Biomedical subjects

A Barth

Publications and source records attributed to A Barth.

At least 55 records · Page 3Linked to original sources

PubMed2000

P(3)-[2-(4-hydroxyphenyl)-2-oxo]ethyl ATP for the rapid activation of the Na(+),K(+)-ATPase.

P(3)-[2-(4-hydroxyphenyl)-2-oxo]ethyl ATP (pHP-caged ATP) has been investigated for its application as a phototrigger for the rapid activation of electrogenic ion pumps. The yield of ATP after irradiation with a XeCl excimer laser (lambda = 308 nm) was determined at pH 6.0-7.5. For comparison, the photolytic yields of P(3)-[1-(2-nitrophenyl)]ethyl ATP (NPE-caged ATP) and P(3)-[1, 2-diphenyl-2-oxo]ethyl ATP (desyl-caged ATP) were also measured. It was shown that at lambda = 308 nm pHP-caged ATP is superior to the other caged ATP derivatives investigated in terms of yield of ATP after irradiation. Using time-resolved single-wavelength IR spectroscopy, we determined a lower limit of 10(6) s(-1) for the rate constant of release of ATP from pHP-caged ATP at pH 7.0. Like NPE-caged ATP, pHP-caged ATP and desyl-caged ATP bind to the Na(+), K(+)-ATPase and act as competitive inhibitors of ATPase function. Using pHP-caged ATP, we investigated the charge translocation kinetics of the Na(+),K(+)-ATPase at pH 6.2-7.4. The kinetic parameters obtained from the electrical measurements are compared to those obtained with a technique that does not require caged ATP, namely parallel stopped-flow experiments using the voltage-sensitive dye RH421. It is shown that the two techniques yield identical results, provided the inhibitory properties of the caged compound are taken into account. Our results demonstrate that under physiological (pH 7.0) and slightly basic (pH 7.5) or acidic (pH 6. 0) conditions, pHP-caged ATP is a rapid, effective, and biocompatible phototrigger for ATP-driven biological systems.

Adenosine Triphosphate↗

PubMed2000

Structural changes of the sarcoplasmic reticulum Ca(2+)-ATPase upon nucleotide binding studied by fourier transform infrared spectroscopy.

Changes in the vibrational spectrum of the sarcoplasmic reticulum Ca(2+)-ATPase upon nucleotide binding were recorded in H(2)O and (2)H(2)O at -7 degrees C and pH 7.0. The reaction cycle was triggered by the photochemical release of nucleotides (ATP, ADP, and AMP-PNP) from a biologically inactive precursor (caged ATP, P(3)-1-(2-nitrophenyl) adenosine 5'-triphosphate, and related caged compounds). Infrared absorbance changes due to ATP release and two steps of the Ca(2+)-ATPase reaction cycle, ATP binding and phosphorylation, were followed in real time. Under the conditions used in our experiments, the rate of ATP binding was limited by the rate of ATP release (k(app) congruent with 3 s(-1) in H(2)O and k(app) congruent with 7 s(-1) in (2)H(2)O). Bands in the amide I and II regions of the infrared spectrum show that the conformation of the Ca(2+)-ATPase changes upon nucleotide binding. The observation of bands in the amide I region can be assigned to perturbations of alpha-helical and beta-sheet structures. According to similar band profiles in the nucleotide binding spectra, ATP, AMP-PNP, and ADP induce similar conformational changes. However, subtle differences between ATP and AMP-PNP are observed; these are most likely due to the protonation state of the gamma-phosphate group. Differences between the ATP and ADP binding spectra indicate the significance of the gamma-phosphate group in the interactions between the Ca(2+)-ATPase and the nucleotide. Nucleotide binding affects Asp or Glu residues, and bands characteristic of their protonated side chains are observed at 1716 cm(-1) (H(2)O) and 1706 cm(-1) ((2)H(2)O) and seem to depend on the charge of the phosphate groups. Bands at 1516 cm(-1) (H(2)O) and 1514 cm(-1) ((2)H(2)O) are tentatively assigned to a protonated Tyr residue affected by nucleotide binding. Possible changes in Arg, Trp, and Lys absorption and in the nucleoside are discussed. The spectra are compared with those of nucleotide binding to arginine kinase, creatine kinase, and H-ras P21.

