The Physical Mechanism for Retinal Discrete Dark Noise: Thermal Activation or Cellular Ultraweak Photon Emission?

For several decades the physical mechanism underlying discrete dark noise of photoreceptors in the eye has remained highly controversial and poorly understood. It is known that the Arrhenius equation, which is based on the Boltzmann distribution for thermal activation, can model only a part (e.g. half of the activation energy) of the retinal dark noise experimentally observed for vertebrate rod and cone pigments. Using the Hinshelwood distribution instead of the Boltzmann distribution in the Arrhenius equation has been proposed as a solution to the problem. Here, we show that the using the Hinshelwood distribution does not solve the problem completely. As the discrete components of noise are indistinguishable in shape and duration from those produced by real photon induced photo-isomerization, the retinal discrete dark noise is most likely due to ‘internal photons’ inside cells and not due to thermal activation of visual pigments. Indeed, all living cells exhibit spontaneous ultraweak photon emission (UPE), mainly in the optical wavelength range, i.e., 350–700 nm. We show here that the retinal discrete dark noise has a similar rate as UPE and therefore dark noise is most likely due to spontaneous cellular UPE and not due to thermal activation.     

Root-Zone-Specific Oxygen Tolerance of Azospirillum spp. and Diazotrophic Rods Closely Associated with Kallar Grass

The effect of oxygen on N₂-dependent growth of two Azospirillum strains and two diazotrophic rods closely associated with roots of Kallar grass (Leptochloa fusca) was studied. To enable precise comparison, bacteria were grown in dissolved-oxygen-controlled batch and continuous cultures. Steady states were obtained from about 1 to 30 μM O₂, some of them being carbon limited. All strains needed a minimum amount of oxygen for N₂-dependent growth. Nitrogen contents between 10 and 13% of cell dry weight were observed. The response of steady-state cultures to increasing O₂ concentrations suggested that carbon limitation shifted to internal nitrogen limitation when N₂ fixation became so low that the bacteria could no longer meet their requirements for fixed nitrogen. For Azospirillum lipoferum Rp5, increase of the dilution rate resulted in decreased N₂ fixation in steady-state cultures with internal nitrogen limitation. Oxygen tolerance was found to be strain specific in A. lipoferum with strain Sp59b as a reference organism. Oxygen tolerance of strains from Kallar grass was found to be root zone specific. A. halopraeferens Au 4 and A. lipoferum Rp5, predominating on the rhizoplane of Kallar grass, and strains H6a2 and BH72, predominating in the endorhizosphere, differed in their oxygen tolerance profiles. Strains H6a2 and BH72 still grew and fixed nitrogen in steady-state cultures at O₂ concentrations exceeding those which absolutely inhibited nitrogen fixation of both Azospirillum strains. It is proposed that root-zone-specific oxygen tolerance reflects an adaptation of the isolates to the microenvironments provided by the host plant.     

Sequential sodium-proton exchange in thrombin-induced human platelets

Thrombin stimulation of human platelets initiates a membrane depolarization attributable to a Na+ influx into, and an alkalinization of, the cytoplasm, both of which follow a similar rapid time scale and thrombin-dose dependence. These responses precede secretion of the contents of the dense granules (serotonin) and, after 1 minute, of lysosomes (beta-glucuronidase). We have evaluated these parameters in the presence of 2H2O in order to determine if the Na+ influx and H+ efflux are sequential or simultaneous. NMR evidence indicates that 2H2O equilibration in rapid, and virtually complete within the 3 min prestimulation platelet equilibration period. In response to an 0.05 U/ml addition of thrombin, the rate of depolarization is 70-80% slower in 2H2O than in H2O. The time to reach maximal depolarization is 5 to 10 seconds longer in 2H2O, the extent of depolarization 60% inhibited, and the pH change 85% inhibited. The serotonin secretion is unaltered, while the beta-glucuronidase secretion is 130-180% enhanced. Dimethylamiloride inhibits the Na+ influx and the pH change completely. These results suggest that the Na+ and H+ fluxes across the plasma membrane are interdependent but neither simultaneous nor electroneutral. Furthermore, granule secretion, previously shown by us to be independent of the existent Na+ gradient, depends on the cytoplasmic K+ and H+ concentrations.     

