Benzoylphenyl ureas inhibit chitin synthesis without interfering with amino sugar uptake in imaginal wing discs of Plodia interpunctella (Hübner)

We tested the hypothesis that the inhibition of chitin synthesis by benzoylphenyl ureas could be explained by their effect on the uptake of GlcNAc into chitin. Our test system consisted of organ cultures of wing imaginal discs from Plodia interpunctella. These wing discs synthesize chitin in response to 20-hydroxyecdysone or RH 5849, a non-steroidal ecdysteroid mimic. Two benzoylphenyl ureas, diflubenzuron and teflubenzuron, inhibited ecdysteroid-dependent chitin synthesis in the wing discs. However, although chitin synthesis was inhibited, there was no corresponding diminution of amino sugar uptake by the imaginal discs. In another experiment 20-hydroxyecdysone stimulated uptake of two sugars, 2-deoxy-D-glucose and 3-O-methyl-D-glucose, which are not synthesized into chitin. Transport of these non-metabolized sugars was unaffected by the inhibitors. In an additional test of the effects on precursor transport, the action of ecdysone (alpha-ecdysone) was examined. Ecdysone stimulated amino sugar uptake, but not chitin synthesis. Neither diflubenzuron nor teflubenzuron inhibited ecdysone-dependent precursor transport. Finally, we examined ecdysteroid-induced uptake of amino sugars by an imaginal disc derived cell line IAL-PID2. In this case, also, GlcNAc transport was not inhibited significantly by either diflubenzuron or teflubenzuron. From these observations we conclude that inhibition of uptake of amino sugars does not account for the ability of teflubenzuron and diflubenzuron to inhibit chitin synthesis in P. interpunctella wing discs.     

Second‐generation decline: Scenarios for the economic and ethnic futures of the post‐1965 American immigrants

‘Second‐generation decline’ questions the current American faith in the myth of nearly automatic immigrant success. In discussing economic scenarios, positive and negative, for the future of the children of the post‐1965 immigrants, the possibility is proposed that a significant number of the children of poor immigrants, especially dark‐skinned ones, might not obtain jobs in the mainstream economy. Neither will they be willing ‐ or even able ‐ to take low‐wage, long‐hour ‘immigrant’ jobs, as their parents did. As a result, they (and young males among them particularly) may join blacks and Hispanics among those already excluded, apparently permanently, from the mainstream economy. The article also deals with the relations between ethnicity and economic conditions in the USA and with the continued relevance of the assimilation and acculturation processes described by ‘straight‐line theory’. This issue, as well as most others discussed, may also be salient for European countries experiencing immigration, especially those countries with troubled economies.     

Studies on the Assembly Characteristics of Large Subunit Ribosomal Proteins in S. cerevisae

During the assembly process of ribosomal subunits, their structural components, the ribosomal RNAs (rRNAs) and the ribosomal proteins (r-proteins) have to join together in a highly dynamic and defined manner to enable the efficient formation of functional ribosomes. In this work, the assembly of large ribosomal subunit (LSU) r-proteins from the eukaryote S. cerevisiae was systematically investigated. Groups of LSU r-proteins with specific assembly characteristics were detected by comparing the protein composition of affinity purified early, middle, late or mature LSU (precursor) particles by semi-quantitative mass spectrometry. The impact of yeast LSU r-proteins rpL25, rpL2, rpL43, and rpL21 on the composition of intermediate to late nuclear LSU precursors was analyzed in more detail. Effects of these proteins on the assembly states of other r-proteins and on the transient LSU precursor association of several ribosome biogenesis factors, including Nog2, Rsa4 and Nop53, are discussed.     

Effective Part-Task Training as Evidence of Distinct Adaptive Processes with Different Time Scales

For some types of visuo-motor transformations like large visuo-motor rotations or the complex transformation of a sliding first-order lever, distinct adaptive processes have been hypothesized that produce a rapid, discrete approximation of the transformation and a slow, graded fine tuning, respectively. Here we investigate whether part-task training of only the second of these processes, namely the fine tuning, transfers to the subsequent performance in a condition with the full transformation of the sliding first-order lever. Therefore, we compared performance of three groups with different practice conditions during transfer to the full transformation. While two groups only practiced the fine tuning without the right-left inversion of the lever prior to transfer, a third group practiced the full lever transformation. Our results show a positive, but less than perfect transfer of the isolated practice of the fine tuning on performance with the full transformation. For the fine tuning itself, transfer was not reliably different from being perfect. The observation that the fine tuning can be acquired separately and added to the later adaptation to the left-right inversion of the lever supports the notion that these slow and fast processes progress rather independently. The additional finding that the preceding acquisition of the fine tuning also facilitates the subsequent rapid process could be due to generalized learning-to-learn or to a more precise assignment of movement errors to the process from which they originate.     