Adenosine Diphosphate↗

PubMed2000

The infrared absorption of amino acid side chains.

Amino acid side chains play fundamental roles in stabilising protein structures and in catalysing enzymatic reactions. These fields are increasingly investigated by infrared spectroscopy at the molecular level. To help the interpretation of the spectra, a review of the infrared absorption of amino acid side chains in H(2)O and 2H(2)O is given. The spectral region of 2600-900cm(-1) is covered.

Amino Acids↗

PubMed2000

Influence of subchronic administration of catechol estrogens on the formation of reactive oxygen species in rat liver microsomes.

Metabolic pathways of estrogens are the formation of catechol estrogens (CE; 2- and 4-hydroxy-estrogens), redox cycling of CE and free radical generation, mediated through cytochrome P450 (P450) oxidase/reductase activity. In previous investigations subchronic administration of estrogens showed prooxidative and antioxidative activities in rat liver microsomes (BARTH et al. 1999). To find out whether or not catechol metabolites are responsible for prooxidative activity, we checked 2- and 4-hydroxy-estradiol (2OH-E2 and 4OH-E2) and the non-catechol metabolite 6alpha-hydroxy-estradiol (6alpha-OH-E2) for formation of reactive oxygen species in liver microsomes of 30-day-old male Wistar rats after 5 days treatment (1, 10 mg/kg b. wt. orally, once a day). The results were compared with those after treatment of the rats with estradiol (E2), estradiol valerate (E2V) and ethinylestradiol (EE2). In liver homogenates glutathione and lipid peroxides were determined, in microsomes NADPH-Fe++-stimulated lipid peroxidation (LPO), H2O2 generation and lucigenin (LUC) and luminol (LUM) amplified chemiluminescence (CL) were investigated. In liver 9000 x g supernatants monooxygenase activities were measured. The two catechol estrogens did not show any antioxidative activity, whereas 6alpha-OH-E2 significantly diminished lipid peroxides in the liver as well as LPO and LUM-CL in liver microsomes. Among estrogens, only EE2 showed antioxidative activity. Both CE inhibited ethoxycoumarin O-deethylation. Peroxidative activity as enhanced LUC-CL was found after 2OH-E2 (1 mg/kg b.wt.) and E2, but 10 times higher doses of both CE did not change LUC-CL. Microsomal H2O2 generation was enhanced by E2, E2V and both CE, not by 6alpha-OH-E2. The lower level of H2O2 enhancement caused by CE in comparison to E2 and E2V together with unchanged LUC-CL after high CE doses did not unequivocally prove the CE to be mainly responsible for the prooxidative activities of E2 and E2V in liver microsomes, at least in 30-day-old male rats. Unchanged GSH in the liver after CE administration supports this hypothesis.

Administration, Oral↗

PubMed2000

Fine-structure enhancement--assessment of a simple method to resolve overlapping bands in spectra.

A simple mathematical procedure--fine-structure enhancement--has been assessed on its ability to resolve overlapping bands in spectra. Its advantages and limitations have been explored using synthetic and experimental spectra. Fine-structure enhancement involves smoothing the original spectrum, multiplying the smoothed spectrum with a weighting factor and subtracting this spectrum from the original spectrum. As a result, the fine-structure of the original spectrum is enhanced in the processed spectrum and bands that overlap in the original spectrum appear as distinct bands in the processed spectrum. To be resolved by fine-structure enhancement, Lorentzian lines have to be separated by more than their quarter width at half maximum, Gaussian lines by more than their half width at half maximum. A comparison of fine-structure enhancement and Fourier self-deconvolution shows that Fourier self-deconvolution has in theory a higher potential to resolve overlapping bands. However, this depends crucially on the correct choice of the parameters. In practice, when parameters commonly used are chosen for Fourier self-deconvolution, fine-structure enhancement leads to similar results. This is demonstrated at the example of the infrared absorbance spectrum of the protein papain, where the amide I band components could be resolved similarly with both methods. Thus, fine-structure enhancement seems to be a simple alternative to Fourier self-deconvolution that does not require specialised software.

