Cell Cycle activation and ouabain-sensitive ion movements of 3T3 and C3H-10T½ fibroblasts

The introduction of either PGF_2α (10^?7 M) or TPA (10^?7 M) stimulated, ouabain-sensitive ⁸⁶Rb⁺ influx at 30 min in postconfluent 3T3-4 mouse fibroblast cultures by 117% and 124%, respectively. Both TPA and PGF_2α at these concentrations stimulated the incorporation of ³H-TdR into DNA. TPA had the greatest stimulatory effect, which was similar to that obtained with 10% fetal calf serum. In accord with the idea that modulation of membrane processes such as Na⁺/K⁺ pump activity in fibroblasts may reflect important events related to the initiation of DNA synthesis, it was observed that in both 3T3-4 and C3H-1 0T½ cells there were parallel increases in ³H-TdR incorporation and ouabain-sensitive ⁸⁶Rb⁺ influxes with 10^?7 M TPA, whereas PGF_2α stimulated a significant increase in ³H-TdR incorporation in 3T3-4 but not C3H-10T½ cells and only marginal increases in ouabain-sensitive ⁸⁶Rb⁺ influx in both. Therefore, although there appears to be a close correlation between Na⁺/K⁺ pump activation and subsequent S-phase entry following TPA stimulation, a similar correlation for PGF_2α cannot be confirmed.     

Interactions of organic pollutants with gills of the bivalve molluscs Anodonta californiensis and Mytilus californianus: uptake and effect on membrane fluxes. II

1. The uptakes of 2,4,5-T, glyphosate, parathion, paranitrophenol, naphthalene, glycine, and inulin by gills of the bivalve molluscs Anodonta californiensis (freshwater) and Mytilus californianus (marine) show non-polar compounds are taken up to a greater extent than polar compounds except where active transport occurs. 2. The uptake of glycine by M. californianus is reduced by pollutants containing complexing functional groups but not by non-polar compounds. 3. The uptake of parathion alters the polyphosphate-inorganic phosphate balance in M. californianus. 4. The uptakes of pollutants parallel their toxicities toward rats.     

Defects in protein modification precede developmental defects in l(3)c21RRW630, a temperature-sensitive Drosophila developmental mutant

The temperature-sensitive Drosophila developmental mutation, l(3)c21RRW630 (abbreviated RW630) disturbs oogenesis and has a maternal effect on embryogenesis. At restrictive temperature, RW630 alters post-translational modification of three abundant proteins. To examine the causal relationship between these biochemical defects and the developmental defects in RW630, a series of temperature-shift experiments was performed. It was found that defects in protein modification could be detected in RW630 ovaries after RW630 females had been exposed to restrictive temperature for 1 day. RW630 females treated in this fashion produce embryos which contain a low level of unmodified proteins. Nevertheless, these embryos hatch at a normal rate. Since these ovaries and these embryos are developmentally normal, but do show defects in protein modification, it is unlikely that the RW630 developmental defects cause the biochemical defects in RW630. It is more likely that accumulation of unmodified proteins after extended exposure to restrictive temperature produces the developmental defects in RW630.     

Hemodynamic effects of rapidly evacuating prolonged pneumothorax in rabbits

Clinical observations suggest that systemic hypotension may be caused by rapid evacuation of persistent pneumothorax. This observation has not been substantiated experimentally and the mechanism(s) are unknown. In this study, we measured systemic hemodynamic parameters in rabbits before and for 2 h during negative pressure evacuation of a right-sided pneumothorax of 7-9 days duration. Three groups of animals were studied: 10 rabbits breathed room air and were hypoxemic during pneumothorax (hypoxemic pneumothorax = HP); 10 rabbits breathed 40% O2-60% N2, which prevented arterial hypoxemia during pneumothorax (supraoxemic pneumothorax = SP); seven normal control animals were untreated during this time period (NC). Pneumothoraces in HP and SP were evacuated by negative pressure applied to the right pleural space for 2 h while animals were anesthetized and mechanically ventilated. The NC group was anesthetized and ventilated without prior pneumothorax. Serial hemodynamic measurements were made before and during pleural suction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Production of acetylcholine in rat brain following thiamine deprivation and treatment with thiamine antagonists

Abstract— The effects of thiamine deprivation and of treatment with the thiamine antagonists, oxythiamine and pyrithiamine, on the storage and synthesis of acetylcholine were studied in rats. Rats treated with pyrithiamine always developed ataxia and convulsions, and they died in an average of 36 ± 5.0 hr after onset of convulsions. Injections of sublethal doses of eserine after onset of convulsions had no effect or shortened survival time. If injections were started before the onset of convulsions, the survival time was increased to 56 ± 3.3 hr. The content of total acetylcholine-like compounds, measured by bioassay, in the brain was decreased in all three types of thiamine deficiency. On the other hand, the amount of parenterally administered [¹⁴C]pyruvate converted to [¹⁴C]acetylcholine in vivo was affected only by treatment with pyrithiamine. The increase found was probably due to an increased permeability of the blood-brain barrier to the pyruvate. Conversion of [¹⁴C]pyruvate to [¹⁴C]acetylcholine in vitro was decreased significantly in homogenates of brains from both oxythiamine and pyrithiamine-treated animals.     

Effect of sodium ion on the affinity of naloxone for the kappa opioid receptor

Several investigators have observed that sodium ion enhances the binding of naloxone to opioid receptors. This effect has generally been attributed to allosteric modulation of the state of the mu receptor. However, a recent claim has been made that the enhancement does not involve a change in the mu receptor, but instead occurs because naloxone becomes a more kappa-specific drug when sodium ion is present in high concentration. Since the claim was not based on experimental evidence from binding studies involving known high-affinity kappa ligands, we have investigated the competition of naloxone for the kappa site using [3H]U-69593 as the marker for receptor binding. Assays were carried out in the presence and absence of 100 mM NaCl. The results of the study indicate that sodium ion does not increase the affinity of naloxone or U-69593 for the kappa receptor.     

Structure insights into mechanisms of ATP hydrolysis and the activation of human heat-shock protein 90

The activation of molecular chaperone heat-shock protein 90 (Hsp90) is dependent on ATP binding and hydrolysis, which occurs in the N-terminal domains of protein. Here, we have determined three crystal structures of the N-terminal domain of human Hsp90 in native and in complex with ATP and ATP analog, providing a clear view of the catalytic mechanism of ATP hydrolysis by Hsp90. Additionally, the binding of ATP leads the N-terminal domains to be an intermediate state that could be used to partially explain why the isolated N-terminal domain of Hsp90 has very weak ATP hydrolytic activity.