Regional heterogeneity in the response of astrocytes following traumatic brain injury in the adult rat

The regional distribution and temporal appearance of astrocytes expressing glial fibrillary acidic protein (GFAP), S100 protein, and vimentin were determined in a nonpenetrating lateral fluid percussion (LFP) brain injury model. Following injury, reactive astrocytes were observed in the subcortical white matter tracts as early as 1 day, in the hippocampus and injured cortex by 3 days, and in the thalamus by 1 week. Reactive astrocytes in the injured cortex, subcortical white matter tracts, and CA3 region of the hippocampus were all vimentin positive at 1 month post-injury. These astrocytes had a distinct morphology characterized by an enlarged cell body and long intertwined processes. In contrast, reactive astrocytes in the thalamic nuclei never expressed vimentin, and displayed an enlarged cell body with thick shortened processes. An increase in S100 protein was detected in all reactive astrocytes following LFP brain injury. Quantitative assessment of GFAP, S100, and vimentin polypeptides confirmed the immunohistochemical evaluation. Our data indicate that although astrogliosis mirrors the spatial pattern of post-traumatic neuronal cell loss, the expression of vimentin and the cellular morphology of the cells were regionally distinct, suggesting that astrogliosis may be modulated by factors present in the post-traumatic brain.

The effect of lipopolysaccharide on growth factor-induced mitogenesis in human gingival fibroblasts

Quiescent and non-quiescent human gingival fibroblasts (HGF) were incubated for 24 hours with Actinobacillus actinomycetemcomitans lipopolysaccharide (LPS) and/or growth factors (interleukin-1 beta [IL-1 beta], insulin, epidermal growth factor [EGF], platelet-derived growth factor [PDGF], fibroblast growth factor [FGF], and transforming growth factor-beta [TGF-beta]) to examine the ability of LPS to modify HGF proliferation in response to these autocrine and paracrine growth factors. A. actinomycetemcomitans LPS at high concentrations (> or = 9 micrograms/well) generally resulted in a reduction in DNA synthesis in quiescent and non-quiescent fibroblasts; however, LPS at low concentrations (< 9 micrograms/well) showed a minimal enhancement of DNA synthesis (40 to 60%) in quiescent and non-quiescent cells. HGF co-incubated with mitogenic agents and LPS (9 micrograms/well) exhibited suppression of growth factor-induced 3H-Tdr uptake compared to growth factor-stimulated controls. In contrast, 3H-Tdr uptake was slightly elevated with addition of LPS at low concentrations (0.09 microgram/well). These trends were seen with all growth factors tested. Non-quiescent cells, in general, were more responsive to the growth factors and LPS/growth factor combinations when compared to the quiescent HGF. HGF were further tested for the ability of LPS to alter growth factor responsiveness by pretreating the cells with LPS prior to incubation of the growth factor, as well as, subsequent addition of LPS to growth factor-pretreated cells. Similar patterns were observed as above, except IL-1 beta-pretreated quiescent and non-quiescent HGF followed by LPS addition demonstrated a marked elevation in proliferation when compared to IL-1 beta stimulated controls. These findings suggest that LPS may potentially modulate the proliferative rate of connective tissue undergoing inflammatory or growth factor-induced reparative processes in periodontal lesions.

Characterization of the human brain putative A2B adenosine receptor expressed in Chinese hamster ovary (CHO.A2B4) cells

1. An [3H]-adenine pre-labelling methodology was employed to assay cyclic AMP generation by adenosine analogues in Chinese hamster ovary (CHO.A2B4) cells, transfected with cDNA which has been proposed to code for the human brain A2B adenosine receptor, and in guinea-pig cerebral cortical slices. 2. Adenosine analogues showing the following rank order of potency in the CHO.A2B4 cells (pD2 value): 5'-N-ethylcarboxamidoadenosine (NECA, 5.91) > adenosine (5.69) > 2-chloroadenosine (5.27) > N6-(2-(4-aminophenyl)-ethylamino)adenosine (APNEA, 4.06). The purportedly A2A-selective agonist, CGS 21680, failed to elicit a significant stimulation of cyclic AMP generation at concentrations up to 10 microM in CHO.A2B4 cells. In the guinea-pig cerebral cortex, NECA was more potent than APNEA with pD2 values of 5.91 and 4.60, respectively. 3. Of these agents, NECA was observed to exhibit the greatest intrinsic activity in CHO.A2B4 cells (ca. 10 fold stimulation of cyclic AMP), while, in comparison, maximal responses to adenosine (32% NECA response), 2-chloroadenosine (61%), and APNEA (73%) were reduced. 4. Antagonists of NECA-evoked cyclic AMP generation showed the rank order of apparent affinity (apparent pA2 value in CHO.A2B4 cells: guinea-pig cerebral cortex): XAC (7.89: 7.46) > CGS 15943 (7.75: 7.33) > DPCPX (7.16: 6.91) > PD 115,199 (6.95: 6.39) > 8FB-PTP (6.52: 6.55) > 3-propylxanthine (4.63: 4.59). 5. We conclude that, using the agents tested, the A2B adenosine receptor cloned from human brain expressed in Chinese hamster ovary cells exhibits an identical pharmacological profile to native A2B receptors in guinea-pig brain.

