Overlapping of normal and malignant mouse cells in pure and mixed cultures

Cultured malignant mouse melanoma cells and mouse ascites carcinoma cells, after 24 h incubation with normal mouse cells or with each other, had much higher homologous overlap indices than those recorded from pure cultures of each cell type. The effect was particularly evident in ascites cells. Normal cells of mice of different ages showed varying responses in overlap frequency when incubated with malignant cells. Conditioned medium from each malignant cell type invoked increased overlapping of cells of the heterologous malignant type but did not affect homologous cells. The effects of whole conditioned medium on heterologous malignant cells showed a graded reduction after dilution of the medium and also occurred after dialysis. A dialysable chemical factor or factors, produced by the cells, is postulated.     

Concentrating Engines and the Kidney: II. Multisolute Central Core Systems

The analysis of the central core model of the renal medulla is extended to multisolute systems. It is shown that total solute concentration obeys the same differential equations for core and ascending limb as in a single solute system. Equations are derived for the concentration of individual solutes. Application of these equations to a two solute system shows that a central core system can concentrate with all transport being down a concentration gradient. This analysis applied to the renal medulla shows that mixing of urea from the collecting duct (CD) and salt from the loop of Henle in the central core of the inner medulla contributes to the concentration of urine during antidiuresis. It also sets criteria for completely passive function of the loop in the inner medulla, but whether these are satisfied cannot be determined from present experimental data.     

Volume-activated chloride permeability can mediate cell volume regulation in a mathematical model of a tight epithelium

Cell volume regulation during anisotonic challenge is investigated in a mathematical model of a tight epithelium. The epithelium is represented as compliant cellular and paracellular compartments bounded by mucosal and serosal bathing media. Model variables include the concentrations of Na, K, and Cl, hydrostatic pressure, and electrical potential, and the mass conservation equations have been formulated for both steady-state and time-dependent problems. Ionic conductance is represented by the Goldman constant field equation (Civan, M.M., and R.J. Bookman. 1982. Journal of Membrane Biology. 65:63-80). A basolateral cotransporter of Na, K, and Cl with 1:1:2 stoichiometry (Geck, P., and E. Heinz. 1980. Annals of the New York Academy of Sciences. 341:57-62.) and volume-activated basolateral ion permeabilities are incorporated in the model. MacRobbie and Ussing (1961. Acta Physiologica Scandinavica. 53:348-365.) reported that the cells of frog skin exhibit osmotic swelling followed by a volume regulatory decrease (VRD) when the serosal bath is diluted to half the initial osmolality. Similar regulation is achieved in the model epithelium when both a basolateral cotransporter and a volume-activated Cl permeation path are included. The observed transepithelial potential changes could only be simulated by allowing volume activation of the basolateral K permeation path. The fractional VRD, or shrinkage as percent of initial swelling, is examined as a function of the hypotonic challenge. The fractional VRD increases with increasing osmotic challenge, but eventually declines under the most severe circumstances. This analysis demonstrates that the VRD response depends on the presence of adequate intracellular chloride stores and the volume sensitivity of the chloride channel.     

Comparison of the nucleotide and amino acid sequences of the RsrI and EcoRI restriction endonucleases

The RsrI endonuclease, a type-II restriction endonuclease (ENase) found in Rhodobacter sphaeroides, is an isoschizomer of the EcoRI ENase. A clone containing an 11-kb BamHI fragment was isolated from an R. sphaeroides genomic DNA library by hybridization with synthetic oligodeoxyribonucleotide probes based on the N-terminal amino acid (aa) sequence of RsrI. Extracts of E. coli containing a subclone of the 11-kb fragment display RsrI activity. Nucleotide sequence analysis reveals an 831-bp open reading frame encoding a polypeptide of 277 aa. A 50% identity exists within a 266-aa overlap between the deduced aa sequences of RsrI and EcoRI. Regions of 75-100% aa sequence identity correspond to key structural and functional regions of EcoRI. The type-II ENases have many common properties, and a common origin might have been expected. Nevertheless, this is the first demonstration of aa sequence similarity between ENases produced by different organisms.     

