The third egg envelope subunit in fish: cDNA cloning and analysis, and gene expression

The inner layer of the egg envelope of a teleost fish, the medaka, Oryzias latipes, consists of two major subunit groups, ZI-1,2 and ZI-3. On SDS-PAGE, the ZI-1,2 group presents three glycoprotein bands that were considered to be composed of a common polypeptide moiety derived from their precursor, choriogenin H (Chg H). ZI-3 is a single glycoprotein derived from the precursor, choriogenin L (Chg L). In the present study, a fraction of a novel subunit protein was found in the V8 protease digest of ZI-1.2 that was partially purified from oocyte envelopes. This protein fraction was not present in the purified precursor, Chg H. By RT-PCR employing the primers based on the amino acid sequence of this fraction, a cDNA for the novel subunit was amplified, and a full-length clone of the cDNA was obtained by screening a cDNA library constructed from the spawning female liver. The clone consisted of 2025 b.p. and contained an open reading frame encoding the novel protein of 634 amino acids. This protein included Pro-X-Y repeat sequences in two-fifths of the whole length from its N-terminus. Northern blot analysis revealed that the gene expression for this protein occurred in the liver but not in the ovary of spawning female fish. This protein is considered as the third major subunit of the inner layer of the egg envelope of medaka.

Effects of point mutation in a flexible loop on the stability and enzymatic function of Escherichia coli dihydrofolate reductase

To elucidate the role of a flexible loop in the stability and function of Escherichia coli dihydrofolate reductase, glycine-121 in the flexible loop (117-131) was substituted to valine and leucine by site-directed mutagenesis. Despite the increased hydrophobicity of the side chains, the free energy changes of unfolding of the two mutants (G121V and G121L) determined by urea denaturation at 15 degrees C were decreased by 1.22 and 0.38 kcal/mol, respectively, compared with that of the wild-type. Thermal denaturation temperature, as monitored by differential scanning calorimetry, was decreased by 2.4 and 5.2 degrees C for G121V and G121L, respectively, accompanying the decrease in enthalpy change of denaturation. These findings indicate that the structure of DHFR is destabilized by the mutations, predominantly due to the large decrease in enthalpy change of denaturation relative to entropy change of denaturation. The steady-state kinetic parameter in the enzyme reaction, Km, was not influenced but kcat was greatly decreased by these mutations, resulting in 240- and 52-fold decreases in kcat/Km for G121V and G121L, respectively. The main effect of the mutations appeared to be modification of the flexibility of the loop due to overcrowding of the bulky side chains, overcoming the enhancement of hydrophobic interaction.

Effect of exercise training on serum leptin levels in type 2 diabetic patients

To evaluate the effect of exercise training on serum leptin levels 50 sedentary subjects with type 2 diabetes were enrolled in either 6 weeks of aerobic exercise training with diet therapy (n = 23) or diet therapy alone (n = 27). The training program consisted of walking and cycle ergometer exercise for 1 hour at least 5 times per week, with the intensity of exercise maintained at 50% of maximum oxygen uptake. Serum leptin levels decreased significantly in the exercise training (TR) group (7.2 +/- 3.6 to 4.6 +/- 2.5 ng/mL, P <.05), but not in the sedentary (SED) group (6.9 +/- 3.4 to 5.6 +/- 2.9 ng/mL). Leptin levels standardized for percentage body fat (dividing serum leptin level by percentage body fat) after treatment were lower in the TR subjects compared with the SED subjects. Body weight and percentage body fat decreased in all patients; however, no significant changes were observed in either group. Fasting concentrations of plasma insulin and cortisol and the urinary excretion of 17-hydroxycorticosteroid (17-OHCS) did not differ between the groups either before or after treatment. Fasting plasma glucose and hemoglobin A(1c) (HbA(1c)) improved significantly in both groups, although no significant differences were observed between the groups either before or after treatment. Ventilatory threshold increased significantly in the exercise training subjects. This study demonstrates that exercise training in type 2 diabetic subjects reduces serum leptin levels independent of changes in body fat mass, insulin, or glucocorticoids.

