Quantitative studies of the rate of insulin internalization in isolated rat hepatocytes.

We studied internalization of 125I-labelled insulin in isolated rat hepatocytes. Using the acidification technique, we were able to dissociate the ligand from its cell-surface receptors, and thus to separate internalized from surface-bound insulin. Because during the first 5 min of incubation of 125I-labelled insulin with freshly isolated hepatocytes there is no loss of internalized label, the ratio of the amount of internalized ligand to the amount of cell-surface-bound ligand may serve as an index of insulin internalization. Within the first 10 min of insulin's interaction with hepatocytes, the plot of the above ratio as a function of time yields a straight line. The slope of this line is referred to as the endocytic rate constant (Ke) for insulin and denotes the probability with which the insulin-receptor complex is internalized in 1 min. At the insulin concentration of 0.295 ng/ml, the Ke is 0.049 min-1. It is independent of insulin concentration until the latter exceeds 1 ng/ml. At the insulin concentration of 3.2 ng/ml, the Ke accelerates to 0.131 min-1. With the Ke being the probability of insulin-receptor-complex internalization, 4.9% of occupied insulin receptors will be internalized in 1 min at an insulin concentration of 0.295 ng/ml, and 13.1% of occupied insulin receptors will be internalized in 1 min at 3.2 ng/ml. When the insulin concentration decreases from 3.2 to 0.3 ng/ml, the Ke decreases accordingly. The half-time of occupied receptor internalization is 15.4 min at the lower insulin concentration and 5.3 min at the higher insulin concentration.     

Outcomes and indications of corpus callosum section for intractable seizure control

Callosotomy (CCS) was performed in 9 cases of rigorously classified drug-refractory epilepsy not eligible for focal cortical resection. Complete CCS was carried out in two stages in 8 patients. 1 case had an anterior CCS only. None of the 9 patients has become seizure free. In 7, seizure frequency has diminished by a factor of 3-60 for at least one seizure type. Drop attacks in 2 cases have ceased. Clinical seizure patterns appeared more helpful in predicting outcome than preoperative EEG and stereoelectroencephalographic studies. Complete CCS may result in prolonged behavioral disturbances in the areas of language, hemisphere competition and attention-memory sequencing with impact on the sphere of daily living.     

Loss processes in the population dynamics of phytoplankton maintained in closed systems

Rates of loss sustained by selected populations of natural phytoplanktonhusbanded in large limnetic enclosures ("Lund Tubes") are derived,in terms of specific biomass units (cells or colonies), fromdirect measurements of the rates of net increase, of sedimentationand zooplankton filtration, corrected for selectivity ("grazing").Partitioning between the losses was found to vary interspecificallybetween almost complete removal by grazers (in the case of nanoplankton)and almost complete elimination by sinking (in the case of somediatom populations). These differences are argued to be criticalin influencing the specific composition of the phytoplanktonand its seasonal dominance. A model simulating the dynamicsof three species experiencing differential loss rates is employedto demonstrate the outcome of interspecific competition. Evidencecontrary to the widely-held contentions that zooplankton controlsphytoplankton biomass and that blue-green algae (cyano-bacteria)dominate by virtue of being "ungrazed" is discussed. ¹Present address: Anglian Water Authority, Oundle, Peterborough,PE8 4AS, UK     

Modulation of the epidermal growth factor receptor of mouse embryonic palatal mesenchyme cells in vitro by growth factors.

A single class of high-affinity receptors for EGF were detected on mouse embryonic palatal mesenchyme (MEPM) cells cultured in vitro. The degree of confluence of the cultured cells did not affect the number or affinity of the binding sites. Culture of MEPM cells in the presence of bFGF, IGF-II or TGF-beta 1 induced changes in 125I-EGF binding. TGF-beta 1 caused a marked reduction in binding to 40% of control levels. This reduction was achieved after 2 h and persisted for 24 h after addition of the growth factor. IGF-II induced a similar reduction but this effect was transitory; after a 12 h pretreatment with IGF-II, binding was restored to control levels. The effects of bFGF were biphasic. Initially, a short pre-treatment period (3-5 h) with bFGF caused a small reduction in 125I-EGF binding; longer periods of pre-incubation (24 h) resulted in a large increase in receptor number. Pre-incubation in medium containing both bFGF and TGF-beta 1 resulted in a decrease in EGF binding. Thus, TGF-beta 1 negated the large increase in receptor number induced by bFGF alone. Changes in receptor number were usually, but not always, directly related to changes in the biological activity of EGF, as assessed by a thymidine incorporation assay. This study highlights the possible interactive role of growth factors known to be present in the developing palate.     

