The rodent granular convoluted tubule cell--an update

The cells of the granular convoluted tubule (GCT) of the rodent submandibular gland (SMG) are under complex developmental and multihormonal regulation. Recent findings indicate that GCT cells also synthesize transforming growth factor alpha (TGF-alpha), hepatocyte growth factor, erythroid differentiation factor, endothelin, and insulin-like growth factor, as well as several novel androgen-dependent proteins of unknown function. The GCTs of hypophysectomized mice provide a convenient model to study multihormonal regulation of gene expression. The GCT system of the rodent SMG also is a fruitful model for study of hormone receptors.

Regulation of Na+,K+-ATPase in submandibular glands of hypophysectomized male mice by steroid and thyroid hormones

The effects of thyroid hormone, androgen, glucocorticoid, and mineralocorticoid on Na+,K+-ATPase activity and on levels of its alpha-subunit protein (alpha 1 isoform) in mouse submandibular gland (SMG) were studied by enzyme assay for ouabain-sensitive ATP hydrolysis, by quantitative densitometric scanning of Western blots, and by immunohistochemistry. To define the specific regulatory effects of various pituitary-dependent hormones on expression of Na+,K+-ATPase in the SMG, we treated hypophysectomized (hypox) male mice with triiodo-L-thyronine (T3), 5 alpha-dihydrotestosterone (DHT), dexamethasone (Dex), and aldosterone (Ald), injected singly or in combination. Na+,K+-ATPase was confined to the duct system of the SMG. In intact mice there was a gender difference in SMG Na+,K+-ATPase, with levels of the enzyme's activity and of its alpha 1-subunit being less in the glands of males. In males, hypophysectomy caused a rise in levels of Na+,K+-ATPase activity and in levels of the alpha 1-subunit protein of this enzyme, and in intensity of immunocytochemical staining for this subunit but there were no such changes in the SMG of hypox females. Changes caused by hormonal replacement to hypox males in Na+,K-ATPase activity, levels of its alpha 1-subunit, or the intensity of immunocytochemical staining for this subunit were complex. Ald had no effect. T3 or dexamethasone, given alone, induced Na+,K+-ATPase activity above control values (hypox males) and increased levels of its alpha 1-subunit protein and immunohistochemical staining for this subunit. By contrast, DHT did not cause a decline in any of these parameters. However, when treatment with T3 was combined with administration of Dex or DHT, enzymatic activity of Na+,K+-ATPase decreased but levels of the alpha 1-subunit protein and immunohistochemical staining for this subunit increased. Therefore, inductions of the alpha 1-subunit of this enzyme are not always correlated with increases in levels of activity of Na+,K+-ATPase, and we propose that both enzymatic and immunochemical analyses are essential for evaluation of hormonal regulation of Na+,K+-ATPase in salivary gland and in other tissues.

Simultaneous measurement of Ca2+ and pH by laser cytometry using fluo-3 and SNARF-1

We present a new convenient method for simultaneous measurement of intracellular calcium concentration ([Ca2+]i) and intracellular pH (pHi) using laser cytometry with a mixture of fluo-3 (for [Ca2+]i) and SNARF-1 (for pHi), with iso excitation (488 nm)-dual emission (530 nm for fluo-3 and > 630 nm for SNARF-1). By using this technique, we measured the changes in [Ca2+]i and pHi in A-431 human epidermoid carcinoma cells and HSG human salivary gland cells stimulated by ATP. We found that alkalization in A-431 cell occurred with the elevation of [Ca2+]i; in contrast, alkalization in HSG cells did not occur at all, even though the elevation of [Ca2+]i was observed. Using BAPTA (a chelating agent of Ca2+) and amiloride (an inhibitor of the Na+/H+ exchanger), we found that the elevation of pHi requires the elevation of [Ca2+]i but that the elevation of [Ca2+]i does not always require a rise in pHi. From our results we conclude that elevation of [Ca2+]i takes precedence over the elevation of pHi in ATP-stimulated signal transduction.

