Biomedical subjects

W J Zhu

Publications and source records attributed to W J Zhu.

At least 19 recordsLinked to original sources

PubMed2006

Transvaginal, ultrasound-guided, ovarian, interstitial laser treatment in anovulatory women with clomifene-citrate-resistant polycystic ovary syndrome.

OBJECTIVE: To assess the effectiveness of transvaginal, ultrasound-guided, ovarian, interstitial laser coagulation treatment in anovulatory women with polycystic ovary syndrome (PCOS). DESIGN: A pilot study. SETTING: Assisted reproductive technology unit. SAMPLE: Twenty-three anovulatory women with clomifene-citrate-resistant PCOS. METHODS: Ultrasound-guided, transvaginal, ovarian, interstitial yttrium-aluminium-garnet laser treatment. MAIN OUTCOME MEASURES: Serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, prolactin and estradiol levels, spontaneous ovulation rate and pregnancy rate were measured over 6 months of follow up. RESULTS: Regular ovulation occurred in 19 out of 22 (86.4%) women in the 6 months following ovarian treatment (one woman was lost to follow up). On the postoperative second, fourth and sixth month, the mean serum LH levels were 4.54 SD 1.21 iu/l, 4.90 SD 2.18 iu/l and 4.42 SD 1.03 iu/l, significantly (P < 0.001, P < 0.001, P < 0.001) lower than the preoperative level of 13.89 +/- 3.62 iu/l; the mean serum testosterone levels were 2.69 SD 1.83 nmol/l, 2.42 SD 1.11 nmol/l and 2.28 SD 1.96 nmol/l and significantly (P < 0.001, P < 0.001, P < 0.001) lower than the preoperative baseline value of 5.37 SD 3.09 nmol/l; the mean LH/FSH ratios of 0.93 SD 0.26, 0.88 SD 0.17 and 0.81 SD 0.14 were also significantly lower than the preoperative value of 2.78 SD 1.21 (P < 0.001). Pregnancy occurred in eight women and there was a cumulative pregnancy rate at 6 months of 36% (8/22) among the subjects. There were no significant operative complications. CONCLUSION: Ultrasound-guided, transvaginal, ovarian, interstitial laser treatment appears effective in improving hormonal profiles and inducing ovulation and successful pregnancy in women with clomifene-resistant PCOS.

Anovulation↗

PubMed2003

Electron energy-loss spectroscopy study of thin film hafnium aluminates for novel gate dielectrics.

We have used conventional high-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS) in scanning transmission electron microscopy to investigate the microstructure and electronic structure of hafnia-based thin films doped with small amounts (6.8 at.%) of Al grown on (001) Si. The as-deposited film is amorphous with a very thin (approximately 0.5 nm) interfacial SiOx layer. The film partially crystallizes after annealing at 700 degrees C and the interfacial SiO2-like layer increases in thickness by oxygen diffusion through the Hf-aluminate layer and oxidation of the silicon substrate. Oxygen K-edge EELS fine-structures are analysed for both films and interpreted in the context of the films' microstructure. We also discuss valence electron energy-loss spectra of these ultrathin films.

Journal Article↗

PubMed2001

Brain-derived neurotrophic factor enhances fast excitatory synaptic transmission in human epileptic dentate gyrus.

Brain-derived neurotrophic factor (BDNF) has trophic effects and modulates synaptic transmission in the hippocampal formation in animal studies. It is also upregulated in acute and chronic epilepsy models and in human temporal lobe epilepsy. This study was undertaken to examine the effects of BDNF on fast synaptic transmission in the human epileptic dentate gyrus. Hippocampal specimens were acquired from patients with temporal lobe epilepsy during surgical removal of the anterior temporal lobe intended to treat the epileptic condition. Whole-cell patch-clamp recordings were obtained from dentate granule cells in transverse hippocampal slices in vitro. Application of BDNF increased the amplitude and frequency of spontaneous excitatory postsynaptic currents and increased the amplitude of evoked excitatory postsynaptic currents. BDNF had no effect on spontaneous inhibitory postsynaptic currents but produced a decrease in amplitude of evoked inhibitory postsynaptic currents. BDNF's effects were abolished by coapplication of the tyrosine kinase inhibitor K252a. Therefore, BDNF enhances fast excitatory transmission in the epileptic human dentate gyrus and may play an important role in epileptogenesis in temporal lobe epilepsy. This raises the possibility of designing therapies for this disorder that may be both anticonvulsant and antiepileptogenic.