Models, Chemical↗

PubMed2000

Silent cerebral ischemia detected by diffusion-weighted MRI after carotid endarterectomy.

BACKGROUND AND PURPOSE: Small emboli arising from a friable plaque during carotid endarterectomy (CEA) constitute an important risk of perioperative ischemic complications. To evaluate the incidence and significance of silent cerebral ischemic lesions of embolic origin after CEA, we prospectively examined a series of surgical patients with high-grade carotid stenosis by using diffusion-weighted MRI (DWI). We also tried to correlate postoperative ischemic lesions with the occurrence of sonographic cerebral embolic signals, the presence of plaque ulcerations, and the use of intraoperative shunting. METHODS: Of a consecutive series of 53 patients undergoing elective CEA for high-grade carotid stenosis, 48 patients with unchanged postoperative neurological status were prospectively studied with DWI of the brain the day before and the day after the operation. The magnetic resonance images were analyzed by 2 neuroradiologists blinded to the clinical result of the operation. Any new hyperintense signal was interpreted as a postoperative ischemic lesion. RESULTS: Forty-six (95.8%) of 48 patients had unchanged postoperative brain DWI. In 2 patients (4.2%), a new single asymptomatic hyperintense signal was observed on the side of the operation. Both lesions were small and presumably of embolic origin. They were not related to sonographic embolic signals, plaque ulcerations, or intraoperative shunting. CONCLUSIONS: These results suggest that the incidence of silent ischemic brain lesions of embolic origin after CEA is low and does not correlate with the occurrence of intraoperative sonographic microemboli. They confirm that CEA is a safe procedure that carries a low risk of postoperative cerebral events.

Aged↗

PubMed2000

Ace/Fgf8 is required for forebrain commissure formation and patterning of the telencephalon.

Fibroblast growth factors (Fgfs) form a large family of secreted signalling proteins that have a wide variety of roles during embryonic development. Within the central nervous system (CNS) Fgf8 is implicated in patterning neural tissue adjacent to the midbrain-hindbrain boundary. However, the roles of Fgfs in CNS tissue rostral to the midbrain are less clear. Here we examine the patterning of the forebrain in zebrafish embryos that lack functional Fgf8/Ace. We find that Ace is required for the development of midline structures in the forebrain. In the absence of Ace activity, midline cells fail to adopt their normal morphology and exhibit altered patterns of gene expression. This disruption to midline tissue leads to severe commissural axon pathway defects, including misprojections from the eye to ectopic ipsilateral and contralateral targets. Ace is also required for the differentiation of the basal telencephalon and several populations of putative telencephalic neurons but not for overall regional patterning of forebrain derivatives. Finally, we show that ace expression co-localises with anterior neural plate cells that have previously been shown to have forebrain patterning activity. Removal of these cells leads to a failure in induction of ace expression indicating that loss of Ace activity may contribute to the phenotypes observed when anterior neural plate cells are ablated. However, as ace mutant neural plate cells still retain at least some inductive activity, then other signals must also be produced by the anterior margin of the neural plate.

Animals↗

PubMed1999

Phosphoenzyme conversion of the sarcoplasmic reticulum Ca(2+)-ATPase. Molecular interpretation of infrared difference spectra.

Time-resolved Fourier transform infrared difference spectra of the phosphoenzyme conversion and Ca(2+) release reaction (Ca(2)E(1)-P --> E(2)-P) of the sarcoplasmic reticulum Ca(2+)-ATPase were recorded at pH 7 and 1 degrees C in H(2)O and (2)H(2)O. In the amide I spectral region, the spectra indicate backbone conformational changes preserving conformational changes of the preceding phosphorylation step. beta-sheet or turn structures (band at 1685 cm(-1)) and alpha-helical structures (band at 1653 cm(-1)) seem to be involved. Spectra of the model compound EDTA for Ca(2+) chelation indicate the assignment of bands at 1570, 1554, 1411 and 1399 cm(-1) to Ca(2+) chelating Asp and Glu carboxylate groups partially shielded from the aqueous environment. In addition, an E(2)-P band at 1638 cm(-1) has been tentatively assigned to a carboxylate group in a special environment. A Tyr residue seems to be involved in the reaction (band at 1517 cm(-1) in H(2)O and 1515 cm(-1) in (2)H(2)O). A band at 1192 cm(-1) was shown by isotopic replacement in the gamma-phosphate of ATP to originate from the E(2)-P phosphate group. This is a clear indication that the immediate environment of the phosphoenzyme phosphate group changes in the conversion reaction, altering phosphate geometry and/or electron distribution.