Cytotoxic action of tri-n-butyltin on dissociated rat cerebellar neurones: a flow-cytometric study

The effects of tri-n-butyltin on cell viability and intracellular Ca2+ concentration ([CA2+]i) were examined by a flow cytometer in rat cerebellar neurones to reveal the contribution of tri-n-butyltin-induced increased in the [Ca2+]i to its cytotoxicity. Tri-n-Butyltin decreased the cell viability in association with increased [Ca2+]i at concentrations of 0.3 microM or more. Decrease or increase of the extracellular Ca2+ concentration ([Ca2+]o) respectively decreased or increased the cell viability. However, cell viability in the presence of ionomycin which increased [Ca2+]i more significantly than tri-n-butyltin was higher than that in the presence of tri-n-butyltin. Tri-n-butyltin also decreased cell viability under nominally [Ca2+]o-free conditions although the [Ca2+]i increase by tri-n-butyltin was still lower than the control [Ca2+]i under normal [Ca2+]o (2 mM). Therefore, it is unlikely that neuronal death induced by tri-n-butyltin is entirely dependent on the tri-n-butyltin-induced increase in [Ca2+]i.

Ginkgo biloba extract protects brain neurons against oxidative stress induced by hydrogen peroxide

Effect of Ginkgo biloba extract was examined on dissociated rat cerebellar neurons suffering from oxidative stress induced by hydrogen peroxide using a flow cytometer and ethidium bromide. Hydrogen peroxide at a concentration of 3 mM increased the number of neurons stained with ethidium (presumably dead neurons) in a time-dependent manner. Pretreatment of neurons with G. biloba extract (10 micrograms/ml) greatly delayed a time-dependent increase in number of dead neurons during exposure to hydrogen peroxide. It was true, but less effective, in the case of treatment with G. biloba extract immediately or 60 min after start of oxidative stress. Results implicate G. biloba extract as a potential agent in protecting the neurons suffering from oxidative stress induced by hydrogen peroxide.

T-cell lymphoma presenting with pericardial and pleural effusion as the initial and primary lesion: cytogenetic and molecular evidence

A 90-year-old woman was admitted with progressive dyspnea. Chest roentgenogram and computed tomography revealed a massive pericardial effusion and bilateral pleural effusion, but no lymphomatous lesion was seen. A diagnosis of malignant lymphoma was made by cytological and immunological studies of the cells obtained from the pericardial effusion. Chromosome analysis showed a clonal abnormality and T-lineage clonality was determined by the rearrangement of the T-cell receptor gamma gene. The patient achieved remission with chemotherapy, but she later relapsed, with right pleural effusion, and died. She exhibited no lymphomatous features throughout the clinical course, indicating the possibility of malignant lymphoma originating from the pericardium and/or pleura.

ATP- and EGF-stimulated phosphatidulinositol synthesis by two different pathways, phospholipase D and diacylglycerol kinase, in A-431 epidermoid carcinoma cells

The [(3)H]inositol incorporation into the membrane fraction of A-431 human epidermoid carcinoma cells was markedly increased by stimulation of the cells with either epidermal growth factor (EGF), ATP, bradykinin, or a calcium ionophore A23187 in the presence of 1 mM extracellular calcium ions; most incorporated [(3)H]inositol was found to have accumulated as phosphatidylinositol (PI). The EGF- and ATP-stimulated PI synthesis was inhibited by two protein kinase C inhibitors, staurosporine and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), and an intracellular calcium chelator, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA/AM), but not by the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7). Pretreatment of cells with pertussis toxin (IAP, islet-activating protein) inhibited the PI synthesis, [Ca(2+)]i elevation, and inositol trisphosphate (IP(3)) production by ATP, suggesting that the phospholipase C(PLC) system coupled with IAP-sensitive G protein is involved in the ATP-stimulated PI synthesis. On the other hand, the ATP stimulation increased the release of [(3)H]choline and [(32)P)phosphatidic acid (PA) from radiolabeled cells, and such release was not inhibited by IAP. In the presence of n-butyl alcohol, which prevents the production of PA by generation of phosphatidylbutanol, the ATP-stimulated PI synthesis was reduced. Because n-butyl alcohol did not inhibit IP(3) production and [Ca(2+)]i elevation, this fact suggests that the lAP-insensitive PLD system is involved in the ATP-stimulated PI synthesis. In A-431 cells, the stimulation of P(2)-purinergic receptors appears to activate the IAP-sensitive PLC system and IAP-insensitive PLD system, both of which are essential for the stimulation of PI synthesis. The present results imply the general prospect that ligand stimulation, which mobilizes second messengers and consumes their precursors, simultaneously provokes the pathway to synthesize and salvage the second messenger precursors as well.