Adolescent↗

PubMed2001

Effect of human oviductal epithelial cell cultural medium on cryopreserved human sperm survival.

The human oviduct is known as a functional site for gamete transportation, retention, fertilization and zygote development. Previous studies have shown that human oviductal epithelial cell cultural medium (OECCM) has a positive effect on prolongation of sperm motility for some cryopreserved human sperm without cryodamage. However, for most cryopreserved sperm, OECCM could not improve their survival prolongation. In this study, we assessed the influence of human OECCM on the motility longevity of cryopreserved human sperm with an in vitro incubation method.

Cell Survival↗

PubMed2001

An essential role for the H218/AGR16/Edg-5/LP(B2) sphingosine 1-phosphate receptor in neuronal excitability.

A wealth of indirect data suggest that the H218/AGR16/Edg-5/LP(B2) sphingosine 1-phosphate (S1P) receptor plays important roles in development. In vitro, it activates several forms of development-related signal transduction and regulates cellular proliferation, differentiation and survival. It is expressed during embryogenesis, and mutation of an H218-like gene in zebrafish leads to profound defects in embryonic development. Nevertheless, the in vivo functions served by H218 signalling have not been directly investigated. We report here that mice in which the H218 gene has been disrupted are unexpectedly born with no apparent anatomical or physiological defects. In addition, no abnormalities were observed in general neurological development, peripheral axon growth or brain structure. However, between 3 and 7 weeks of age, H218(-/-) mice have seizures which are spontaneous, sporadic and occasionally lethal. Electroencephalographic abnormalities were identified both during and between the seizures. At a cellular level, whole-cell patch-clamp recordings revealed that the loss of H218 leads to a large increase in the excitability of neocortical pyramidal neurons. Therefore, H218 plays an essential, unanticipated and functionally important role in the proper development and/or mediation of neuronal excitability.

Action Potentials↗

PubMed2001

[Higher lint percent and drought tolerant cotton line selected by radiation breeding].

The Gossypium hirsutum cv. Liaomian No. 9 were mutagenized by 60Co gamma ray, from which the mutant line Zhonghuzhi PI 935 (be called "PI 935" for short) was bred by family selection method. The PI 935 not only has some good traits (growing period, drought tolerance, lint color and fiber quality) similar to the original cultivar, but also has higher lint outturn and lint yield than that of the Liaomian No. 9. The PI 935 has been identified and regional tested in nine places times for four years in the southern Xinjiang Weiwuer autonomous region. It was shown that the PI 935 had the higher lint outtrn for the average 47.3% was ten-point percentage more than that of the check cultivars (Junmian No. 1 or Xinluzhong No. 5), the similar lint yield by and large and the growing period by five days later than that of the checks. The PI 935 was collected in the National Bank of Crop Germplasm (unified No. ZM 114274 and named "Zhonghuzhi PI 935").

Cobalt Radioisotopes↗

PubMed2000

Reduced inhibition in an animal model of cortical dysplasia.

