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Biomedical subjects

R P Shank

Publications and source records attributed to R P Shank.

At least 37 records · Page 2Linked to original sources
PubMed1995

Characterization of a benzodiazepine receptor site with exceptionally high affinity for Ro 15-4513 in the rat CNS.

The binding of [3H]Ro 15-4513, [3H]flunitrazepam and [3H]flumazenil to rat CNS membranes was studied at 2 degrees C, 22 degrees C and 37 degrees C using ligand concentrations ranging from approximately 0.06 nM to 10 microM. Analysis of the binding saturation data suggested the existence of high-affinity sites (Kd < 10 nM) and low-affinity sites (Kd > 100 nM) for each ligand. When binding was performed using very low ligand concentrations a benzodiazepine site with an exceptionally high affinity for Ro 15-4513 (Kd approximately 0.1 nM) was evident in all major regions of the CNS except the cerebellum. This site was most prevalent in the hippocampus, medulla and spinal cord where it accounted for approximately 70% of the specific binding when [3H]Ro 15-4513 was approximately 0.06 nM. The selectivity of Ro 15-4513 for this site as compared to other high-affinity sites was 20- to 60-fold depending on the incubation temperature and CNS region. The affinity for the very high-affinity site was decreased approximately 3-fold as temperature was increased from 2 degrees C to 37 degrees C (Kd approximately 0.1 nM and approximately 0.3, respectively), which was similar to the effect of temperature on other high-affinity sites (Kd approximately 2.6 nM at 2 degrees C and approximately 8 nM at 37 degrees C). Flumazenil, flunitrazepam, and diazepam did not differentiate the very high-affinity [3H]Ro 15-4513 site from other BZ sites, but alpidem exhibited a low affinity for it (IC50 approximately 5 microM). GABA at 100 microM had little effect on the Kd value for the very high-affinity site (GABA shift: approximately 0.8 to 1.0), suggesting that Ro 15-4513 is a partial inverse agonist or an antagonist at this site. These findings provide further evidence for the pharmacologic diversity of BZ sites on different subtypes of GABAA receptors.

Affinity Labels↗
PubMed1995

Interaction of abecarnil, bretazenil, and RO 19-8022 with diazepam-sensitive and -insensitive benzodiazepine sites in the rat cerebellum and cerebral cortex.

Abecarnil, bretazenil, and Ro 19-8022 inhibited the binding of [3H]Ro 15-4513 to diazepamsensitive and -insensitive sites in the rat cerebellum and cerebral cortex, but all three had a much higher affinity for the diazepam-sensitive sites in both tissues. The GABA-shift for bretazenil and Ro 19-8022 was low ( < 2) for all sites studied, consistent with their partial agonistic profile. The GABA-shift for abecarnil was appreciably higher for diazepam-sensitive binding in the cerebellum than in the cerebral cortex (1.97 vs 1.18). Furthermore, the GABA-shift for abecarnil was markedly different for the diazepam-sensitive and -insensitive sites in the cerebellum (1.97 vs 0.71). All three compounds inhibited [3H]Ro 15-4513 binding to the diazepam-sensitive sites with a slope factor > 1, suggestive of positive cooperativity in their binding to GABAA receptors. Abecarnil only partially inhibited diazepam-insensitive binding of [3H]Ro 15-4513 in the cerebellum, indicating that this site can be differentiated into abecarnil-sensitive and -insensitive components.

Animals↗
PubMed1995

Serotonin and norepinephrine uptake inhibiting activity of centrally acting analgesics: structural determinants and role in antinociception.

Although it is well established that the analgesic effects of morphine are mediated by opioid receptors, previous studies have shown that some opioids additionally inhibit the uptake of serotonin and norepinephrine. The present investigation of a diverse group of opioids revealed that structurally identifiable subgroups inhibited the neuronal reuptake of these monoamines. Phenanthrene opioids with an oxygen bridge between C4 and C5, such as morphine and naloxone (group I), did not block norepinephrine or serotonin uptake, whereas phenanthrene opioids without the oxygen bridge and the C6-OH moiety, such as levorphanol and levomethorphan (group II), did inhibit uptake, as did nonphenanthrene opioids, such as d-propoxyphene and methadone (group III). Affinity at the mu opioid receptor correlated with antinociceptive potency (r = 0.87, P < .05). Although the antinociceptive activity of the "active enantiomers" of group II and III compounds also correlated with their affinity at the mu opioid receptor (r = 0.85, P = .007), additional consideration of serotonin uptake inhibiting activity (but not of norepinephrine uptake inhibiting activity) significantly improved the correlation between antinociceptive potency and the in vitro activity of these compounds (r = 0.915, P = .0017). Additionally, for group II and III (but not group I) compounds, smaller differences between enantiomers in antinociceptive potency than in mu receptor affinity were noted, presumably because of the contribution of uptake inhibition to the antinociceptive activity of group II and III compounds. Evidence also is provided suggesting a broader role for the combination of mu opioid affinity and 5-hydroxytryptamine uptake inhibition in the activity of other antinociceptive agents.