Alpha-adrenoceptor mediated responses of the cauda epididymis of the guinea-pig

1. The subtypes of alpha-adrenoceptor mediating the contractile responses of the cauda epididymis of the guinea-pig were investigated. The alpha 1-adrenoceptor agonist phenylephrine, but not the alpha 2-adrenoceptor agonist, xylazine (up to 10 microM), elicited concentration-dependent contractions from preparations of cauda epididymis (EC50 3.4 microM). The L-type Ca2+ channel antagonist, nifedipine (10 microM), reduced the maximal response to phenylephrine (by 77%). Preincubation of tissues with the alpha 1B-adrenoceptor-alkylating agent, chloroethylclonidine (50 microM, 30 min), shifted phenylephrine concentration-response curves to the right (4 fold) only when the alpha 2-adrenoceptor antagonist idazoxan (100 nM) was included during the pre-incubation with chloroethylclonidine. 2. Xylazine (1 microM) significantly shifted phenylephrine concentration-response curves to the left (3 fold); this effect was attenuated by idazoxan (100 nM). Both the incubation of preparations with nifedipine (10 microM) and the pre-incubation of preparations with chloroethylclonidine (50 microM, 30 min) attenuated the potentiating effects of xylazine (1 microM). Protection of alpha 2-adrenoceptors with idazoxan (100 nM) during the chloroethylclonidine (50 microM, 30 min) incubation restored the xylazine-mediated enhancement of phenylephrine concentration-response curves. Pertussis toxin (200 ng ml-1, 24 h) attenuated the xylazine (1 microM)-mediated potentiation of phenylephrine concentration-response curves. 3. Following the pre-incubation of preparations with chloroethylclonidine (50 microM, 30 min) 5-methylurapidil (10 nM to 3 microM) shifted phenylephrine concentration-response curves, in parallel, to the right with mean pKB values in the range of 8.27 (at 10 nM 5-methylurapidil) to 7.76 (at 3 microM 5-methylurapidil), the addition of idazoxan (100 nM) to the incubation medium did not significantly affect the 5-methylurapidil (10 to 300 nM) pKB values (8.41 to 7.64, respectively). In the presence of both idazoxan (100 nM) and nifedipine (10 microM), and following the pre-incubation with chloroethylclonidine (50 microM, 30 min), 5-methylurapidil (30 to 300 nM) still shifted phenylephrine concentration-response curves to the right (pKB values 7.77 to 7.36, respectively). 4. Phenylephrine (1 microM to 1 mM) increased the accumulation of [3H]-inositol phosphates (10 fold) in preparations of cauda epididymis (EC50 12 microM). This effect was sensitive to chloroethylclonidine pretreatment (50 microM, 30 min), antagonized with low affinity by 5-methylurapidil (- log pKi 7.8), but not potentiated by xylazine (1 microM). Xylazine (10 nM - 100 microM) reversed the forskolin (10 or 30 microM) stimulated accumulation of [3H]-adenosine 3':5'-cylic monophosphate (cyclic AMP) in preparations of cauda epididymis (by approximately 45%). Incubation of tissues with both pertussis toxin (200 ng ml-1, 24 h) and pertussis toxin vehicle increased the basal activity of adenylate cyclase (3 fold) but did not increase the capacity of forskolin (30 microM) to stimulate the accumulation of [3H]-cyclic AMP in these tissues. Xylazine did not significantly inhibit the forskolin-stimulated accumulation of [3H]-cyclic AMP in either vehicle or pertussis toxin treated tissues. 5. These studies indicate that the epididymis of the guinea-pig contains alpha 1- and alpha 2-adrenoceptors. On the basis of the actions of chloroethylclonidine and 5-methylurapidil the alpha 1-adrenoceptors of this tissue may be of the alpha 1A- and alpha 1B-subtypes and are linked to both the influx of extracellular Ca2+ and to phospholipase C. The alpha 2-adrenoceptors of this tissue are negatively coupled to adenylate cyclase, sensitive to pertussis toxin, but do not amplify phenylephrine-stimulated [3H]-inositol phosphate accumulation. Stimulation of the alpha 2-adrenoceptors of this tissue may selectively potentiate the influx of extracellular Ca2+.

Adenosine A1 receptor-mediated inhibition of cyclic AMP accumulation in type-2 but not type-1 rat astrocytes

The effects of adenosine receptor-selective ligands on [3H]cyclic AMP accumulation have been investigated in type-1 and type-2 astrocyte-enriched cultures derived from neonatal rat forebrains. In type-1 astrocytes, 5'-N-ethylcarboxamidoadenosine (NECA) caused a concentration-dependent increase in [3H]cyclic AMP accumulation (EC50 = 1.2 microM) which was antagonised by pretreatment with either xanthine amine congener (8-[4-[[[[(2-aminoethyl)amino]carbonyl]methyl]oxy]-phenyl]- 1,3-dipropylxanthine, apparent Kd = 9 nM) or PD115,199 (N-[2-(dimethylamino)ethyl]-N-methyl-4-(1,3-dipropylxanthine) benzene sulphonamide, apparent Kd = 122 nM). In these cultures, N6-cyclopentyladenosine (CPA), did not affect forskolin- or isoprenaline-mediated elevations of [3H]cyclic AMP accumulation. These data indicate that type-1 astrocytes possess adenosine A2B but not adenosine A1 receptors coupled to adenylyl cyclase. In type-2 astrocyte-enriched cultures, 10 microM NECA caused significant elevations of [3H]cyclic AMP accumulation which were similarly inhibited by either 1 microM xanthine amine congener or 10 microM PD115,199 suggesting that they were primarily due to adenosine A2B receptor stimulation. However, CGS 21680 ((2-[[4-(2-carboxyethyl) phenethyl]-amino]adenosine-5'-N-ethylcarboxamide, 10 microM), also significantly increased [3H]cyclic AMP accumulation in type-2 astrocytes suggesting the additional presence of adenosine A2A receptors. Forskolin-mediated elevations of [3H]cyclic AMP accumulation in type-2 astrocytes were inhibited in a concentration-dependent manner by CPA. This effect was reversed by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 microM), confirming the presence of adenosine A1 receptors negatively coupled to adenylyl cyclase in type-2 astrocytes.

A high performance liquid chromatography ? inductively coupled plasma-mass spectrometry interface employing desolvation for speciation studies of platinum in chemotherapy drugs

A novel interface between high performance liquid chromatography (HPLC) and inductively coupled plasma-mass spectrometry (ICP-MS) is described. The eluent from the HPLC is nebulised into a heated cyclone spray-chamber and the solvent removed using a Nafion membrane drier, held at 75 degrees C, and a cryogenic condenser. The condenser consists of 6 Peltier heat pumps connected to liquid cooled aluminium blocks. At a nebuliser gas flow rate of 0.6 l min(-1), the membrane drier removes 58% of the vapour and the Peltier condenser 75% of the remaining vapour, i.e. a total desolvation efficiency of 89%. This enables the use of HPLC solvents which otherwise would destabilise the ICP, e.g. 100% acetonitrile or methanol, and permits the use of solvent gradients with minimal baseline drift. The system has been applied to the determination of platinum species in an organoplatinum drug used for chemotherapy in human plasma ultrafiltrate of patients treated with this new drug (JM-216). The limit of detection for platinum species has been 0.6 ng nl(-1) (i.e. 120 pg of Pt) and several species have been separated with good resolution.

