Diet spectra and resource partitioning in the larvae and juveniles of three species and six cohorts of cyprinids from a subalpine lake

Summary Diet composition based on gut analyses was studied in larvae and juveniles belonging to six (out of eight) age groups (cohorts) of three species of cyprinids (Rutilus rutilus L., Leuciscus cephalus L., Scardinius erythrophthalmus L.) from a small meso-oligotrophic lake in Tyrol, Austria.A basic pattern of ontogenetic shifts of resource use is postulated for the first weeks after hatching, consisting of the sequence: phytoplankton-rotifers-crustaceans-chironomid larvae. However, there are several variations to this general theme.Diet overlap is of about the same magnitude between representatives of different species or different cohorts, and between members of schools belonging to one cohort. This points to the importance of random food selection in all larvae and juveniles during this phase of life.Prey size is a very poor predictor of food choice by young cyprinids, but there is greater similarity in diet between the larger juveniles than between the smaller larvae, irrespective of whether the fish compared represent different species, different cohorts or are members of homogeneous groups.The lack of correlation between prey size and predator size may be explained by assuming that out of a limited range of available prey size the fish always try to include in their diet also the largest items they are able to swallow. This would be a good strategy considering that growth rates are positively correlated with food size.One clearcut interspecific difference in resource use may be noted: The larvae of L. cephalus are distinguished from those of the other two species by the absence of rotifers and nauplii in their diet, and by their greater ability to handle both adult copepods and chironomid larvae.     

Role of mitochondrial DNA in cell death induced by 125I decay

The role of mitochondrial DNA in radiation-induced cell death was determined by selective [125I]iododeoxyuridine (125IUdR) incorporation into exclusively nuclear sites compared to labelling in both nuclear and mitochondrial DNA of Chinese hamster cells. Such selectivity was achieved by using berenil (25 micrograms/ml for 24 h), a drug which inhibits mitochondrial DNA synthesis without affecting incorporation of 125IUdR into nuclear DNA but does not result in reduced clonogenicity or cell cycle perturbations or alteration in the X-ray response of cells. There was no difference in cell killing between cells with nuclear labelling alone compared with nuclear plus mitochondrial labelling. The absence of decays in mitochondrial DNA does not affect the ability of 125I to induce lethal cell damage. The two treatment groups have superimposable curves with a D0 of 96 decays/cell. These findings indicate that mitochondrial DNA is not the most sensitive target for radiation-induced cell death from 125I decay.     

Relative phosphate contents of phosphofructokinase and other soluble phosphoproteins in skeletal muscle

In vivo phosphorylation of muscle proteins has been studied by incorporation of [³²P]phosphate with emphasis placed upon the phosphorylation of glycolytic enzymes. Of the approximately 25 soluble proteins resolved by two-dimensional electrophoresis that contain significant ³²P, phosphofructokinase was the sole glycolytic enzyme identified as a phosphoprotein. The extent of phosphorylation found for this enzyme was the same as determined previously for purified phosphofructokinase and was about the same as the extent of phosphorylation of phosphorylase in resting muscle. Subsequent partial purification of several glycolytic enzymes confirmed the absence of significant amount of phosphate. However, phosphoglycerate mutase contained small amounts of covalently bound ³²P that was exchangeable with 3-phosphoglycerate and therefore, most likely was incorporated during the catalytic reaction cycle. Analogous results were obtained for phosphoglucomutase. Both mutases were also phosphorylated at the same sites by the catalytic subunit of cyclic AMP-dependent protein kinase.     

Function of calmodulin in postsynaptic densities. II. Presence of a calmodulin- activatable protein kinase activity

