Endocytosis by the corneal endothelium. I. Regulation of binding and transport of hemeproteins and peroxidase-conjugated lectins across the tissue

 Binding, internalization, and movement of hemeproteins and peroxidase-conjugated lectins across organ cultured rat corneal endothelia has been investigated. Horseradish peroxidase (HRP) type II, bound to the surface, was minimally internalized and was easily washed off. In contrast, HRP-VI bound and was rapidly internalized. Reaction product was observed in vesicles, endosomes, multivesicular bodies, and extended along the length of the intercellular space (ICS) to Descemet’s membrane. Studies at 4° C indicated HRP-VI bound uniformly along the surface in a punctate fashion. Exposure to polylysine or mannose significantly decreased uptake. Other tracers such as HRP-VIII, -IX, catalase, and microperoxidase exhibited limited uptake by the tissue. However, endothelia vigorously internalized soybean agglutinin (SBA)–HRP, and reaction product was found intracellularly and within the ICS at the cell/Descemet’s membrane interface. Internalization and the appearance of SBA–HRP within the ICS was diminished following polylysine or mannose treatment. Experiments at 4° C indicated that SBA–HRP binding and uptake were temperature sensitive. Wheat germ agglutinin (WGA)–HRP was also strongly endocytosed and reaction product was visualized within vesicles, endosomes, and multivesicular bodies. Although WGA-HRP reaction product was observed within the ICS, none was detected at the level of Descemet’s membrane. The WGA competitive sugar N-acetyl-d-glucosamine, reduced endocytosis, whereas exposure to unlabeled WGA and mannose together reduced uptake. These results indicate endothelia exhibit differential uptake of various hemeproteins and lectins which is dependent on charge, mannose receptors, and appropriate surface sugars. Accepted: 3 Mach 1998     

Notes from some crypt watchers: regulation of renewal in the mouse intestinal epithelium

The mouse intestinal epithelium undergoes rapid renewal throughout life, thereby requiring continuous coordination of its cellular proliferation, differentiation, and death programs. Recent advances in our understanding of this process have highlighted some of the molecules that regulate renewal and their potential roles in gut neoplasia.     

Intergenerational context discontinuity affects the onset of puberty

The assumption that the onset of puberty is a context-sensitive marker of a reproductive strategy is tested by comparing parental and filial childhood context and somatic development in West and East Germany. Sixty-eight mother-daughter dyads and 35 father-son dyads were taken from two samples of families from Osnabrück in West Germany and Halle in East Germany. According to the observed context discontinuity between the generations in the male dyads, linear regression models show that no indicator of male sexual maturation was influenced significantly by the somatic development of the father. Instead of an inherited timing of maturation, antecedent distal factors like socioeconomic childhood context variables and critical life events lead to an acceleration of male sexual maturation. Finally we test the effect of two different conditions of childhood context continuity on daughter’s age at menarche with maternal age at menarche controlled. Linear regression models show that mother’s age at menarche predicts daughter’s age at menarche only under the condition of contextual continuity between generations, which was the case in the West German sample only. In East Germany, where mother’s age at menarche had no significant effect, the amount of variance explained by childhood context variables was almost the same. These results indicate the context sensitivity of somatic development which seems to follow an evolutionary rationale.     

Hypoxia, temperature, and pH/CO2 effects on respiratory discharge from a turtle brain stem preparation

Johnson, Stephen M., Rebecca A. Johnson, and Gordon S. Mitchell. Hypoxia, temperature, andpH/CO₂ effects on respiratory discharge from a turtle brain stem preparation. J. Appl. Physiol. 84(2): 649-660, 1998.An in vitrobrain stem preparation from adult turtles (Chrysemyspicta) was used to examine the effects of anoxia andincreased temperature and pH/CO₂on respiration-related motor output. At pH ~7.45, hypoglossal (XII)nerve roots produced patterns of rhythmic bursts (peaks) of discharge(0.74 ± 0.07 peaks/min, 10.0 ± 0.6 s duration) that werequantitatively similar to literature reports of respiratory activity inconscious, vagotomized turtles. Respiratory discharge was stable for 6 h at 22°C; at 32°C, peak amplitude and frequency progressivelyand reversibly decreased with time. Two hours of hypoxia had no effecton respiratory discharge. Acutely increasing bath temperature from 22 to 32°C decreased episode and peak duration and increased peakfrequency. Changes in pH/CO₂increased peak frequency from zero at pH 8.00-8.10 to maxima of0.81 ± 0.01 and 1.44 ± 0.02 peaks/min at 22°C (pH 7.32) and32°C (pH 7.46), respectively;pH/CO₂ sensitivity was similar atboth temperatures. We conclude that1) insensitivity to hypoxiaindicates that rhythmic discharge does not reflect gasping behavior,2) increased temperature altersrespiratory discharge, and 3)central pH/CO₂ sensitivity isunaffected by temperature in this preparation (i.e.,Q₁₀ ~1.0).