Effects of protein kinase inhibitors and protein phosphatase inhibitors on cyclic AMP-dependent down-regulation of vesicular monoamine transport in pheochromocytoma PC12 cells

Cyclic AMP down-regulates vesicular monoamine transport in PC12 cells and thereby decreased catecholamine reuptake from the extracellular fluid. We examined the effects of protein kinase inhibitors and protein phosphatase inhibitors on this cAMP action. Treatment of cells with a protein kinase inhibitor, K252a, increased vesicular amine transport and cellular amine uptake, thereby antagonizing the regulatory action of cAMP. In contrast, a protein phosphatase inhibitor, okadaic acid, had the opposite effect on the amine transport, i.e. it enhanced the cAMP action. These results suggest the involvement of a protein phosphorylation process in the cAMP-dependent modulation of vesicular monoamine transport.

Change in membrane permeability induced by amyloid beta-protein fragment 25-35 in brain neurons dissociated from rats

Effects of amyloid beta-protein fragment 25-35, A beta P(25-35), on the membrane permeability of organic molecules were examined in the brain neurons dissociated from rats by using an argon laser (equipped in flow cytometer and laser microscope) and a combination of two fluorescent dyes, fluo-3-AM and ethidium bromide. A beta P(25-35) at concentrations of 1 microM or greater induced both leakage of fluo-3 from the neurons and permeation of ethidium across the membrane in a dose-dependent manner, although both dyes are highly impermeant to the intact plasma membrane. Thus, A beta P(25-35) seems to increase not only membrane permeability of inorganic ions such as Ca2+, Na+ and K+, as previously suggested, but also that of organic molecules. Therefore, the brain neuron membrane is suggested to lose its integrity in the presence of A beta P(25-35) that leads to neuronal death.

Effect of tri-n-butyltin on intracellular Ca2+ concentration of mouse thymocytes under Ca(2+)-free condition

Effect of tri-n-butyltin at concentrations ranging from 100 nM to 1 microM on the intracellular Ca2+ concentration of mouse thymocytes was examined under Ca(2+)-free conditions in comparison with those of 50 nM A23187, 100 nM thapsigargin and 10 microM cyclopiazonic acid, using the fluorescent dye for intracellular Ca2+, fluo-3. Tri-n-butyltin persistently increased the intensity of fluo-3 fluorescence while A23187, thapsigargin and cyclopiazonic acid produced a transient augmentation of the fluorescence. Pretreatment with A23187 greatly decreased the fluorescence responses induced by 1 microM tri-n-butyltin. However, the effect of thapsigargin and cyclopiazonic acid on the tri-n-butyltin-induced response was much weaker than that of A23187. In the presence of tri-n-butyltin, the transient response produced by A23187 was greatly prolonged. Results may suggest that tri-n-butyltin increases the membrane Ca2+ permeability of the intracellular organelles (cellular calcium stores) and decreases the Ca2+ pump activity of thymocyte membrane, resulting in a sustained increase in the intracellular Ca2+ concentration under Ca(2+)-free concentration.

Involvement of high-affinity binding site for EGF receptor in formation of rounding in A-431 epidermoid carcinoma cells

The introduction of a bacterial aminoglycoside phosphotransferase gene (neo gene) into A-431 cells was found to result in disappearance of high-affinity binding sites of the epidermal growth factor receptor (EGFR), probably by affecting the phosphorylation level of the receptors. Using A-431 cells and their neo gene-transfectants, we studied the relation between "rounding" and the high-affinity sites for EGF; and we also examined the role of protein kinase C (PKC) and A (PKA) in the EGF-induced cell rounding. Pretreatment of A-431 and their transfectant cells with 12-O-tetradecanoylphorbol 13-acetate (TPA; 100 ng/ml), an activator of PKC, for 30 min inhibited both the EGF-induced cell rounding and expression of high-affinity binding sites for EGF. However, both of these responses were recovered when cells were pretreated with TPA for 20 h, which treatment is known to result in depletion of PKC by a process called "down regulation". A similar recovery was also observed when cells were pretreated with forskolin (100 microM), an activator of PKA, for 30 min. Both cell rounding and EGFR high-affinity binding sites disappeared by activation of PKC, and reappeared by activation of PKA. These results suggest that the rounding of A-431 cells by EGF was induced via the high-affinity binding sites of EGFR.

