Lys-bradykinin stimulates Na+ influx and DNA synthesis in cultured human fibroblasts

The effect of Lys-bradykinin on net Na+ influx in serum-deprived cultured human fibroblasts (HSWP cells) was measured. It was found that Lys-bradykinin stimulates net Na+ influx with a K1/2 of 1 nM. When Lys-bradykinin was combined with epidermal growth factor, vasopressin and insulin, the net Na+ influx stimulated was comparable with that measured in response to 10% serum. The above combination of growth factors also was found to stimulate DNA synthesis to 92% of the serum-stimulated levels in HSWP cells and to support cell growth over a period of 6 days. In addition, it was observed that the Na+ influx stimulated by Lys-bradykinin or by the combination of four growth factors was completely inhibited by the amiloride analog benzamil. Thus Lys-bradykinin presumably stimulates the same Na+ transport system as is stimulated by serum. Finally, the present results suggest that an increase in Na+ influx always accompanies DNA synthesis in HSWP cells. On the basis of these observations, it can be hypothesized that Na+ influx is a necessary event to stimulate DNA synthesis.     

Differentiation between strains ofFlavobacterium breve and allied bacteria by comparisons of deoxyribonucleic acids

Chromosomal deoxyribonucleic acid was isolated and purified from 10 strains ofFlavobacterium breve, originating from human or other animal sources. The mean and standard deviation for the species in base content was 32.4±0.6% G+C, and in genome size was 3.21±0.37×10⁹ daltons. In vitro DNA reassociation showed that sevenF. breve strains (mainly from human sources) had high levels of intraspecific base sequence similarity (>70%) as derived from reassociations done at the optimum temperature of reassociation (TOR) or TOR—10°C (nonstringent conditions). The three otherF. breve strains contained a high degree of base sequence divergence. All 10 strains ofF. breve were readily distinguishable in their DNA characteristics fromF. meningosepticum, F. odoratum, and allied Gram-negative bacteria.     

Host recognition in the Rhizobium-soybean symbiosis

Polar binding of Rhizobium japonicum to roots and root hairs of Glycine soja (L.) Sieb. and Zucc. is specifically inhibited by d-galactose and N-acetyl-d-galactosamine, haptens of Glycine max seed lectin. A protein, immunologically cross-reactive with the G. max seed lectin, is present in G. soja seed extracts. Peptide mapping of the purified G. max and G. soja lectins indicates that the two are similar in structure. Soybean lectin can be localized on the surface of both G. max and G. soja roots by indirect immunolatex techniques. These observations indicate that the Rhizobium-binding lectin, previously isolated from seeds, also is present on the root surface-the site of the initial steps in the infection. This lectin is capable of binding Rhizobium japonicum to the root.     

Albumin associated with purified pig lymphocyte plasma membrane.

Plasma-membrane preparations purified from pig lymphocytes contained a major polypeptide component of mol.wt. about 68 000. This component was identified as pig albumin by the following comparisons with authentic pig serum albumin: (a) co-migration when analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis under reducing and non-reducing conditions; (b) identical isoelectric points; (c) similar "fingerprints" of arginine-containing tryptic peptides; (d) reactivity with anti-(pig albumin) serum. The albumin was bound tightly to the plasma membrane. Biosynthetic labelling of pig lymphocytes under a variety of conditions failed to provide evidence that albumin was synthesized by lymphocytes, suggesting that the plasma-membrane-associated albumin was of extraneous origin. Radiolabelled pig serum albumin, however, failed to bind to the plasma-membrane fraction when added before cell disruption. Although lymphocyte plasma membrane preparations from other species possessed a polypeptide of about 68 000 mol.wt., this was judged not to be albumin on the basis of electrophoretic mobility under non-reducing conditions; also, no polypeptide was precipitated by anti-albumin sera. It is concluded that pig lymphocyte plasma-membrane preparations possess albumin which, although firmly attached, was probably of extraneous origin. This association appeared not to be common to lymphocytes from other species.     

Ecological aspects of polymorphism in an African land snail, Limicolaria martensiana

In Uganda the herbivorous land snail, Limicolaria martensiana occurs in well-defined populations. Samples of snails from 49 populations reveal the existence of five distinct colour forms, the frequency of which varies markedly from population to population. There is a common streaked form that occurs in all populations and a series of pallid forms that may be present or absent. Late Pleistocene fossils from the Western Rift indicate that the polymorphism is at least 8000–10,000 years old. The polymorphism is not correlated with broad geographical components of the environment or with habitat. It is however correlated with population density, and in one population a change in density resulted in a change in the relative frequency of the colour forms. Human activities have probably contributed to the dispersal of the snails to new areas, and because of these the founder effect cannot be ruled out as contributing to the polymorphism.     