     

Plant Functional Type Effects on Trace Gas Fluxes in the Shortgrass Steppe

Plant community structure is expected to regulate the microbial processes of nitrification and denitrification by controlling the availability of inorganic N substrates. Thus it could also be a factor in the concomitant release of NO and N2O from soils as a result of these processes. C3 and C4 plants differ in several attributes related to the cycling of nitrogen and were hypothesized to yield differences in trace gas exchange between soil and atmosphere. In this study we estimated fluxes of NO, N2O and CH4 from soils of shortgrass steppe communities dominated by either C3 plants, C4 plants or mixtures of the two types. We collected gas samples weekly from two sites, a sandy clay loam and a clay, throughout the growing seasons of 1995 and 1996. Plant functional type effects on gas fluxes at the clay site were not apparent, however we found several differences among plant communities on the sandy clay loam. CH4 uptake from atmosphere to soil was significantly greater on C4 plots than C3 plots in both years. NO fluxes were significantly greater from C4 plots than from C3 plots in 1995. NO fluxes from C3 and mixed plots were not significantly different between 1995 and 1996, however fluxes from C4 plots were significantly greater in 1995 compared to 1996. Results indicate that under certain environmental conditions, particularly when factors such as moisture and temperature are not limiting, plant community composition can play an important role in regulating trace gas exchange.     

New Polyazaporphine Chemistry for the Origin of Life. A Porphine Solar Energy Transducer for Origin of Life Chemistry: A Possible Synthetic Patj from HCN to an Octaazaporphine via 4H-Imidazol-4-Imine [(HCN)3] Related Chemistry

Molecular orbital spectral predictions suggest that 2,5,7,10,12,15,17,20-octaaza-21H, 23H-porphine has a visible spectral range closely matching that of chlorophyll-a. Since the octaazaporphine is, in its core, a simple derivative of an (HCN)₁₂ oligomer, this fact, together with its spectral properties, would suggest that it occupies a high rank as a primordial porphinic solar energy transducer for photochemistry essential to life's formation. The demonstration that the mass 324 hexahydrooctaazaporphine is formed in protic media by the cyclotetramerization of imidazol-4-aminohydroxonium ion or the derived nitrenium ion, and that a mass 318 species consonant with that of the Hückel aromatic octaazaporphine is observed in the course of these studies, strongly supports the proposed octaazaporphine synthesis in a prebiotic hydrocyanic acid milieu.     

Patch Defence in the Parasitoid Wasp Trissolcus basalis (Insecta: Scelionidae): The Time Structure of Pairwise Contests,and the ‘Waiting Game’

Aggressive defence of host patches has been reported in many parasitoid wasps, but rarely examined in quantitative detail. One aspect of interest is that foraging female parasitoids do not simply consume resource patches, they invest offspring in them. Therefore, patch defence in parasitoids can involve not only resource defence prior to oviposition, but also postoviposition defence of offspring (maternal care). In this paper, the time-structure and sequence of pairwise agonistic contests between females of the parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) are analysed. Three main periods were evident in contests. In the first period, both females exploited the patch with no aggression. After the initiation of fighting, they entered a ‘contest period’, during which resident and intruder roles became clearly resolved. The resident then usually guarded the patch for up to several hours before leaving. This signalled the beginning of the third period, in which the intruder returned to superparasitise the patch. During the contest period, resident behaviour initially reflected the trade-off between exploiting fresh hosts, and defending those it had already parasitised from the intruder, which persistently returned to the patch to try and oviposit, with some success. However, when the patch became fully parasitised, both resident and intruder switched to a ‘waiting game’, in which they sat motionless for extended periods, the resident on the patch and the intruder at a distance. These stand-offs were punctuated by occasional aggressive patrolling by the resident, and cryptic returns to the palch by the intruder. This waiting game appears to be an informational war of attrition, suggesting a conceptual basis for modelling patch-leaving decisions using evolutionary game theory.