Oral water ingestion in the pulmonate freshwater snail,Lymnaea stagnalis

InLymnaea stagnalis, oral uptake of ambient medium was studied using⁵¹Cr-ethylenediaminetetra-acetic acid. In normal snails Cr-ethylenediaminetetra-acetic acid uptake showed two components: a high uptake rate within the first hour followed by moderate uptake proportional with time. The tracer accumulated mainly in the digestive system. All animals showed initial, transient uptake. Moderate uptake proportional with time did not occur in snails in which the buccal ganglia had been extirpated, in which both the buccal ganglia had been extirpated and the oesophagus was sectioned, or in snails provided with an oesophageal fistula. These snails did not accumulate tracer in the intestinal system. This type of tracer accumulation clearly represented oral ingestion of surrounding water. The oral water ingestion rate ranged from 8 to 12 μl·h⁻¹·g⁻¹. Assuming complete absorption, this accounts for 20–30% of the urine production rate. At low external concentrations the contribution of oral water ingestion to Na⁺ balance is negligible. However, its importance will grow with increasing external concentrations and becomes a major factor at higher concentrations. The ingestion rate increased almost sixfold when starving snails were allowed to feed. It is suggested that oral water ingestion is a consequence of making bite cycles and swallowing.     

PHYSIOLOGICAL ONTOGENY : A. CHICKEN EMBRYOS. XII. THE METABOLISM AS A FUNCTION OF AGE.

1. The previous findings that the rate of metabolism per gm. of body weight decreased with age, and that during the incubation period catabolism was mostly at the expense of fat, have been confirmed. 2. These determinations of the rate of oxygen uptake have afforded more precise values for the catabolic rate and thus permit estimations of the changes with age in the rate of absorption.     

PHYSIOLOGICAL ONTOGENY : A. CHICKEN EMBRYOS. XI. THE PH,CHLORIDE, CARBONIC ACID,AND PROTEIN CONCENTRATIONS IN THE TISSUES AS FUNCTIONS OF AGE.

Investigations of the chicken embryo during its incubation period show that: 1. The pH and the chloride concentration of the tissues decrease with age; the fall is most rapid between the 10th and the 13th days of incubation. 2. The concentration of total CO₂ increases with age. This fact is not considered inconsistent with a possible decrease in the concentration of active bicarbonate ions, since the increased CO₂ might well be the result of absorption of calcium carbonate from the shell and its precipitation as bone in the embryo. 3. The concentration of protein increases with age, especially between the 12th and the 16th days of incubation. The fact that the electrolytes change with the greatest rapidity at about 11½ days, the protein at 14 days, and the fat at 16½ days might be taken as a demonstration of the phenomenon of unequal development in the realm of biochemical differentiation and consequently that some notion of order, depending upon molecular reactivity and mobility would describe the process better than any concept of dynamic equilibrium.     

Contractile and morphological properties of hamster retractor muscle following 16 h of cold preservation

Introduction

Cold hypoxia is a common factor in cold tissue preservation and mammalian hibernation. The purpose of this study was to determine the effects of cold preservation on the function of the retractor (RET) muscle of the hamster in the non-hibernating state and compare these with previously published data (van der Heijden et al., 2000) [52] on the rat cutaneus trunci (CT) muscle.

Materials and methods

After cold storage (16 h at 4 °C), muscles were stimulated electrically to measure maximum tetanus tension (P₀) and histologically analyzed. The protective effects of addition of the antioxidants trolox and deferiprone and the calcium release inhibitor BDM to the storage fluid were determined.

Results

After storage, the twitch threshold current was increased (from 60 to 500 μA) and P₀ was decreased to 27% of control. RET morphology remained unaffected. RET muscle function was protected by trolox and deferiprone (P₀, resp., 43% and 59% of control). Addition of BDM had no effect on the RET.

Conclusions

The observed effects of cold preservation and of trolox and deferiprone on the RET were comparable to those on CT muscle function, as reported in a previously published study (van der Heijden et al., 2000) [52]. Both hamster RET and rat CT muscles show considerable functional damage due to actions of reactive oxygen species. In contrast to the CT, in the RET cold preservation-induced functional injury could not be prevented by BDM and was not accompanied by morphological damage such as necrosis and edema. This suggests that the RET myocytes possess a specific adaptation to withstand the Ca²⁺ overload induced by cold ischemia.     