Calcium↗

PubMed1999

Influence of oestrogens on formation of reactive oxygen species in liver microsomes of differently aged male Wistar rats.

Metabolic pathways of oestrogens are the formation of catechol oestrogens (CE; 2- and 4-hydroxy-oestrogens), redox cycling of CE and free radical generation, mediated through cytochrome P450 (P450) oxidase/reductase activity. We checked the oestrogens oestradiol (E2), oestradiol valerate (E2V) and ethinyloestradiol (EE2) for formation of reactive oxygen species in vitro and ex vivo in male Wistar rats in dependence on age. In liver microsomes of 10-, 30-, 60- and 270-day-old rats the influence of E2, E2V and EE2 (10(-7)-10(-3) M) on NADPH-Fe(++)-stimulated lipid peroxidation (LPO), H2O2 generation and lucigenin (LUC) and luminol (LUM) amplified chemiluminescence (CL) was investigated. The same parameters, additionally P450 content and monooxygenase activities were measured in liver 9000 x g supernatants after subchronic administration of the oestrogens (1, 10 mg/kg b. wt. orally). The most important results are the strong inhibitory capacities of the oestrogens in vitro on LPO in the order of E2V < E2 < EE2, most pronounced in 10-, 60- and 270-day-old animals. In microsomes of 30-day-old rats with the highest control LPO the antioxidative effect of the oestrogens was lower. Whereas the H2O2 generation was not changed by E2, enhanced by E2V, but diminished by EE2 in all age groups, CL(LUC) and CL(LUM) were inhibited in the order of E2 < E2V < EE2. Also after subchronical treatment of the rats the antioxidative action of the oestrogens was evident, microsomal LPO was inhibited in the order of E2 < E2V < EE2. All oestrogens inhibited ethylmorphine N-demethylation. But enhanced H2O2 generation and increased CL(LUC) also indicate a formation of reactive oxygen species by these oestrogens. Obviously in vitro the antioxidative phenolic structure of the oestrogens dominates, whereas after in vivo administration the dose- and age-dependent biotransformation produces prooxidative in addition to antioxidative structures.

Aging↗

PubMed1998

Specificity and symmetry in the interaction of calmodulin domains with the skeletal muscle myosin light chain kinase target sequence.

The specificity of interaction of the isolated N- and C-terminal domains of calmodulin with peptide WFFp (Ac-KRRWKKNFIAVSAANRFK-amide) and variants of the target sequence of skeletal muscle myosin light chain kinase was investigated using CD and fluorescence. Titrations show that two molecules of either domain bind to 18-residue target peptides. For WFFp, the C-domain binds with 4-fold higher affinity to the native compared with the non-native site; the N-domain shows similar affinity for either site. The selectivity of the C-domain suggests that it promotes occupancy of the correct binding site for intact calmodulin on the target sequence. Far UV CD spectra show the extra helicity induced in forming the 2:1 C-domain-peptide or the 1:1:1 C-domain-N-domain-peptide complex is similar to that induced by calmodulin itself; binding of the C-domain to the Trp-4 site is essential for developing the full helicity. Calmodulin-MLCK-peptide complexes show an approximate two-fold rotational relationship between the two highly homologous domains, and the 2:1 C (or N)-domain-peptide complexes evidently have a similar rotational symmetry. This implies that a given domain can bind sequences with opposite peptide polarities, significantly increasing the possible range of conformations of calmodulin in its complexes, and extending the versatility and diversity of calmodulin-target interactions.

Amino Acid Sequence↗

PubMed1998

Resolution of Trp near UV CD spectra of calmodulin-domain peptide complexes into the 1La and 1Lb component spectra.

