The quantity and quality of overwintered larvae in five species of Myrmica (Hymenoptera: Formicidae)

The numbers of queens, workers and larvae were recorded for a sample of hibernating colonies from five different species of Myrmica. The larvae were divided into three size classes. The frequencies and distribution of larvae within these size classes have been compared between species and between queened and queenless colonies. A sample of each larval class was reared to the pupal stage and the resulting castes were recorded. The Discussion compares all the species with Myrmica rubra and attempts to explain the differences observed for the different species.     

Interactions of lanthanum with purified and intact cell acetylcholinesterase of electrophorus electricus

Summary The effects of lanthanum on the activity of purified preparations of acetylcholinesterase (AChE) from the electric organ ofE. electricus and on the activity of AChE in intact electro-plaques from the same species were studied. 0.1mm LaCl₃ produced an initial inhibition of purified AChE which was followed by a delayed activation of the enzyme. Upon pretreatment of purified enzyme with LaCl₃, initial activity was markedly increased. LaCl₃ exerted a marked, concentration-dependent inhibition of intact cell AChE.La³⁺ and Ca²⁺ appear to interact competitively. In the presence of both 10mm CaCl₂ and 0.1mm LaCl₃, the initial activity of purified AChE was increased at lower ACh concentrations and inhibited at ACh concentrations greater than 3 × 10^–4 m. Inhibition of intact cell enzyme by 0.1mm LaCl₃ was relieved by increasing the CaCl₂ concentration to 10mm at ACh concentrations less than 2 × 10^–4 m.The data were analyzed assuming Michaelis-Menten kinetics and interpreted with reference to the differential binding of divalent and trivalent cations to regulatory anionic sites which are separate and distinct from the anionic site of the active center of the enzyme.     

Receptor-mediated phagocytosis of zymosan is unaffected by some conditions which reduce macrophage lysosomal enzyme secretion

We have previously shown that several agents which interfere with binding of ligands to the mannose-glycoprotein receptor on macrophages can inhibit zymosan-induced lysosomal enzyme secretion. Here we show that mannose only reduces the association of zymosan with macrophages during the first hour of exposure; after longer periods of uptake no effect is detectable. We have previously shown that mannose reduces surface binding of zymosan, probably by interfering selectively with binding to the mannose receptor. The present inhibition of association of zymosan with macrophages during short exposures can be entirely explained by this reduction of binding. Macrophages must therefore internalize zymosan at sites in addition to the mannose receptor. In contrast to macrophages the murine macrophage-like cell line P388D1 is lacking the mannose-glycoprotein receptor. Accordingly we find that binding of zymosan to P388D1 is much slighter than to macrophages and is unaffected by mannose or mannose-6-phosphate. The spontaneous lysosomal enzyme secretion of P388D1 is also unaffected by mannose. The data on macrophages confirm our previous suggestion that agents interfering with the mannose receptor inhibit the induction of lysosomal enzyme secretion by acting directly on the receptor. The data on P388D1 cells support this assertion by excluding effects at later steps in the secretory pathway.     

Development and characterization of monoclonal antibodies to human type III procollagen

Hybridomas which secrete monoclonal antibodies against human type III procollagen have been developed. By an enzyme-linked immunosorbent assay, three of the monoclonal antibodies have been determined to be against non-helical extensions of the molecules while two of the antibodies are against helical portion of the molecules which is sensitive to bacterial collagenase action. These findings have been further confirmed by carrying out immuno-reaction of the pro α-chains transferred on nitrocellulose paper from sodium dodecyl sulfate polyacrylamide gels. These monoclonal antibodies have been found to be suitable reagents for immunohistochemical studies as well as for immunoassays of type III procollagen and collagen.     

The effect of temperature, water activity and sorbic acid on ketone rancidity produced by Penicillium crustosum Thom in coconut and palm kernel oils

In a model system medium-chain fatty acids (MCFA) C₆–C₁₂ in coconut and palm kernel oil are converted to methyl ketones, one carbon atom less than the parent fatty acids, by two strains of Penicillium crustosum Thom. Conversion rates of up to 32% were seen for decanoic acid at 25°C. The optimum temperature for ketone production was 25°C in liquid suspension culture. Coconut oil contains 3.23 mmol/g MCFAs compared with 2.34 mmol/g for palm kernel oil. Coconut oil is more prone to fungal spoilage (growth and ketone production) than palm kernel oil. The main end product of fermentation was 2-undecanone reflecting the high concentration of dodecanoic acid in the substrates. Ketonic rancidity is fungal engendered. The reaction can be controlled by reducing the temperature (4°C), reducing the water activity (0.91) or by addition of sorbic acid (20 mmol/l).     

Sex Determination in Caenorhabditis elegans

In Caenorhabditis elegans, the decision to develop as a hermaphrodite or male is controlled by a cascade of regulatory genes. These genes and other tissue-specific regulatory genes also control sexual fate in the hermaphrodite germline, which makes sperm first and then oocytes. In this review, we summarize the genetic and molecular characterization of these genes and speculate how they mutually interact to specify sexual fate.     

Thidiazuron stimulates shoot organogenesis and somatic embryogenesis in white ash (Fraxinus americana L.)