Characterization of 2',7'-dichlorofluorescin fluorescence in dissociated mammalian brain neurons: estimation on intracellular content of hydrogen peroxide

The fluorescence of 2',7'-dichlorofluorescin (DCF) was measured in acutely dissociated rat cerebellar neurons as a mean of estimating the formation of reactive oxygen species (ROS). N,N-Diethyldithiocarbamate, an inhibitor for superoxide dismutase, reduced the intensity of DCF fluorescence in a dose-dependent fashion at concentrations of 30 nM to up to 10 microM. N-Ethylmaleimide, an inhibitor for glutathione peroxidase, augmented the DCF fluorescence in a dose-dependent manner at concentration of 10 microM to 1 mM while 3-amino-1,2,4-triazole, an inhibitor for catalase, did not change the fluorescence intensity even at concentrations as high as 1 mM. Hydrogen peroxide, applied externally at concentrations between 3 microM and 3 mM, augmented the fluorescence in a dose-dependent fashion. These results suggest the possibility that the DCF fluorescence may be useful in estimating the intracellular content of hydrogen peroxide of mammalian brain neurons.

Effects of nerve growth factor and dexamethasone on Na+,K(+)-ATPase of cultured PC12h cells

When PC12h cells were cultured for 4 days in the presence of 50 ng/ml of nerve growth factor (NGF), they showed elongated dendrites and specifically increased Na+,K(+)-ATPase activity. Either singly or in combination with NGF, dexamethasone also increased the specific activity of this enzyme. Western blot analysis using anti-alpha 1 and anti-alpha 2 antisera showed that PC12h cells, either before or after hormone treatment, contained the alpha 1 isoform but not the alpha 2 one. We conclude, therefore, that NGF induces Na+,K(+)-ATPase concomitantly with neuronal differentiation in PC12h cells but that the growth factor does not induce formation of the myelin sheath, which normally expresses the alpha 2 isoform of Na+,K(+)-ATPase.

Effects of pertussis toxin on signal transductions via P2-purinergic receptors in A-431 human epidermoidal carcinoma cells

In A-431 cells, stimulation of P2-purinergic receptors with extracellular ATP caused production of inositol 1,4,5-trisphosphate (InsP3), followed by mobilization of Ca2+ from intracellular stores; Ca2+ influx from the extracellular fluid and breakdown of phosphatidylcholine (PtdCho) also accompanied this InsP3/Ca2+ signalling. When A-431 cells were pretreated with pertussis toxin (PTX), production of InsP3 and elevation of cytosolic Ca2+ were strongly inhibited. PTX also inhibited the Ca2+ influx, but the effect was much weaker than that for InsP3/Ca2+ elevation. No inhibitory effect was observed in ATP-stimulated PtdCho breakdown. These results suggest that there is a system(s) which mediates the functions of P2-purinergic receptors in addition to PTX-sensitive G-proteins.

Identification of mK1, a true tissue (glandular) kallikrein of mouse submandibular gland: tissue distribution and a comparison of kinin-releasing activity with other submandibular kallikreins

The protein structure, kinin-releasing activity, and tissue distribution of four major proteinases of mouse submandibular gland (mK22, mK9, proteinase F, proteinase P) were studied. When compared with the deduced amino acid sequence of each member of the tissue (glandular) kallikrein gene family, the amino acid sequence of proteinase F determined (approximately 40% of the total) was found to agree completely with the deduced amino acid sequence of mKlk-1. The proteinase P sequence, on the other hand, agreed with that of the product of mKlk-13, mK13 (prorenin-converting enzyme). Proteinase F had the strongest kininogenase activity for both low-molecular-weight and high-molecular-weight kininogen, while mK22 had 1/6 and 1/50 the activity of proteinase F for the respective kininogen substrate. Kininogenase activities of mK9 and proteinase P were less than 1/100 of the activity of proteinase F for both substrates. Acting on the two kininogen substrates, kallikreins mK22, mK9, and proteinase F, but not proteinase P, specifically released bradykinin, suggesting that the former three kallikreins strictly recognized peptide sequences around bradykinin in these substrate molecules but proteinase P recognized several sites in these molecules. Significant amounts of proteinase F, but not mK22 and others, were present in the urine, pancreas and digestive organs, as well as in the salivary glands. The present results revealed that the former proteinase F is identical to mK1, tissue/renal kallikrein, and confirmed its characteristics as a true kallikrein on the basis of its kinin-releasing activity and tissue distribution.