Cortical dysplasia has a strong association with epilepsy in humans, but the underlying mechanisms for this are poorly understood. In utero irradiation of rats produces diffuse cortical dysplasia and neuronal heterotopia in the neocortex and hippocampus. Using in vitro neocortical slices, whole-cell patch-clamp recordings were obtained from pyramidal neurons in dysplastic cortex and control neocortex. Spontaneous IPSCs were reduced in amplitude (35%) and frequency (70%) in pyramidal cells from dysplastic cortex. Miniature IPSCs were reduced in frequency (66%) in dysplastic cortex. Two additional measures of cortical inhibition, monosynaptic evoked IPSCs and paired pulse depression of evoked EPSCs, were also impaired in dysplastic cortex. Spontaneous EPSCs were increased in amplitude (42%) and frequency (77%) in dysplastic cortex, but miniature EPSCs were not different between the two groups. These data demonstrate significant physiological impairment in inhibitory synaptic transmission in experimental cortical dysplasia. This supports previous immunohistochemical findings in this model and observations in humans of a reduction in the density of inhibitory interneurons in dysplastic cortex.

Abnormalities, Radiation-Induced↗

PubMed2000

Cryodamage to plasma membrane integrity in head and tail regions of human sperm.

AIM: To investigate the effect of cryopreservation on the plasma membrane integrity in the head and tail regions of individual sperm, and the relationship between intact cryopreserved sperm and its motility and zona-free hamster oocyte penetration rate. METHODS: The eosin Y exclusion and the hypoosmotic swelling tests were combined to form a single test (HOS-EY test) to identify the spermatozoa with four types of membrane integrity. RESULTS: After cryopreservation, there was a marked decline in the percentage of spermatozoa with Type IV membrane integrity (head membrane intact/tail membrane intact), and a significant increase in those with Type I (head membrane damaged/tail membrane damaged) and Type III (head membrane damaged/tail membrane intact) membrane integrity (n = 50, P < 0.01). The value of Type II integrity had a wide range of variability, whereas Type II (head membrane intact/tail membrane damaged) was uncommon after thawing. A high correlation was observed between the percentage of Type IV integrity and sperm motility ( n = 50, r = 0.74, P < 0.01). However, the values of Type IV integrity were usually lower than those of post-thaw motility in most cryopreserved samples. The value of Type IV integrity did not correlate with the sperm penetration rate (n = 25, r = 0.22, P > 0.05). CONCLUSION: (1) The HOS-EY test has the advantage of showing four patterns of membrane integrity in individual spermatozoon; (2) Cryopreservation causes a significant membrane rupture in the head and tail regions of spermatozoa; Type III is the main transitional state of membrane cryodamage; (3) Cryodamage to head and tail membrane may occur independently; the presence of an intact tail membrane does not necessarily indicate the intactness of head membrane. (4) Intact membranes are closely related to post-thaw motility, but do not reflect the fertilizing potential.

Adult↗

PubMed1998

Lanthanum-mediated modification of GABAA receptor deactivation, desensitization and inhibitory synaptic currents in rat cerebellar neurons.

1. We investigated La3+ effects on recombinant and native gamma-aminobutyric acid A (GABAA) receptors using rapid agonist applications and on inhibitory synaptic currents (IPSCs) in granule and stellate neurons of rat cerebellar slices. 2. Rapid desensitization of currents elicited by 200 ms pulses of 1 mM GABA to small lifted cells transfected with alpha1beta3gamma2 cDNAs was greatly decreased by the coapplication of 100 microM LaCl3. 3. GABA responses were unaffected when coapplication lasted only 2 ms. In contrast, with LaCl3 pre-perfusion, a significant slowing of deactivation in response to 2 ms applications was observed. LaCl3 pre-perfusion also prolonged the duration of responses to 20 mM taurine. 4. Outside-out patches excised from cells transfected with alpha1beta3gamma2 subunit cDNAs were briefly exposed to a saturating concentration of GABA, eliciting a transient activation of single channel currents with a main conductance of 30 pS. Opening and burst durations increased by pre-equilibration of patches with LaCl3. 5. LaCl3 depressed the peak amplitude without affecting the slow deactivation and desensitization of GABA responses in cells transfected with alpha6beta3gamma2 and alpha6beta3delta cDNAs. No significant difference in La3+ modulation of GABA-gated currents was observed between alpha1beta3gamma2 and alpha1beta3delta receptors. 6. The effects of LaCl3 on deactivation and desensitization of GABA responses observed in nucleated patches excised from rat cerebellar granule and stellate neurons were comparable to those in the cells transfected with alpha1beta3gamma2 cDNAs. In addition, La3+ clearly prolonged the spontaneous IPSC time course without changing the amplitude. 7. Our results indicate that La3+ has a dual action on GABA-gated currents: it decreases desensitization and increases channel opening duration. These actions depend on receptor subunit composition and contribute to the prolongation of IPSCs.