Immature and mature nonstratified seeds of white ash (Fraxinus americana L.) were dissected transversely and 2/3 of each seed was placed onto agar-solidified Murashige and Skoog medium. Adventitious buds, shoots, and somatic embryos formed on callus, cotyledons, and hypocotyls of the resulting seedlings. Shoot organogenesis was induced on explants cultured on medium with 10 M thidiazuron but not on explants on media with benzyladenine (BA) or isopentenyladenine. Not all seed sources were equally capable of shoot organogenesis and embryogenesis. Atypical of adventitious regeneration of other woody plants, mature seed explants of white ash were more organogenic with shoots that elongated better than explants from immature seeds. Somatic embryogenesis was observed in cultures where mature seeds were first cultured for 4 weeks on a medium containing 10 M adenine 2,4-dichlorophenoxyacetic acid in combination with 0.1 and 1.0 M thidiazuron, followed by transfer to a medium containing 0.05 M 6-benzyladenine and 0.5 M naphthaleneacetic acid. Adventitious shoots and epicotyls from both seedlings and germinated somatic embryos were rooted under intermittent mist and acclimatized to the greenhouse.Abbreviations BA 6-benzyladenine - 2,4-d 2,4-dichlorophenoxyacetic acid - IBA indolebutyric acid - 2iP isopentenyladenine - NAA naphthaleneacetic acid - TDZ thidiazuron-N-phenyl-N-1,2,3-thiadiazol-5-ylurea - WPM woody plant medium     

Cellular mechanisms of paired electrical stimulation in ferret ventricular myocardium: relationship between myocardial force and stimulus interval change

Summary The subcellular mechanisms of twitch-force potentiation with paired electrical stimulation was studied in ferret ventricular myocardium using the bioluminescent calcium indicator aequorin. It is demonstrated for the first time that interpolation of an extrasystole in a train of conditioned twitches results in a beat-to-beat change in [Ca²⁺]_i and force. Steady-state twitch force and Ca _i ²⁺ were increased with paired stimulation. Increased [Ca²⁺]₀ in the setting of paired stimulation resulted in an increase in the amplitude of the postextrasystole and associated Ca²⁺ transient. Verapamil, a Ca²⁺ channel antagonist, had the opposite effect of increased [Ca²⁺]₀. Postextrasystole potentiation was still present, but diminished in amplitude. These results indicate that postextrasystole potentiation is in part due to a verapamil-depletable store (Ca²⁺). Postextrasystole potentiation is therefore predominantly dependent on sarcoplasmic reticulum (SR) Ca²⁺ loading. Ryanodine, an alkaloid which induces Ca²⁺ leakage from the SR, abolished postextrasystole potentiation; however, in the presence of ryanodine the extrasystole was potentiated. Caffeine, a phosphodiesterase inhibitor which induces SR Ca²⁺ release and impairs uptake, also abolished postextrasystole potentiation. As with ryanodine there was resultant potentiation of the extrasystole. In the case of caffeine the calcium transient consisted of a second slow component associated with extrasystole twitch potentiation. The results are consistent with sarcolemmal Ca²⁺ influx playing a role in potentiation of the extrasystole in the presence of an impaired SR. These data indicate that transsarcolemmal Ca²⁺ influx in the presence of impaired intracellular Ca²⁺ buffering can directly activate the myofilaments in agreement with reports on human myocardium.Abbreviations C conditioned stimulus - ESI extrasystolic interval - L_max active tension - PES postextrasystole - PESI postextrasystolic interval - SR sarcoplasmic reticulum - T test stimulus     

Effects of diphenyl ether herbicides on porphyrin accumulation by cultured hepatocytes

Several diphenyl ether herbicides, such as acifluorfen methyl, have been previously shown to cause large accumulations of the heme and chlorophyll precursor, protoporphyrin, in plants. Lightinduced herbicidal damage is mediated by the photoactive porphyrin. Here we investigate whether diphenyl ether herbicides can affect porphyrin synthesis in rat and chick hepatocytes. In rat hepatocyte cultures, protoporphyrin, as well as coproporphyrin, accumulated after treatment with acifluorfen or acifluorfen methyl. Combination of acifluorfen methyl with an esterase inhibitor to prevent the conversion of acifluorfen methyl to acifluorfen resulted in a greater accumulation of porphyrins than caused by acifluorfen methyl or acifluorfen alone. In vitro enzyme studies of hepatic mitochondria isolated from rat and chick embryos demonstrated that protopor-phyrinogen oxidase, the penultimate enzyme of heme biosynthesis, was inhibited by low concentrations of acifluorfen, nitrofen, or acifluorfen methyl with the latter being the most potent inhibitor. These findings indicate that diphenyl ether treatment can cause protoporphyrin accumulation in rat hepatocyte cultures and suggest that this accumulation was associated with the inhibition of protoporphyrinogen oxidase. In cultured chick embryo hepatocytes, treatment with acifluorfen methyl plus an esterase inhibitor caused massive accumulation of uroporphyrin rather than protoporphyrin or coproporphyrin. Specific isozymes of cytochrome P450 were also induced in chick embryo hepatocytes. These effects were not observed in the absence of an esterase inhibitor. These results suggest that diphenyl ether herbicides can cause uroporphyrin accumulation similar to that induced by other cytochrome P450-inducing chemicals such as polyhalogenated aromatic hydrocarbons in the chick hepatocyte system.