Synchronous production of the low- and high-molecular-weight precursors of the egg envelope subunits, in response to estrogen administration in the teleost fish Oryzias latipes

Estrogen stimulation of production and accumulation of L-SF and H-SF, the low- and high-molecular-weight precursors of the egg envelope subunits in Oryzias latipes, was analyzed by immunohistochemical and immunoblotting methods. Both SF substances were detected in the liver of the male fish as quickly as 16-24 hr after estrogen treatment, and their production and accumulation in the liver and blood plasma increased as estrogen treatment continued. Immunohistochemical analysis revealed that the number of cells producing both SF substances was increased in the liver as estrogen treatment continued. These results strongly suggest the occurrence of synchronous production of L-SF and H-SF in response to estrogen. In liver extracts, but not in blood plasma, an additional L-SF-like immunoreactive protein was detected on immunoblots. Preliminary data indicate parallel appearance of vitellogenin and SF substances in the liver of estrogenized fish.

Isolation of H-SF substances, the high-molecular-weight precursors of egg envelope proteins, from the ascites accumulated in the oestrogen-treated fish, Oryzias latipes

High- and low-molecular weight spawning-female-specific (H-SF and L-SF) substances are liver-derived putative precursors of the inner layer of egg envelope of the medaka Oryzias latipes, and are also found in the ascites which are accumulated in the male fish on prolonged treatment with oestrogen. In the present study, the H-SF substances purified from the ascites of the oestrogen-treated male medaka were found to consist of three proteins. Their molecular weights ranged from 74,000 to 76,000, which corresponds to those of ZI-1 and ZI-2, the major components of medaka egg envelope. The amino acid composition of the H-SF substances was characterised by high contents of proline (17.58 mol%) and glutamic acid/glutamine (13.34 mol%). The characteristics were almost identical to those of ZI-1 and ZI-2 but differed from those of L-SF substance, a precursor of ZI-3, another major component of the egg envelope. These results confirm our view that H-SF substances are the precursors of ZI-1 and ZI-2. The average amino acid compositions of H-SF substances and L-SF substance coincided with the amino acid composition of whole egg envelope. This result strongly suggests that an equal amount of H-SF substances and L-SF substance would construct the inner layer of egg envelope after a little modification.

Formation of 8-hydroxy-2'-deoxyguanosine and 4-hydroxy-2-nonenal-modified proteins in rat liver after ischemia-reperfusion: distinct localization of the two oxidatively modified products

Ischemia-reperfusion (IR) injury is an intractable process associated not only with therapeutic recanalization of vessels, but also with partial resection or transplantation of solid organs including liver. To develop methods for predicting the degree of hepatic IR injury and further to identify injured cells, we studied the formation of 8-hydroxy-2'-deoxy-guanosine (8-OHdG) and 4-hydroxy-2-nonenal (HNE)-modified proteins in the normothermic hepatic IR model of rats using immunohistochemistry, high-performance liquid chromatography (HPLC) determination and Western blot. The Pringle maneuver for either 15 or 30 min duration produced reversible or lethal damage, respectively. The levels of both products were significantly increased in proportion to ischemia duration 40 min after reperfusion, suggesting the involvement of hydroxyl radicals. Increased immunoreactivity of 8-OHdG was observed not only in the nuclei of hepatocytes but also in those of bile canalicular and endothelial cells. However, immunoreactivity of HNE-modified proteins was detected in the cytoplasm of hepatocytes, which was confirmed by Western blot, and in addition, in the nuclei of hepatocytes after severe injury. Thus, localization of the two oxidatively modified products was not identical. Our data suggest that these two products could be used for the assessment of hepatic IR injury in tissue, but that the biological significance of the two products might be different.

Effects of antipsychotic drugs on neurotoxicity, expression of fos-like protein and c-fos mRNA in the retrosplenial cortex after administration of dizocilpine