Bradykinin-stimulated transient modulation of epidermal growth factor receptors in A-431 human epidermoid carcinoma cells

Of nine biological factors (ATP, bradykinin, vasopressin, substance P, angiotensin II, norepinephrine, epinephrine, 12-tetradecanoylphorbol 13-acetate (TPA), and A23187 calcium ionophore) examined, bradykinin, as well as ATP, TPA, and A23187, significantly increased the phosphorylation of epidermal growth factor (EGF) receptors and reduced the binding of EGF to their high-affinity site. The reduction in EGF binding by bradykinin, ATP, and TPA was similarly reversed by concomitant incubation with staurosporine, a protein kinase C inhibitor, implying that the phosphorylation of EGF receptors was catalyzed probably by a protein kinase C of the same or similar type in each case. This possibility was confirmed by the fact that the major phosphorylation site of EGF receptors by the stimulation with either bradykinin, ATP, or TPA was the same (Thr-654). Different from the stimulations with ATP and TPA, the effect of bradykinin of decreasing the high-affinity EGF binding was transient (a minimum binding at 2.5 min); the reduced EGF binding was, however, sustained for up to 30 min in the presence of calyculin A, a phosphoprotein phosphatase inhibitor. Moreover, the homogenate prepared from bradykinin-stimulated A-431 cells had stronger dephosphorylation activity for phosphorylated EGF receptors than that from control cells. These results suggest that bradykinin stimulates both the protein kinase C system and a phosphoprotein phosphatase(s) activity in A-431 cells. Such biphasic effects of bradykinin to phosphorylate and dephosphorylate EGF receptors via protein kinase C and a phosphoprotein phosphatase, respectively, imply a homeostatic control of receptor function in regulating phosphorylation level by the same bioactive factor.

Effects of female hormones and 3,5,3'-triiodothyronine or dexamethasone on induction of epidermal growth factor and proteinases F, D, A, and P in the submandibular glands of hypophysectomized male mice

The effects of progesterone (Pro), 5 alpha-dihydrotestosterone (DHT), 17 beta-estradiol (E2), T3, and dexamethasone (Dex), given alone or in combination, on induction of epidermal growth factor (EGF) and proteinase isozymes in the submandibular glands of hypophysectomized mice were examined. Each hormone, except E2, acting alone had essentially comparable inductive effects on EGF concentrations and on total proteinase activity. E2 alone had no inductive effect at all. Pro acted synergistically with T3, but its inductive effect was diminished when given with Dex. E2 was not synergistic with T2, and it inhibited the effect of Dex; it also partially blocked the action of DHT on induction of proteinase activity but not of EGF. Simultaneous administration of all five hormones restored total proteinase activity completely but EGF levels to only 50% of values for intact males, respectively. Submandibular proteinases were resolved by isoelectric focusing into four isozymes: proteinase F (pI 4.8), proteinase D (pI 5.8), proteinase A (pI 6.2), and proteinase P (pI 10.0). Pro alone slightly increased levels of proteinase F but greatly raised levels of the other three isozymes. This inductive action was augmented when Pro was given with T3 but blocked when it was given with Dex. E2 alone not only failed to induce any of the isozymes, but even further reduced levels of proteinase F. It also decreased the inductive effects of T3 on these isozymes, and with Dex completely blocked induction of proteinases D, A, and P. E2 plus DHT suppressed proteinase F levels and only induced proteinase A. All five hormones together reestablished the isozyme profile seen in intact males. These results show that Pro by itself is as capable as androgens, thyroid hormone, or glucocorticoid in regulating expression of these submandibular polypeptides, and that its action can be modulated by other pituitary-dependent hormones. In addition, they demonstrate that E2 does not regulate their expression, and that it has an inhibitory effect on the inductive action of other hormones. Last, they indicate that these various hormones may regulate expression of EGF and of each of the individual proteinase isozymes differently.