Functional Separation of the Na-K Exchange Pump from the Volume Controlling Mechanism in Enlarged Duck Red Cells

Previous publications have described a "volume controlling mechanism" in duck erythrocytes that returns both enlarged and shrunken cells to their original isotonic volume. Enlarged cells return to their original size by readjusting their K content. To study the specificity of this aspect of the mechanism for K, we prepared enlarged cells with various Na and K contents. Only cells containing a high K content resume their original size in the standard isotonic medium. The process of regulation resembles that described above. In contrast, cells containing a high Na content fail to reestablish this volume, but shrink instead until they reach a limiting minimal volume (four-fifths of normal). Here, another mechanism, the cation pump rather than the volume controlling mechanism, removes Na and is responsible for the changes in cell size. Enlarged cells with an intermediate Na and K content utilize both mechanisms to reduce their cation content. Only if Na is prevented from leaving the cell and sufficient K is present initially, will these cells reestablish their original size. These studies demonstrate that the cation pump and volume controlling mechanism function independently and, when cells enlarge, only K can effectively traverse the pathway associated with the volume controlling mechanism. This route differs from the one used by the cation pump to eject Na.     

THE EFFECT OF TRYPSIN, CHYMOTRYPSIN, RIBONUCLEASE, AND DESOXYRIBONUCLEASE ON ACTIVE, INACTIVE, AND REVERSIBLY INACTIVATED MEGATHERIUM PHAGE

The effect of trypsin, chymotrypsin, and desoxyribonuclease on active, reversibly inactivated, and heat-inactivated B. megatherium phage, and on living and dead B. megatherium and B. coli has been determined. The results are summarized in Table I.     

OXIDATIVE ASSIMILATION IN RELATION TO PHOTOSYNTHESIS IN CHLORELLA

1. An oxidative assimilation of acetic add and glucose in darkness has been demonstrated in the green alga, Chlorella pyrenoidosa. From manometric experiments it has been shown that 1 mol (CH₂O) per mol acetic add and 5 mols (CH₂O) per mol glucose are produced. 2. The time required for complete utilization of a limited amount of acetic acid or glucose is not affected by illumination in the absence of carbon dioxide. 3. The time required for complete utilization of a limited amount of glucose is not affected by the simultaneous occurrence of photosynthesis. It must therefore be concluded that the accumulating product of photosynthesis cannot be glucose but must be some slowly respirable (storage) material. 4. Possible interrelationships between oxidative assimilation and photosynthesis may be further studied by following, in darkness and in light, the time course of oxidative assimilation of substrates which are possible intermediates in the two processes.     

Direct versus indirect effects of habitat fragmentation on community patterns in experimental landscapes

Habitat area and fragmentation are confounded in many ecological studies investigating fragmentation effects. We thus devised an innovative experiment founded on fractal neutral landscape models to disentangle the relative effects of habitat area and fragmentation on arthropod community patterns in red clover (Trifolium pratense). The conventional approach in experimental fragmentation studies is to adjust patch size and isolation to create different landscape patterns. We instead use fractal distributions to adjust the overall amount and fragmentation of habitat independently at the scale of the entire landscape, producing different patch properties. Although habitat area ultimately had a greater effect on arthropod abundance and diversity in this system, we found that fragmentation had a significant effect in clover landscapes with ≤40 % habitat. Landscapes at these lower habitat levels were dominated by edge cells, which had fewer arthropods and lower richness than interior cells. Fragmentation per se did not have a direct effect on local-scale diversity, however, as demonstrated by the lack of a broader landscape effect (in terms of total habitat area and fragmentation) on arthropods within habitat cells. Fragmentation—through the creation of edge habitat—thus had a strong indirect effect on morphospecies richness and abundance at the local scale. Although it has been suggested that fragmentation should be important at low habitat levels (≤20–30 %), we show that fragmentation per se is significant only at intermediate (40 %) levels of habitat, where edge effects were neither too great (as at lower levels of habitat) nor too weak (as at higher levels of habitat).