Animals↗

PubMed1998

Chronic dizocilpine (MK-801) reversibly delays GABA(A) receptor maturation in cerebellar granule neurons in vitro.

We investigated the effect of chronically blocking NMDA receptor stimulation to examine changes in GABA(A) receptor expression and pharmacology in cerebellar granule cells at different stages of maturation. We have previously shown that NMDA-selective glutamate receptor stimulation alters GABA(A) receptor pharmacology in cerebellar granule neurons in vitro by altering the levels of selective subunits. When NMDA receptor stimulation is blocked with MK-801 during the first week in vitro, a decrease in the alpha1, gamma2S, and gamma2L receptor subunit mRNAs occurred. When present only during the second week, changes were limited to the alpha1 and gamma2L mRNAs. Finally, if MK-801 was present during the first week and removed during the second week, these changes reversed. Whole-cell voltage-clamp recordings showed that treatment with MK-801 during either the first or second week increased the EC50 of the receptors for GABA and attenuated the potentiation mediated by flunitrazepam. Last, these properties were reversed if MK-801 was removed after the first week in vitro. Our results suggest that MK-801 reversibly inhibits GABA(A) receptor maturation by modulating receptor subunit expression and that the altered pharmacological responses appear to be dominated by changes in the levels of allosteric modulation mediated by the gamma2 receptor subunit.

Animals↗

PubMed1998

Functional and pharmacological differences between recombinant N-methyl-D-aspartate receptors.

N-methyl-D-aspartic acid (NMDA) receptors transiently transfected into mammalian HEK-293 cells were characterized with subunit-specific antibodies and electrophysiological recordings. Deactivation time course recorded in response to fast-glutamate pulses were studied in isolated and lifted cells, as well as in outside-out membrane patches excised from cells expressing recombinant NR1 subunits in combination with the NR2A, NR2B, NR2C, or NR2D NMDA receptor subunits. Transfected cells were preidentified by the fluorescence emitted from the coexpressed Aequorea victoria jellyfish Green Lantern protein. Currents generated by NR1/NR2A channels displayed double exponential deactivation time course being faster than that in NR1/NR2B or NR1/NR2C channels. However, a large decay variability was observed within each cotransfection, suggesting that mechanisms additional to subunit composition may also regulate deactivation time course. NR1/NR2D channels displayed slowly deactivating currents. Channel deactivation was fast and comparable among receptors obtained by cotransfecting five distinct spliced variants of the NR1 subunit, each with the NR2A subunit. Additionally, recovery from desensitization was slower for NR1/NR2B than for NR1/NR2A channels. The average deactivation time course of responses to brief L-glutamate applications in cells where NR1/NR2A/NR2B cDNAs were cotransfected at variable ratio was intermediate between those of the NR1/NR2A and NR1/NR2B channels. Although immunocytochemical evidence indicates that the majority of cells are cotransfected by all plasmids in triple transfection, our experimental condition did not allow for a tight control of the expression of NMDA receptor subunits. This produced the result that many cells were characterized by deactivation time course and haloperidol sensitivities of separate NR1/NR2A and NR1/NR2B subunit heteromers. We also speculate on the possible formation of channels resulting from the coassembly in the same receptor of NR1/NR2A/NR2B subunits from a minority of cells that gave responses to brief application of L-glutamate characterized by slow deactivation time course and decreased haloperidol sensitivity.

Antibodies, Monoclonal↗

PubMed1997

Neurosteroid prolongs GABAA channel deactivation by altering kinetics of desensitized states.