Analgesics, Opioid↗
PubMed1993

2-Oxoglutarate transport: a potential mechanism for regulating glutamate and tricarboxylic acid cycle intermediates in neurons.

2-Oxoglutarate (alpha-ketoglutarate) is transported into synaptosomal and synaptoneurosomal preparations by a Na(+)-dependent, high-affinity process that exhibits complex kinetics, and is differentially modulated by glutamate, glutamine, aspartate, malate, and a soluble, heat-labile substance of high molecular weight present in rat brain extracts. Glutamate and aspartate generally inhibit 2-oxoglutarate uptake, but under certain conditions may increase uptake. Glutamine generally increases 2-oxoglutarate uptake, but under certain conditions may inhibit uptake. One interpretation of our results is that 2-oxoglutarate uptake is mediated primarily by a transporter that exhibits negative cooperativity and possesses three regulatory sites that differentially modulate substrate affinity, Vmax, and negative cooperatively. Glutamate, aspartate, malate, and 2-oxoglutarate itself may interact with a site that reduces substrate affinity; whereas glutamine, and possibly glutamate and aspartate, appear to interact with another site that increases Vmax. A putative regulatory protein appears to abolish negative cooperativity and increases substrate affinity in the absence of glutamine. Based on the evidence that glutamatergic and GABAergic neurons depend on astrocytes to supply precursors to replenish their neurotransmitter and tricarboxylic acid cycle pools, the uptake of 2-oxoglutarate, presumably into synaptic terminals, may reflect a role for this metabolite in replenishing the transmitter and tricarboxylic acid pools, and a role for the transporter as a site at which these pools are regulated.

Ammonium Sulfate↗
PubMed1993

Cerebral metabolic compartmentation as revealed by nuclear magnetic resonance analysis of D-[1-13C]glucose metabolism.

Nuclear magnetic resonance (NMR) was used to study the metabolic pathways involved in the conversion of glucose to glutamate, gamma-aminobutyrate (GABA), glutamine, and aspartate. D-[1-13C]Glucose was administered to rats intraperitoneally, and 6, 15, 30, or 45 min later the rats were killed and extracts from the forebrain were prepared for 13C-NMR analysis and amino acid analysis. The absolute amount of 13C present within each carbonatom pool was determined for C-2, C-3, and C-4 of glutamate, glutamine, and GABA, for C-2 and C-3 of aspartate, and for C-3 of lactate. The natural abundance 13C present in extracts from control rats was also determined for each of these compounds and for N-acetylaspartate and taurine. The pattern of labeling within glutamate and GABA indicates that these amino acids were synthesized primarily within compartments in which glucose was metabolized to pyruvate, followed by decarboxylation to acetyl-CoA for entry into the tricarboxylic acid cycle. In contrast, the labeling pattern for glutamine and aspartate indicates that appreciable amounts of these amino acids were synthesized within a compartment in which glucose was metabolized to pyruvate, followed by carboxylation to oxaloacetate. These results are consistent with the concept that pyruvate carboxylase and glutamine synthetase are glia-specific enzymes, and that this partially accounts for the unusual metabolic compartmentation in CNS tissues. The results of our study also support the concept that there are several pools of glutamate, with different metabolic turnover rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1993

Analysis of [1-13C]D-glucose metabolism in cultured astrocytes and neurons using nuclear magnetic resonance spectroscopy.

