, and decreased the ½ width of, evoked inhibitory postsynaptic currents (eIPSCs) in VB neurons and attenuated isoflurane-induced prolongation of the eIPSC. The hypnotic zolpidem, a selective modulator of GABA A -Rs containing the α1 subunit, prolonged eIPSC duration regardless of genotype, indicating that mutant mice incorporate α1-subunit containing GABA A -Rs into synapses. In RTN neurons, which lack the α1 subunit, eIPSC duration was longer than in VB, regardless of genotype. Isoflurane reduced the efficacy of GABAergic transmission from RTN to VB, independent of genotype, suggesting a presynaptic action in RTN neurons. Consistent with this observation, isoflurane inhibited both tonic action potential and rebound burst firing in the presence of GABA A -R blockade. The suppressed excitability in RTN neurons is likely mediated by isoflurane-enhanced Ba 2+ -sensitive, but 4-aminopyridine-insenstive, potassium conductances. We conclude that isoflurane enhances inhibition of thalamic neurons in VB via GABA A -R-dependent, but in RTN via GABA A -R-independent, mechanisms.
Propofol block of Ih contributes to the suppression of neuronal excitability and rhythmic burst firing in thalamocortical neurons
European Journal of Neuroscience, 2006
Although the depressant effects of the general anesthetic propofol on thalamocortical relay neuro... more Although the depressant effects of the general anesthetic propofol on thalamocortical relay neurons clearly involve gamma-aminobutyric acid (GABA)(A) receptors, other mechanisms may be involved. The hyperpolarization-activated cation current (I(h)) regulates excitability and rhythmic firing in thalamocortical relay neurons in the ventrobasal (VB) complex of the thalamus. Here we investigated the effects of propofol on I(h)-related function in vitro and in vivo. In whole-cell current-clamp recordings from VB neurons in mouse (P23-35) brain slices, propofol markedly reduced the voltage sag and low-threshold rebound excitation that are characteristic of the activation of I(h). In whole-cell voltage-clamp recordings, propofol suppressed the I(h) conductance and slowed the kinetics of activation. The block of I(h) by propofol was associated with decreased regularity and frequency of delta-oscillations in VB neurons. The principal source of the I(h) current in these neurons is the hyperpolarization-activated cyclic nucleotide-gated (HCN) type 2 channel. In human embryonic kidney (HEK)293 cells expressing recombinant mouse HCN2 channels, propofol decreased I(h) and slowed the rate of channel activation. We also investigated whether propofol might have persistent effects on thalamic excitability in the mouse. Three hours following an injection of propofol sufficient to produce loss-of-righting reflex in mice (P35), I(h) was decreased, and this was accompanied by a corresponding decrease in HCN2 and HCN4 immunoreactivity in thalamocortical neurons in vivo. These results suggest that suppression of I(h) may contribute to the inhibition of thalamocortical activity during propofol anesthesia. Longer-term effects represent a novel form of propofol-mediated regulation of I(h).
Activin A inhibits growth and hexamethylene bisacetamide-induced differentiation in human retinoblastoma Y-79 cells
Anticancer research
Activin regulates the growth and differentiation of a variety of cells and is a member of the tra... more Activin regulates the growth and differentiation of a variety of cells and is a member of the transforming growth factor-beta (TGF-beta) family. Previously, we found that the retinoblastoma cell line Y-79 expresses both activins and activin receptors, suggesting that activin may have an autocrine function in these cells. In this study, the effects of exogeneous activin A on cultured Y-79 cells were examined. The results demonstrate that activin A inhibits hexamethylene bisacetamide (HMBA) -induced Y-79 cell differentiation in both serum-containing and serum-free medium. Activin A also inhibits Y-79 cell growth in serum-containing medium but not in serum-free medium.
p53 is involved in the inhibition of cell proliferation mediated by activin A in cultured human prostate cancer LNCaP cells
International Journal of Oncology, 1997
Activin A in a concentration ranging from 0.7 to 75 ng/ml specifically inhibited cell growth of a... more Activin A in a concentration ranging from 0.7 to 75 ng/ml specifically inhibited cell growth of an androgen-sensitive human prostate cancer line, LNCaP, but had no effects on two androgen-insensitive human prostate cancer lines, PC3 and DU-145. This activin-mediated inhibition of cell growth in LNCaP cells results from a decrease of cell proliferation and an increase of apoptosis. Northern blot analysis of mRNA expression encoding human p53 in untreated and activin-treated LNCaP cells resulted in upregulation of p53 gene expression. We conclude that autocrine inhibition of cell growth in LNCaP cells by activin is in part related to the expression of the p53 gene.