Comparison of duration of agonist action at beta 1- and beta 2- adrenoceptors in C6 glioma cells: evidence that the long duration of action of salmeterol is specific to the beta 2-adrenoceptor

The C6 glioma cell line, which expresses beta 1- and beta 2-adrenoceptors at a ratio of 80:20, was used to investigate the durations of action of formoterol at beta 1-adrenoceptors and of salmeterol at both beta 1- and beta 2-adrenoceptors in an attempt to determine whether the sustained duration of action of salmeterol was unique to beta 2-adrenoceptors or, as with formoterol, resulted from its lipophilic nature and partitioning into the bulk lipid of the plasma membrane. In this cell line, formoterol, like the nonselective beta-adrenoceptor agonist isoprenaline, behaved as a potent, full agonist at beta 1-adrenoceptors and did not seem to exhibit a high degree of selectivity for beta 2-adrenoceptors. Salmeterol seemed to stimulate cAMP accumulation in C6 cells predominantly via activation of the subpopulation of beta 2-adrenoceptors. However, at high (micromolar) agonist concentrations, salmeterol also activated beta 1-adrenoceptors, albeit with low potency and efficacy. At high concentrations (30 microM), salmeterol attenuated cAMP responses mediated by activation of beta 1-adrenoceptors by isoprenaline (Kp = 1.6 microM), indicating that salmeterol exhibited a low affinity for beta 1-adrenoceptors in C6 cells. In multiple washout experiments, cAMP responses to isoprenaline and formoterol waned with increasing numbers of washing processes. Therefore, it seemed that formoterol relied on its moderately lipophilic nature to partition into bulk lipid of the plasma membrane to produce sustained activity, particularly at high agonist concentrations. Salmeterol was found to persist at beta 2-adrenoceptors in C6 cells despite washing cell monolayers up to four times. To determine the duration of action of salmeterol at beta 1-adrenoceptors expressed on the same cells, use was made of full/partial agonist interactions. In cells exposed to a single washout of agonist-containing medium, salmeterol (30 microM) lost its ability to attenuate responses to the more efficacious agonist, isoprenaline. This observation provided convincing evidence to support the hypothesis that salmeterol exhibits sustained agonist activity at beta 2-adrenoceptors, but not beta 1-adrenoceptors, expressed on the same cells. Therefore, the sustained activity of salmeterol at beta 2-adrenoceptors seems to be unique and does not result solely from its partitioning into bulk lipid of the plasma membrane.

Synergistic interactions between human transfected adenosine A1 receptors and endogenous cholecystokinin receptors in CHO cells

The effect of Gi coupled receptor activation (adenosine A1 and 5-HT1B receptors) on cholecystokinin receptor-stimulated inositol phosphate accumulation has been investigated in Chinese hamster ovary cells transfected with the human adenosine A1 receptor cDNA (CHO-A1). CHO cells constitutively express the 5-HT1B receptor [Berg, Clarke, Sailstad, Saltzman and Maayani (1994) Mol. Pharmacol. 46, 477-484]. Our previous studies using CHO-A1 cells have revealed that both the adenosine A1 and 5-HT1B receptor are negatively coupled to adenylyl cyclase activity and stimulate increases in [Ca2+]i, through a pertussis toxin-sensitive pathway. In the present study the selective adenosine A1 receptor agonist N6-cyclopentyladenosine stimulated a pertussis toxin-sensitive increase in total [3H]inositol phosphate accumulation. The sulphated C-terminal octapeptide of cholecystokinin (CCK-8) stimulated a robust and pertussis toxin-insensitive increase in [3H]inositol phosphate accumulation through the activation of CCKA receptors. Co-stimulation of CHO-A1 cells with N6-cyclopentyladenosine and CCK-8 produced a synergistic increase in [3H]inositol phosphate accumulation. The synergistic interaction between N6-cyclopentyladenosine and CCK-8 was abolished in pertussis toxin-treated cells. Synergy between N6-cyclopentyladenosine and CCK-8 still occurred in the absence of extracellular calcium. The 5-HT1B receptor agonist 5-carboxyamidotryptamine did not stimulate a measurable increase in [3H]inositol phosphate accumulation. Furthermore, 5-carboxyamidotryptamine had no significant effect on CCK-8 mediated [3H]inositol phosphate production. Activation of endogenous P2U receptors (Gq/Gll coupled) with ATP gamma S produced a significant increase in [3H]inositol phosphate accumulation. Co-stimulation of CHO-A1 cells with ATP gamma S and CCK-8 produced additive increases in [3H]inositol phosphate accumulation. These data indicate that CHO-A1 cells may prove a useful model system in which to investigate further the mechanisms underlying the intracellular 'cross-talk' between phospholipase C coupled receptors (Gq/Gll linked) and Gi/Go coupled receptors.

Desensitization of muscarinic receptor-coupled inositol phospholipid hydrolysis in human detrusor cultured smooth cells

PURPOSE

The aim of this study was to investigate the desensitization characteristics of muscarinic M3 receptors in primary cultures of human detrusor smooth muscle cells.

MATERIALS AND METHODS

Cell cultures were prepared from cold cup pinch biopsies of the human detrusor muscles by explant culture methods. Accumulation of (3)H-inositol phosphates was measured on confluent monolayers as described previously in detail. Desensitization was achieved by preincubating the cells with carbachol or histamine for 5 to 60 minutes.

RESULTS

Carbachol induced a concentration-dependent increase in phosphoinositide turnover in naive cells, the response being rapid and evident after only a 30-second exposure to the agonist. Preincubation of the cells with carbachol produced a concentration-dependent decrease in the inositol phosphate response to a second challenge with carbachol. Preexposure to carbachol for only 5 minutes prior to a rechallenge reduced the mean size of response of the second stimulation to 49% of that observed in naive cells. Preexposure of the cells to histamine did not alter the response of the cells to a subsequent challenge with carbachol and vice versa.

