Regulation of potassium conductance in the cellular membrane at early embryogenesis.

At the early stages of development of the fresh water fish loach (Misgurnus fossilis) the resting membrane potential (Er) of cleaving cells oscillates periodically with an amplitude of 8-12 mV. Er oscillation correlates with the cell cycle and is accompanied by changes of K+ conductivity. Two types of K(+)-selective ionic channels with conductance of approximately 70 and 25 pS in symmetrical (150 mM KCl) solution were observed in the membrane of cleaving loach embryos. 'High' conductance and 'low' conductance channels were recorded in approximately 90% and 10% of patches investigated (n = 275), respectively? The activity of 'high' conductance channels was regulated by the application of pressure to the membrane, ie these channels were stretch-activated (SA). The activity of SA channels changes dramatically during the cell-cleavage cycle. At the beginning of interphase the probability of SA channels being in the open state (P0) was minimal, while at prometaphase the probability was increased 10-100-fold. Application of ATP to the cytoplasmic inside-out patches induced a reversible elevation of stretch sensitivity of the SA channels in 50% of the patches, while the non-hydrolyzable analogue of ATP was not effective. Combined application of ATP, cAMP and cAMP-dependent protein kinase (PK) induced a reversible elevation in the SA channel activity while inhibitors of PK prevented its activating effects. Phosphatase inhibitors prolonged the activating effect of PK on SA channels. We propose that oscillations of the resting potential during the cell-cleavage cycle arise due to modulation of SA channel sensitivity to stretch through cAMP-dependent phosphorylation.     

Affinity thermoprecipitation of trypsin using soybean trypsin inhibitor conjugated with a thermo-reactive polymer,poly(N-vinyl caprolactam)

The soybean trypsin inhibitor conjugate with a thermo-reactive water soluble polymer, poly(N-vinyl caprolactam), was successfully used for thermally induced affinity precipitation of trypsin. The validity of the developed procedure was proven by a model separation of trypsin from dilute solution containing a large excess of bovine serum albumin.     

Nonuniform size distribution of nascent globin peptides, evidence for pause localization sites, and a cotranslational protein-folding model

Examination of nascent globin peptides accumulatingin vitro during globin synthesis in rabbit reticulocyte lysates was carried out. A view was supported that nonrandom distribution of codons with different usage frequencies in mRNA may determine the messenger's translation kinetics. Regions of reduced translation of - and -globin polypeptide chains were localized, and the cotranslational protein-folding model suggested previously was substantiated. An active conjunction of synthesis and folding of proteins was proposed as one of the main destinations of a translation nonuniformity.     

A clonal derivative of mammary epithelial cell line COMMA-D retains stem cell characteristics of unique morphological and functional heterogeneity

The COMMA-D cell line derived from mammary epithelial cells of midpregnant mice was shown previously to be heterogeneous as determined by phase-contrast microscopy, immunocytochemical staining, DNA content, and oncogenic potential (K.D. Danielson et al. (1984) Proc. Natl. Acad. Sci. USA 81, 3756; D. Medina et al. (1986) J. Natl. Cancer Inst. 76, 1143). Clonal subpopulations of COMMA-D cells have now been isolated by both transfection and selection using a dominant-selectable gene transfer vector and by limiting dilution. Despite their clonal origin, these subpopulations in many cases retained the heterogeneity of the parental COMMA-D line. Of 18 clonal lines assayed, only 5 were able to express beta-casein mRNA. Pooled populations of G418-resistant cells expressed substantially higher levels of beta-casein mRNA than the clonal lines. One of the expressing clonal lines, BNW-7, was characterized further, using immunocytochemical techniques. Approximately 10% of BNW-7 cells expressed casein under the appropriate hormonal and cell-substratum conditions by indirect immunofluorescent staining. Casein immunoperoxidase staining of BNW-7 cells on floating collagen gels revealed that casein-producing cells were localized in small alveolar structures, which were formed in a non-hormone-dependent fashion. The cells in these alveolar structures were cuboidal with basally located nuclei, expressed keratin intermediate filament proteins preferentially, and comprised approximately 18% of the total cells. Cells elsewhere on the surface of the gel displayed a flattened morphology, and expressed vimentin intermediate filament proteins preferentially. A proportion of COMMA-D cells, therefore, appeared to have some of the characteristics of mammary stem cells, and retained the ability to differentiate and form phenotypically heterogeneous cell populations in vitro.     

