Vasoactive intestinal peptide effects on GH3 pituitary tumor cells: high affinity binding, affinity labeling, and adenylate cyclase stimulation. Comparison with peptide histidine isoleucine and growth hormone-releasing factor

The vasoactive intestinal polypeptide (VIP) receptor was characterized on the GH3 rat pituitary tumor cell line using competitive binding studies with peptides having sequence homology with VIP. Further studies investigated receptor coupling to the adenylate cyclase complex by measurement of cAMP levels. Finally, the molecular weight of the receptor was estimated by affinity labeling techniques. Studies using 125I-VIP and unlabeled competing peptides revealed a single class of high affinity binding sites with a dissociation constant (KD) of 17 +/- 2 nM (mean +/- S.E.M.) for VIP, 275 +/- 46 nM for peptide histidine isoleucine (PHI), and 1380 +/- 800 nM for human pancreatic growth hormone releasing factor (GHRF). VIP and PHI each stimulated intracellular cAMP accumulation in a dose-dependent manner; both peptides demonstrated synergism with forskolin. In contrast, GHRF neither stimulated accumulation of cAMP nor demonstrated synergism with forskolin. VIP plus PHI (1 microM each) caused no significant increase in cAMP over either VIP or PHI alone, implying that the two peptides act through the same receptor. Covalent crosslinking of 125I-VIP to its binding site using either disuccinimidyl suberate (DSS) or ethylene glycol bis(succinimidyl succinate) (EGS) was followed by SDS-PAGE and autoradiography. The result is consistent with an Mr 47 000 VIP-binding subunit comprising or being associated with the VIP receptor of GH3 pituitary tumor cells.     

Effects of photoperiodicity and light irradiance on phosphate-limited Oscillatoria agardhii in chemostat cultures

The cyanobacterium Oscillatoria agardhii was grown in continuous culture under various light conditions in order to study the interactions of light on phosphorus-limited growth. Under severe P-limiting (light-saturating) conditions, a low chlorophyll a and C-phycocyanin content was found. In addition, the light-harvesting capacity, reflected in the values of P _max (maximum light-saturated oxygen production rate) and (photosynthetic affinity), were low compared to light-limited cultures.Reduction of the light climate, either by reduction of the length of the photoperiod or light-intensity, resulted in an increase in light-harvesting capacity (higher pigment content, P _m and ) during growth under P-limiting conditions. Light-induced changes in P _max and could be related to the relative growth rate, being the actual growth rate as a fraction of the growth rate which would be observed under light-limiting conditions.Under P-limiting conditions, reduction of the light-climate caused a reduction in dry weight of the culture. This decrease was mainly due to a decrease in carbohydrate content of the cells. Under all conditions tested, carbohydrates were found to accumulate during the light-period and to be consumed during the dark-period.Evaluation of carbohydrate consumption in the dark yielded a specific maintenance rate constant of 0.001 h^-1. This observation leads to the conclusion that the specific maintenance rate constant is independent on the character of the growth rate limiting nutrient for O. agardhii.     

Effects of weak acids on proline accumulation in barley leaves: a comparison between abscisic acid and isobutyric acid

Abstract. When isobutyric acid (IBA) or abscisic acid (ABA) are supplied to leaf sections a similar rapid and marked decrease in the intracellular pH is observed. This acidification is accompanied by an increase in proline level which is about the same for both 3 mol m⁻³ IBA and 1 mol m⁻³ ABA treatments.
Fusicoccin (FC), known to act at the proton pump level, almost completely suppresses the ABA-induced acidification of the cell sap, whereas it only partially counteracts the acidifying effect of IBA, in particular during short periods of treatment. This effect of FC is paralleled by a similar inhibition of the induced proline accumulation: in fact, FC completely suppresses the ABA-induced increase in proline during short treatment periods, whereas it is only effective in inhibiting the IBA-induced proline accumulation after long treatment periods.
These data seem to suggest that the ABA- and IBA-induced changes in proline level might be mediated by changes in the intracellular pH.     