Because the calmodulin in postsynaptic densities (PSDs) activates a cyclic nucleotide phosphodiesterase, we decided to explore the possibility that the PSD also contains a calmodulin-activatable protein kinase activity. As seen by autoradiographic analysis of coomassie blue-stained SDS polyacrylamide gels, many proteins in a native PSD preparation were phosphorylated in the presence of [γ-(32)P]ATP and Mg(2+) alone. Addition of Ca(2+) alone to the native PSD preparation had little or no effect on phosphorylation. However, upon addition of exogenous calmodulin there was a general increase in background phosphorylation with a statistically significant increase in the phosphorylation of two protein regions: 51,000 and 62,000 M(r). Similar results were also obtained in sonicated or freeze thawed native PSD preparations by addition of Ca(2+) alone without exogenous calmodulin, indicating that the calmodulin in the PSD can activate the kinase present under certain conditions. The calmodulin dependency of the reaction was further strengthened by the observed inhibition of the calmodulin-activatable phosphorylation, but not of the Mg(2+)-dependent activity, by the Ca(2+) chelator, EGTA, which also removes the calmodulin from the structure (26), and by the binding to calmodulin of the antipsychotic drug chlorpromazine in the presence of Ca(2+). In addition, when a calmodulin-deficient PSD preparation was prepared (26), sonicated, and incubated with [γ-(32)P]ATP, Mg(2+) and Ca(2+), one could not induce a Ca(2+)-stimulation of protein kinase activity unless exogenous calmodulin was added back to the system, indicating a reconstitution of calmodulin into the PSD. We have also attempted to identify the two major phosphorylated proteins. Based on SDS polyacrylamide gel electrophoresis, it appears that the major 51,000 M(r) PSD protein is the one that is phosphorylated and not the 51,000 M(r) component of brain intermediate filaments, which is a known PSD contaminant. In addition, papain digestion of the 51,000 M(r) protein revealed multiple phosphorylation sites different from those phosphorylated by the Mg(2+)-dependent kinase(s). Finally, although the calmodulin-activatable protein kinase may phosphorylate proteins I(a) and I(b), the cyclic AMP-dependent protein kinase, which definitely does phosphorylate protein I(a) and I(b) and is present in the PSD, does not phosphorylate the 51,000 and 62,000 M(r) proteins, because specific inhibition of this kinase has no effect on the levels of the phosphorylation of these latter two proteins.     

Structure of rapidly frozen gap junctions

The structure of gap junctions in the rabbit ciliary epithelium, corneal endothelium, and mouse stomach and liver was studied with the freeze-fracturing technique after rapid freezing to near 4 degrees K from the living state. In the ciliary epithelium, the connexons were randomly distributed, separated by smooth membrane matrix. In the corneal endothelium, both random and crystalline arrangements of the connexons were observed. In the stomach and liver, the connexons were packed but not crystalline. Experimental anoxia or lowered pH caused crystallization of the connexons within 20-30 min. In the ciliary epithelium, the effects of prolonged anoxia or low pH could not be reversed . In addition, invaginated or annular gap junctions increased in number, but their connexons were usually distributed at random. Rapid freezing thus demonstrates that gap junctions of different tissues are highly pleiomorphic in the living state, and this may explain their variations in structure after chemical fixation. The slow time-course and irreversibility of the morphological changes induced by prolonged anoxia or low pH suggest that connexon crystallization may be a long-term consequence rather than the morphological correlate of the switch to high resistance.     

Electron microscopic study of the origin and formation of Reissner's fiber in the subcommissural organ of Cebus apella (Primates,Platyrrhini)

Summary Two kinds of secretion are formed in cells of the subcommissural organ (SCO) of Cebus apella. The light secretion is found in saccules originating from the endoplasmic reticulum. This secretion is stored in the peripheral portion of the cells and is not involved in formation of Reissner's fiber (RF). In close association with the Golgi complex, electron-dense granules are developed, containing a finely granular substance. These granules accumulate beneath the apical plasmalemma of the cell. Their content is discharged into the third ventricle, where it occurs in the form of a thin layer of secretion. This material appears to constitute the RF at the level of the entrance to the mesencephalic aqueduct.     

The interactions between indomethacin and cytotoxic drugs in mice bearing B-16 melanomas

We have compared the effects of indomethacin alone (100 μg/mouse/day) with those of indomethacin plus adriamycin, 5-FU, nitrogen mustard, thioTEPA, and vincristine on B-16 tumor cell proliferation in vivo. As we have previously descriged, after four days of treatment with indomethacin, subcutaneous tumors were slightly smaller and lighter in weight, but contained $\text{more}$ melanoma cells. Addition of indomethacin to cytotoxic regimens resulted in either no change or a decrease in the effectiveness of the chemotherapy. In previous studies we demonstrated that treatment of tumor-bearing mice with a long-acting synthetic analogue of PGE₂ (di-M-PGE₂) stimulated the synthesis of endogenous prostaglandins. In order to evaluate if these endogenously synthesized prostaglandins were responsible for the inhibition of B-16 growth in vivo, mice were treated with di-M-PGE₂ or di-M-PGE₂ plus indomethacin. Addition of indomethacin did not alter the tumor inhibitory effects of di-M-PGE₂.