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels generate a pacemaking current,... more Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels generate a pacemaking current, I h , which regulates neuronal excitability and oscillatory activity in the brain. Although all four HCN isoforms are expressed in the brain, the functional contribution of HCN3 is unknown. Using immunohistochemistry, confocal microscopy, and whole-cell patch-clamp recording techniques, we investigated HCN3 function in thalamic intergeniculate leaflet (IGL) neurons, as HCN3 is reportedly preferentially expressed in these cells. We observed that I h recorded from IGL, but not ventral geniculate nucleus, neurons in HCN2 ϩ/ϩ mice and rats activated slowly and were cAMP insensitive, which are hallmarks of HCN3 channels. We also observed strong immunolabeling for HCN3, with no labeling for HCN1 and HCN4, and only very weak labeling for HCN2. Deletion of HCN2 did not alter I h characteristics in mouse IGL neurons. These data together indicate that the HCN3 channel isoform generated I h in IGL neurons. Intracellular phosphatidylinositol-4,5-bisphosphate (PIP 2) shifted I h activation to more depolarized potentials and accelerated activation kinetics. Upregulation of HCN3 function by PIP 2 augmented low-threshold burst firing and spontaneous oscillations; conversely, depletion of PIP 2 or pharmacologic block of I h resulted in a profound inhibition of excitability. The results indicate that functional expression of HCN3 channels in IGL neurons is crucial for intrinsic excitability and rhythmic burst firing, and PIP 2 serves as a powerful modulator of I h-dependent properties via an effect on HCN3 channel gating. Since the IGL is a major input to the suprachiasmatic nucleus, regulation of pacemaking function by PIP 2 in the IGL may influence sleep and circadian rhythms.
Absence seizures occur in several types of human epilepsy and result from widespread, synchronous... more Absence seizures occur in several types of human epilepsy and result from widespread, synchronous feedback between the cortex and thalamus that produces brief episodes of loss of consciousness. Genetic rodent models have been invaluable for investigating the pathophysiological basis of these seizures. Here, we identify tetratricopeptide-containing Rab8binteracting protein (TRIP8b) knockout mice as a new model of absence epilepsy, featuring spontaneous spike-wave discharges on electroencephalography (EEG) that are the electrographic hallmark of absence seizures. TRIP8b is an auxiliary subunit of the hyperpolarization-activated
Serotonin 5-HT has been shown to phase shift circadian rhythms in mammals and to affect responses... more Serotonin 5-HT has been shown to phase shift circadian rhythms in mammals and to affect responses of the circadian system to light, but it is not clear which receptors are involved in these actions. We found that drugs which act as 5-HT receptor agonists suppressed 1A photic responses of hamster SCN cells, but these drugs also exhibit high affinity for the recently cloned 5-HT receptor. We therefore 7 studied the effects of 5-HT agonists and antagonists with differential affinities for 5-HT and 5-HT receptors on responses of hamster 7 1 A SCN cells to retinal illumination. We confirmed that the 5-HT receptor agonists 5-HT, 8-OH-DPAT and 5-CT, dose-dependently reduced photic activation of SCN cells. These effects could be blocked by co-application of antagonists with high affinities for 5-HT receptors: 7 ritanserin or clozapine. The 5-HT antagonist, cyanopindolol, which is inactive at 5-HT receptors, did not antagonize the actions 1ArBrD 7 of 8-OH-DPAT. Selective 5-HT antagonists, WAY100635 and p-MPPI, had weak or no antagonist effects on the responses to 1A 8-OH-DPAT in the SCN, but they effectively antagonized the actions of 8-OH-DPAT in the hippocampus. In the cerebellar cortex where few 5-HT receptors are present, ritanserin failed to antagonize the effects of 8-OH-DPAT. Our results indicate that the 5-HT receptor 7 7 subtype plays a major role in mediating the effects of 5-HT on photic responses of SCN cells in the hamster.
Propofol is a widely used intravenous general anesthetic. Propofol-induced unconsciousness in hum... more Propofol is a widely used intravenous general anesthetic. Propofol-induced unconsciousness in humans is associated with inhibition of thalamic activity evoked by somatosensory stimuli. However, the cellular mechanisms underlying the effects of propofol in thalamic circuits are largely unknown. We investigated the influence of propofol on synaptic responsiveness of thalamocortical relay neurons in the ventrobasal complex (VB) to excitatory input in mouse brain slices, using both current-and voltage-clamp recording techniques. Excitatory responses including EPSP temporal summation and action potential firing were evoked in VB neurons by electrical stimulation of corticothalamic fibers or pharmacological activation of glutamate receptors. Propofol (0.6 -3 µM) suppressed temporal summation and spike firing in a concentration-dependent manner. The thalamocortical suppression was accompanied by a marked decrease in both EPSP amplitude and input resistance, indicating that a shunting mechanism was involved. The propofol-mediated thalamocortical suppression could be blocked by a GABA A receptor antagonist or chloride channel blocker, suggesting that postsynaptic GABA A receptors in VB neurons were involved in the shunting inhibition. GABA A receptor-mediated inhibitory postsynaptic currents (IPSCs) were evoked in VB neurons by electrical stimulation of the reticular thalamic nucleus. Propofol markedly increased amplitude, decay time, and charge transfer of GABA A IPSCs. The results demonstrated that shunting inhibition of thalamic somatosensory relay neurons by propofol at clinically relevant concentrations is primarily mediated through the potentiation of the GABA A receptor chloride channel-mediated conductance, and such inhibition may contribute to the impaired thalamic responses to sensory stimuli seen during propofol-induced anesthesia.