CONCLUSIONS

The muscarinic receptors retained by human detrusor smooth muscle cells in culture are susceptible to a desensitization of the carbachol-induced increase phosphoinositide turnover observed in these cells. This desensitization is rapid, and the results indicate that it is homologous and does not occur via a postreceptor mechanism but at the level of the receptor itself.

Sensitivity of histamine H3 receptor agonist-stimulated [35S]GTP gamma[S] binding to pertussis toxin

The effect of histamine H3 receptor-selective ligands on [35S]guanosine 5'-o-(gamma-thio)triphosphate ([35S]GTP gamma[S]) binding has been examined in rat cerebral cortical membranes. R alpha-Methylhistamine and N alpha-methylhistamine produced a concentration-dependent stimulation of [35S]GTP gamma[S] binding which was attenuated in the presence of the selective histamine H3 receptor antagonist thioperamide. In addition, treatment of brain membranes with pertussis toxin abolished the histamine H3 receptor agonist stimulated binding of [35S]GTP gamma[S]. These results provide the first evidence that histamine H3 receptors couple directly to a Gi/Go protein in mammalian brain.

Coupling of an endogenous 5-HT1B-like receptor to increases in intracellular calcium through a pertussis toxin-sensitive mechanism in CHO-K1 cells

1. Chinese hamster ovary cells (CHO-K1) express an endogenous 5-hydroxytryptamine (5-HT)1B-like receptor that is negatively coupled to adenylyl cyclase through a pertussis toxin (PTX)-sensitive mechanism. Furthermore, the human adenosine A1 receptor when expressed in CHO-K1 cells (CHO-A1) has been shown to mobilize intracellular Ca2+ through a PTX-sensitive mechanism. Therefore the aim of this investigation was to determine whether the endogenous 5-HT1B-like receptor was able to stimulate increases in intracellular free [Ca2+] ([Ca2+]i) in CHO-A1 cells. 2. In agreement with previous studies using CHO cells, 5-hydroxytryptamine (5-HT) elicited a concentration-dependent inhibition of forskolin-stimulated [3H]-cyclic AMP production in CHO-A1 cells (p[EC50] = 7.73 +/- 0.13). 5-HT (1 microM) inhibited 47 +/- 5% of the [3H]-cyclic AMP accumulation induced by 3 microM forskolin. Forskolin stimulated [3H]-cyclic AMP accumulation was also inhibited by the 5-HT1 receptor agonists (p[EC50] values) 5-carboxyamidotryptamine (5-CT; 8.07 +/- 0.08), RU 24969 (8.12 +/- 0.33) and sumatriptan (5.80 +/- 0.31). 3. 5-HT elicited a concentration-dependent increase in [Ca2+]i in CHO-A1 cells (p[EC50] = 8.07 +/- 0.05). In the presence of 2 mM extracellular Ca2+, 5-HT (1 microM) increased [Ca2+]i from 174 +/- 17 nM to 376 +/- 22 nM. The 5-HT1 receptor agonists (p[EC50] values), 5-carboxyamidotryptamine (5-CT; 7.9 +/- 0.02), RU 24969 (8.1 +/- 0.07) and sumatriptan (5.9 +/- 0.11) all elicited concentration-dependent increases in [Ca2+]i. Similar maximal increases in [Ca2+]i were obtained with each agonist. The selective 5-HT1A receptor agonist, 8-OH-DPAT (10 microM) did not stimulate increases in [Ca2+]i. 5-HT (100 microM) and 5-CT (10 microM) did not stimulate a measurable increase in [3H]-inositol phosphate accumulation in CHO-A1 cells. 4. 5-HT (1 microM)-mediated increases in [Ca2+]i were insensitive to the 5-HT receptor antagonist, ritanserin (5-HT2; 100 nM), ketanserin (5-HT2; 100 nM), LY-278,584 (5-HT3; 1 microM) and WAY 100635 (5-HT1A; 1 microM). The response to 5-HT (100 nM) was antagonized by the non-selective 5-HT1 antagonist, methiothepin (pKb = 8.90 +/- 0.09) and the 5-HT1D antagonist GR 127935 (pKb = 10.44 +/- 0.06). 5. Pretreatment with PTX (200 ng ml-1 for 4 h) completely attenuated the Ca2+ response to 100 microM 5-HT. 6. In untransfected CHO-K1 cells, 5-HT (1 microM), RU 24969 (1 microM), and 5-CT (1 microM) elicited increases in [Ca2+]i similar to those observed in CHO-A1 cells. 7. These data demonstrate that in CHO-K1 cells the endogenously expressed 5-HT1B-like receptor couples to the phospholipase C/Ca2+ signalling pathway through a PTX-sensitive pathway, suggesting the involvement of Gi/Go protein(s).

Expression of muscarinic M3-receptors coupled to inositol phospholipid hydrolysis in human detrusor cultured smooth muscle cells

PURPOSE

To investigate the effect of muscarinic receptor agonists and antagonists on the accumulation of inositol phosphates in cultures of human detrusor smooth muscle cells.

MATERIALS AND METHODS

Primary explant culture was used to derive smooth muscle cell lines from small bladder biopsies. The cells were loaded with [3H]-myoinositol, stimulated with muscarinic agonists, and the accumulation of [3H]-inositol phosphates was measured by liquid scintillation counting.

RESULTS

Carbachol (EC50 8.3 microM.), methacholine (EC50 7.5 microM.), oxotremorine (EC50 2.5 microM.) and pilocarpine (EC50 8.3 microM.) produced concentration-dependent rises in the accumulation of total [3H]-inositol phosphates. M1 (pirenzepine), M2 (methoctramine) and M3 (4-DAMP and pf-HHSiD) muscarinic receptor antagonists significantly antagonized the response induced by a submaximal concentration of carbachol (100 microM.). The apparent pA2 values were atropine (9.4), 4-DAMP (9.2), pfHHSid (7.4), pirenzepine (6.9) and methoctramine (6.3).

CONCLUSIONS

These results indicate that human detrusor smooth muscle cells in culture express M3 muscarinic receptors which are linked to phosphoinositide hydrolysis.

