Requirement for extracellular calcium or magnesium in mitogen-induced activation of human peripheral blood lymphocytes

The importance of calcium in lymphocyte activation is well recognized, but the levels of extracellular ionized free calcium (Ca++) necessary for lymphocyte proliferation via various pathways have not been investigated in detail. We studied the ability of a lectin mitogen (PHA) and a calcium ionophore (ionomycin) to induce interleukin 2 receptors, interleukin 2 (IL2) production, and proliferation over various concentrations of extracellular Ca++. Reducing the Ca++ levels from the normal 200 microM to 10 microM in PHA-stimulated cultures partially inhibited IL2 receptor expression, IL2 production, and subsequent proliferation. At 1 microM Ca++, both IL2 activity and proliferation were eliminated, but partial IL2 receptor expression was still observed. Ionomycin did not induce any of these events in cultures where the extracellular Ca++ concentration was below 100 microM. Restoring calcium in the medium resulted in normal levels of IL2 receptor expression, IL2 activity, and proliferation when PBL were stimulated with either mitogen. Exogenous magnesium partially restored these events in PHA-stimulated cultures, but had no effect when ionomycin was used as the mitogen. These data indicate that stimulation by ionomycin is much more dependent upon the levels of extracellular Ca++ than is PHA. Extracellular calcium also appears to be necessary subsequent to IL2 receptor acquisition, since the latter was seen without IL2 activity or proliferation at very low extracellular Ca++, and IL2 failed to restore the proliferative response under these conditions. The data also suggest that PHA, but not ionomycin, can activate lymphocytes via a magnesium-dependent pathway, or that PHA has a lower specificity for divalent cation cofactors.     

Life-history analysis of an Artemia population in a changing environment

The Anemia monica Verrill population in Mono Lake, Californiahas two generations per year. Despite similarities in the year-to-yearlife history patterns, some important differences developedbetween 1979 and 1981. The first generation hatches from overwinteringcysts in early spring and reaches maturity by the end of May.The first-generation females reproduce ovoviviparously, givingrise to a second generation which matures between mid-July andAugust. In July, both first and second generation females beginproducing overwintering cysts. The population reaches it maximumin late summer, then declines to low numbers by November. Theabundance of the first generation in June declined from a meanof 20 000 m^–2 to 2400 m^–2. Despite the smaller firstgeneration, the second generation in 1980 and 1981 was at leastas abundant as in 1979. These differences are indicative ofa change in the Artemia population dynamics in Mono Lake. ¹Address for correspondence: Hawaii Institute of Marine Biology,University of Hawaii, P.O. Box 1346 Kaneohe, HI 96744-1346,USA.     

Phosphorylation on basic amino acids in myelin basic protein.

Isolated rat brain myelin when incubated with γ³²P labelled ATP yields proteins bearing acid labile, base stable phosphoryl groups. Phosphorylated myelin basic protein can be isolated and degraded with trypsin and pronase to yield principally phosphoarginine and phosphohistidine. Only a very small amount of phosphorerine survives the base treatment used in the isolation procedure.     

The Chlamydomonas cell cycle is regulated by a light/dark-responsive cell-cycle switch

Cultures of the unicellular green alga Chlamydomonas reinhardii can be synchronized by light/dark cycling not only under photoautotrophic but also under mixotrophic growth conditions. We observed that cultures synchronized in the presence of acetate continue to divide synchronously for one cell-cycle period when transferred to heterotrophic growth conditions. This finding enabled us to investigate the differential effects of light on cell growth and cell division. When cells were exposed to continuous light at the beginning of the growth period they entered the division phase earlier than dark-grown cells as a consequence of an increased growth rate. Illumination at the end of the growth period, however, caused a considerable delay in cell division and an extended growth period. The light-induced delay in cell division was also observed in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II. This finding demonstrates that cell division is directly influenced by a light/dard-responsive cell-cycle switch rather than by light/dark-dependent changes in energy metabolism. The importance of this light/dark control to the regulation of the Chlamydomonas cell cycle was investigated in comparison with other control mechanisms (size control, time control). We found that the light/dard-responsive cell-cycle switch regulates the transition from G1-to S-phase. This control mechanism is effective in cells which have attained the commitment to at least one round of DNA replication and division but have not attained the maximal cell mass which initiates cell division in the light.Abbreviations dCTP deoxycytidine 5-triphosphate - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Contraceptive steroids increase cholesterol in bile: mechanisms of action