Near uv CD spectra of Trp residues in proteins frequently show a complex line shape deriving from the overlap of 1La and 1Lb electronic transitions. This study presents an original empirical method of resolving these components, based on the near uv CD spectra of well-defined complexes of calmodulin domains with target peptides containing a single Trp residue and derived from the skeletal muscle myosin light chain kinase target sequence. Spectra of 4 complexes were used to obtain the 1La and 1Lb component spectra that were then used to analyze further complexes. The broad and featureless 1La spectrum is centered at 279 nm, the 1Lb spectrum shows vibrational fine structure with maxima at 274.9, 281.5, and 289.8 nm. The CD spectrum of most complexes could successfully be fitted with one 1La and one 1Lb spectrum, the 1Lb spectrum being negative for all complexes but the 1La spectrum showing either positive or negative sign. Spectra of some complexes, however, failed to be adequately represented by only one 1La and one 1Lb spectrum. Instead, they could be fitted with one 1Lb spectrum and two 1La spectra with different sign and position. The method is successful in identifying and quantitating the relative intensities of a two-component system, consistent with a single conformation for tryptophan in a protein, and provides a simple indication of cases where a more complicated explanation is required.

Animals↗

PubMed1998

ATP-Induced phosphorylation of the sarcoplasmic reticulum Ca2+ ATPase: molecular interpretation of infrared difference spectra.

Time-resolved infrared difference spectra of the ATP-induced phosphorylation of the sarcoplasmic reticulum Ca2+-ATPase have been recorded in H2O and 2H2O at pH 7.0 and 1 degrees C. The reaction was induced by ATP release from P3-1-(2-nitro)phenylethyladenosine 5'-triphosphate (caged ATP) and from [gamma-18O3]caged ATP. A band at 1546 cm-1, not observed with the deuterated enzyme, can be assigned to the amide II mode of the protein backbone and indicates that a conformational change associated with ATPase phosphorylation takes place after ATP binding. This is also indicated between 1700 and 1610 cm-1, where bandshifts of up to 10 cm-1 observed upon protein deuteration suggest that amide I modes of the protein backbone dominate the difference spectrum. From the band positions it is deduced that alpha-helical, beta-sheet, and probably beta-turn structures are affected in the phosphorylation reaction. Model spectra of acetyl phosphate, acetate, ATP, and ADP suggest the tentative assignment of some of the bands of the phosphorylation spectrum to the molecular groups of ATP and Asp351, which participate directly in the phosphate transfer reaction: a positive band at 1719 cm-1 to the C==O group of aspartyl phosphate, a negative band at 1239 cm-1 to the nuas(PO2-) modes of the bound ATP molecule, and a positive band at 1131 cm-1 to the nuas(PO32-) mode of the phosphoenzyme phosphate group, the latter assignment being supported by the band's sensitivity toward isotopic substitution in the gamma-phosphate of ATP. Band positions and shapes of these bands indicate that the alpha- and/or beta-phosphate(s) of the bound ATP molecule become partly dehydrated when ATP binds to the ATPase, that the phosphoenzyme phosphate group is unprotonated at pH 7.0, and that the C==O group of aspartyl phosphate does not interact with bulk water. The Ca2+ binding sites seem to be largely undisturbed by the phosphorylation reaction, and a functional role of the side chains of Asn, Gln, and Arg residues was not detected.

Adenosine Triphosphate↗

PubMed1998

Influence of hypoxia and hypoxia/hypercapnia upon brain and blood peroxidative and glutathione status in normal weight and growth-restricted newborn piglets.