Synergy between the inositol phosphate responses to transfected human adenosine A1-receptors and constitutive P2-purinoceptors in CHO-K1 cells

1. The effect of adenosine A1-receptor and P2-purinoceptor agonists on [3H]-inositol phosphate accumulation has been investigated in CHO-K1 cells transfected with the human adenosine A1-receptor. 2. Adenosine receptor agonists stimulated [3H]-inositol phosphate accumulation in CHO-K1 cells with a rank potency order of N6-cyclopentyladenosine (CPA) > 5'-N-ethylcarboxamidoadenosine (NECA) > 2-chloroadenosine > N6-2-(4-aminophenyl) ethyladenosine (APNEA). The responses to both CPA and APNEA were antagonized by the A1 selective antagonist, 1,3-dipropylcyclopentylxanthine (DPCPX) yielding KD values of 1.2 nM and 4.3 nM respectively. 3. ATP, UTP and ATP gamma S were also able to stimulate [3H]-inositol phosphate accumulation in these cells with EC50 values of 1.9 microM, 1.3 microM and 5.0 microM respectively. 2-Methyl-thio-ATP was a weak agonist of this response (EC50 > 100 microM). 4. The [3H]-inositol phosphate response to CPA was completely attenuated by pertussis toxin treatment (24 h; 100 ng ml-1). In contrast, the responses to ATP, UTP and ATP gamma S were only reduced by circa 30% in pertussis toxin-treated cells. 5. The simultaneous addition of CPA and either ATP, UTP or ATP gamma S produced a large augmentation of [3H]-inositol phospholipid hydrolysis. This was due to an increase in the maximal response and was significantly greater than the predicted additive response for activation of these two receptor systems. The synergy was not observed in pertussis toxin-treated cells. 6. No synergy was observed between the [3H]-inositol phosphate responses to histamine and ATP in CHO-K1 cells transfected with the bovine histamine H1-receptor. In these cells the response to histamine was completely resistant to inhibition by pertussis toxin treatment. 7. This study provides a clear demonstration of a synergy between pertussis toxin-sensitive and insensitive receptor systems in a model cell system which is an ideal host for transfected cDNA sequences. This model system should provide a unique opportunity to unravel the mechanisms underlying this example of receptor cross-talk involving phospholipase C.

Adenosine A1 receptor-mediated changes in basal and histamine-stimulated levels of intracellular calcium in primary rat astrocytes

1. The effects of adenosine A1 receptor stimulation on basal and histamine-stimulated levels of intracellular free calcium ion concentration ([Ca2+]i) have been investigated in primary astrocyte cultures derived from neonatal rat forebrains. 2. Histamine (0.1 microM-1 mM) caused rapid, concentration-dependent increases in [Ca2+]i over basal levels in single type-2 astrocytes in the presence of extracellular calcium. A maximum mean increase of 1,468 +/- 94 nM over basal levels was recorded in 90% of type-2 cells treated with 1 mM histamine (n = 49). The percentage of type-2 cells exhibiting calcium increases in response to histamine appeared to vary in a concentration-dependent manner. However, the application of 1 mM histamine to type-1 astrocytes had less effect, eliciting a mean increase in [Ca2+]i of 805 +/- 197 nM over basal levels in only 30% of the cells observed (n = 24). 3. In the presence of extracellular calcium, the A1 receptor-selective agonist, N6-cyclopentyladenosine (CPA, 10 microM), caused a maximum mean increase in [Ca2+]i of 1,110 +/- 181 nM over basal levels in 30% of type-2 astrocytes observed (n = 53). The size of this response was concentration-dependent; however, the percentage of type-2 cells exhibiting calcium increases in response to CPA did not appear to vary in a concentration-dependent manner. A mean calcium increase of 605 +/- 89 nM over basal levels was also recorded in 23% of type-1 astrocytes treated with 10 microM CPA (n = 30). 4. In the absence of extracellular calcium, in medium containing 0.1 mM EGTA, a mean increase in [Ca2+]i of 504 +/- 67 nM over basal levels was recorded in 41% of type-2 astrocytes observed (n = 41) after stimulation with 1 microM CPA. However, in the presence of extracellular calcium, pretreatment with the A1 receptor-selective antagonist, 8-cyclopentyl-1,3-dipropylxanthine, for 5-10 min before stimulation with 1 microM CPA, completely antagonized the response in 100% of the cells observed. 5. In type-2 astrocytes, prestimulation with 10 nM CPA significantly increased the size of the calcium response produced by 0.1 microM histamine and the percentage of responding cells. Treatment with 0.1 microM histamine alone caused a mean calcium increase of 268 +/- 34 nM in 41% of the cells observed (n = 34). After treatment with 10 nM CPA, mean calcium increase of 543 +/- 97 nM was recorded in 100% of the cells observed (n = 33). 6. These data indicate that adenosine Al receptors couple to intracellular calcium mobilization and extracellular calcium influx in type-1 and type-2 astrocytes in primary culture. In addition, the simultaneous activation of adenosine Al receptors on type-2 astrocytes results in an augmentation of the calcium response to histamine H1 receptor stimulation.

Adenosine receptor-induced cyclic AMP generation and inhibition of 5-hydroxytryptamine release in human platelets

1. We have assessed the effects of adenosine receptor agonists and antagonists on collagen-induced 5-hydroxytryptamine (5-HT) release and cyclic AMP generation in human platelets. 2. 5'-N-ethylcarboxamidoadenosine (NECA) and CGS 21680 elicited accumulations of cyclic AMP with mean EC50 values of 2678 and 980 nM, respectively. The maximal response to CGS 21680 was approximately half that of the response to 10 microM NECA. 3. NECA and CGS 21680 inhibited collagen-induced 5-hydroxytryptamine release with mean EC50 values of 960 and 210 nM, respectively. The maximal response to CGS 21680 was approximately 25% of the response to 10 microM NECA. 4. The A1/A2a-selective adenosine receptor antagonist PD 115,199 was more potent as an inhibitor of NECA-elicited responses than the A1-selective antagonist DPCPX with calculated Ki values of 22-32 nM and > 10 microM, respectively. 5. In the presence of a cyclic AMP phosphodiesterase inhibitor, the effects of CGS 21680 on cyclic AMP accumulation and 5-HT release were enhanced to levels similar to those elicited by 10 microM NECA. In the absence of phosphodiesterase inhibition, CGS 21680 did not antagonise the effects of NECA. Furthermore, endogenous adenosine did not contribute to the effects of CGS 21680 when phosphodiesterase was inhibited. 6. We conclude that an A2a adenosine receptor appears to be involved in the NECA-elicited increases in cyclic AMP levels and inhibition of 5-HT release in human platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Enantioselective metabolism and pharmacokinetics of Casodex in the male rat

