Fast Reactivation Research Articles

In vitro interactions between pyridinium aldoximes and endogenous bio-scavenger butyrylcholinesterase in tabun poisoning

Kinetic parameters were evaluated for inhibition and reactivation of tabun-inhibited human plasma butyrylcholinesterase (BChE ; EC 3.1.1.8) by five pyridinium aldoximes: K027 [1-(4-hydroxyiminomethylpyridinium)-3-(4-carbamoylpyridinium) propane dibromide], K048 [1-(4-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide], K033 [1, 4-bis(2-hydroxyiminomethylpyridinium) butane dibromide], HI-6 [(1-(2’ -hydroxyimi-nomethyl-1'-pyridinium)-3-(4''-carbamoyl-1''-pyridinium)-2-oxapropane dichloride)] and TMB-4 [1, 3-bis(4-hydroxyiminomethylpyridinium) propane dibromide]. Selected aldoximes have been recently evaluated as protectors/reactivators of tabun-inhibited human erythrocyte AChE [1]. Since BChE can be considered an endogenous bio-scavenger of anticholinesterase compounds, in order to discuss the possible use of BChE as scavenging agent, and BChE prophylactic properties, we examined aldoxime interactions with BChE. Progressive inhibition by tabun was faster for BChE than for AChE, indicating that BChE would scavenge tabun prior to AChE inhibition [1]. The reactivation of tabun-inhibited BChE by selected aldoximes was very slow, reaching maximum of 70%, which means that BChE in combination with the aldoximes investigated cannot be considered as catalytic scavenger of tabun. The overall reactivation rate constants were between 2.2 and 53.6 min-1M-1. Interestingly, the fastest reactivation was achieved by K033, aldoxime with the lowest efficacy for reactivation of tabun-inhibited AChE. The phosphorylated BChE had lower affinities for two potent AChE reactivators, K027 and K048, than phosphorylated AChE, indicating that fast AChE reactivation by these aldoximes would not be obstructed by interactions between BChE and aldoxime [1]. All aldoximes reversibly inhibited BChE and the enzyme-aldoxime dissociation constants ranged between 0.04 and 0.70 mM. However, BChE had lower affinities for aldoximes than AChE (except for TMB-4 for which both enzymes had similar affinity) indicating aldoxime preference for binding to the native AChE [1]. These results imply possible use of the aldoximes as protectors of AChE against phosphorylation by tabun. [1] Calic, M. et al (2006) Toxicology 219, 85-96.

Antecedent reactivation by surface and deep anaphora in Norwegian

Anaphora are expressions in language that depend on other linguistic entities for their full meaning. They can furthermore be divided into two types according to the level of representation where they find their antecedents: Surface anaphora, which resolve their reference at the sentence representation level, and deep anaphora, which resolve their reference at the non-grammatical level of discourse representation. The linguistic theory of these two anaphor types, and recent findings about processing differences at these two levels, combine to predict that surface anaphora should show fast and immediate reactivation of their antecedents, whereas deep anaphora should have a slower time course of antecedent re-access. These predictions were confirmed with two lexical decision task experiments with Norwegian stimuli.

Receptor endocytosis counteracts the development of opioid tolerance.

In contrast to endogenous opioids, the highly addictive drug morphine activates the mu-opioid receptor without causing its rapid endocytosis. It has recently been reported that coapplication of low concentrations of [d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) facilitates the ability of morphine to stimulate mu-opioid receptor endocytosis and prevents the development of morphine tolerance in rats. To investigate the clinical relevance of this finding for analgesic therapy, the endocytotic efficacies of a series of clinically used opioids were determined, and the effect of a combination of these drugs with morphine on the mu-opioid receptor endocytosis in receptor-expressing human embryonic kidney (HEK) 293 cells was quantified. The combination of morphine and opioid drugs with high endocytotic efficacies (e.g., DAMGO, etonitazene, sufentanil, beta-endorphin, piritramide, or methadone) did not result in a facilitation of morphine-mediated endocytosis but rather in a decrease of the receptor endocytosis mediated by the tested opioid drugs. These findings demonstrate a partial agonistic effect of morphine on the agonist-induced receptor endocytosis. Moreover, we demonstrated that the endocytotic potencies of opioid drugs are negatively correlated with their ability to cause receptor desensitization and opioid tolerance in HEK 293 cells. These results strongly support the hypothesis that mu-opioid receptor endocytosis counteracts receptor desensitization and opioid tolerance by inducing fast receptor reactivation and recycling. In addition, it is shown that agonist-induced receptor endocytosis facilitates the compensatory up-regulation of the cAMP pathway, a cellular hallmark of opioid withdrawal. Our findings suggest that opioids with high endocytotic efficacies might cause reduced opioid tolerance but can facilitate compensatory mechanisms, resulting in an enhanced opioid dependence.