Effect of KB-2796, a new diphenylpiperazine Ca2+ antagonist, on voltage-dependent Ca2+ currents and oxidative metabolism in dissociated mammalian CNS neurons

The effects of KB-2796, 1-[bis(4-fluorophenyl)methyl]-4-(2,3,4- trimethoxybenzyl)piperazine-2HCl, on the low- and high-voltage activated Ca2+ currents (LVA and HVA ICa, respectively) and on oxidative metabolism were studied in neurons freshly dissociated from rat brain. KB-2796 reduced the peak amplitude of LVA ICa in a concentration-dependent manner with a threshold concentration of 10(-7) M when the LVA ICa was elicited every 30 s in the external solution with 10 mM Ca2+. The concentration for half-maximum inhibition (IC50) was 1.9 x 10(-6) M. At 10(-5) M or more of KB-2796, a complete suppression of the LVA ICa was observed in the majority of neurons tested. There was no apparent effect on the current-voltage (I-V) relationship and the current kinetics. KB-2796 delayed the reactivation and enhanced the inactivation of the Ca2+ channel for LVA ICa voltage- and time-dependently, suggesting that KB-2796 preferentially binds to the inactivated Ca2+ channel. KB-2796 at a concentration of 3.0 x 10(-6) M also decreased the peak amplitude of the HVA ICa without shifting the I-V relationship. In addition, KB-2796 reduced the oxidative metabolism (the formation of reactive oxygen species) of the neuron in a concentration-dependent manner with a threshold concentration of 3 x 10(-6) M. It is suggested that the inhibitory action of KB-2796 on the neuronal Ca2+ influx and the oxidative metabolism, in combination with a cerebral vasodilatory action, may reduce ischemic brain damage.

Effect of tri-n-butyltin on intracellular Ca2+ concentration of rat cerebellar neurons

The effect of tri-n-butyltin on the intracellular Ca2+ concentration ([Ca2+]i) of cerebellar neurons dissociated from rats was examined using fluo-3 and a flow cytometer. Tri-n-butyltin at 100 nM or more (up to 1 microM) increased the [Ca2+]i in a dose-dependent manner. The effect of tri-n-butyltin on the [Ca2+]i was greatly reduced under external Ca(2+)-free ([Ca2+]o-free) conditions, suggesting its dependence on the presence of [Ca2+]o. Lower trialkyltins, such as triethyltin and trimethyltin at 1 microM, exerted little or no action on the [Ca2+]i. Therefore, the cytotoxic action of tri-n-butyltin may be different from those of lower trialkyltins.

Fluorescent estimation on the effect of Ca2+ antagonists on the oxidative metabolism in dissociated mammalian brain neurons

Effect of organic Ca2+ antagonists on the oxidative metabolism or the formation of reactive oxygen species was estimated on dissociated mammalian neurons using a flow cytometer and 2',7'-dichlorofluorescin which is oxidized to be fluorescent by cellular oxidants. Of the organic Ca2+ antagonists used, flunarizine and nifedipine decreased the intensity of fluorescence at 1 microM or more while it was not the case for verapamil and diltiazem, suggesting one of the favourable actions of flunarizine and nifedipine on ischemic brain damage.

Ca(2+)-induced increase in oxidative metabolism of dissociated mammalian brain neurons: effect of extract of ginkgo biloba leaves

Effect of an extract of Ginkgo biloba leaves (EGb) on oxidative metabolism was studied using rat brain neurons and 2',7'-dichlorofluorescin fluorescence. Ionomycin (100 nM to 1 microM), a Ca(2+)-ionophore, dose-dependently augmented the 2',7'-dichlorofluorescin fluorescence in the presence of external Ca2+, but not under the external Ca(2+)-free condition. Preincubation of neurons with EGb (3 micrograms/ml) greatly reduced the ionomycin-induced increase in 2',7'-dichlorofluorescin fluorescence. Results suggest that EGb may reduce the Ca(2+)-induced increase in the oxidative metabolism of brain neurons.

Flow cytometric estimation of the effect of Ginkgo biloba extract on the content of hydrogen peroxide in dissociated mammalian brain neurons

The effect of Ginkgo biloba extract (GBE) on the content of hydrogen peroxide was estimated in cerebellar neurons dissociated from rats, by means of a flow-cytometer and 2',7'-dichlorofluorescein (DCF) diacetate, a fluorescent dye for intracellular hydrogen peroxide. The GBE started to reduce the DCF fluorescence of the neuron at 0.1 microgram/ml to 0.3 microgram/ml. Further increases in the GBE concentration (up to 3 micrograms/ml) produced a dose-dependent decrease in the DCF fluorescence, suggesting that GBE reduces the content of hydrogen peroxide or suppresses the reactive oxygen species (ROS) formation of cerebellar neurons. The present technique may be useful for preliminary evaluations of agents affecting the ROS formation in mammalian brain neurons.