Time-dependent subpopulation induction in heterogeneous tumors

Time-dependent induction of clonal heterogeneity in the neoplastic micro-environment is analysed within the context of a competitive ecology. A model that describes a constant source for clonal emergence was analysed by Michelsonet al. (1987) as an extension of a model proposed by Jansson and Revesz (1974). The extended model has been termed the JRE Model. This paper extends these analyses to time-dependent emergence rates which may represent induction in the presence of a cytotoxic agent. If the analysis is constrained to the tumor micro-environment, and if the emergent subpopulation is drug resistant, then the model may describe the induction and emergence of drug resistant subclones in a growing neoplasm. Asymptotic closed form solutions are derived for a class of emergence rate functions which decay asymptotically to a constant mutation rate. This underlying mutation rate may represent spontaneous mutation to the resistant phenotype, and has been analysed stochastically (Coldmanet al., 1985). The asymptotic solutions to the time-dependent model approach the steady state solution for the JRE Model which represents the dynamics observed in the presence of a constant, spontaneous mutation rate. The clinical and biological implications of these results are discussed. Research support provided in part by Hungarian National Foundation for Scientific Research Grant No. 6032/6319 and ACS Grant IN45-Z and ACS PDT 243B.     

IFN-gamma regulates the isotypes of Ig secreted during in vivo humoral immune responses

The lymphokine IFN-gamma has been shown in vitro to stimulate IgG2a secretion and inhibit IgG1 and IgE secretion by LPS-activated B lymphocytes. To determine whether IFN-gamma has a similar isotype regulatory role in vivo, we studied the abilities of rIFN-gamma and a mAb to IFN-gamma to modify the isotypes of Ig secreted in mice injected with a goat antibody to mouse IgD, which by itself induces large increases in levels of serum IgG1 and IgE and a relatively small increase in serum IgG2a. Multiple injections of IFN-gamma substantially inhibited production of IgG1 and IgE, and stimulated production of IgG2a in affinity purified goat antibody specific for mouse IgD-treated mice; anti-IFN-gamma antibody blocked the effects of IFN-gamma and in fact enhanced IgG1 and IgE secretion and inhibited the IgG2a response in these mice. The role of IFN-gamma in the selection of isotypes of Ig produced in response to injection of mice with the bacterium Brucella abortus (BA) was also studied, because killed, fixed BA are known to stimulate IFN secretion and a predominantly IgG2a antibody response. Anti-IFN-gamma antibody strongly suppressed IgG2a secretion and stimulated IgG1, but not IgE, secretion in BA-immunized mice. BA suppressed IgG1 and IgE secretion and enhanced IgG2a secretion in affinity purified goat antibody specific for mouse IgD-injected mice; treatment of these mice with anti-IFN-gamma antibody reversed the effects of BA on IgG1 and IgG2a secretion, but not the suppressive effect of BA on IgE secretion. These observations demonstrate that IFN-gamma has an important and perhaps unique physiologic role in the stimulation of IgG2a secretion and in the suppression of secretion of IgG1, whereas bacterial antigens can suppress IgE secretion by other mechanisms in addition to IFN-gamma secretion.     

Anti-Ig-mediated proliferation of human B cells in the absence of protein kinase C

Cross-linking of surface Ig has been shown to stimulate phosphatidylinositol hydrolysis in murine B cells, leading to increases in [Ca2+]i and activation of protein kinase C (PKC). Preliminary evidence suggests that a similar activation mechanism occurs in human B cells. We wished to examine whether anti-Ig antibody-stimulated human B cell proliferation is as dependent upon the presence of PKC as is anti-Ig-mediated murine B cell proliferation. Using highly purified, small, dense peripheral-blood B lymphocytes from healthy adult donors, we confirmed that PMA, a direct activator of PKC, is a potent mitogen for human B cells that synergizes with anti-mu antibody. Furthermore, we demonstrated that PMA treatment abolishes detectable cellular stores of immunoreactive PKC. However, after such depletion of cellular PKC, anti-mu antibody is still capable of delivering a proliferative signal to human B cells. It is unlikely that this signal occurs solely on the basis of increases in [Ca2+]i, because the calcium ionophore A23187 does not induce a proliferative response in PMA-treated B cells similar in magnitude to that seen with anti-mu. Additionally, the finding that pretreatment of B cells with PMA ablates the ability of anti-Ig antibody to mobilize intracellular and extracellular calcium also suggests that the ability of PMA to enhance anti-Ig mediated stimulation does not depend on elevations of [Ca2+]i induced by anti-Ig. Together, these observations suggest that anti-Ig signaling of human B cells may occur via other pathways in addition to the phosphatidylinositol system of calcium influx and PKC activation.     

