Modeling dynamic PET-SPECT studies in the wavelet domain.
(73/4453)This work develops a theoretical framework and corresponding algorithms for the modeling of dynamic PET-SPECT studies both in time and space. The problem of estimating the spatial dimension is solved by applying the wavelet transform to each scan of the dynamic sequence and then performing the kinetic modeling and statistical analysis in the wavelet domain. On reconstruction through the inverse wavelet transform, one obtains parametric images that are consistent estimates of the spatial patterns of the kinetic parameter of interest. The theoretical setup allows the use of linear techniques currently used in PET-SPECT for kinetic analysis. The method is applied to artificial and real data sets. The application to dynamic PET-SPECT studies was performed both for validation purposes, when the spatial patterns are known, and for illustration of the advantages offered by the technique in case of tracers with an unknown pattern of distribution. (+info)
Involvement of poly(ADP-ribose) polymerase and activation of caspase-3-like protease in heat shock-induced apoptosis in tobacco suspension cells.
(74/4453)The cleavage of poly(ADP-ribose) polymerase (PARP) by caspase (casp)-3 is an essential link in the apoptotic pathway in animal cells. In plant cells, however, there is no authentic evidence for the similar role that PARP may play during apoptosis. Using a heat shock (HS)-induced apoptosis system of tobacco cells, we found that immediately after a 4 h heat treatment, PARP was cleaved to form an 89 kDa signature fragment, while DNA laddering appeared only after a 20 h recovery following the HS. An activation of casp-3-like protease was also observed. The results suggest that apoptosis in plants and animals may share common mechanisms. On the other hand, when cells were preincubated with 4 mM 3-aminobenzamide or 2-8 mM nicotinamide, the specific inhibitors of PARP, before HS treatment, apoptotic cell death was reduced significantly. Our results thus imply that PARP may also be involved in apoptosis in a different way from the casp-related events. (+info)
Sarcolemmal and mitochondrial adenosine triphosphate- dependent potassium channels: mechanism of desflurane-induced cardioprotection.
(75/4453)BACKGROUND: Volatile anesthetic-induced preconditioning is mediated by adenosine triphosphate-dependent potassium (KATP) channels; however, the subcellular location of these channels is unknown. The authors tested the hypothesis that desflurane reduces experimental myocardial infarct size by activation of specific sarcolemmal and mitochondrial KATP channels. METHODS: Barbiturate-anesthetized dogs (n = 88) were acutely instrumented for measurement of aortic and left ventricular pressures. All dogs were subjected to a 60-min left anterior descending coronary artery occlusion followed by 3-h reperfusion. In four separate groups, dogs received vehicle (0.9% saline) or the nonselective KATP channel antagonist glyburide (0.1 mg/kg intravenously) in the presence or absence of 1 minimum alveolar concentration desflurane. In four additional groups, dogs received 45-min intracoronary infusions of the selective sarcolemmal (HMR 1098; 1 microg. kg-1. min-1) or mitochondrial (5-hydroxydecanoate [5-HD]; 150 microg. kg-1. min-1) KATP channel antagonists in the presence or absence of desflurane. Myocardial perfusion and infarct size were measured with radioactive microspheres and triphenyltetrazolium staining, respectively. RESULTS: Desflurane significantly (P < 0.05) decreased infarct size to 10 +/- 2% (mean +/- SEM) of the area at risk as compared with control experiments (25 +/- 3% of area at risk). This beneficial effect of desflurane was abolished by glyburide (25 +/- 2% of area at risk). Glyburide (24 +/- 2%), HMR 1098 (21 +/- 4%), and 5-HD (24 +/- 2% of area at risk) alone had no effects on myocardial infarct size. HMR 1098 and 5-HD abolished the protective effects of desflurane (19 +/- 3% and 22 +/- 2% of area at risk, respectively). CONCLUSION: Desflurane reduces myocardial infarct size in vivo, and the results further suggest that both sarcolemmal and mitochondrial KATP channels could be involved. (+info)
Dopamine-deficient mice are hypersensitive to dopamine receptor agonists.
(76/4453)Dopamine-deficient (DA-/-) mice were created by targeted inactivation of the tyrosine hydroxylase gene in dopaminergic neurons. The locomotor activity response of these mutants to dopamine D1 or D2 receptor agonists and l-3,4-dihydroxyphenylalanine (l-DOPA) was 3- to 13-fold greater than the response elicited from wild-type mice. The enhanced sensitivity of DA-/- mice to agonists was independent of changes in steady-state levels of dopamine receptors and the presynaptic dopamine transporter as measured by ligand binding. The acute behavioral response of DA-/- mice to a dopamine D1 receptor agonist was correlated with c-fos induction in the striatum, a brain nucleus that receives dense dopaminergic input. Chronic replacement of dopamine to DA-/- mice by repeated l-DOPA administration over 4 d relieved the hypersensitivity of DA-/- mutants in terms of induction of both locomotion and striatal c-fos expression. The results suggest that the chronic presence of dopaminergic neurotransmission is required to dampen the intracellular signaling response of striatal neurons. (+info)
Subsensitivity to opioids is receptor-specific in isolated guinea pig ileum and mouse vas deferens after obstructive cholestasis.