1. Casodex, a non-steroidal antiandrogen, is a racemic mixture of R-Casodex, the pharmacologically active (-)-enantiomer, and S-Casodex, the inactive (+)-enantiomer. Single oral doses of pseudo-racemic 14C-Casodex (10 mg/kg), prepared from mixtures of either 14C-labelled R-Casodex and unlabelled S-Casodex, or 14C-S-Casodex and unlabelled R-Casodex, were administered to the intact and bile duct-cannulated male rat. 2. Neither enantiomer underwent stereochemical inversion, but the pharmacokinetics of Casodex showed marked enantioselectivity. 3. After dosing R-labelled Casodex, plasma concentrations of R-Casodex increased slowly to reach a peak of 3.50 +/- 0.05 micrograms/ml (mean +/- SEM) at 12 h and, thereafter, declined monoexponentially with an elimination half-life of 24 h. Plasma concentrations of S-Casodex rose rapidly to reach a much lower peak of 0.97 +/- 0.06 microgram/ml at 3 h and, thereafter, declined rapidly, although there were insufficient data to determine the half-life. R-Casodex had a much higher AUC0-24 (66 micrograms.h/ml) than S-Casodex (12 micrograms.h/ml). Plasma drug concentrations measured using an achiral assay were in very good agreement with the sum of the enantiomer concentrations throughout the profile. R-Casodex comprised 94% of the total plasma radioactivity at 12 h, decreasing to 75% at 120 h. 4. Plasma concentration data generated after administration of S-Casodex were similar to those observed after dosing R-labelled Casodex. S-Casodex comprised about 74% of the total plasma radioactivity at 6 h and only 41% at 24 h. 5. The urine of intact animals contained 36 +/- 2 and 48 +/- 3% of the dose respectively up to 48 and 120 h after dosing with R-labelled Casodex, and 33 +/- 4 and 34 +/- 4% respectively after dosing with S-labelled Casodex. The urine and bile of the cannulated rat contained 43 +/- 2 and 21 +/- 2% of the dose respectively up to 48 h after dosing with R-labelled Casodex and 37 (n = 2) and 50% respectively after dosing with S-labelled Casodex. 6. After dosing with R- or S-labelled Casodex, the urinary radioactivity consisted of the carboxylic acid metabolite formed by hydrolytic cleavage at the amide, whereas biliary radioactivity consisted of hydroxy-Casodex and Casodex, mainly conjugated with glucuronic acid. The clearance of R-Casodex by each of these pathways of metabolism was less than that of S-Casodex, with direct glucuronidation and hydroxylation showing greater enantioselectivity than hydrolysis.

Distribution of receptors mediating phosphoinositide hydrolysis in cultured human umbilical artery smooth muscle and endothelial cells

Cultures of human umbilical artery smooth muscle and endothelial cells have been established and the effect of a range of calcium-mobilizing receptor agonists on inositol phospholipid hydrolysis has been compared in the two cell types. In human umbilical artery endothelial cells, histamine (EC50 20 microM), ATP (EC50 6.7 microM), sodium fluoride (20 mM) and thrombin (1 U/mL) produced marked increases in [3H]inositol phosphate accumulation. In contrast, bradykinin (1 microM), 5-hydroxytryptamine (5-HT) (0.1 mM) and carbachol (1 mM) produced only a small (< 1% of the response to 1 mM histamine) effect on [3H]inositol phosphate accumulation in these cells. In human umbilical artery smooth muscle cells, histamine (EC50 16 microM), bradykinin (EC50 4.5 nM), 5-HT (EC50 0.7 microM) and carbachol (EC50 21 microM) produced substantial effects (> 20% of the response to 1 mM histamine) on inositol phospholipid hydrolysis while ATP (1 mM) and thrombin (1 U/mL) were much less effective. The response to histamine in both smooth muscle and endothelial cells was antagonized by 50 nM mepyramine (apparent Kd = 5.6 and 2.9 nM in the two cell types, respectively). The response to 5-HT in smooth muscle cells was antagonized by 50 nM ketanserin (apparent Kd = 4.5 nM). In human umbilical artery smooth muscle cells the inositol phosphate response to carbachol was antagonized by 4-diphenylacetoxy-N-methylpiperidine (4-DAMP; pKd = 9.3), atropine (pKd = 9.7), pirenzepine (pKd = 6.7) and methoctramine (pKd = 6.9). These data are consistent with the involvement of an M3-muscarinic receptor in this response. These studies suggest that receptors mediating inositol phospholipid hydrolysis are differentially distributed between human umbilical artery endothelial and smooth muscle cells.

Activation of phospholipase C by G-protein beta gamma subunits in DDT1MF-2 cells

Adenosine A1 receptors directly stimulate inositol phospholipid hydrolysis and Ca2+ mobilization through a pertussis toxin sensitive mechanism in DDT1MF-2 cells. In the present study we have investigated whether G protein beta gamma subunits (G beta gamma) are capable of stimulating phospholipase C in DDT1MF-2 cell membrane preparations using lipid vesicles containing [3H]phosphatidylinositol 4,5-bisphosphate. DDT1MF-2 cell membrane and soluble fractions were found to contain phospholipase C activity which was stimulated by increases in free Ca2+ ion concentration. G beta gamma purified from bovine retinal transducin produced significant increases in phospholipase C activity in DDT1MF-2 cell membranes. G beta gamma-dependent activation of phospholipase C, while virtually absent in the presence of low Ca2+ ion concentrations, increased markedly with increasing free Ca2+ ion concentration. These data suggest that membrane bound phospholipase C in DDT1MF-2 cells is sensitive to Ca2+, and may be stimulated conditionally by G beta gamma subunits, i.e. G beta gamma subunits activate the enzyme only in the presence of Ca2+. G beta gamma subunits also stimulated soluble phospholipase C in DDT1MF-2 cells. These findings support the hypothesis that Gi beta gamma subunits are involved in adenosine A1 receptor stimulated phospholipase C/Ca2+ signaling in DDT1MF-2 cells.