In this study, we examined the effect of clozapine, olanzapine, risperidone and haloperidol on the neuropathology (i.e. neuronal vacuolization) and the expression of Fos-like protein and c-fos mRNA in the retrosplenial cortex of female Sprague-Dawley rats induced by the NMDA receptor antagonist dizocilpine. Pretreatment (15 min) with clozapine or olanzapine, but not risperidone or haloperidol, blocked the neuronal vacuolization produced by dizocilpine (0.5 mg/kg, s.c.) in the rat retrosplenial cortex in a dose-dependent manner. Furthermore, pretreatment (15 min) with clozapine or olanzapine, but not risperidone or haloperidol, significantly attenuated the expression of Fos-like protein in the retrosplenial cortex induced by dizocilpine (0.5 mg/kg, s.c.) in a dose-dependent manner. The marked expression of c-fos mRNA in the rat retrosplenial cortex induced by the administration of dizocilpine (0.5 mg/kg, s.c.) was significantly attenuated by pretreatment (15 min) with clozapine (10 mg/kg) or olanzapine (10 mg/kg), but not risperidone (10 mg/kg) or haloperidol (10 mg/kg). The present results suggest that pharmacologically relevant doses of clozapine or olanzapine, but not risperidone or haloperidol, block the neuropathological changes and the expression of Fos-like protein and c-fos mRNA in the rat retrosplenial cortex elicited by the administration of dizocilpine. It is possible that the blockade of dizocilpine-induced neuropathological changes by clozapine and olanzapine may be related to the unique antipsychotic actions of these drugs in schizophrenic patients, although this remains to be verified.

The effects of aging on muscarinic receptor/G-protein coupling in the rat hippocampus and striatum

In the striatum and hippocampus, there is a loss of sensitivity to muscarinic agonists with age which has been traced to events early in the signal transduction pathway. Our laboratory has therefore focussed on investigations at this level. The current experiments investigate the effects of age on G-protein/receptor interactions by using competitive binding assays to measure the ability of GppNHp to decrease the proportion of receptors bound to G-proteins in the absence and the presence of added Mg2+. L-[3H]Quinuclidinyl benzilate was used as a nonselective ligand and [3H]pirenzepine as an M1 selective ligand. We find that: (1) muscarinic receptors and G-proteins in the striatum appear to become loosely coupled with age, with no change in Mg2+ sensitivity. (2) M1-receptor/G-protein complexes in the hippocampus display increased sensitivity to the presence of Mg2+ with age, with those from old but not young tissue requiring added Mg2+ in order to uncouple. This effect, however, may not be M1 specific.

Internal Ca2+ mobilization by muscarinic stimulation increases secretion from adrenal chromaffin cells only in the presence of Ca2+ influx

The cytosolic free Ca2+ concentration ([Ca2+]in) in single cat and bovine adrenal chromaffin cells was measured to determine whether or not there was any correlation between the [Ca2+]in and the catecholamine (CA) secretion caused by muscarinic receptor stimulation. In cat chromaffin cells, methacholine (MCh), a muscarinic agonist, raised [Ca2+]in by activating both Ca2+ influx and intracellular Ca2+ mobilization with an accompanying CA secretion. In bovine cells, MCh elevated [Ca2+]in by mobilizing intracellular Ca2+ but did not cause CA secretion. The MCh-induced rise in [Ca2+]in in cat cells was much higher than that in bovine cells, but when Ca2+ influx was blocked, the rise was reduced, with a concomitant loss of secretion, to a level comparable to that in bovine cells. Intracellular Ca2+ mobilization due to muscarinic stimulation substantially increased secretion from depolarized bovine and cat cells, where a [Ca2+]in elevated above basal values was maintained by a continuous Ca2+ influx. These results show that Ca2+ released from internal stores is not effective in triggering secretion unless Ca2+ continues to enter across the plasma membrane, a conclusion suggesting that secretion depends on [Ca2+]in in a particular region of the cell.

Cd2+ and Co2+ at micromolar concentrations mobilize intracellular Ca2+ via the generation of inositol 1,4,5-triphosphate in bovine chromaffin cells

To understand the mechanisms underlying the Cd2+- and Co2+-induced intracellular Ca2+ mobilization, we measured the levels of inositol phosphates using bovine chromaffin cells. Studies using HPLC indicated that Cd2+, Co2+ and methacholine significantly increased the generation of 1,4,5-IP3. The results suggest that Cd2+ and Co2+ mobilize Ca2+ from IP3-sensitive Ca2+ stores, possibly through the presumptive Cd2+ receptor.