Changes in the extracellular matrix of the normal human breast during the menstrual cycle

Summary The normal human mammary gland undergoes a well defined sequence of histological changes in both epithelial and stromal compartments during the menstrual cycle. Studies in vitro have suggested that the extracellular matrix surrounding the individual cells plays a central role in modulating a wide variety of cellular events, including proliferation, differentiation and gene expression. We therefore investigated the distribution of a number of extracellular matrix molecules in the normal breast during the menstrual cycle. By use of indirect immunofluorescence, with specific antibodies, we demonstrated that laminin, heparan sulphate proteoglycan, type IV collagen, type V collagen, chondroitin sulphate and fibronectin undergo changes in distribution during the menstrual cycle, whereas collagen types I, III, VI and VII remain unchanged. These changes were most marked in the basement membrane, sub-basement membrane zone and delimiting layer of fibroblasts surrounding the ductules where basement membrane markers such as laminin, heparan sulphate proteoglycan, and type IV and V collagens appear greatly reduced during the mid-cycle period (days 8 to 22). These results suggest that some extracellular matrix molecules may act as medittors in the hormonal control of the mammary gland, whereas others may have a predominantly structural role.     

Inositol is a constituent of detergent-solubilized immunoaffinity-purified rat liver 5''-nucleotidase.

myo-Inositol analysis of detergent-solubilized immunoaffinity-purified rat liver 5'-nucleotidase showed the presence of 1 mol of myo-inositol/mol of enzyme monomer. This provides unequivocal evidence that the ectoenzyme 5'-nucleotidase is attached to liver membranes by a glycosyl-phosphatidylinositol lipid anchor.     

Precipitins to Dietary Proteins in Serum and Upper Intestinal Secretions of Coeliac Children

We have used precipitin tests to detect antibodies to 10 dietary proteins in the serum (71 cases) and intestinal secretions (51 cases) of a group of children. Thirty-three of the patients had untreated coeliac disease. Our aims were to find out if, in coeliac patients, there was intestinal secretion of antibodies to wheat proteins only or if, as in coeliac serum, antibodies to many food proteins were present; and to confirm that secretion of antibodies to wheat or gluten was specific for coeliac disease.Precipitins to one or more dietary antigens were detected in the intestinal secretions of 26 out of 30 coeliacs and of 11 out of 21 children who did not have coeliac disease. Most of the positive reactions were with the antigens wheat flour, gluten, oatmeal, and egg. Though precipitins to wheat flour or gluten were present in the intestinal secretions of 22 out of 30 coeliacs this was not specific for coeliac disease for these precipitins were also present in 8 out of 21 non-coeliac children.Serum precipitins were detected in 27 out of 33 coeliacs (to the antigens wheat flour, gluten, oatmeal, rice flour, milk, bovine calf serum, sheep serum, and egg) and in 5 out of 33 non-coeliacs (mainly to milk and calf serum, but two infants aged 3 and 5 months had precipitins to several antigens).     

Myoglobin polymorphism in the pollan (Osteichthyes: Coregoninae).

Three electrophoretically separable phenotypes of heart and lateral line muscle myoglobin were found in the Irish pollan (Coregonus pollan). This polymorphism appears to be under the control of two co-dominant alleles. The allele frequencies were found to be virtually identical in samples from two lakes which have probably been isolated since the close of the last Ice Age. A significant excess of heterozygotes was found in samples from both lakes. This myoglobin polymorphism appears to be balanced, maintained due to heterozygote superiority.