Glucagon Affinity Absorbents: Selective Binding of Receptors of Liver Cell Membranes

AFFINITY chromatography has been used in the rapid isolation of enzymes, antibodies, antigens and other ligand-binding proteins^1–6. Selective adsorbents with biological specificity perhaps may best be used in the resolution and isolation of complex biological structures and important regulatory macromolecules present in cells in very low amounts. For example, polypeptide and steroid hormone receptors, drug receptors, transport proteins and repressor molecules may be well suited for study by this technique because they display specific binding functions with a high degree of affinity.     

THE INFLUENCE OF INGESTIVE CONDITIONING ON FOOD CHOICES IN THE LAND SNAIL HELIX ASPERSAMULLER (GASTROPODA: PULMONATA: STYLOMMATOPHORA)

An experiment of food choice in one-day-old naïve landsnail Helix aspersa Müller was carried out, involving threephases. First, a training period on a monophagous diet of leafdiscs of Taraxacum officinale or Urtica dioica was given for1, 5, 10, 15 or 30 days. The area of leaf discs consumed byeach snail during this stage was assessed. In the intermediatephase, the animals were not fed for 24hours. Finally, food choicewas tested over 24 hours, when animals could eat leaf discsof each species of plant usedfor training. A coefficient offood preference for Urtica dioica was calculated (UPC = areaof Vrtica leaf disc consumed/area of Urtica and Taraxacum discsof leaves consumed for 24 hours). The length of the training phase did not reduce the percentageof individuals preferring the plant previously consumed. Onthe contrary, after 15 days of monophagous diet, animals formerlyfed on Urtica showed a coefficient of food preference for Urticasignificantly higher than Taraxacum fed animals, and after 30days of training this phenomenon was more pronounced. Thus,during the choice test, snails ate more of the previously eatenplant leaf. Our experiment highlighted the feeding behaviourplasticity of H. aspersa. The significant correlation betweenthe area of Urtica eaten during the training phase and the coefficientof food preference for Urtica is discussed. (Received 10 April 1994; accepted 10 January 1995)     

INFLUENCE OF THE QUINOLIZIDINE ALKALOID CONTENT OF LUPINUS ALBUS (FABACEAE) ON THE FEEDING CHOICE OF HELIX ASPERSA (GASTROPODA: PULMONATA)

Adult Helix aspersa snails were maintained individually forone week in plastic cages with 9 living Lupinus albus plantsas their only food. Among these 9 plants, 3 chemotypes bitter,intermediate and sweet which differed in their alkaloid contentwere equally represented. Each day, the leaf surface grazed and the number of leaves attackedby the snails were recorded for each chemotype and each snail.A consumption/ attack (C/A) ratio was calculated by dividing thesurface grazed (C) by the number of attacks (A). The numberof attacks and the grazed area were positively correlated foreach chemotype during the whole experiment, and the snails atesimilar quantities of lupin each day. After 4 and 6 days ofexperiment, we noticed a rejection of the bitter chemotype infavor of the intermediate and sweet ones respectively. Afterthe 6th day, the surface grazed per attack was significantlyhigher on the sweet chemotype than on the bitter plants. Wehypothesize that rejection of the bitter chemotype might berelated to (i) an alkaloids reaction threshold associated withan increase in the amount of alkaloids in the wounded plantsand/or (ii) aversive ingestive conditioning. (Received ; accepted 16 April 1999)     

Phenotypic plasticity in reproductive traits: importance in the life history of Helix aspersa (Mollusca: Helicidae) in a recently colonized habitat

Reproductive traits of the land snail Helix aspersa Mtiller were investigated under artificial conditions from two samples, one collected from a population exposed to unpredictable human pressures in its natural environment, i.e. a recently created polders area with intensive agriculture, and the other from a snail farm in which animals were reared under constant conditions denned as 'optimal' for growth and reproduction. Results were compared with data collected from natural populations of the same region (Brittany) and from habitats spanning the environmental heterogeneity of the range of the species. A large part of the variation among populations could be explained by different phenotypic covariances between shell size, clutch size and egg size, but not by the number of clutches per snail. Thus, the higher egg production of snails from the polders was related to (i) a strong correlation between clutch size and shell size, shell size being in the upper limit of the overall range for the region concerned; (ii) an uncommonly low egg weight in comparison with the 'norm' of Helix aspersa , this trait seeming to be involved in a trade-off with clutch size. Second clutches were smaller than the first ones, but their eggs were significantly heavier. This difference may be linked to a size-dependent mortality of juveniles during winter which arises in all populations in which hibernation occurs as an adaptation to low temperatures. In addition to the selective regime usually involved for populations of helicid snails from Western Europe, several unpredictable mortality factors occurred in the polders area: herbicide and pesticide treatments (lethal for young snails), human predation (lethal for adults) and burning (letiial for all snails). Life-history patterns of Helix aspersa are discussed in relation to its ability to successfully colonize a large range of habitats modified by humans, to such an extent that it can become a pest.     

Independence of Glucagon Receptors and Glucagon Inactivation in Liver Cell Membranes

THERE is increasing evidence that receptors for polypeptide hormones are localized on the cell membrane. Hormone-receptor interactions have been studied primarily by measuring the bmding of ¹²⁵I-labelled hormones to intact¹ or broken-cell preparations^2–6. Peptide hormones, however, are often inactivated after exposure to the cell extract and numerous enzymes reported as specific hormone-degrading have been described. With some hormones, such as insulin^1,6,7, biologically significant receptor interactions have been demonstrated in the absence of hormone degradation, but with other hormones, such as glucagon, it has not been possible to dissociate the processes of specific receptor binding and of hormone inactivation³, which suggests that these two processes may be functionally or structurally related. Until this question is resolved, it will not be possible to characterize properly the kinetics of the hormone-receptor interaction or to isolate and purify the receptor.     

VARIABILITY OF EGG CANNIBALISM IN THE LAND SNAIL HELIX ASPERSA IN RELATION TO THE NUMBER OF EGGS AVAILABLE AND THE PRESENCE OF SOIL

Egg cannibalism by hatchlings has been demonstrated in somepulmonate land snails; this behaviour is promoted by a highhatching asynchrony within the egg-batch. Under laboratory conditions,the percentage of new-born snails Helix aspersa having cannibalisedunhatched eggs was not influenced by the soil factor: about70% of them ingested one egg within their first four days oflife whether soil was present or not. The propensity to eggcannibalism in hatchlings of H. aspersa increased with egg density.However, most of the new-born hatchlings consumed a single eggduring the four days following hatching, and only exceptionallytwo. The consumption of one egg increased the snails wet weightby 38.7% within four days. A weak ingestion of soil componentsalso occurred, but it induced a growth that was three-timesless than that due to the consumption of an egg. In addition,the survival of newly hatched snails maintained under non-dehydratingthermohygrometric conditions was high, even when they were submittedto four days food-deprivation. (Received 22 July 1999; accepted 24 November 1999)