Heat-shock preconditioning reduces oxidative protein denaturation and ameliorates liver injury by carbon tetrachloride in rats

Membrane lipids and cytosolic proteins are major targets of oxidative injury. This study examined the effect of heat-shock preconditioning associated with the induction of heat-shock protein 72 on liver injury, from the aspect of lipid peroxidation and protein denaturation after carbon tetrachloride (CCl4) administration in rats--one of the representative oxidative injuries. Male Wistar rats were divided into two groups, group HS (preconditioned by heat exposure) and group C (not preconditioned). Expression of HSP72 in the liver tissue was confirmed by Western blot analysis. After a 48-h recovery period, all rats were given CCl4 intragastrically. Liver damage was assessed by measuring serum liver-related enzyme levels and adenine nucleotide concentration in the liver tissue. Lipid peroxidation and protein denaturation were evaluated by measuring tiobarbituric acid reactive substances (TBARS) and by immunohistochemical staining of 4-hydroxy-2-nonenal(HNE)-modified proteins in the liver. Survival rates of the rats after CCl4 administration were also compared. Expression of HSP72 was clearly detected in group HS, but not in group C. Heat-shock preconditioning significantly improved the survival rate, suppressed the increase in liver-related enzyme levels and maintained adenosine triphosphate levels (P<0.01 each). HNE-modified proteins--denatured proteins by free radical attack--were significantly less stained in group HS than in group C (P<0.05). However, TBARS levels did not differ between groups. Because heat-shock preconditioning did not alter TBARS levels but reduced HNE-modified proteins in association with the expression of HSP72, it is suggested that HSP72 did not prevent lipid peroxidation but decreased the lipid peroxidation-induced denaturation of proteins. This seemed to be a mechanism of heat-shock preconditioning to ameliorate oxidative liver injury.

A unique proteolytic action of HCE, a constituent protease of a fish hatching enzyme: tight binding to its natural substrate, egg envelope

High choriolytic enzyme (HCE), a constituent protease of the hatching enzyme of the teleost, Oryzias latipes, swells its natural substrate, egg envelope (chorion) by hydrolyzing it partially. This enzyme was found to be bound tightly to the chorion when it exerted catalytic action. This was evidenced by the experimental results showing (i) that the turnover of this enzyme seemed to be hindered by the chorion, (ii) that the enzyme bound to the chorion could be recovered by washing with an alkaline medium, and (iii) that the bound enzyme could be quantified by radioimmunological estimation. The bound enzyme sustained its original activity and the binding between the enzyme and the chorion seems to be stoichiometric.

The effect of the antipsychotic drug mosapramine on the expression of Fos protein in the rat brain: comparison with haloperidol, clozapine and risperidone

In this study, we examined the effect of the acute p.o. administration of the antipsychotic drug mosapramine, as well as the antipsychotic drugs clozapine, haloperidol and risperidone, on the expression of Fos protein in the medial prefrontal cortex, nucleus accumbens and dorsolateral striatum of rat brain. The administration of mosapramine (1 or 3 mg/kg) significantly increased the number of Fos protein positive neurons in the medial prefrontal cortex, but not in the dorsolateral striatum. In addition, mosapramine (1, 3 or 10 mg/kg) produced a dose-dependent increase in the number of Fos protein positive neurons in the nucleus accumbens. The acute administration of 10 mg/kg of mosapramine significantly increased the number of Fos protein positive neurons in all brain regions. The acute administration of clozapine (30 mg/kg), similarly to mosapramine at lower doses (1 or 3 mg/kg), significantly increased the number of Fos protein positive neurons in the medial prefrontal cortex and nucleus accumbens, but not dorsolateral striatum. In contrast, haloperidol (0.3 mg/kg) significantly increased the number of Fos protein positive neurons in the nucleus accumbens and dorsolateral striatum, but not medial prefrontal cortex. The acute administration of risperidone (0.3 or 1 mg/kg) did not affect the number of Fos protein positive neurons in the medial prefrontal cortex, nucleus accumbens or dorsolateral striatum of rat brain, whereas a 3 mg/kg dose of risperidone significantly increased the number of Fos protein positive neurons in all brain regions. These results suggest that the ability of mosapramine to enhance expression of Fos protein in the medial prefrontal cortex may contribute to a clozapine-like profile with respect to actions on negative symptoms in schizophrenia. Furthermore, the lack of effect of low doses of mosapramine on Fos protein expression in the dorsolateral striatum, an area believed to play a role in movement, suggests that it may have a lower tendency to induce neurological side effects.

Possible occurrence of Na+-dependent Ca2+ influx mechanism in isolated bovine chromaffin cells

Chromaffin cells were isolated from bovine adrenals and the effects of experimental manipulations which alter the level of internal Na+ on the release of catecholamines and 45Ca uptake by these cells were investigated. In response to NA+ deprivation both parameters were increased or decreased when internal NA+ was raised or reduced, respectively. The results suggest the existence of Na+-dependent Ca2+ influx mechanism in these cells.