Cis-analysis of a seed protein gene promoter: the conservative RY repeat CATGCATG within the legumin box is essential for tissue-specific expression of a legumin gene

A 2.4 kb fragment containing the 5'-flanking region and the 5'-noncoding sequence of the Vicia faba legumin gene LeB4 mediates high level seed-specific expression in transgenic tobacco plants. Deleted derivatives of this legumin upstream sequence were fused to the npt-II reporter gene to determine the tissue-specific activity of the chimeric constructs in stably transformed tobacco plants. The results indicate the presence of positive regulatory, enhancer-like cis elements within 566 bp of the upstream sequence. Most importantly, however, these elements are only fully functional in conjunction with the core motif CATGCATG of the legumin box around position -95, since destruction of the motif by a 6 bp deletion in an otherwise intact 2.4 kb upstream sequence drastically reduces expression in seeds. At the same time, low level expression in leaves is observed. The occurrence of similar CATGCATG consensus cis elements with alternating purine and pyrimidine base pairs in front of several other plant genes suggests a functional role of the motif in a wider range of plant promoters.     

Growth characteristics of the copepodsEurytemora affinis andE. herdmani in laboratory cultures

Die calanoiden CopepodenEurytemora affinis (Poppe) undE. herdmani Thompson &Scott wurden über zahlreiche Generationen im Laboratorium gezüchtet. Mit einem Überschuß an Algennahrung vermehrt sichE. affinis in Salzgehalten zwischen 5 und 33 ‰ und bei Temperaturen zwischen 2° und 23,5° C.E. herdmani pflanzt sich in Salzgehalten unter 15 ‰ und bei 21,5° C und höheren Temperaturen nicht fort. Diese Ergebnisse stimmen überein mit Untersuchungen im natürlichen Lebensraum und zeigen, daßE. herdmani an kälteres und salzhaltigeres Wasser gebunden ist als die weiter verbreiteteE. affinis. An den Jungtieren, die von einzelnen Weibchen erhalten worden waren, wurden die Entwicklungszeitspannen vom Ei bis zum ersten Nauplius, ersten Copepoditen, Adultus und eiertragenden Weibchen ermittelt. In 20 ‰ Salzgehalt variiert die Generationszeit beiE. affinis von etwa 105 Tagen bei 2° C bis 9 Tagen bei 23,5° C. Die entsprechenden Generationszeiten fürE. herdmani betragen 73 Tage bei 2° C und 19 Tage bei 15° C. Die Körperlänge beider Arten nimmt bei niedrigeren Temperaturen zu. Die Errechnung des Zahlenverhältnisses der Geschlechter der Jungtiere einzelner Weibchen legt die Vermutung nahe, daß die Temperatur das Geschlechtsverhältnis beeinflußt. Überlebenszeiten wurden ermittelt für Weibchen, welche unter verschiedenen Temperatur- und Salzgehaltsbedingungen gehalten worden waren. Die Lebensspannen von Weibchen beider Arten übertreffen 100 Tage bei 2° C und nehmen bei höheren Temperaturen ab. Weibchen beider Arten vermögen noch lange nach der Kopulation fertile Eier zu produzieren. Diese Beobachtungen sprechen dafür, daß kleine Lokalpopulationen möglicherweise im Herbst kopulieren, dann überwintern und daß die Weibchen im Frühjahr ohne erneute Kopulation Junge produzieren.     

Depression and other psychiatric morbidity in carers of elderly people living at home.

OBJECTIVE--To describe the mental health of a community sample of carers of elderly people with dementia, depression, or physical disability and to compare that with the mental health of other adults living in the household and of those living alone. DESIGN--Assessment of psychiatric morbidity and physical disability with standardised questionnaire in randomly selected enumeration districts; subjects were interviewed at home. SETTING--London Borough of Islington. SUBJECTS--700 people aged > or = 65 and other coresidents. MAIN OUTCOME MEASURE--Depression measured with standardised interview. RESULTS--The prevalence of depression was not significantly higher in carers overall (15%) than in coresidents (11%). Being a woman carer was a significant predictor of psychiatric illness. Depression was more common in the carers of people with a psychiatric disorder than in coresidents (24% v 11%, P < 0.05) and in those living alone (19%). Depression was most common (47%) in women carers of people with dementia. CONCLUSION--The increase in psychiatric morbidity reported in carers of people with psychiatric disorders may reflect the lack of a confiding relationship.