The metabolism of [1-13C]D-glucose by astrocytes, neurons and mixed astroglial/neuronal cultures derived from the striatum of fetal rats was studied using NMR. Metabolic activity was studied in resting and depolarized cells (55 mM K+), with dibutyryl cyclic-AMP added to the medium to promote cell differentiation, and with glutamate (0.1 mM) included in the medium. Due to sample limitations the accumulation of 13C label in metabolites within the cells was not sufficient to quantitate. Of the metabolites released into the medium by the astrocyte cultures and the mixed astroglial/neuronal cultures, measurable amounts of label were present in lactate C-3 and C-2, glutamine C-2, C-3 and C-4, acetate C-2, citrate C-2 or C-4 and C-3, glycerol C-1 or C-3, succinate C-2 or C-3 and several unidentified metabolites. Of the labeled metabolites released into the medium, only succinate was markedly affected by K(+)-induced depolarization, dBcAMP, or glutamate. The label in succinate was increased, especially in the K(+)-depolarized astrocyte cultures (3- to 6-fold). The neuronal cultures consumed [1-13C]D-glucose much more slowly than the astrocyte cultures or the mixed cultures. Except for lactate C-3, there was no measurable 13C in metabolites in the medium of the neuronal cultures.

Acetates↗
PubMed1993

Kinetics of 2-oxoglutarate uptake by synaptosomes from bovine and rat retina and cerebral cortex and regulation by glutamate and glutamine.

2-Oxoglutarate (2-OG) is a metabolic precursor of glutamate and may be utilized to replenish the neurotransmitter pool. 2-OG is rapidly transported into neurons by a high-affinity carrier that is particularly prevalent in glutamatergic terminals. Here we report the kinetics of [U-14C]2-OG uptake by crude synaptosomal preparations from bovine and rat retina and brain, and the modulatory effects of glutamate and glutamine. In all four tissues, 2-OG uptake was mediated by a high-affinity system (Kt approximately 1 microM) that was subject to negative feedback control by glutamate and biphasic modulation by glutamine (another precursor of neurotransmitter glutamate).

Animals↗
PubMed1993

Complementary and synergistic antinociceptive interaction between the enantiomers of tramadol.

The explanation for the co-existence of opioid and nonopioid components of tramadol-induced antinociception appears to be related to the different, but complementary and interactive, pharmacologies of its enantiomers. The (+) enantiomer had Ki values of only 1.33, 62.4 and 54.0 microM at mu, delta and kappa receptors, respectively. The (-) enantiomer had even lower affinity at the mu and delta sites (Ki = 24.8, 213 and 53.5 microM, respectively. The (+) enantiomer was the most potent inhibitor of serotonin uptake (Ki = 0.53 microM) and the (-) enantiomer was the most potent inhibitor of norepinephrine uptake (Ki = 0.43 microM). Basal serotonin release was preferentially enhanced by the (+) enantiomer and stimulation-evoked norepinephrine release was preferentially enhanced by the (-) enantiomer. The (+) and (-) enantiomers each independently produced centrally mediated antinociception in the acetylcholine-induced abdominal constriction test (ED50 = 14.1 and 35.0 micrograms i.t., respectively). Racemic tramadol was significantly more potent (P < .05) than the theoretical additive effect of the enantiomers (antinociceptive synergy). Synergy was also demonstrated (P < .1) in the mouse 55 degrees C hot-plate test (i.p. route) and (P < .05) the rat Randall-Selitto yeast-induced inflammatory nociception model (i.v. and i.p. routes). Critically, the enantiomers interacted less than synergistically in two side-effects of inhibition of colonic propulsive motility and impairment of rotarod performance. The racemate and the (+) enantiomer were active in a chronic (arthritic) inflammatory pain model. Taken together, these findings provide a rational explanation for the coexistence of dual components to tramadol-induced antinociception and might form the basis for understanding its clinical profile.

Acetylcholine↗
PubMed1992

1,3-Di(2-[5-3H]tolyl)guanidine labels more than one site in rat forebrain.