Heat shock preconditioning on mitochondria during warm ischemia in rat livers

BACKGROUND

The aim of this study was to investigate the effects of stress tolerance from heat shock preconditioning on changes in mitochondrial functions during ischemia-reperfusion injury of the liver.

MATERIALS AND METHODS

Rats were divided into a heat shock group (group HS) and a control group (group C). In group HS, rats received heat shock pretreatment 48 h prior to ischemia-reperfusion. Heat shock pretreatment was performed in a water bath at 42 degrees C for 15 min under general anesthesia. In group C, the same treatment was done with the water bath at 37 degrees C instead of at 42 degrees C. A 30-min warm ischemia by cramping the hepatoduodinal ligament (Pringle's maneuver) followed by a 60-min reperfusion was administered to all rats. Changes in membrane potential of hepatic mitochondria (MPM); mitochondrial respiratory function before ischemia (n = 5), after ischemia (n = 10), and after reperfusion (n = 10); and ATP recovery after reperfusion were compared between the groups.

RESULTS

After a 30-min ischemia, MPM in group C decreased significantly and did not recover even after reperfusion. On the other hand, MPM in group HS was maintained even after a 30-min ischemia and 60 min into reperfusion as well. The respiratory control ratio (RCR) of the mitochondria in group C decreased to as low as 5.06 +/- 0.72 after a 30-min ischemia, but in group HS, RCR was maintained near a normal level. The ATP level recovered significantly earlier in group HS than in group C after reperfusion.

CONCLUSIONS

Heat shock preconditioning of the liver protected mitochondria from loss of membrane integrity during ischemia and contributed to their ability to produce energy-rich phosphates during reperfusion.

Xanthine oxidase mediates paraquat-induced toxicity on cultured endothelial cell

The role of xanthine oxidase in paraquat toxicity was investigated using cultured bovine pulmonary artery endothelial cells. Exposure to paraquat 0.1 mM was done for 24 hr with or without tungsten pretreatment and in the presence or absence of xanthine oxidase inhibitors. Exposure to paraquat significantly increased O2- production and relative xanthine oxidase activity (xanthine oxidase activity divided by total xanthine dehydrogenase plus xanthine oxidase) while depressing cell growth. In contrast, tungsten and allopurinol inhibited the increase of xanthine oxidase activity and decreased O2- release. Cell injury was assessed by leakage of lactate dehydrogenase and by fluorescein diacetate staining; it was found that oxidase inhibitors (both allopurinol and tungsten) reduced paraquat cytotoxicity. Thus the toxicity of paraquat was at least partly due to intracellular O2- production mediated by xanthine oxidase and the subsequent formation of other free radicals.

Lipopolysaccharide-mediated hepatic glutathione depletion and progressive mitochondrial damage in mice: protective effect of glutathione monoethyl ester

Overproduction of reactive oxygen intermediates (ROI) may have an important role in the pathophysiology of lipopolysaccharide-mediated liver-injury. This study examined the role of cytosolic and mitochondrial glutathione in protecting hepatocytes from oxidative stress during exposure to lipopolysaccharide. In addition, the possible participation of changes of inner mitochondrial membrane permeability in lipopolysaccharide-induced hepatotoxicity was investigated. The changes of hepatic glutathione content following lipopolysaccharide challenge (2 mg/kg) were measured in mice by reverse-phase high-performance liquid chromatography. Glutathione depletion and a glutathione-rich state were produced by intraperitoneal administration of a specific inhibitor of gamma-glutamyl cysteine synthetase, buthionine sulfoximine (3 mmol/kg), and by administration of glutathione monoethyl ester (10 mmol/kg), respectively. Intracellular ROI generation and the mitochondrial membrane potential were quantified by flow cytometry. Changes of inner mitochondrial membrane permeability in hepatocytes were assessed by radioactive sucrose entrapment. There was increased production of ROI along with depletion of cellular and mitochondrial glutathione in the liver after lipopolysaccharide administration. There was also a change of inner mitochondrial membrane permeability in hepatocytes, with the loss of coupled functions. Buthionine sulfoximine decreased the hepatic antioxidant capacity, worsened mitochondrial function, and reduced the survival rate of the mice. In contrast, glutathione monoethyl ester improved all of these parameters. Glutathione may have an important role in cellular defenses against lipopolysaccharide-induced liver damage in mice, and excessive oxidative stress may precipitate the mitochondrial membrane permeability transition in hepatocytes and lead to cell death.

