Biochemical events associated with PHA-induced lymphocyte activation in human ageing II. Characteristics of the early Ca2+ uptake

Since the early biochemical changes are critical in defining the triggering mechanism of a mitogen-induced lymphocyte activation, their study could provide a good understanding of the processes that might be relevant to the immune deficiency associated with ageing.The increase of Ca²⁺ influx appears to be one of these earliest events which takes place in the first minutes following the contact with stimulating agents, as a consequence of membrane activation. Therefore, the timing and the magnitude of Ca²⁺ influx were analyzed in unstimulated and PHA-stimulated peripheral blood lymphocytes (PBL) from old and adult subjects.Whereas PBL from elders exhibited a decrease in DNA synthesis, the characteristics of Ca²⁺ accumulation into unstimulated and PHA-stimulated PBL were found unaltered in the elderly.The data support the evidence that the cellular defect relevant to the depressed response to T-mitogens associated with ageing, does not result from the defect of Ca²⁺ transport induced by membrane activation.     

Cotranslational disassembly of tobacco mosaic virus in vitro

Heterogeneous nucleoprotein preparations of tobacco mosaic virus (TMV), stored at pH 7.0, were treated briefly at pH 8 and then incubated in mRNA-dependent rabbit reticulocyte lysate. The treatment at pH 8.0, under conditions which did not cause detectable polar disassembly as judged by exposure to micrococcal nuclease, caused TMV to stimulate in vitro translation up to 100-fold over background. High-molecular-weight products, characteristic of TMV, appeared, albeit at a significantly slower rate than when naked TMV RNA was used as template. Ribonucleoprotein material from cycloheximide-treated incubations was examined in the electron microscope to reveal a subpopulation of rodlets (approx 5%) with clusters of ribosomes at their concave 5' ends. It is proposed that pH 8 treatment removes the last turn of protective coat protein subunits from the rods and "exposes" at least a 49-nucleotide segment of the efficient 5'-leader sequence of TMV RNA for interaction with 40 S ribosomal subunits. Ribosome translocation during protein synthesis presumably dislodges further coat protein subunits progressively while continuing protection of the incoming TMV RNA.     

惰性气体对黄瓜酶活和呼吸强度的影响

研究了黄瓜切片在10℃，氙气压力0．3Mpa条件下的变化情况，黄瓜采后在空气常压，氙气0．1，0．2，0．3Mpa压力下放置12，24，48h后，过氧化物酶和多酚氧化酶活性的变化，并且作了氮气，氪气及氩气的对照．研究了黄瓜在0．3Mpa氙气处理24h后呼吸强度的变化，处理后的呼吸强度比对照组有明显的下降．     

Binding of [3H]MK-801 in subcellular fractions of Schistosoma mansoni: evidence for interaction with nicotinic receptors

Several studies have suggested that l-glutamate is a putative neurotransmitter in Schistosoma mansoni. Recently, we detected the presence of low-affinity binding sites for [(3)H]kainic acid in the heterogeneous (P(1)) subcellular fraction of S. mansoni. In an attempt to characterize N-methyl-d-aspartate (NMDA) receptors in this worm, we performed binding assays with [(3)H]MK-801, a NMDA non-competitive antagonist, in the P(1) fraction of adult S. mansoni. In competition experiments, MK-801 (IC(50) approximately 200 microM) and ketamine (IC(50) approximately 500 microM) exhibited a low affinity for the sites labeled with [(3)H]MK-801. Along with the lack of modulation of this binding by glutamatergic agonists and antagonists and the absence of stereoselectivity for MK-801 isomers, these results suggest that [(3)H]MK-801 could label a site different from the classical NMDA receptor in S. mansoni. Based on the evidences that MK-801 interacts with mammalian muscle and central nervous system nicotinic receptors as a low-affinity noncompetitive antagonist, we have investigated the effects of MK-801 on the nicotine-induced flaccid paralysis of the worm, in vivo. The motility of S. mansoni was quantified by image analysis through a measure of displacement of the worm's extremities. In the presence of (-)-nicotine (10-100 microM), we observed an immediate paralysis of the worms, that was inhibited by 1mM MK-801. Besides nicotine, choline (10-50mM) was also able to inhibit the worm's motility. As a conclusion, we suggest that [(3)H]MK-801 binds to nicotinic receptors, and not NMDA receptors, in subcellular fractions of S. mansoni.     