Fast applications of GABA (1 mM) to nucleated and outside-out patches excised from granule neurons in cerebellar slices from developing rats evoked currents with a double exponential time course reminiscent of that of IPSCs. A neurosteroid 3alpha, 21dihydroxy-5alpha-pregnan-20-one (THDOC) remarkably increased the slow deactivation time constant and slowed down recovery from desensitization, as estimated by paired-pulse GABA applications. THDOC also reduced the amplitude of GABA currents, whereas it failed to affect the fast deactivation component and its relative contribution to peak amplitude. The effects of THDOC on slow deactivation were greater in rats younger than postnatal day 13 (P13) as compared with rats at P30-P35. THDOC failed to alter deactivation of short responses induced by a less-potent agonist taurine at saturating doses. These responses had deactivation kinetics described by a fast single exponential decay, little desensitization, and quick recovery. However, THDOC slowed deactivation if taurine responses were long enough to allow consistent desensitization, suggesting that desensitized states are required for the neurosteroid to modulate GABA responses. In outside-out patches, just as desensitized states prolonged GABA responses by producing reopening of channels activated by brief GABA pulses, THDOC increased the channel open probability by further increasing the number of late channel openings, resulting in a prolongation of the slow deactivation. Our data suggest that neurosteroid potentiates the inhibitory postsynaptic transmission via the prolongation of the slow deactivation and that the alteration of kinetics of entry and exit from desensitized states underlies the allosteric modification of GABAA receptors by neurosteroids.

Age Factors↗

PubMed1996

Delta subunit inhibits neurosteroid modulation of GABAA receptors.

Neurosteroid modulation of GABAA receptors has been observed with all subunit combinations investigated; however, hetero-oligomeric GABAA receptors containing delta subunits were not studied previously. We describe the effect of delta subunit expression on 3alpha,21-dihydroxy-5alpha-pregnan-20-1 (THDOC)-induced potentiation of GABA-gated currents in transfected HEK 293 cells and in cerebellar granule cells in vitro. THDOC (100 nM) significantly potentiated GABA-gated currents in cells transfected with combinations of alpha1, alpha6, beta3, and gamma2 subunit cDNAs, whereas cotransfection of delta subunit cDNA inhibited this potentiation. In contrast, the direct Cl- channel activation by THDOC at higher concentrations (1-10 microM) was not significantly dependent on delta subunit cotransfection. These results suggest that the presence of the delta subunit inhibits GABAA receptor modulation but not the direct activation by neurosteroids. Cotransfection with delta subunit also affected the negative allosteric modulation by pregnenolone sulfate. THDOC potentiation of GABA-gated currents was greater in cerebellar granule cell cultures at 4 d in vitro (DIV) compared with those at 14 DIV. Single-cell reverse transcription-PCR analysis of the mRNAs expressed in cultured cerebellar granule cells shows that an increased number of granule cells at 14 DIV express delta subunit mRNAs as compared with 4 DIV granule cells. The presence of delta subunit mRNAs detected in individual cells correlated well with the lack of sensitivity to THDOC. These results suggest that developmental expression of GABAA receptor delta subunits may play an important role in determining the region-specific neurosteroid-induced modification of fast inhibitory synaptic function.

Allosteric Regulation↗

PubMed1996

Chronic flumazenil alters GABA(A) receptor subunit mRNA expression, translation product assembly and channel function in neuronal cultures.