Area specific alterations in muscarinic stimulated low Km GTPase activity in aging and Alzheimer's disease: implications for altered signal transduction

Carbachol-stimulated low Km GTPase activity (an index of muscarinic receptor-G protein coupling) was examined in hippocampus, basal ganglia, orbital frontal gyrus and superior frontal gyrus obtained from mature, aged and Alzheimer's Disease (AD) groups. Results indicated that carbachol-stimulated low Km GTPase activities in basal ganglia were as follows: mature controls > aged > AD, and there was a trend toward a similar pattern of decline in the hippocampus. No differences were seen in the two cortical areas examined; however, carbachol-stimulated low Km GTPase activity was small in the mature controls. Importantly, there were significant negative correlations between disease duration and carbachol-stimulated low Km GTPase activity in all areas examined except the orbital frontal gyrus. The longer the duration of the disease the lower the carbachol-stimulated low Km GTPase activity. Results suggest that age and disease-related changes in mAChR-G protein interactions in the basal ganglia may contribute to reduced signal transduction (ST). In addition, since decreased carbachol-stimulated low Km GTPase activity has also been observed in the aged rat; thus, investigations of the factors involved in decrements in signal transduction in the aged rat may be useful for understanding these alterations in aged humans or victims of AD.

Spontaneous and secretagogue-induced changes in cytosolic free Ca concentration measured by microfluorimetry with fura-2 on single bovine adrenal chromaffin cells

The concentration of cytosolic Ca2+ ([Ca]in) was examined in single bovine adrenal chromaffin cells by monitoring fura-2 fluorescence with microspectrofluorimetry. To see the correlation between [Ca]in and secretion, we also measured the rates of catecholamine (CA) secretion and 45Ca efflux from populations of cells. [Ca]in was constant in the majority of single cells, but the small oscillatory changes in [Ca]in were observed in a population of cells. These spontaneous Ca oscillations, when observed, disappeared either after removal of extracellular Ca2+ or by addition of D-600 or Mn2+, but still persisted in the presence of tetrodotoxin (TTX) or after removal of extracellular Na+. In the silent cells the Ca fluctuations were often induced by Bay-K-8644. The characteristics of Bay-K-8644-induced Ca fluctuations were very similar to those of spontaneous ones. Low concentrations of nicotine (1 microM), acetylcholine (ACh; 1-2 microM), or KCl (12.5 mM) often induced oscillations riding on a steady rise in [Ca]in. These changes were rapidly suppressed by removal of either extracellular Ca2+ or Na+, or by addition of either D-600 (methoxyverapamil) or TTX. A low concentration of ACh (1 microM) or KCl (12.5 mM) also increased the rate of 45Ca efflux, but substantial secretion was not detected. On the other hand, the sustained rise in [Ca]in was evoked by 0.1 mM ACh, 20 microM nicotine, or 30 mM KCl, which was suppressed by removal of extracellular Ca2+, but was little affected by TTX. A sustained increase in 45Ca efflux upon exposure to ACh was observed, possibly reflecting the sustained rise in [Ca]in. ACh also stimulated CA secretion, which was faded out during the prolonged application. Veratridine, a Na channel activator, caused repetitive sequence of Ca transients followed by a sustained rise in [Ca]in. These results, together with the previous electrophysiological findings, suggest that: (1) the spontaneous Ca fluctuations are closely associated with occurrence of spontaneous Ca2+ and Na+ action potentials; (2) the rise in [Ca]in induced by a low concentration of nicotinic agonists of KCl is mediated by Na+ action potentials as well as gradual membrane depolarizations; (3) the oscillatory changes subsequent to a rise in [Ca]in reflect fluctuations in Ca2+ influx through the Ca2+ channels; (4) the critical [Ca]in needs to be attained before the CA secretion takes place.