(77/4453)The rate and degree of subsensitivity development to morphine (mu-opioid receptor, preferred, but not selective agonist) and U50488H (highly selective kappa-opioid receptor agonist) were assessed in vitro on guinea pig ileum (GPI) of cholestatic animals 2, 5, and 7 days after bile duct ligation. In addition to this phenomenon of morphine, the effects of U50488H and SNC 80 (highly selective delta-opioid receptor agonist) were studied in vitro on mice vas deferens (MVD) of cholestatic animals 2, 5, 7, 10, and 15 days after bile duct ligation. The IC(50) for each compound was determined in these preparations. The ratio of the IC(50) in bile duct-ligated animals to sham and control animals provides a quantitative index for the degree of subsensitivity development to each agonist. For any given time, the highest degree of subsensitivity to morphine was observed in GPI of cholestatic animals, whereas in MVD obtained from the cholestatic animals, the highest degree of subsensitivity developed to inhibitory effect of SNC 80. The subsensitivity development in cholestatic animals was time dependent; in GPI the maximum subsensitivity developed after 7 days of the operation, whereas the maximum subsensitivity in MVD developed 15 days after bile duct ligation. Moreover, subsensitivity to exogenous acetylcholine and norepinephrine in GPI and MVD, respectively, did not develop in the presence of subsensitivity to opioids in cholestatic animals. Significant accumulation of endogenous opioids in plasma of cholestatic animals has been shown in several studies and this may account for a significant development of subsensitivity to inhibitory effects of opioid agonists. (+info)
Z-338 facilitates acetylcholine release from enteric neurons due to blockade of muscarinic autoreceptors in guinea pig stomach.
(78/4453)The mechanism by which Z-338, a novel gastroprokinetic agent, stimulates gastric motility was studied in relation to muscarinic receptors in the guinea pig. Z-338 (3-30 microM) enhanced electrically stimulated contractions and the release of acetylcholine (ACh) that was tetrodotoxin sensitive and extracellular Ca(2+) dependent, in gastric strips. Membrane-binding assay revealed that Z-338 possessed binding affinity for muscarinic M(1) and M(2), but not M(3) receptors. In Xenopus oocytes expressing M(1) and M(2) muscarinic receptors, Z-338 did not produce any response, but inhibited ACh-induced outward currents, thereby indicating that Z-338 acts on the M(1) and M(2) muscarinic receptors as an antagonist. The M(1) receptor antagonist pirenzepine (0.5 microM) and M(2) receptor antagonist AF-DX 116 (1 microM) also enhanced electrically stimulated release of ACh. These results indicate that Z-338 facilitates ACh release from cholinergic nerve terminals by blocking muscarinic M(1) and M(2) autoreceptors, which regulate the release of ACh. (+info)
Exosite interactions determine the affinity of factor X for the extrinsic Xase complex.
(79/4453)The initiation of coagulation results from the activation of factor X by an enzyme complex (Xase) composed of the trypsin-like serine proteinase, factor VIIa, bound to tissue factor (TF) on phospholipid membranes. We have investigated the basis for the protein substrate specificity of Xase using TF reconstituted into vesicles of phosphatidylcholine, phosphatidylserine, or pure phosphatidylcholine. We show that occupation of the active site of VIIa within Xase by a reversible inhibitor or an alternate peptidyl substrate is sufficient to exclude substrate interactions at the active site but does not alter the affinity of Xase for factor X. This is evident as classical competitive inhibition of peptidyl substrate cleavage but as classical noncompetitive inhibition of factor X activation by active site-directed ligands. This implies that the productive recognition of factor X by Xase arises from a multistep reaction requiring an initial interaction at sites on the enzyme complex distinct from the active site (exosites), followed by active site interactions and bond cleavage. Exosite interactions determine protein substrate affinity, whereas the second binding step influences the maximum catalytic rate for the reaction. We also show that competitive inhibition can be achieved by interfering with exosite binding using factor X derivatives that are expected to have limited or abrogated interactions with the active site of VIIa within Xase. Thus, substrate interactions at exosites, sites removed from the active site of VIIa within the enzyme complex, determine affinity and binding specificity in the productive recognition of factor X by the VIIa-TF complex. This may represent a prevalent strategy through which distinctive protein substrate specificities are achieved by the homologous enzymes of coagulation. (+info)
Effects of neurokinin receptor antagonists in virus-infected airways.
(80/4453)We investigated the effects of a neurokinin-1 (NK(1)) receptor antagonist (SR-140333) and a NK(2) receptor antagonist (SR-48968) on airway responsiveness and on the function of neuronal M(2) muscarinic receptors, which normally inhibit vagal acetylcholine release, in guinea pigs infected with parainfluenza virus. Antagonists were given 1 h before infection and daily thereafter. Four days later, bronchoconstriction induced by either intravenous histamine (which is partly vagally mediated) or electrical stimulation of the vagus nerves was increased by viral infection compared with control. In addition, the ability of the muscarinic agonist pilocarpine to inhibit vagally induced bronchoconstriction was lost in virus-infected animals, demonstrating loss of neuronal M(2) receptor function. Macrophage influx into the lungs was inhibited by pretreatment with both antagonists. However, only the NK(1) receptor antagonist prevented M(2) receptor dysfunction and inhibited hyperresponsiveness (measured as an increase in either vagally induced or histamine-induced bronchoconstriction). Thus virus-induced M(2) receptor dysfunction and hyperresponsiveness are prevented by a NK(1) receptor antagonist, but not by a NK(2) receptor antagonist, whereas both antagonists had similar anti-inflammatory effects. (+info)