The nitrogen balance of Raphanus sativus X raphanistrum plants. I. Daily nitrogen use under high nitrate supply

Abstract Growth-chamber cultivated Raphanus plants accumulate nitrate during their vegetative growth. After 25 days of growth at a constant supply to the roots of 1 mol m^?3 (NO^?₃) in a balanced nutrient solution, the oldest leaves (eight-leaf stage) accumulated 2.5% NO^?₃-nitrogen (NO₃-N) in their lamina, and almost 5% NO₃-N in their petioles on a dry weight basis. This is equivalent to approximately 190 and 400 mol^?3 m^?3 concentration of NO^?₃ in the lamina and the petiole, respectively, as calculated on a total tissue water content basis. Measurements were made of root NO^?₃ uptake, NO^?₃ fluxes in the xylem, nitrate uptake by the mesophyll cells, and nitrate reduction as measured by an in vivo test. NO^?₃ uptake by roots and mesophyll cells was greater in the light than in the dark. The NO^?₃ concentration in the xylem fluid was constant with leaf age, but showed a distinct daily variation as a result of the independent fluxes of root uptake, transpiration and mesophyll uptake. NO^?₃ was reduced in the leaf at a higher rate in the light than in the dark. The reduction was inhibited at the high concentrations calculated to exist in the mesophyll vacuoles, but reduction continued at a low rate, even when there was no supply from the incubation medium. Sixty-four per cent of the NO^?₃ influx was turned into organic nitrogen, with the remaining NO^?₃ accumulating in both the light and the dark.     

Differences in reactivity of confluent and nonconfluent cultures of human endothelial cells toward thrombin-stimulated platelets or heparinized salt solution

Summary This study examined whether nonconfluent endothelial cell cultures reacted differently than confluent ones toward thrombin-stimulated platelets or a heparinized salt solution. The adherence to the endothelial cell cultures of⁵¹Cr-labeled human platelets stimulated at different thrombin concentrations was studied. There was significantly higher adherence of stimulated platelets to nonconfluent cultures compared with confluent ones. This was confirmed by scanning electron microscopy, which also revealed a tendency for the platelets to adhere at the cell periphery. Electron microscopy also showed that thrombin-stimulated platelets induced endothelial cell contraction. Part of the peripheral endothelial cell surface toward the bottom of the culture dish was inverted, facing the lumen of the dish. This phenomenon was particularly seen in nonconfluent cultures. When⁵¹Cr-labeled endothelial cultures were incubated with a mildly injurious fluid as heparinized sodium acetate and 20% serum, at 20° C for 30 min, the nonconfluent cultures showed significantly more cell detachment and release of⁵¹Cr than the confluent ones. We conclude that under the conditions of the present experiments there are differences in the reactivity of confluent and nonconfluent endothelial cell cultures. These differences probably reflect biological dissimilarities. In experiments where properties of cultured endothelium are studied, care should be taken that the degree of confluency is standardized.     

Effects of increased salinity on the diatom assemblage in Fonda Lake,Michigan

A salt storage facility has been located adjacent to Fonda Lake since 1953. In February 1981 a core was taken from the profundal sediments of the lake and analyzed to determine the effects of salt perturbation on the diatom community over a 32-year period. Diatom assemblages from different levels were compared using multivariate techniques including cluster analysis and principal component analysis. Shifts in diatom composition related to salinification were revealed most clearly by subdominant taxa. Five distinct groups of diatom taxa were found to correspond with 5 depth intervals. The diatom component of the lake up to 1960 included two groups of taxa which were alkaliphilous and chloride indifferent. A reduction in species diversity beginning in 1960 may indicate a salt effect. By 1968, when diversity reached a minimum, a variety of halophilic taxa (including Diatoma tenue, Navicula gregaria and Synedra fasciculata) attained their highest relative abundances. At the top of the core, diversity increased slightly and some halophilic taxa decreased in relative abundance, which suggests a possible decrease in salt loading to the lake.     

Heterogeneity of hepatic microsomal UDP-glucuronosyltransferase(s) activities: comparison between human and mammalian species activities

The first comparative profiles of UDP-glucuronosyltransferase(s) (UDPGT) activities obtained under standard conditions in vitro in mammals (man, rat [Wistar and Gunn], mouse, monkey [Papio papio and Cynomolgus], pig, guinea pig, rabbit, dog) are presented for 16 aglycones. A decreasing scale of these activities was obtained from planar to bulky molecules. The scale was identical for each of the mammals studied, including man. Statistical analysis of the results revealed a division of the aglycones into three groups, one being correlated with the molecular form called GT1 the two others with the GT2 form. The profile of activities in the Gunn rat revealed very weak activity towards planar molecules (GT1). These results provide evidence that under standard conditions, human UDPGT activities are comparable to those from other animals.     