Glutathione (reduced (GSH) and oxidized (GSSG)), lipid peroxidation products (TBAR) and in vitro production of reactive oxygen species (ROS, by means of stimulated lipid peroxidation, H2O2 formation and amplified chemiluminescence (CL) in 9000 xg brain supernatants) were studied in the cerebellum (C) and temporoparietal area (TP) of the brain of normal weight (NW) and spontaneously intra-uterine growth-restricted newborn piglets (IUGR) after 1 hour hypoxia (fractional inspired oxygen concentration (FiO2) 8%), and in combination with 10% CO2, followed by 3 hours recovery (FiO2 30%). The strong GSH depletion accompanied by an increased concentration of GSSG and TBAR, more distinct in IUGR, is the most important result in the brain after hypoxia and reoxygenation. Hypercapnia-related acidosis seems to protect the brain of IUGR from hypoxia/reoxygenation induced injury by reducing GSH depletion as well as GSSG and TBAR increases. But stimulated lipid peroxidation and H2O2 formation in 9000 xg supernatants of C and TP were found to be higher in acidosis and hypercapnia. Decreased or unchanged amplified CL, demonstrating lower in vitro production of ROS, cannot explain the GSH depletion after hypoxia and reoxygenation. The scarce changes in erythrocyte GSH and GSSG as well as plasma TBAR concentrations did not reflect the findings in the brain. Nevertheless, the changes in the brain support the hypothesis that oxidative stress plays a role in neuronal damage after hypoxic stress, but the brain of IUGR did not reveal a special response to moderate hypoxia.

Acid-Base Equilibrium↗

PubMed1998

Influence of hypoxia and hyperthermia upon peroxidative and glutathione status in growth-restricted newborn piglets.

Normal weight (NW) and spontaneously intra-uterine growth-restricted newborn piglets (IUGR) were submitted to 1 hour hypoxia and hyperthermia followed by 3 hours reoxygenation. Glutathione (GSH, GSSG), lipid peroxidation products (TBAR) and cytochrome P450 dependent production of reactive oxygen species were studied by determination of H2O2 production and amplified chemiluminescence (CL) in brain and peripheral organs of NW and IUGR. A severe decrease of GSH was accompanied by enhanced H2O2 formation and lipid peroxidation in the brain of both NW and IUGR after hypoxia/hyperthermia and reoxygenation. In the other organs studied, only muscles showed enhanced lucigenine amplified CL and TBAR production. Nearly the same results in NW and IUGR reveal no higher risk of IUGR.

Animals↗

PubMed1998

Two males with childhood disintegrative disorder: a prospective 14-year outcome study.

A prospective 14-year outcome study of two children meeting DSM-IV criteria for childhood disintegrative disorder is presented. Their ages at first evaluation were 4 years 7 months and 6 years 3 months. Both are now adults and continue to have a severe pervasive developmental disorder, mental retardation, seizure disorder, and are non-verbal. Both require residential care.

Child↗

PubMed1998

Stress and the menstrual cycle: relevance of cycle quality in the short- and long-term response to a 5-day endotoxin challenge during the follicular phase in the rhesus monkey.

The notion that stress activates central and peripheral pathways to inhibit the menstrual cycle is well accepted, but the initial processes through which this occurs have not been investigated. This study uses a relevant nonhuman primate model to document the cyclic endocrine effects imposed by a moderate short-term stress episode in the follicular phase. The stress paradigm is a 5-day inflammatory/immune-like challenge produced by the administration of bacterial endotoxin [lipopolysaccharide (LPS)], which, through the release of endogenous cytokines and other mediators, induces a physiopathological response similar to a bacterial infection. LPS was administered iv twice daily for 5 days starting on days 2-8 of the follicular phase. The stress challenge resulted in a significant lengthening of the follicular phase in all monkeys. Two distinct groups were observed. In group 1 (n = 5), the mean (+/- SE) length of the follicular phase in the LPS-treated cycle was significantly increased, from 10.2 +/- 0.2 in control cycle 2 to 30.8 +/- 4.3 days (except in one monkey that had a 4-month amenorrheic interval). In group 2 (n = 5), the length of the follicular phase significantly increased but not to exceed the duration of the LPS treatment (9.7 +/- 1.1 vs. 13.6 +/- 1.2). Estradiol concentrations decreased significantly after LPS in group 1 (34.8 +/- 5.5 vs. 16.2 +/- 6.5 pg/mL) and remained suppressed after the challenge. In group 2, estradiol levels remained stationary throughout the 5-day LPS treatment (26.0 +/- 6.5 vs. 25.6 +/- 3.9). Compared with control values at a similar stage of the follicular phase, most LH and FSH values during LPS treatment were higher than controls. Estradiol and gonadotropin surges were delayed by LPS treatment for a varying length of time according to each grp. Significant differences in integrated luteal progesterone concentrations characterized control cycles of groups 1 and 2 (group 1: 36.5 +/- 1.5, group 2: 47.5 +/- 2.6). In group 1, there were no further effects of LPS on luteal progesterone during the treatment and two post-LPS cycles. In contrast, in group 2, integrated luteal progesterone concentrations were significantly decreased in post-LPS cycle 1 (to 36.0 +/- 4.4). Cortisol significantly increased at hour 3 after each morning LPS injection but the amplitude of the response decreased over the 5-day period. Progesterone increased significantly by hour 3 after the first LPS injection but remained unchanged after subsequent LPS administration. Our data demonstrate that a 5-day inflammatory-like episode during the follicular phase can delay folliculogenesis and that damage to this process is intensified in individuals who already demonstrate a subtle cyclic degradation, in the form of decreased progesterone secretion in the luteal phases preceding the stress episode. Long-term endocrine effects, in the form of decreased luteal secretory activity in the first poststress cycle, are observed in normally cycling individuals, suggesting that inadequacy of the luteal phase may represent the first stage in the damage that a stress episode can inflict upon the normal menstrual cycle.