Peroxisomes in the digestive diverticula of the bivalve mollusc Nucula sulcata

Summary Electron microscopy of the digestive diverticula of the protobranch bivalve, Nucula sulcata, revealed the presence of peroxisomes in the basal regions of the epithelial cells lining the main and secondary ducts, and in the digestive and secretory (basophil) cells of the tubules. Those in the secretory cells are elongate and somewhat flattened, while those of the other cell types have a spherical form. Two distinct types of nucleoid are normally present within the secretory cell peroxisomes, one compact, crystalline, and finely polytubular, the other comprising isolated secondary tubules arranged in a linear series across the width of the organelle. The peroxisomes of the digestive and duct cells contain coarsely polytubular cores arranged in two clusters orientated more or less at right angles; the duct cell peroxisomes may also contain a second nucleoid in the form of a compact finely polytubular core. Sections incubated in a medium containing 3,3'-diaminobenzidine (DAB) and hydrogen peroxide reveal an electron dense reaction product within the peroxisomes of all the cell types. Catalase is considered to be responsible for the reaction.     

Relationship between plasma and muscle concentrations of ketone bodies and free fatty acids in fed, starved and alloxan-diabetic states

1. Concentrations of ketone bodies, free fatty acids and chloride in fed, 24–120h-starved and alloxan-diabetic rats were determined in plasma and striated muscle. Plasma glucose concentrations were also measured in these groups of animals. 2. Intracellular metabolite concentrations were calculated by using chloride as an endogenous marker of extracellular space. 3. The mean intracellular ketone-body concentrations (±s.e.m.) were 0.17±0.02, 0.76±0.11 and 2.82±0.50μmol/ml of water in fed, 48h-starved and alloxan-diabetic rats, respectively. Mean (intracellular water concentration)/(plasma water concentration) ratios were 0.47, 0.30 and 0.32 in fed, 48h-starved and alloxan-diabetic rats respectively. The relationship between ketone-body concentrations in the plasma and intracellular compartments appeared to follow an asymptotic pattern. 4. Only intracellular 3-hydroxybutyrate concentrations rose during starvation whereas concentrations of both 3-hydroxybutyrate and acetoacetate were elevated in the alloxan-diabetic state. 5. During starvation plasma glucose concentrations were lowest at 48h, and increased with further starvation. 6. There was no significant difference in the muscle intracellular free fatty acid concentrations of fed, starved and alloxan-diabetic rats. Mean free fatty acid intramuscular concentrations (±s.e.m.) were 0.81±0.08, 0.98±0.21 and 0.91±0.10μmol/ml in fed, 48h-starved and alloxan-diabetic states. 7. The intracellular ketosis of starvation and the stability of free fatty acid intracellular concentrations suggests that neither muscle membrane permeability nor concentrations of free fatty acids per se are major factors in limiting ketone-body oxidation in these states.     

Control of mitochondrial respiration by the phosphate potential

The rate of respiration of suspensions of mitochondria in the presence of excess oxygen and substrate is shown to be dependent on the ratio of the concentration of adenosine triphosphate (ATP) to the product of the concentrations of adenosine diphosphate and orthophosphate. The mitochondrial respiratory chain is essentially in equilibrium with the reactions for ATP synthesis. The rate of mitochondrial respiration is controlled by the free energy requirement for ATP synthesis and this control is expressed on the rates of the reactions for reduction of the dehydrogenases by substrate and the oxidation of cytochrome $\text{a}{}_3$ by molecular oxygen.     

CELL POPULATION KINETICS OF AN OSTEOGENIC TISSUE · II

A study of the cell kinetics on the actively growing periosteal surface of the femur of rabbits aged 2 weeks has been continued. A single injection of tritiated thymidine was given and the rabbits killed from 1 hour to 4 days after injection. The grain count spectra of the different cell types, pre-osteoblast, osteoblast, and osteocyte, have been compared at different times after injection. The results showed evidence for the uptake of thymidine in nuclei which is not associated with cell division. A small percentage of osteoblasts was initially labeled at 1 hour and there was evidence that the majority of these had not divided by 3 or 4 days after injection. Some thymidine-labeled cells had also become osteocytes without division. Furthermore, it appeared that a considerable fraction of the initially labeled pre-osteoblasts did not divide. The S period for the pre-osteoblasts and osteoblasts was measured using a double-labeled thymidine technique.