Contraceptive steroids increase the risk of acquiring cholesterol gallstones. The factors responsible include an increase in cholesterol saturation of bile and an increase in rate of secretion of cholesterol into bile. The goal of this study was to investigate the mechanism(s) of these increases in biliary cholesterol. During the use of contraceptive steroids, cholesterol saturation of gallbladder bile and the amount of cholesterol secreted per mole of bile acid increased (P less than 0.05 and P less than 0.02, respectively). Cholesterol absorption, cholesterol synthesis, chylomicron remnant clearance, and the concentration of plasma and lipoprotein lipids were not altered by contraceptive steroids. Despite this apparent lack of effect, important correlations were present during steroid use. LDL (low density lipoprotein) cholesterol increased as dietary cholesterol increased (r = 0.58, P less than 0.025). Cholesterol synthesis correlated directly with VLDL cholesterol concentration (r = 0.64, P less than 0.01), biliary cholesterol secretion (r = 0.68, P less than 0.01) and with molar percent cholesterol in bile (r = 0.49, P = 0.06). Chylomicron remnant clearance also correlated with cholesterol secretion (r = 0.85, P less than 0.001). As either remnant uptake or synthesis increased, the effect of the other source of hepatic cholesterol on biliary cholesterol secretion diminished. These relationships were not observed in the same subjects when they were not taking the hormones. The findings suggest that both newly synthesized and dietary cholesterol contribute to the cholesterol secreted in bile. This is consistent with the hypothesis that cholesterol for secretion into bile and VLDL is derived from a common metabolic pool of free cholesterol. It is proposed that contraceptive steroids exert their effect on biliary cholesterol by increasing cholesterol entering the pool and/or by inhibiting hepatic ACAT (acylcoenzyme A:cholesterol acyltransferase) activity, a known effect of progesterone, so that an increase in free cholesterol entering the pool leads to an increase in output.     

Cholesterol synthesis in the perfused liver of pregnant hamsters

Pregnancy is a risk factor for the development of cholesterol gallstones. In pregnant women, biliary cholesterol saturation and secretion are increased. To investigate whether this was due to increased cholesterol synthesis, we studied hepatic cholesterol synthesis in Syrian Golden hamsters. Female controls and animals 10- to 14-days pregnant were studied. The studies were performed in the in situ perfused hamster liver. Cholesterol synthesis was determined by measuring the incorporation of 3H2O added to the perfusate into hepatic, perfusate, and bile cholesterol during a 90-min period. In both pregnant groups, bile flow decreased significantly, but biliary cholesterol concentration increased only in the 14-day pregnant group. The cholesterol synthesis rate averaged (mean +/- SD) 172 +/- 27, 127 +/- 37, and 552 +/- 79 nmol X hr-1 X g liver-1 in controls, 10-day, and 14-day pregnant animals, respectively. The 14-day pregnant animals secreted a markedly higher fraction (47.3 +/- 11.3 vs. 11.1 +/- 13.4%; P less than 0.01) of newly synthesized cholesterol into bile but not into perfusate. Chenodeoxycholate, but not cholate, synthesis rate was decreased in both pregnant groups. We conclude from our studies that hepatic cholesterol synthesis increases towards the end of pregnancy in the hamster and that more newly synthesized cholesterol is secreted into bile at that time. This could at least partially explain the increased biliary cholesterol saturation and secretion observed in women in the third trimenon, and explain pregnancy as a risk factor in the development of cholesterol gallstones.     

Assimilatverteilung in Sommergerstensorten mit unterschiedlicher Resistenz gegenüber dem Echten Mehltau (Erysiphe graminis f. sp. hordei)

Distribution of assimilates in cultivars of spring barley with different resistance against powdery mildew (Erysiphe graminis f. sp. hordei) Transport and distribution of radioactive labelled assimilates in spring barley cultivars with different degrees of resistance to powdery mildew were studied after ¹⁴CO₂-treatment of single leaves. Plants of the cultivars ‘Amsel’ (susceptible), ‘Asse’ (adult plant resistant), and ‘Rupee’ (resistant) were analyzed at the vegetative growth stage (5. leaf unfolded) and the generative growth stage (anthesis). At the vegetative growth stage the assimilate export from the mildew inoculated 5. leaf of ‘Amsel’ and ‘Rupee’ is decreased; in ‘Asse’, there is no considerable change of assimilate distribution due to infection. At the generative growth stage the assimilate export from the infected flag leaf of ‘Amsel’ is reduced when the fungus, is sporulating. In the cultivar ‘Asse’ the assimilates are bound at the infection site until the seventh day after inoculation, then the transport of assimilates to the ear is increased. In ‘Rupee’ mildew inoculation causes an enhanced assimilate transport to the ear. The changes in assimilate distribution due to mildew inoculation are discussed with respect to the different types of host-parasite-interactions and the source-sink-activities in the different cultivars.