Background: Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels generate the pace... more Background: Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels generate the pacemaking current, I h , which regulates neuronal excitability, burst firing activity, rhythmogenesis, and synaptic integration. The physiological consequence of HCN activation depends on regulation of channel gating by endogenous modulators and stabilization of the channel complex formed by principal and ancillary subunits. KCNE2 is a voltage-gated potassium channel ancillary subunit that also regulates heterologously expressed HCN channels; whether KCNE2 regulates neuronal HCN channel function is unknown. Methodology/Principal Findings: We investigated the effects of Kcne2 gene deletion on I h properties and excitability in ventrobasal (VB) and cortical layer 6 pyramidal neurons using brain slices prepared from Kcne2 +/+ and Kcne2 2/2 mice. Kcne2 deletion shifted the voltage-dependence of I h activation to more hyperpolarized potentials, slowed gating kinetics, and decreased I h density. Kcne2 deletion was associated with a reduction in whole-brain expression of both HCN1 and HCN2 (but not HCN4), although co-immunoprecipitation from whole-brain lysates failed to detect interaction of KCNE2 with HCN1 or 2. Kcne2 deletion also increased input resistance and temporal summation of subthreshold voltage responses; this increased intrinsic excitability enhanced burst firing in response to 4-aminopyridine. Burst duration increased in corticothalamic, but not thalamocortical, neurons, suggesting enhanced cortical excitatory input to the thalamus; such augmented excitability did not result from changes in glutamate release machinery since miniature EPSC frequency was unaltered in Kcne2 2/2 neurons. Conclusions/Significance: Loss of KCNE2 leads to downregulation of HCN channel function associated with increased excitability in neurons in the cortico-thalamo-cortical loop. Such findings further our understanding of the normal physiology of brain circuitry critically involved in cognition and have implications for our understanding of various disorders of consciousness.
GABAergic neurons in the reticular thalamic nucleus (RTN) synapse onto thalamocortical neurons in... more GABAergic neurons in the reticular thalamic nucleus (RTN) synapse onto thalamocortical neurons in the ventrobasal (VB) thalamus, and this reticulo-thalamocortical pathway is considered an anatomic target for general anesthetic-induced unconsciousness. A mutant mouse was engineered to harbor two amino acid substitutions (S270H, L277A) in the GABA A receptor (GABA A -R) α1 subunit; this mutation abolished sensitivity to the volatile anesthetic isoflurane in recombinant GABA A -Rs, and reduced in vivo sensitivity to isoflurane in the loss-of-righting-reflex assay. We examined the effects of the double mutation on GABA A -R-mediated synaptic currents and isoflurane sensitivity by recording from thalamic neurons in brain slices. The double mutation accelerated the decay, and decreased the ½ width of, evoked inhibitory postsynaptic currents (eIPSCs) in VB neurons and attenuated isoflurane-induced prolongation of the eIPSC. The hypnotic zolpidem, a selective modulator of GABA A -Rs containing the α1 subunit, prolonged eIPSC duration regardless of genotype, indicating that mutant mice incorporate α1-subunit containing GABA A -Rs into synapses. In RTN neurons, which lack the α1 subunit, eIPSC duration was longer than in VB, regardless of genotype. Isoflurane reduced the efficacy of GABAergic transmission from RTN to VB, independent of genotype, suggesting a presynaptic action in RTN neurons. Consistent with this observation, isoflurane inhibited both tonic action potential and rebound burst firing in the presence of GABA A -R blockade. The suppressed excitability in RTN neurons is likely mediated by isoflurane-enhanced Ba 2+ -sensitive, but 4-aminopyridine-insenstive, potassium conductances. We conclude that isoflurane enhances inhibition of thalamic neurons in VB via GABA A -R-dependent, but in RTN via GABA A -R-independent, mechanisms.