Submicrosecond range surface heating and temperature measurement for efficient sensor reactivation

A method for submicrosecond heating of sensor surfaces and simultaneous detection of the surface temperature was developed enabling accurate and fast reactivation of a semiconductor based oxygen sensor. High power electrical pulses with current densities of more than 10 7 A/cm 2 were applied to the 60-nm-thick Pt layer of a chemical semiconductor sensor structure resulting in surface temperatures as high as 700 K maintained in the nanosecond to microsecond range. Temperature measurement was carried out using the temperature dependent electrical resistance of the Pt film. Electrical power pulses of defined shape allowed accurate control of the surface temperature with ns time resolution. The high reactivation surface temperatures required high current densities, eventually leading to fatal destruction of the sensor structure. Comparative numerical simulations of the thermal impact as well as photo thermal and scanning force microscopy measurements were performed to optimize the heating process and to investigate the destruction mechanism.

Calcium current reactivation after flash photolysis of nifedipine in skeletal muscle fibres of the frog.

1. L-type calcium currents were activated by depolarization of cut muscle fibres of the frog. The current was blocked by the dihydropyridine compound nifedipine (5-10 microM) and reactivated by flash photolysis of the drug. 2. In the presence of nifedipine, increasing the time interval between the onset of depolarization and the flash resulted in progressively faster kinetics of the flash-induced current. This change developed with a slow time course similar to that of normal current activation. 3. A fast gating mode of the normally slow L-type channel was induced by conditioning activation (500 ms prepulses) applied 80 ms before a test step to the same potential. After block by nifedipine, flash-photolysis was carried out 40 ms before the end of the long conditioning pulse. The flash-induced current had the same rapid time course as the current activated by the subsequent test voltage step. 4. Similarly, the time course of current activation was comparable for the voltage-induced fast mode activation (flash applied 5 ms before the test step) and the flash-induced activation 40 ms after the onset of the test depolarization. 5. Our data suggest that in frog skeletal muscle nifedipine inhibits calcium current activation by blocking a rapid channel gating step while the slow conformational change that normally limits the rate of activation of the L-type calcium channel remains unaffected. UV flash illumination results in a fast reactivation indicating that the channels need not be inactivated to be blocked by nifedipine.

Work function and gas desorption studies during turn-on of various shelf-stored cathodes

A comparative study has been made of the oxide-type coated powder cathode (CPC), and impregnated types B, M, tungstate and scandate cathodes in their ability to rapidly turn on after extended periods of shelf life. Particular performance objectives were to attain pulsed emission levels in the 4–5 A/cm 2 region within a few seconds after shelf lives corresponding up to several years. Preliminary surface studies indicate that all cathodes significantly poison within a few hours or days after being shut down in a typical sealed-off tube environment. Therefore, apart from bringing the cathode up to thermionic emission temperature, the kinetics of the turn-on step must also involve the kinetics of reactivation. Comparative data are presented of the work function variation with reactivation temperature for the various cathodes, thus showing the degree of poisoning, the thermal reactivation characteristics and the work function-temperature relationship in their respective active states. The results show that in the active state, the CPC has the highest emission, the M and scandate impregnated cathodes are somewhat lower in emission, i.e. ∼50 K higher temperature for the same emission, while the type-B impregnated cathode requires ∼100 K more. The shelf-life poisoning among the impregnated cathodes, on the other hand, was greatest for the M cathodes, a bit less for the scandate and least for the type B. For typical fast turn-on reactivation schedules, the CPC reactivated below its normal operating temperature of ∼1250 K but all impregnated cathodes required activation temperatures of ∼1500 K and above (i.e., about 200 K above their operating temperatures). Studies were also made on the pick-up and desorption of various gases present in the shelf-life vacuum ambient. The data demonstrated a direct correlation between the chemical reactivity that the different cathodes had with the residual ambient gases and the corresponding extent to which these cathodes poisoned during shelf life. While a study of the shelf-life poisoning and reactivation mechanisms for the impregnated-type cathodes is still in progress, initial results have been completed for the oxide-type cathodes and these are presented elsewhere in this issue.