Studies of 1,3-di-(2-[5-3H]tolyl)guanidine ([3H]DTG) binding to rat brain membranes revealed that [3H]DTG binds to a high and a low affinity site with Kd values of 19.8 nM and 1.31 microM (corresponding Bmax values 291 fmol/mg protein and 8.68 pmol/mg protein). The order of potency of competitors for [3H]DTG binding revealed a binding profile typical of sigma site ligands. Several sigma ligands such as the enantiomers of 3-PPP (3-(3-hydroxyphenyl)-N- (n-propyl)piperidine) and (+/-)-pentazocine exhibited biphasic competition profiles for [3H]DTG binding, whereas other sigma ligands such as haloperidol displayed monotonic competition curves. Neither phenytoin nor carbamazepine were observed to enhance [3H]DTG binding. These data support the hypothesis that multiple sigma binding sites exist. The lack of phenytoin and carbamazepine modulation of [3H]DTG binding are in agreement with the proposed greater density of sigma site 2 in the rat, since allosteric modulation has been ascribed to the DM1/sigma 1 site.

Animals↗
PubMed1992

Adenosine 5'-monophosphate transport across the membrane of synaptosomes and myelin.

Synaptosome-enriched preparations from rat and guinea pig brain tissue vigorously accumulated [3H]-adenosine 5'-monophosphate ([3H]AMP). When the accumulation of [3H]AMP was determined using incubation periods of 30 s or less, high concentrations of adenosine, dipyridamole and soluflazine did not inhibit the accumulation of label appreciably. The accumulation of [3H]AMP was saturable, temperature-dependent, osmotic-sensitive and exhibited structural specificity. Based on the kinetics of uptake by different subcellular fractions, and the inhibitory effects of other nucleotides, the uptake of AMP appeared to be mediated by three saturable systems with Kt values of approximately 0.2, 6, and 100 microM. The transport system with the highest affinity for AMP was selectively inhibited by guanosine 5'-monophosphate, and its Vmax was several fold higher in a myelin-enriched fraction than in synaptosome-enriched fractions. The transport system with the Kt approximately 6 microM was selectively inhibited by alpha, beta-methylene adenosine diphosphate, and its Vmax was several times higher in a fraction enriched in high-density synaptosomes than in fractions enriched in low-density synaptosomes or myelin. Both of these transport systems were potently inhibited by ATP and ADP. Nucleotides that were either weak or inactive as inhibitors of AMP transport included 3'-AMP, cyclic AMP, guanosine 5'-diphosphate, and the 5'-mononucleotides of cytosine, inosine, and uridine. GTP consistently enhanced uptake at concentrations greater than or equal to 1 microM. The transport of AMP was not Na(+)-dependent and was not inhibited by membrane depolarization. This transport system may mediate the release of AMP for subsequent conversion to adenosine extracellularly.

Adenosine Diphosphate↗
PubMed1992

Etoperidone, trazodone and MCPP: in vitro and in vivo identification of serotonin 5-HT1A (antagonistic) activity.

The Ki values for etoperidone, trazodone and MCPP (m-chlorophenylpiperazine dihydrochloride) at 5-HT1A sites (using rat cerebral cortical synaptosomes and [3H]8-OH-DPAT) were determined to be 20.2, 23.6 and 18.9 nM, respectively. In an effort to elucidate the functional nature of the interaction at 5-HT1A sites in vivo, the ability of each compound to elicit reciprocal forepaw treading (RFT) or to block the RFT induced by 8-OH-DPAT in reserpinized rats was tested. Specifically, 8-OH-DPAT (1.0 mg/kg SC)-challenged or non-challenged (control) reserpinized (1.0 mg/kg SC) rats were administered etoperidone, trazodone or MCPP (IP) and scored for the elicitation of RFT (indicative of 5-HT1A agonistic activity) or for block of RFT induced by 8-OH-DPAT (indicative of 5-HT1A antagonistic activity). Reference compounds confirmed the specificity of the test. We report that etoperidone, trazodone and MCPP inhibited 8-OH-DPAT-induced RFT (ID50 = 17.4, 23.8 and 13.4 mg/kg, respectively). Only marginal RFT was produced in non-challenged animals by etoperidone and trazodone at a high dose (40 mg/kg). Taken together, the results suggest a predominant antagonistic activity of etoperidone, trazodone and MCPP at 5-HT1A receptor sites in rat central nervous system. However, one cannot rule out the possibility that these compounds are weak partial agonists. This activity may be relevant to the antidepressant action of these compounds.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1992

Opioid and nonopioid components independently contribute to the mechanism of action of tramadol, an 'atypical' opioid analgesic.