Differential effect of sodium ions and guanine nucleotides on the binding of thioperamide and clobenpropit to histamine H3-receptors in rat cerebral cortical membranes

1. Conflicting reports in the literature over heterogeneity (West et al., 1990) or homogeneity (Arrange et al., 1990) of histamine H3-receptor binding sites may be attributed to the use of different incubation conditions. In the present study we have investigated the extent to which the binding of H3-receptor ligands to rat cerebral cortical membranes can be modified by both sodium ions and guanine nucleotides. 2. The H3-selective antagonist, thioperamide, discriminated between two specific binding sites for [3H]-N alpha-methylhistamine (IC50 1 = 2.75 +/- 0.87 nM, IC50 2 101.6 +/- 12.0 nM, % site 1 = 24 +/- 2%) in 50 mM Tris HCl buffer, but showed homogeneity of binding in 50 mM Na/K phosphate buffer. 3. Sodium ions markedly altered the binding characteristics of thioperamide (i.e. heterogeneity was lost and IC50 value shifted towards the high affinity site). The competition curves for a second H3-antagonist, clobenpropit and the H3-agonist N alpha-methylhistamine however, were unaltered in the presence of sodium ions. 4. Guanylnucleotides displaced only 60% of specific [3H]-N alpha- methylhistamine binding and modulated thioperamide binding in the same way as sodium ions. 5. These data suggest that the H3-receptor can exist in different conformations for which thioperamide, but not N alpha-methylhistamine and clobenpropit, show differential affinity. 6. The potential nature of these sites, and the implications of this apparent receptor heterogeneity for H3-receptor antagonism by thioperamide, are discussed.

Endogenous expression of histamine H1 receptors functionally coupled to phosphoinositide hydrolysis in C6 glioma cells: regulation by cyclic AMP

1. The effects of histamine receptor agonists and antagonists on phospholipid hydrolysis in rat-derived C6 glioma cells have been investigated. 2. Histamine H1 receptor-stimulation caused a concentration-dependent increase in the accumulation of total [3H]-inositol phosphates in cells prelabelled with [3H]-myo-inositol. The rank order of agonist potencies was histamine (EC50 = 24 microM) > N alpha-methylhistamine (EC50 = 31 microM) > 2-thiazolylethylamine (EC50 = 91 microM). 3. The response to 0.1 mM histamine was antagonized in a concentration-dependent manner by the H1-antagonists, mepyramine (apparent Kd = 1 nM) and (+)-chlorpheniramine (apparent Kd = 4 nM). In addition, (-)-chlorpheniramine was more than two orders of magnitude less potent than its (+)-stereoisomer. 4. Elevation of intracellular cyclic AMP accumulation with forskolin (10 microM, EC50 = 0.3 microM), isoprenaline (1 microM, EC50 = 4 nM) or rolipram (0.5 mM), significantly reduced the histamine-mediated (0.1 mM) inositol phosphate response by 37%, 43% and 26% respectively. In contrast, 1,9-dideoxyforskolin did not increase cyclic AMP accumulation and had no effect on the phosphoinositide response to histamine. 5. These data indicate the presence of functionally coupled, endogenous histamine H1 receptors in C6 glioma cells. Furthermore, the results also indicate that H1 receptor-mediated phospholipid hydrolysis is inhibited by the elevation of cyclic AMP levels in these cells.

A1 adenosine receptor inhibition of cyclic AMP formation and radioligand binding in the guinea-pig cerebral cortex

1. A1 adenosine receptors were investigated by radioligand binding and functional studies in slices and particulate preparations from guinea-pig cerebral cortex. 2. Binding of the adenosine receptor antagonist radioligand, 8-cyclopentyl-[3H]-1,3-dipropylxanthine (DPCPX) to guinea-pig cerebral cortical membranes exhibited high density (1410 +/- 241 fmol mg-1 protein) and high affinity (Kd 3.8 +/- 0.3 nM). 3. [3H]-DPCPX binding to guinea-pig cerebral cortical membranes was displaced in a monophasic manner by adenosine receptor antagonists with the rank order of affinity (Ki values, nM): DPCPX (6) < xanthine amine congener (XAC, 153) < PD 115,199 (308). 4. Agonist displacement of [3H]-DPCPX binding was biphasic and exhibited the following rank order at the low affinity site (Ki values): 2-chloro-N6-cyclopentyl-adenosine (CCPA, 513 nM) = N6-R-phenylisopropyladenosine (R-PIA, 526 nM) = N6-cyclopentyladenosine (CPA, 532 nM) < 2-chloroadenosine (2CA, 3.2 microM) = 5'-N-ethylcarboxamidoadenosine (NECA, 4.6 microM) < N6-S-phenylisopropyladenosine (S-PIA, 19.9 microM). 5. In cerebral cortical slices, [3H]-DPCPX binding was displaced by antagonists and agonists in an apparently monophasic manner with the rank order of affinity (Ki values, nM): DPCPX (14) < XAC (45) < R-PIA (266) < PD 115,199 (666) < S-PIA (21000). 6. Cyclic AMP accumulation stimulated by 30 microM forskolin in guinea-pig cerebral cortical slices was inhibited by R-PIA, CCPA and CPA up to 1 microM in a concentration-dependent fashion with IC50 values of 14, 18, and 22 nM, respectively. All three analogues inhibited the forskolin response to a similar extent (82-93% inhibition). NECA, S-PTA and 2CA failed to inhibit the forskolin response, but rather enhanced the accumulation of cyclic AMP at concentrations of 100 nM or greater, presumably through activation of A2b adenosine receptors coupled to stimulation of cyclic AMP accumulation in guinea-pig cerebral cortical slices.7. The inhibition of forskolin-stimulated cyclic AMP accumulation by CPA was antagonized with the rank order of affinity (Ki values, nM): DPCPX (6)<XAC (52)<PD 115,199 (505).8 Xanthine-based antagonists inhibited the adenosine receptor augmentation of histamine-induced phosphoinositide turnover in guinea-pig cerebral cortical slices with the rank order of affinity (Ki, nM):DPCPX (12)=XAC (17)<PD 155,199 (640).9 In summary, we observe a good correlation between antagonist affinity at A1 receptors defined by radioligand binding, inhibition of cyclic AMP generation or augmentation of histamine-evoked phosphoinositide turnover in guinea-pig cerebral cortex.