Animals↗

PubMed1997

Ca2+ release from the phosphorylated and the unphosphorylated sarcoplasmic reticulum Ca2+ ATPase results in parallel structural changes. An infrared spectroscopic study.

Structural changes of the sarcoplasmic reticulum Ca2+-ATPase occurring in the reaction step involving phosphoenzyme conversion and Ca2+ release (Ca2E1-P --> E2-P) were followed using time-resolved infrared spectroscopy in H2O and 2H2O. The difference spectra measured between 1800 and 1500 cm-1 were almost identical to those of Ca2+ release from the unphosphorylated ATPase (Ca2E1 --> E), implying that parallel structural changes occur in both steps. This suggests that characteristic structural features of the high affinity Ca2+ binding sites of Ca2E1 are still present in the ADP-sensitive phosphoenzyme Ca2E1-P. In both Ca2+ release steps at least two carboxyl groups become protonated, each of them experiencing the same strength of hydrogen bonding irrespective of whether or not the Ca2+ free ATPase is phosphorylated. This suggests that the same amino acid residues are involved and that they are most likely those that participate in high affinity Ca2+ binding and H+ countertransport. We propose that during Ca2+ release from the phosphoenzyme protons from the lumenal side have access to these residues. Our results are consistent with only one pair of Ca2+ binding sites on the ATPase that serves both Ca2+ translocation and H+ countertransport.

Animals↗

PubMed1997

Neurotoxicity in organotypic hippocampal slices mediated by adenosine analogues and nitric oxide.

Adenosine (ADO) and nitric oxide (NO) have been implicated in a variety of neurophysiological actions, including induction of long-term potentiation, regulation of cerebral blood flow, and neurotoxicity/neuroprotection. ADO has been shown to promote NO release from astrocytes by a direct effect on A1 and A2 receptors, thus providing a link between actions of NO and adenosine in the brain. However, while adenosine acts as an endogenous neuroprotectant, NO is believed to be the effector of glutamate neurotoxicity. To resolve this apparent paradox, we have further investigated the effects of adenosine and NO on neuronal viability in cultured organotypic hippocampal slices exposed to sub-lethal (20') in vitro ischemia. Up to a concentration of 500 microM ADO did not cause toxicity while exposures to 100 microM of the stable ADO analogue chloroadenosine (CADO) caused widespread neuronal damage when paired to anoxia/hypoglycemia. CADO effects were significantly prevented by the ADO receptor antagonist theophylline and blockade of NO production by L-NA (100 microM). Moreover, CADO effects were mimicked by the NO donor SIN-1 (100 microM). Application of 100 microM ADO following blockade of adenosine deaminase (with 10 microM EHNA) replicated the effects of CADO. CADO, ADO + EHNA but not ADO alone caused a prolonged and sustained release of nitric oxide as measured by direct amperometric detection. We conclude that at high concentrations and/or following blockade of its enzymatic catabolism, ADO may cause neurotoxicity by triggering NO release from astrocytes. These results demonstrate for the first time that activation of pathways other than those involving neuronal glutamate receptors can trigger NO-mediated neuronal cell death in the hippocampus.

2-Chloroadenosine↗