Tramadol hydrochloride produced dose-related antinociception in mouse abdominal constriction [ED50 = 1.9 (1.2-2.6) mg/kg i.p.], hot-plate [48 degrees C, ED50 = 21.4 (18.4-25.3) mg/kg s.c.; 55 degrees C, ED50 = 33.1 (28.2-39.1) mg/kg s.c.] and tail-flick [ED50 = 22.8 (19.2-30.1) mg/kg s.c.] tests. Tramadol also displayed antinociceptive activity in the rat air-induced abdominal constriction [ED50 = 1.7 (0.7-3.2) mg/kg p.o.] and hot-plate [51 degrees C, ED50 = 19.5 (10.3-27.5) mg/kg i.p.] tests. The antinociceptive activity of tramadol in the mouse tail-flick test was completely antagonized by naloxone, suggesting an opioid mechanism of action. Consistent with this, tramadol bound with modest affinity to opioid mu receptors and with weak affinity to delta and kappa receptors, with Ki values of 2.1, 57.6 and 42.7 microM, respectively. The pA2 value for naloxone obtained with tramadol in the mouse tail-flick test was 7.76 and was not statistically different from that obtained with morphine (7.94). In CXBK mice, tramadol, like morphine, was devoid of antinociceptive activity after intracerebroventricular administration, suggesting that the opioid component of tramadol-induced antinociception is mediated by the mu-opioid receptor. In contrast to the mouse tail-flick test and unlike morphine or codeine, tramadol-induced antinociception in the mouse abdominal constriction, mouse hot-plate (48 degrees or 55 degrees C) or rat hot-plate tests was only partially antagonized by naloxone, implicating a nonopioid component. Further examination of the neurochemical profile of tramadol revealed that, unlike morphine, it also inhibited the uptake of norepinephrine (Ki = 0.79 microM) and serotonin (0.99 microM). The possibility that this additional activity contributes to the antinociceptive activity of tramadol was supported by the finding that systemically administered yohimbine or ritanserin blocked the antinociception produced by intrathecal administration of tramadol, but not morphine, in the rat tail-flick test. These results suggest that tramadol-induced antinociception is mediated by opioid (mu) and nonopioid (inhibition of monoamine uptake) mechanisms. This hypothesis is consistent with the clinical experience of a wide separation between analgesia and typical opioid side effects.

Animals↗
PubMed1991

Structurally novel antihypertensive compound, McN-5691, is a calcium channel blocker in vascular smooth muscle.

These studies were conducted to gain greater understanding of the mechanism of action of the chemically novel antihypertensive agent, McN-5691. McN-5691 (1 and 10 microM) prevented 60 mM KCl-induced contraction and calcium uptake and caused concentration-dependent relaxation (EC50 = 190 microM) of 30 mM KCl-contracted aortic rings. At or below 10 microM, McN-5691 had no effects on basal tone or calcium uptake (45Ca) in isolated rings of rabbit thoracic aorta. McN-5691 caused complete high affinity inhibition (Kd = 39.5 nM) of specific diltiazem binding to the benzothiazepine receptor on the voltage-sensitive calcium channel in skeletal muscle microsomal membranes. In contrast to diltiazem, McN-5691 inhibited specific dihydropyridine receptor binding, but the effect was biphasic with high (Kd = 4.7 nM) and low (Kd = 919.8 nM) affinity components. These findings suggest that McN-5691 is a voltage-sensitive calcium channel blocker. Unlike other calcium channel blockers, McN-5691 inhibited norepinephrine (NE)-induced contraction (10 microM) and calcium uptake (1 and 10 microM) and caused concentration-dependent relaxation (EC50 = 159 microM) of 1 microM NE-contracted rings of rabbit thoracic aorta. The vascular relaxant effects of McN-5691 were not related to increased calcium (45Ca) efflux from vascular smooth muscle cells. The effects of McN-5691 on NE-induced contraction were unrelated to intracellular mechanisms because McN-5691 did not affect NE-induced contraction in the absence of extracellular calcium. McN-5691 had weak activity in rat cerebral cortical membrane alpha-1 or alpha-2 adrenergic receptor binding assays. McN-5691-induced vasodilation of phenylephrine-contracted rat aortic strips was not reversible by high potassium, indicating that McN-5691 does not induce relaxation of blood vessels through potassium channel activation. In summary, these studies suggest that the primary vasodilator mechanism of McN-5691 is calcium channel blockade through competitive binding at the diltiazem site on the voltage sensitive calcium channel. McN-5691 may possess an additional vasodilator mechanism of action distinct from alpha adrenergic receptor blockade but involving a cell membrane-related event apparently leading to attenuation of receptor-operated calcium channel activity.