Agonist-induced desensitization of histamine H1 receptor-mediated inositol phospholipid hydrolysis in human umbilical vein endothelial cells

1. The regulation of histamine-induced [3H]-inositol phosphate formation was studied in human cultured umbilical vein endothelial cells (HUVEC). 2. Histamine (EC50 4.8 microM) produced a 12.7 fold increase in [3H]-inositol phosphate formation over basal levels. Prior exposure to 0.1 mM histamine (2 h) produced a 78% reduction in the response to subsequent histamine (0.1 mM) challenge. The IC50 for this histamine-induced desensitization was 0.9 microM. 3. The inositol phosphate response to histamine (0.1 mM) was inhibited by phorbol dibutyrate (IC50 40 nM; maximal reduction 64%). This effect was antagonized by both staurosporine (100 nM) and Ro 31-8220 (10 microM). However, the histamine-induced desensitization of the H1-receptor-mediated inositol phosphate response was insensitive to the protein kinase inhibitors, staurosporine, Ro 31-8220, K252a and KN62. 4. Prior exposure to sodium nitroprusside (100 microM), forskolin (10 microM) or dibutyryl cyclic AMP (1 mM) had no effect upon histamine-induced [3H]-inositol phosphate formation. 5. NaF (20 mM) and thrombin (EC50 0.4 u ml-1) also induced inositol phosphate formation in HUVEC. Histamine pretreatment (0.1 mM, 10-120 min) failed to modify the inositol phosphate response to a subsequent NaF or thrombin challenge. 6. We conclude that the desensitization of histamine H1-receptor-mediated [3H]-inositol phosphate formation occurs at the level of the receptor and involves a mechanism independent of activation of protein kinase A, G, or C, or calcium calmodulin-dependent protein kinase II.

Selective potentiation of histamine H1-receptor stimulated calcium responses by 1,4-dithiothreitol in DDT1MF-2 cells

The effect of 1,4-dithiothreitol (DTT) on agonist-stimulated increases in intracellular free calcium concentration ([Ca2+]i) has been investigated in the smooth muscle cell line, DDT1MF-2, derived from hamster vas deferens. Pretreatment with DTT (1 mM) produced a large leftward parallel shift in concentration-response curve for histamine H1-receptor mediated increases in [Ca2+]i. The EC50 values for H1-receptor stimulated increases in [Ca2+]i in the absence and presence of DTT were 11.3 +/- 1.5 microM (N = 6) and 0.52 +/- 0.15 microM (N = 6), respectively. DTT had no significant effect on the maximum Ca2+ response elicited by histamine (100 microM). In the presence of DTT the partial H1-receptor agonist 2-pyridylethylamine (100 microM) increased [Ca2+]i from 112 +/- 14 nM to 237 +/- 24 nM (N = 10). In control cells 2-pyridylethylamine (100 microM) did not elicit a Ca2+ response. DTT had no significant effect on the maximum Ca2+ response elicited by 1 mM 2-pyridylethylamine. The enhancement of histamine H1-receptor Ca2+ responses by DTT was reversed by the sulphydryl oxidizing agent dithiobis-(2-nitrobenzoic acid). DTT had no significant effect on adenosine A1-, bradykinin and ATP-receptor stimulated increases in [Ca2+]i. [3H]mepyramine binding experiments confirmed that DTT increased agonist affinity. DTT produced a small, but significant, leftward shift in concentration-response curve for histamine displacement of [3H]mepyramine binding. These data suggest that DTT potentiates H1-receptor mediated Ca2+ responses by increasing agonist affinity.

Augmented tumor necrosis factor response to lipopolysaccharide after thermal injury is regulated posttranscriptionally

BACKGROUND AND OBJECTIVE

Thermal injury has been shown to enhance macrophage sensitivity to lipopolysaccharide (LPS), resulting in augmented tumor necrosis factor alpha (TNF-alpha) production. This study was designed to examine whether enhanced TNF-alpha response after thermal injury and LPS stimulation is regulated at the level of transcription.

DESIGN

Tumor necrosis factor alpha release in alveolar macrophages harvested from sham- or thermal-injured Wistar rats was determined using an L929 cytotoxicity bioassay on days 1, 3, and 5 following 40% scald burn and incubation for 24 hours with LPS (0 or 10 micrograms/mL). Separate groups of rats underwent intraperitoneal injection of LPS (5 mg/kg) 3 days following sham or thermal injury. Lung tissue RNA was isolated and probed for TNF-alpha messenger RNA (mRNA), using nuclease protection analysis. Finally, pooled alveolar macrophages were harvested 3 days following sham or thermal injury and cultured in the presence or absence of LPS (10 micrograms/mL) for 4 hours. The RNA from the pooled alveolar macrophages was extracted and probed for TNF-alpha mRNA levels.

RESULTS

Thermal injury alone did not significantly increase alveolar macrophage TNF-alpha bioactivity, whole-lung TNF-alpha mRNA levels, or pooled alveolar macrophages TNF-alpha mRNA levels when compared with levels in sham-injured rats. However, alveolar macrophages from postburn day 3 (PBD 3) demonstrated increased sensitivity to LPS (10 micrograms/mL) compared with alveolar macrophages from sham-injured animals undergoing similar LPS treatment (2365 +/- 1011 vs 169 +/- 79 ng/mL; P < .05). Whole-lung mRNA levels in both sham-injured and PBD-3 rats receiving intraperitoneal LPS, while elevated approximately 2.5-fold from those of non-LPS treated rats, were not different from each other. Finally, pooled alveolar macrophages from sham-injured and PBD-3 rats cultured in the presence of LPS had approximately 1.7-fold and threefold increased TNF-alpha mRNA levels, respectively, compared with alveolar macrophages not cultured with LPS.

CONCLUSIONS

Thermal injury induces priming of alveolar macrophages, resulting in significant increases in macrophage TNF-alpha production after exposure to LPS. The majority of this effect appears to be regulated at a posttranscriptional level, since there were only moderate increases in TNF-alpha mRNA levels after LPS stimulation, which did not coincide with large differences in bioactivity.