Flumazenil competitively blocks the pharmacological effects of both positive and negative allosteric modulators acting at the benzodiazepine binding sites of gamma-aminobutyric acid (GABA(A)) receptors. Using quantitative reverse transcription polymerase chain reaction, label-fracture immunocytochemistry and whole-cell patch-clamp recordings, we determined changes in the contents of selected GABA(A) receptor subunit mRNA(s), in their translation products and in the electrophysiological characteristics of the receptor channels in cultured cerebellar granule cells treated daily with flumazenil (10 microM) for 4 days in vitro. The contents of the alpha1 and alpha6 receptor subunit mRNAs were significantly increased in the flumazenil-treated group as compared with the dimethyl sulfoxide vehicle-treated control group, whereas there were no significant differences in the absolute amounts of the beta2, beta3, gamma2S, gamma2L++ + and delta receptor subunit mRNAs. The gold immunolabeling densities of the alpha1 and delta receptor subunits were significantly increased, whereas those of the alpha6, beta2/beta3 and gamma2 receptor subunits were decreased. Double-immunolabeling experiments using 5- and 10-nm gold particles suggest that after chronic flumazenil treatment, receptor subunit assemblies containing the alpha1/gamma2 and alpha6/delta subunits may be replaced by a receptor assembly containing the alpha1/delta subunits. The GABA potency in eliciting Cl- channel activity decreased significantly, as indicated by the elevated EC50 values, and the positive modulation of GABA action by diazepam also decreased. These results suggest that flumazenil, perhaps by blocking the action of endogenous allosteric modulators of GABA(A) receptors, may trigger a change in the expression and assembly of the subunits of the GABA(A) receptor. This implies that there might be a dynamic state in the regulation of GABA(A) receptor structure.

Animals↗

PubMed1996

Alpha 6 and gamma 2 subunit antisense oligodeoxynucleotides alter gamma-aminobutyric acid receptor pharmacology in cerebellar granule neurons.

To characterize the role of the alpha 6 subunit in gamma-aminobutyric acid (GABA) receptors in cerebellar granule cells, primary cerebellar cultures were treated with antisense oligodeoxynucleotides (ODNs) complementary to and overlapping the initial codon of the alpha 6 subunit cDNA. The specific reduction in the expression of the alpha 6 receptor subunit protein after a 48-hr antisense ODN treatment was assessed with the use of immunoblot assays. Sister cultures were treated in parallel with mismatched (scrambled) ODNs. Inhibition of GABA-gated currents by furosemide, a selective inhibitor of GABAA receptors containing alpha 6 subunits, was attenuated after the alpha 6 antisense treatment. Furosemide was tested in parallel in transfected cells expressing various combinations of the alpha 1 and alpha 6 subunits, which showed that the relative abundance of these subunit mRNAs determines the extent of furosemide-induced inhibition of GABA-gated currents. Compared with control or mismatched ODN-treated cell cultures, treatment of granule neurons with alpha 6 antisense ODNs caused a decrease in GABA-induced maximal current density and increased the half-maximal concentration derived from GABA dose-response curves. Furthermore, the depletion of alpha 6 subunits from cerebellar granule cells enhanced flunitrazepam-induced potentiation of GABA-activated currents. In contrast, gamma 2 antisense ODN treatments of cell cultures increased the receptor sensitivity to GABA and potently decreased the response to flunitrazepam. Our results show that alpha 6 and gamma 2 subunit expression can be blocked with the use of synthetic ODNs and that these subunits are crucial determinants of the pharmacological properties of native GABAA receptors in cerebellar granule cells.

Allosteric Regulation↗

PubMed1995

NMDA-mediated modulation of gamma-aminobutyric acid type A receptor function in cerebellar granule neurons.

GABAA receptors are ligand-gated CI- ion channels with multiple clinically relevant drug-recognition sites. We have previously shown that stimulation of N-methyl-D-aspartic acid (NMDA)-specific glutamate receptors quantitatively alters selected GABAA receptor subunit mRNAs and proteins in primary cultures of rat cerebellar granule neurons. We used whole-cell recordings of GABA-elicited CI- currents and flunitrazepam binding experiments in granule cell cultures maintained in low K+ (12.5 mM), cells maintained in low K+ and treated with a single dose of NMDA (10 microM), and cell cultures maintained in depolarizing concentrations of K+ (25 mM). The EC50 obtained from the dose-response curves for GABA in eliciting a maximal response was comparable in neurons maintained in high K+ or in low K+ and treated with a single dose of NMDA, but that it increased significantly in cells maintained in low K+. The potentiation of GABA-gated CI- currents by flunitrazepam increased significantly, while the negative allosteric modulator methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) was significantly more effective in cultures either maintained in high K+ or treated with NMDA. This was coincident with a twofold increase in the Bmax associated with flunitrazepam binding. To further characterize the receptor assemblies present in the depolarization and NMDA induced paradigms, the Zn(2+)-induced inhibition of GABA-gated CI- currents was reduced as was the inhibition mediated by furosemide. Our data indicate that GABAA receptor assemblies alter their composition in response to excitatory afferent receptor stimulation.