Redescription of Scapholeberis echinulata Sars 1903 (Crustacea,Cladocera)

Scapholeberis echinulata Sars is rediscribed, based on type material of Sars (S. echinulata), Daday (s. erinaceus) and the author's own samples. A differential diagnosis with Scapholeberis spinifera Nicolet and S. mucronata O. F. Müller, S. microcephala Sars, S. kingi Sars and S. aurita Fischer is given.     

Heterogeneity of Benzodiazepine Receptors: Experimental Differences Between [3H]Flunitrazepam and [3H]Ethyl-β-carboline-3-carboxylate Binding Sites in Rat Brain Membranes

Abstract: This study was designed to analyze possible differences in the binding of [³H]flunitrazepam ([³H]FNZP) and [³H]ethyl - β - carboline - 3 - carboxylate ([³H]β-CCE), to rat brain membranes, in various experimental conditions. In cerebral cortex, hippocampus, cerebellum, and orain stem the number of binding sites for [³H]β-CCE was higher than for [³H]FNZP; both were displaced by clonazepam. Until the 7th day of postnatal brain development the numbers of [³H]FNZP and [³H]β-CCE sites were equivalent; but later on, the β-carboline sites increased to a higher level. Noradrenergic denervation by 6-hydroxydopamine was followed in the hippocampal formation. Already after 2 days, there was a decrease in [³H]FNZP sites, which reached 70% of control after 14 days. Similar results were obtained with DSP-4 denervation. This change was only in B_max and not in K_D, In contrast, the [³H]β-CCE sites did not change with denervation. Neonatal injection of l - 2,4,5 - trihydroxyphenylalamine or DSP-4 produced in the adult a decrease in [³H]FNZP sites in the cerebral cortex, in parallel with the noradrenergic denervation. On the other hand, there was an increase in the cerebellum and brain stem, in correspondence with the hyperinnervation by sprouting. In these rats, the number of sites for [³H]β-CCE did not change in the different brain regions. With 0.1% Triton X-100, applied to synaptosomal membranes, [³H]FNZP binding was reduced by 35%, while that of [³H]β-CCE was not significantly changed. These results suggest that there is heterogeneity of binding sites for benzodiazepine receptors in rat brain. A tentative interpretation of the experiments involving noradrenergic denervation and hyperinnervation, as well as those with Triton X-100, is that [³H]FNZP binds to pre- and postsynaptic receptors, while [³H]β-CCE binds mainly to postsynaptic benzodiazepine receptors.     

Stage specificity of selenium-mediated inhibition of mouse mammary tumorigenesis

The experiments reported herein examined the inhibitory role of selenium in chemical carcinogen-induced mouse mammary tumorigenesis. The results from four different experiments are presented herein and are summarized briefly. First, the results demonstrated that relatively low doses of dietary selenium (0.5–2.0 ppm) inhibited 7,12-dimethylbenzanthracene (DBMA)-induced mouse mammary tumorigenesis. At 2 ppm Se, the mammary tumor incidence was reduced from 56 to 15%. Second, the results suggested that the later stages of mammary tumorigenesis (preneoplastic to neoplastic transformation and tumor growth) are not as sensitive to selenium-mediated inhibition as the early stages, i.e., the induction and/or expression of mammary preneoplastic lesions. Finally, the results demonstrated that selenium markedly inhibited mammary tumorigenesis (from 42 to 8%) even when the mice were exposed to selenium only after the carcinogen treatments had been concluded. The results from these experiments are discussed from the viewpoint that selenium-mediated inhibition is a result of a direct block of DNA synthesis.     

Regulation of lipogenesis in vivo by glucose availability and insulin secretion in maternal and foetal tissues during late gestation in the rat. Effect of glucose intubation, streptozotocin-induced diabetes and starvation.

Administration of an oral load of glucose did not change the rate of lipogenesis in maternal liver during late gestation. However, streptozotocin-induced diabetes or starvation decreased maternal liver lipogenesis at 20-22 days of gestation. Glucose intubation, on the other hand, increased foetal lipogenesis at 21-22 days. In addition, maternal starvation decreased foetal lipogenesis and plasma insulin concentration. However, chronic hyperglycaemia induced by streptozotocin administration to the mother did not change foetal liver lipogenesis.     

The Avoidance Response in Phycomyces

Phycomyces sporangiophores grow away from stationary objects, a phenomenon known as the avoidance response. Evidence is presented suggesting that a growth-stimulating gas is emitted from the sporangiophore and is then swept to the leeward side by air currents resulting in higher gas concentration on that side. The presence of a stationary barrier decreases the passive movement of the gas away from the leeward side. It is proposed that an increase of this gas on one side causes that side to grow faster. Indirect evidence suggests that the gas is water vapor.