Muscarinic receptor concentrations and dopamine release in aged rat striata

The extent to which age-related decreases in muscarinic enhancement of K(+)-evoked dopamine release (K(+)-ERDA) from perifused striatal slices is dependent upon the loss of striatal muscarinic receptors (mAChR) was determined. Both K(+)-ERDA and mAChR (M1, M2) concentrations were assessed from the same animals (3, 5-7 and 24-27 months). Results indicated associated decreases of 70% in oxotremorine-enhanced K(+)-ERDA and 36% in Bmax (3H-QNB) (3 and 24-27 months groups). Decrease of mAChR Bmax was not the result of membrane sequestration. Although both the concentrations of M1 and M2 muscarinic receptor subtypes decline with age, only the M2 receptor decline was correlated with the age-related decreases in muscarinic enhancement of K(+)-ERDA (r = .71, p less than 0.001). Results suggest that age-related decreases in mAChR concentrations as being partially responsible for deficits in muscarinic enhancement of K(+)-evoked release of DA.

Interaction of the cell-binding domain of fibronectin with VLA-5 integrin induces monokine production in cultured human monocytes

The effect of fibronectin on IL-1 alpha, IL-1 beta, tumour necrosis factor-alpha (TNF-alpha), and IL-6 production was investigated with cultured monocytes isolated from human peripheral blood. Monokine concentrations were determined by both ELISA and bioassay. Fibronectin markedly stimulated the secretion of IL-1 alpha, IL-1 beta, TNF-alpha and IL-6 from cultured monocytes in a dose-dependent manner, with the maximal effect apparent within 24 h. Northern blot analysis revealed a marked increase in the abundance of mRNA specific for each monokine on exposure of monocytes to fibronectin. Monoclonal antibodies to the alpha chain of very late antigen (VLA)-5, the beta 1 integrin, the alpha chain of Mac-1, and the beta 2 integrin, as well as the synthetic peptide of GRGDSP (which corresponds to the cell-binding domain of fibronectin), inhibited (> 50%) fibronectin-induced monokine production. Monoclonal antibodies to the alpha chain of VLA-4, and the alpha chain of LFA-1, as well as the synthetic peptide CS-1 (which corresponds to the alternatively spliced connecting segment of fibronectin) and the control peptide GRADSP, had no inhibitory effect on monokine production. A MoAb, R60, that recognizes an epitope of the fibronectin molecule that includes the RGD sequence, inhibited monokine production, whereas the MoAb Y16, which recognizes another epitope of fibronectin not including RGD, did not. These results indicate that fibronectin-induced production of IL-1 alpha, IL-1 beta, TNF-alpha and IL-6 from cultured monocytes is mediated predominantly by interaction of the cell-binding domain of fibronectin with VLA-5, although Mac-1 also may contribute to this effect of fibronectin. Our results indicate that the interaction of fibronectin with integrins may contribute to the cytokine network in inflammatory response.

Tetraethylammonium stimulates adrenomedullary secretion by causing fluctuations in a cytosolic free Ca concentration

Tetraethylammonium (TEA) caused marked fluctuations in a cytosolic free Ca concentration, which was measured by fura-2 microfluorimetry in bovine adrenal chromaffin cells. At the same time. TEA stimulated catecholamine secretion from cat and bovine chromaffin cells. Present results suggest that TEA indirectly increases the Ca2+ influx by depolarizing the cell membrane and consequently stimulates catecholamine secretion.

Age-specific alterations in muscarinic stimulation of K(+)-evoked dopamine release from striatal slices by cholesterol and S-adenosyl-L-methionine

The present experiments were carried out in order to test the hypothesis that age-related signal transduction (ST) deficits may occur as a result of structural changes in the membrane that are reflected partially as increased membrane microviscosity. Oxotremorine (oxo) enhancement of K(+)-evoked release of dopamine (K(+)-ERDA) was examined in superfused striatal slices from mature (6 months) and old (24 months) Wistar rats incubated (1 or 4 h, 37 degrees C) with graded concentrations of S-adenosyl-L-methionine (SAM) or cholesterol hemisuccinate (CHO) in a modified Krebs medium. Tissue was then assessed for one of the following: (a) the degree of oxo-enhanced K(+)-ERDA, (b) carbachol stimulated low Km GTPase activity, or (c) alterations in membrane microviscosity. In other experiments the tissue was incubated in CHO followed by SAM (or the reverse), and oxo-enhanced K(+)-ERDA examined. Results indicated that SAM treatment increased all the parameters in the striatal tissue from old animals, while CHO had selective, opposite effects in the striatal tissue obtained from young animals. CHO-SAM, or the reverse, produced the same pattern of results. These results suggest that ST deficits may involve age-related structural alterations in membranes that interfere with receptor-G protein coupling/uncoupling.