POTASSIUM ACCUMULATION IN THE PROXIMAL CONVOLUTED TUBULES OF THE FROG'S KIDNEY

1. In a manner similar to that of the sartorius muscle, the isolated kidney of the frog can accumulate K against a gradient to upwards of three times its normal concentration. 2. The K-accumulating region is identified as the proximal tubule, which in the isolated tissue immersed over 24 hours in the cold (2–3°C.) amounts to about 90 per cent of the nephron minus the glomerulus. In the fresh tissue it constitutes about 70 per cent. The cells of the proximal tubule are impermeable to Na, but freely permeable to K and Cl. 3. The distal tubule in the isolated kidney does not accumulate K over the external concentration. The cells are permeable to Na which they actively extrude. This extrusion of Na goes parallel with a loss of osmotically associated water amounting to about 15 per cent of the weight of the fresh kidney, but varying somewhat with the conditions. 4. The accumulation of K in the proximal tubules is in accordance with the equations established for the sartorius muscle, and, as theoretically expected, there is no volume increase (but rather a small decrease) with the large accumulations, when the external Na concentration is maintained throughout. 5. With K accumulation in isotonic mixtures large volume changes occur as K is progressively substituted for Na. Over the range of external K concentration of 10 to 100 mM per litre the weight of the whole kidney changes to 2.5 times and the water of the cells of the proximal tubules increases to over four times. Up to an external K value of 90 mM per litre the mean weight of the kidney shows a linear relation when plotted against the reciprocal of the Na concentration plus the small glucose and Ca concentration. This relation is interpreted theoretically. 6. The effect of cyanide in the isotonic mixtures is to prevent the contraction of the distal tubules and to cause swelling of the same. It does not affect the volume, volume changes, or differential permeability of the proximal tubule. At the same time the membranes of the proximal tubule cells lose their characteristic permeability at a lower level of distension in the presence of cyanide. 7. The mean Na ratio for the kidney after 24 hours'' immersion in the cold is 0.26 ± 0.014 (giving standard deviation of mean). The ratio is defined as See PDF for Equation. For the fresh kidney the mean ratio is 0.39 ± 0.006. 8. The mean inulin ratio (28 observed in the cold) is 0.23 ± 0.012 and the same value for 10 observed at room temperature. At room temperature—2 hour immersion—the ratio is increased by cyanide to a mean of 0.32 ± 0.028, but only a slight increase is caused by cyanide in the cold. 9. The mean hemoglobin ratio after 24 hours'' immersion in the cold is 0.17 ± 0.004 and is unaffected by cyanide.     

Biochemical and Molecular Responses to Loss of Renal Mass: Atpase and Cyclic Nucleotides: Evidence for Altered Cyclic Nucleotide Metabolism During Compensatory Renal Hypertrophy and Neonatal Kidney Growth

In adult male Sprague-Dawley rats contralateral nephrectomy was followed by an initial fall of the concentration of cGMP in renal cortical tissue followed by a rise to a peak level of 300 percent of the initial concentration within two hours. cGMP concentration in the remaining renal cortex remained at about 300 percent of the initial value during the subsequent 72 hours and slowly declined to 150-200 percent in the following two weeks. The changes in cGMP concentration were due to exactly parallel changes in the soluble fraction of renal cortical guanylate cyclase activity, while cGMP-phosphodiesterase activity remained unchanged. cAMP concentration after contralateral nephrectomy fell significantly by about 25 percent within two hours and remained below baseline level for up to eight hours. In the kidneys of newborn rats the concentration of cAMP was approximately one-half that found in adult kidneys: it slightly fell between the fourth and the seventh day after birth and subsequently continuously rose to reach adult values approximately two weeks after birth. The concentration of cGMP was significantly greater four days after birth than in adult rats, further rose between the fourth and the seventh day after birth and subsequently gradually declined to adult levels. The increased cGMP concentration appears to be due to an increase of guanylate cyclase activity in total kidney homogenates which, in turn, was mainly due to an increase of the particulate (membrane-bound) fraction of the enzyme. cGMP-phosphodiesterase activity, however, was also increased in respect to adult levels, one or three weeks after birth. Renal growth from the seventh day after birth to adulthood is accompanied by a continuous increase of the ratio cAMP/cGMP. Removal of one kidney four to seven days after birth resulted in a slower increase of this ratio. The data suggest that cGMP may trigger renal growth and that increases of cGMP concentration in the kidneys are the result of a primary increase in the activity of guanylate cyclase.     

Professor Dr. Geoffrey Burnstock (1929–2020)

Purinergic Signalling -