Seasonal changes of glycogen/trehalose contents,supercooling points and survival rate in mature larvae of the overwintering soybean pod borer Leguminivora glycinivorella

The mature larvae of the soybean pod borer Leguminivora glycinivorella, spend over 9 months (October-next August) in the inactive state until pupation down to 3 cm below the surface in soil. Trehalose content of inactive larvae increases in early winter, attaining a maximum (ca 30 mg/g), and decreases in spring, with a concomitant decrease and increase of glycogen. The median supercooling points seasonally change from ?19.8°C (October) to ?25.0°C (February), and to ?17.0°C (June). The lower supercooling points in winter are in part due to the absence of unusually high values (> ?18°C). The increase in trehalose does not seem to be effective in depressing the supercooling points. The larvae are freeze-intolerant, but ambient temperatures in outdoor conditions are always above the supercooling points. The survival rates are very high throughout the inactive period.     

The relationship between the levels of DNA-hydrocarbon adducts and the formation of sister-chromatid exchanges in Chinese hamster ovary cells treated with derivatives of polycyclic aromatic hydrocarbons

The frequencies of the induction of sister-chromatid exchanges and the levels of deoxyribonucleoside-hydrocarbon adducts formed in Chinese hamster ovary cells that had been treated with either dihydrodiols or a diol-epoxide derived from polycyclic aromatic hydrocarbons were determined. Up to 6-fold increases in the incidence of these exchanges were observed when the cells were treated either with the dihydrodiols, trans-3,4-dihydro-3,4-dihydroxy-7-methylbenz[a]anthracene,trans-7,8-dihydro-7,8-dihydroxybenzo[a]pyrene or the diol-epoxide, (±)-r-7, t-8dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a] pyrene but when the cells were transferred to media free of these compounds, there were rapid reductions in the frequency of these exchanges. When the exchanges were induced by the diol-epoxide, the decreases in frequency were paralleled by decreases in the levels of deoxyribonucleoside-diol-epoxide adducts that were present in hydrolysates of DNA isolated from the cells. There thus appears to be a close relationship between the frequency of sister-chromatid exchanges and the levels of deoxyribonucleoside-diol-epoxide adduct formation.     

Regulation of carbonic-anhydrase activity,inorganic-carbon uptake and photosynthetic biomass yield inChlamydomonas reinhardtii

The regulation of carbonic anhydrase by environmental conditions was determined forChlamydomonas reinhardtii. The depression of carbonic anhydrase in air-grown cells was pH-dependent. Growth of cells on air at acid pH, corresponding to 10 m CO₂ in solution, resulted in complete repression of carbonic-anhydrase activity. At pH 6.9, increasing the CO₂ concentration to 0.15% (v/v) in the gas phase, corresponding to 11 M in solution, was sufficient to completely repress carbonic-anhydrase activity. Photosynthesis and intracellular inorganic carbon were measured in air-grown and high-CO₂-grown cells using a silicone-oil centrifugation technique. With carbonic anhydrase repressed cells limited inorganic-carbon accumulation resulted from non-specific binding of CO₂. With air-grown cells, inorganic-carbon uptake at acid pH, i.e. 5.5, was linear up to 0.5 mM external inorganic-carbon concentration whereas at alkaline pH, i.e. 7.5, the accumulation ratio decreased with increase in external inorganic-carbon concentration. It is suggested that in air-grown cells at acid pH, CO₂ is the inorganic carbon species that crosses the plasmalemma. The conversion of CO₂ to HCO ₃ ^- by carbonic anhydrase in the cytosol results in inorganic-carbon accumulation and maintains the diffusion gradient for carbon dioxide across the cell boundary. However, this mechanism will not account for energy-dependent accumulation of inorganic carbon when there is little difference in pH between the exterior and cytosol.