吡虫啉胁迫对生菜中多酚氧化酶活性的影响

目的研究在吡虫啉胁迫下,生菜中多酚氧化酶(PPO)活性的变化。方法用分光光度法测定多酚氧化酶的活性。结果二个浓度的吡虫啉均诱导了生菜中PPO的活性,含量明显高于对照组,并随时间变化而逐渐减少,最终基本与对照组一致。结论在生菜遭受吡虫啉胁迫初期PPO活性即变化显著,可作为吡虫啉迫胁生菜比较敏感的生物指标。     

Temperature sensitivity of axonal transport in hibernating and nonhibernating rodents.

The temperature sensitivity of fast axonal transport of labeled protein in peripheral sensory axons was investigated in rats and hibernating and non-hibernating ground squirrels (Spermophilus r. richardsonii), using an in vitro technique which permitted incubation of the sciatic nerve for various periods of time at different temperatures. The relationship between velocity and temperature was exponential between 13 and 38°C, but below 13°C transport ceased or became too slow to detect. There were no significant differences in the relationship between temperature and velocity for the three classes of nerve studied. It is concluded that the peripheral nerves of hibernating ground squirrels are not modified to permit axonal transport to continue at the low body temperatures characteristic of the hibernating state.     

Renal transport of 2'-deoxytubercidin in mice

Previous results [J. F. Kuttesch, Jr. and J. A. Nelson, Cancer Chemother, Pharmac. 8, 221 (1982)] from this laboratory indicate that mechanisms exist for renal secretion of 2'-deoxyadenosine and possibly for reabsorption of adenosine in humans and in mice. Since significant metabolism of these purine nucleosides occurs even in the presence of adenosine deaminase inhibitors, the renal handling of a compound which is not significantly metabolized by the deaminase or by kinases was studied. Unlike 2'-deoxyadenosine itself, the 2'-deoxyadenosine analog, [4-amino-7-(2'-deoxy-beta-D-erythro-pentofuranosyl)-pyrrolo-(2,3-d)pyrimidine; 2'-deoxytubercidin], is not significantly metabolized by mammalian tissues. In mice, the renal plasma clearance of 2'-deoxytubercidin exceeded that of inulin by about 3-fold. Also, mouse kidney slices concentratively accumulated 2'-deoxytubercidin by a saturable and metabolically dependent process. The uptake by mouse kidney slices was inhibited by classical substrates for the organic cation secretory system (tetraethylammonium, choline and N1-methylnicotinamide) but was not markedly inhibited by classical substrates for the organic anion secretory system (p-aminohippurate, phenol red and probenecid). Since 2'-deoxytubercidin inhibited the active, concentrative uptake of [14C]tetraethylammonium, but failed to inhibit the uptake of p-[14C]aminohippurate by mouse kidney slices, it is concluded that 2'-deoxytubercidin may be secreted by the organic cation system. Additional studies are required, however, to unequivocally establish the relationships between 2'-deoxytubercidin, 2'-deoxyadenosine and tetraethylammonium renal secretory mechanisms.     

Ethacrynic acid influx and efflux in kidney cortex slices: Dependence on sodium gradient

Ethacrynic acid (EA) accumulation in rat kidney cortex slices was inhibited by reduction of sodium concentration in the incubation medium. Preloading of slices with sodium reduced EA accumulation at medium sodium concentration of 30–140 mM. Ouabain (10^?3 M) inhibited EA accumulation in kidney cortex slices of rabbit, guinea-pig, Psammomys obesus, rat, mouse and Acomys cahirinus in decreasing order. Ouabain inhibited the sodium pump in kidney cortex slices of these species in the same order. Ethacrynic acid efflux was faster from slices of rat kidney medulla than from kidney cortex. the efflux rate from cortical slices increased when sodium concentration in the incubation medium was lowered. Probenecid (10^?3 M) in the medium enhanced the efflux rate of EA from kidney cortex slices. It was concluded that EA fluxes in kidney cortex slices fit the model of a sodiumactivated carrier mechanism and that the sodium gradient across the cell membrane determines the direction of net EA transport.