Animals↗

PubMed1995

gamma-Aminobutyric acid gating of Cl- channels in recombinant GABAA receptors.

We studied gamma-aminobutyric acid (GABA) gated whole-cell Cl- currents after rapid transmitter application (< 10 ms) to cells expressing structurally different recombinant GABAA receptors. A variety of recombinant receptors were transiently transfected in a human cell line with three cDNAs encoding for different molecular forms of alpha-, beta- and gamma-subunits of the GABAA receptors. The maximal current amplitude elicited by GABA on recombinant GABAA receptors was greater when the alpha-subunits were combined with beta 2 gamma 2-subunits than with beta 1 gamma 2-subunits, with the exception of receptors including the alpha 6-subunit. The maximal current amplitude elicited by GABA was greater when the beta-subunits were combined with gamma 2 alpha 1-subunits than with gamma 1 alpha 1 subunits, with the exception of receptors including the beta 3-subunit. Furthermore, receptors comprising the beta 3-subunit had a greater sensitivity to GABA than those including the beta 1-or beta 2-subunits. When the gamma-subunits were substituted in receptors including alpha- and beta-subunits, the greatest current amplitude elicited by GABA was obtained with the alpha 1 beta 2 gamma 2 combination, whereas the GABA potency was greater with alpha 1 beta 2 gamma 1 and alpha 1 beta 1 gamma 3 than with the alpha 1 beta 2 gamma 2 combination. In receptors including alpha 6 beta 2-subunits the rank order of GABA maximal current amplitude was gamma 1 > gamma 2 > delta subunits.

Chloride Channels↗

PubMed1994

Changes in gamma-aminobutyrate type A receptor subunit mRNAs, translation product expression, and receptor function during neuronal maturation in vitro.

The amounts of mRNAs encoding alpha 1, alpha 6, beta 2, beta 3, gamma 2, and delta subunits of gamma-aminobutyrate type A (GABAA) receptors and the gold immunolabeling density of their translation products were monitored during the growth of neonatal rat granule cells in primary culture. We investigated possible correlations (i) between temporal changes in mRNA content and expression density of their respective translation products and (ii) between the quantitative changes of receptor subunit expression, the GABA EC50 for Cl- channel activation, and diazepam efficacy in modulating GABA action on the Cl- channels. At 3 days in vitro, the amount of GABAA receptor subunit mRNAs and the expression of their respective translation products were very low. During the next 2 weeks both parameters for every subunit studied increased asynchronously; moreover, at 14 days in vitro the sum of gamma 2 and delta subunit expression was smaller than the expression of the alpha 1 or alpha 6 or beta 2/beta 3 subunits. This suggests that during in vitro maturation each subunit may be regulated independently and invites speculation as to possible changes in specific GABAA receptor subtype abundance during development in vitro. The maximal current intensity elicited by GABA failed to increase from 5 to 14 days in vitro, though the amount of mRNA encoding various subunits and the expression density of their respective translation products increased. Thus, qualitative changes in the GABAA receptor subtypes expressed and/or abnormalities in the subunit assembly very likely account for the uniformity of the maximal current intensity elicited by GABA during in vitro development. Also, during maturation of neuronal cultures from 5 to 20 days in vitro the extent of the positive modulation of GABA action by diazepam decreased dramatically. This finding might be related to an increase in the abundance of GABAA receptors including the alpha 6 subunit and/or to the expression, during granule cell maturation in vitro, of GABAA receptors devoid of gamma 2 subunits.

Animals↗