Functional alterations in cerebral GABAA receptor complex associated with formation of alcohol dependence: analysis using GABA-dependent 36Cl- influx into neuronal membrane vesicles

The effect of alcohol dependence induced by ethanol inhalation on GABA-dependent 36Cl- influx into membrane vesicles prepared from the mouse brain has been examined. Ethanol, flunitrazepam and salsolinol induced a significant facilitation of the GABA-dependent 36Cl- influx into membrane vesicles obtained from the normal mouse brain. Ethanol inhalation induced the facilitation of GABA-dependent 36Cl- influx at 3-12 hr after the initiation of inhalation, but this facilitation returned to a normal level within 12 hr. In membrane vesicles obtained from the brain of an alcohol-dependent mouse at 7 days after the initiation of ethanol inhalation, not only was there a significant decrease of the GABA-dependent 36Cl- influx but there occurred also the disappearance of the activating effects of ethanol, flunitrazepam and salsolinol on the influx. This decrease in GABA-dependent 36Cl- influx was found to be recovered within 8 hr after the withdrawal of ethanol inhalation. On the other hand, behavioural withdrawal signs such as tonic-clonic convulsions with grimaces and heads thrown back appeared at 8 hr after the withdrawal of ethanol inhalation and continued for 8-16 hr. These results suggest that the observed functional deteriorations at cerebral GABAA receptors such as the decrease of GABA-dependent 36Cl- influx and the disappearance of the activating effects of ethanol, flunitrazepam and salsolinol on the influx may contribute to the preparation of the exhibition of ethanol withdrawal signs and/or the establishment of functional tolerance to alcohol, but are not directly related to the exhibition of alcohol withdrawal signs.

Triphenyltin-induced increase in the intracellular Ca2+ of dissociated mammalian CNS neuron: its independence from voltage-dependent Ca2+ channels

To test the possibility that triphenyltin (TPT) increases the intracellular Ca2+ ([Ca2+]i) in neurons as found previously in thymocytes, the effect of TPT on [Ca2+]i was examined in rat cerebellar neurons by a flow-cytometer with fluorescent dyes. TPT at concentrations ranging from 3 x 10(-7) M to 1 x 10(-5) M dose-dependently increased the [Ca2+]i. The TPT-induced increase in [Ca2+]i was not attenuated by a Ca2+ channel blocker, suggesting that it was not dependent on voltage-dependent Ca2+ channels. As the concentration of external Ca2+ ([Ca2+]e) increased, TPT produced a more profound increase in the [Ca2+]i. However, the increase in the [Ca2+]i by TPT was observed even in nominally [Ca2+]e-free solution. These results suggest two possibilities. First, TPT may promote Ca(2+)-influx to the neuron. Secondly, TPT may affect the intracellular Ca-store sites. This study is relevant to the neurotoxicity of organotins because it has become progressively clear that sustained increases in the [Ca2+]i can activate various Ca(2+)-dependent degradative processes.

P2 purinergic receptors and cellular calcium metabolism in A 431 human epidermoid carcinoma cells

Stimulation of P2 purinergic receptors on A 431 human epidermoid cells with ATP rapidly mobilized intracellular calcium and increased cytosolic free Ca2+ ([Ca2+]i). Incorporation of 45Ca2+ was also stimulated by ATP at a rate less than that of [Ca2+]i elevation. Among a number of nucleosides, nucleotides, and their analogues examined, ATP, GTP, UTP, ADP, UDP, adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), and 5'-adenylylimidodiphosphate (AMP-PNP) increased both [Ca2+]i and 45Ca2+ influx, whereas others did not; these latter two analogues (ATP gamma S and AMP-PNP) blocked the ATP-stimulated 45Ca2+ influx only very slightly, suggesting that they are not prominent antagonists but rather agonists. A high correlation between [Ca2+]i increase and 45Ca2+ influx, in terms of nucleotide specificity, suggests the involvement of [Ca2+]i in influx of 45Ca2+. It appeared that [Ca2+]i elevated by several nucleotides or nucleotide analogues opened a calcium gate, thus allowing the influx of 45Ca2+. P2 purinergic receptors on these cells had such a characteristic that they were rapidly desensitized. These nucleotides or analogues also affected epidermal growth factor (EGF) receptors by inhibiting the EGF binding. The differences of ligand or substrate specificities between P2 purinergic receptors and ecto-nucleotidases indicates that the two components are different molecules involved in different systems.