Propofol block of Ih contributes to the suppression of neuronal excitability and rhythmic burst firing in thalamocortical neurons
European Journal of Neuroscience, 2006
Although the depressant effects of the general anesthetic propofol on thalamocortical relay neuro... more Although the depressant effects of the general anesthetic propofol on thalamocortical relay neurons clearly involve gamma-aminobutyric acid (GABA)(A) receptors, other mechanisms may be involved. The hyperpolarization-activated cation current (I(h)) regulates excitability and rhythmic firing in thalamocortical relay neurons in the ventrobasal (VB) complex of the thalamus. Here we investigated the effects of propofol on I(h)-related function in vitro and in vivo. In whole-cell current-clamp recordings from VB neurons in mouse (P23-35) brain slices, propofol markedly reduced the voltage sag and low-threshold rebound excitation that are characteristic of the activation of I(h). In whole-cell voltage-clamp recordings, propofol suppressed the I(h) conductance and slowed the kinetics of activation. The block of I(h) by propofol was associated with decreased regularity and frequency of delta-oscillations in VB neurons. The principal source of the I(h) current in these neurons is the hyperpolarization-activated cyclic nucleotide-gated (HCN) type 2 channel. In human embryonic kidney (HEK)293 cells expressing recombinant mouse HCN2 channels, propofol decreased I(h) and slowed the rate of channel activation. We also investigated whether propofol might have persistent effects on thalamic excitability in the mouse. Three hours following an injection of propofol sufficient to produce loss-of-righting reflex in mice (P35), I(h) was decreased, and this was accompanied by a corresponding decrease in HCN2 and HCN4 immunoreactivity in thalamocortical neurons in vivo. These results suggest that suppression of I(h) may contribute to the inhibition of thalamocortical activity during propofol anesthesia. Longer-term effects represent a novel form of propofol-mediated regulation of I(h).
Activin A inhibits growth and hexamethylene bisacetamide-induced differentiation in human retinoblastoma Y-79 cells
Anticancer research
Activin regulates the growth and differentiation of a variety of cells and is a member of the tra... more Activin regulates the growth and differentiation of a variety of cells and is a member of the transforming growth factor-beta (TGF-beta) family. Previously, we found that the retinoblastoma cell line Y-79 expresses both activins and activin receptors, suggesting that activin may have an autocrine function in these cells. In this study, the effects of exogeneous activin A on cultured Y-79 cells were examined. The results demonstrate that activin A inhibits hexamethylene bisacetamide (HMBA) -induced Y-79 cell differentiation in both serum-containing and serum-free medium. Activin A also inhibits Y-79 cell growth in serum-containing medium but not in serum-free medium.
p53 is involved in the inhibition of cell proliferation mediated by activin A in cultured human prostate cancer LNCaP cells
International Journal of Oncology, 1997
Activin A in a concentration ranging from 0.7 to 75 ng/ml specifically inhibited cell growth of a... more Activin A in a concentration ranging from 0.7 to 75 ng/ml specifically inhibited cell growth of an androgen-sensitive human prostate cancer line, LNCaP, but had no effects on two androgen-insensitive human prostate cancer lines, PC3 and DU-145. This activin-mediated inhibition of cell growth in LNCaP cells results from a decrease of cell proliferation and an increase of apoptosis. Northern blot analysis of mRNA expression encoding human p53 in untreated and activin-treated LNCaP cells resulted in upregulation of p53 gene expression. We conclude that autocrine inhibition of cell growth in LNCaP cells by activin is in part related to the expression of the p53 gene.
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels generate a pacemaking current,... more Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels generate a pacemaking current, I h , which regulates neuronal excitability and oscillatory activity in the brain. Although all four HCN isoforms are expressed in the brain, the functional contribution of HCN3 is unknown. Using immunohistochemistry, confocal microscopy, and whole-cell patch-clamp recording techniques, we investigated HCN3 function in thalamic intergeniculate leaflet (IGL) neurons, as HCN3 is reportedly preferentially expressed in these cells. We observed that I h recorded from IGL, but not ventral geniculate nucleus, neurons in HCN2 ϩ/ϩ mice and rats activated slowly and were cAMP insensitive, which are hallmarks of HCN3 channels. We also observed strong immunolabeling for HCN3, with no labeling for HCN1 and HCN4, and only very weak labeling for HCN2. Deletion of HCN2 did not alter I h characteristics in mouse IGL neurons. These data together indicate that the HCN3 channel isoform generated I h in IGL neurons. Intracellular phosphatidylinositol-4,5-bisphosphate (PIP 2) shifted I h activation to more depolarized potentials and accelerated activation kinetics. Upregulation of HCN3 function by PIP 2 augmented low-threshold burst firing and spontaneous oscillations; conversely, depletion of PIP 2 or pharmacologic block of I h resulted in a profound inhibition of excitability. The results indicate that functional expression of HCN3 channels in IGL neurons is crucial for intrinsic excitability and rhythmic burst firing, and PIP 2 serves as a powerful modulator of I h-dependent properties via an effect on HCN3 channel gating. Since the IGL is a major input to the suprachiasmatic nucleus, regulation of pacemaking function by PIP 2 in the IGL may influence sleep and circadian rhythms.
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Papers by Shui Ying