Animals↗
PubMed1990

Pyrroloisoquinoline antidepressants. 3. A focus on serotonin.

A collection of hexahydropyrroloisoquinoline derivatives (1-22), which represent a class of compounds that inhibit the neuronal uptake of dopamine (DA), norepinephrine (NE), and serotonin (5-HT), was investigated in vivo for serotonin-potentiating properties in the mouse head-twitch and rat serotonin syndrome assays. The p-methylthio compound 3b (McN-5652-Z) was found to possess exceptional activity in these assays, and the activity was attributable almost exclusively to the (+)-6S,10bR enantiomer. Ten closely related analogues were synthesized, tested, and compared among themselves and with some previously prepared compounds, both in vivo and in vitro. Several trans diastereomers exhibited strong inhibition of 5-HT uptake and substantial potentiation of 5-HT, while the cis diastereomers (3a, 4a, and 10a) tested were virtually devoid of such activity. Although 3b was only moderately selective in inhibiting the uptake of 5-HT vs NE, its 10-substituted analogues 4b, 7b-9b had improved 5-HT selectivity relative to NE, to the extent of 20-25 times (150-200 times relative to DA). Of these more selective compounds (in vitro), only 4b and 7b had substantial activity in vivo. Sulfoxide 11b appeared to function as a prodrug of 3b in vivo.

Animals↗
PubMed1990

Adenosine transport by rat and guinea pig synaptosomes: basis for differential sensitivity to transport inhibitors.

Adenosine transport by rat and guinea pig synaptosomes was studied to establish the basis for the marked differences in the potency of some transport inhibitors in these species. An analysis of transport kinetics in the presence and absence of nitrobenzylthioinosine (NBTI) using synaptosomes derived from several areas of rat and guinea pig brain indicated that at least three systems contributed to adenosine uptake, the Km values of which were approximately 0.4, 3, and 15 microM in both species. In both species, the system with the Km of 3 microM was potently (IC50 of approximately 0.3 nM) and selectively inhibited by NBTI. This NBTI-sensitive system accounted for a greater proportion of the total uptake in the guinea pig than in the rat and was inhibited by dipyridamole, mioflazine, and related compounds more potently in the guinea pig. Preliminary experiments with other species indicate that adenosine transport in the mouse is similar to that in the rat, whereas in the dog and rabbit, it is more like that in the guinea pig. In the rat, none of the systems appeared to require Na+, but the two systems possessing the higher affinities for adenosine were inhibited by veratridine- and K(+)-induced depolarization. The transport systems were active over a broad pH range, with maximal activity between pH 6.5 and 7.0. Our results are consistent with the possibility that adenosine transport systems may be differentiated into uptake and release systems.

Adenosine↗
PubMed1990

Ion and temperature effects on the binding of gamma-aminobutyrate to its receptors and the high-affinity transport system.

A set of procedures was developed to study the binding of gamma-[3H]aminobutyric acid ([3H]GABA) to GABAA and GABAB receptors, and to the Na(+)-dependent transport carrier, at 25 and 37 degrees C in the presence of physiological concentrations of Na+. The membrane preparation used in these procedures was not subjected to freeze-thawing or treatment with Triton X-100. Isoguvacine, (-)-baclofen, and (-)-nipecotate were used to block selectively the binding to GABAA receptors, GABAB receptors, and the transport site, respectively. Analysis of the binding characteristics of [3H]GABA to the GABAA receptor suggested the existence of high-(KD less than 30 nM), middle- (KD = 100-500 nM), and low-affinity (KD greater than 5 microM) binding sites. However, the binding data in the middle-affinity region (100-1,000 nM) were often indicative of cooperativity. The affinity between GABA and the GABAA receptor was reduced modestly by increases in temperature and by the presence of Cl- at physiological concentrations. Binding to the GABAB receptor required Ca2+ and Cl-. Apparent binding to the transport carrier required both Na+ and Cl-. A comparison of Bmax values in three brain regions revealed an inverse relationship between the high-affinity site of the GABAA receptor and the transport binding site.

Animals↗