Simplification and analysis of models of calcium dynamics based on IP3-sensitive calcium channel kinetics.

We study the models for calcium (Ca) dynamics developed in earlier studies, in each of which the key component is the kinetics of intracellular inositol-1,4,5-trisphosphate-sensitive Ca channels. After rapidly equilibrating steps are eliminated, the channel kinetics in these models are represented by a single differential equation that is linear in the state of the channel. In the reduced kinetic model, the graph of the steady-state fraction of conducting channels as a function of log10(Ca) is a bell-shaped curve. Dynamically, a step increase in inositol-1,4,5-trisphosphate induces an incremental increase in the fraction of conducting channels, whereas a step increase in Ca can either potentiate or inhibit channel activation, depending on the Ca level before and after the increase. The relationships among these models are discussed, and experimental tests to distinguish between them are given. Under certain conditions the models for intracellular calcium dynamics are reduced to the singular perturbed form epsilon dx/d tau = f(x, y, p), dy/d tau = g(x, y, p). Phase-plane analysis is applied to a generic form of these simplified models to show how different types of Ca response, such as excitability, oscillations, and a sustained elevation of Ca, can arise. The generic model can also be used to study frequency encoding of hormonal stimuli, to determine the conditions for stable traveling Ca waves, and to understand the effect of channel properties on the wave speed.     

GABAA Receptor Subtypes Expressed in Cerebellar Granule Cells: A Developmental Study

Abstract: The developmental properties of primary rat cerebellar granule cells have been characterised with respect to their expression of GABA_A receptor subtypes using both an immunological approach and radioligand binding assays. At day 1 in culture, the GABA_A receptor α1 subunit was detectable in immunoblots and increased in level up to day 9. The GABA_A receptor α6 subunit was not detectable at day 1; however, at days 3–5, a specific M_r 58,000 anti-α6 1–16 Cys immunoreactive species was present which further increased in level up to 9 days in culture. Similar qualitative results were obtained for the expression of the GABA_A receptor α6 subunit in age-matched rat cerebellar membranes. In parallel studies, it was found that although there was an overall increase in [³H]Ro 15–4513 binding sites with days in culture, the relative contributions of diazepam-sensitive and diazepam-in-sensitive [³H]Ro 15–4513 binding changed. A time-dependent enrichment of the diazepam-insensitive binding site up to a maximum of 74% of total [³H]Ro 15–4513 sites was found. This was concomitant with the appearance of the GABA_A receptor α6 subunit. These results are in agreement with the pharmacology described for α6βγ2 cloned receptors. They suggest a developmentally regulated expression of the GABA_A receptor α6 subunit gene at a time that is correlated in vivo with establishment of neuronal connections.     

Effects of soil phosphorus on pollen production,pollen size,pollen phosphorus content,and the ability to sire seeds in Cucurbita pepo (Cucurbitaceae)

To determine the effects of soil phosphorus on pollen production, pollen grain size, phosphate concentration per pollen grain, and the siring ability of pollen, two cultivars of the common zucchini (Cucurbita pepo) were grown under two soil phosphorus conditions in an experimental garden. Overall, soil phosphorus availability had a significant effect on reproductive output through the female function and on traits affecting the male function of plants (staminate flower production, pollen production per flower, and pollen grain size). In addition, pollen produced by plants in the high phosphorus soils had a higher phosphate concentration than pollen produced by plants in the low phosphorus soils. A pollen mixture experiment revealed that pollen produced by plants in the high phosphorus treatment sired significantly more seeds than pollen produced by plants in the low phosphorus treatment. This study showed that growing conditions such as soil phosphorus can influence the size of a pollen grain and its chemical composition, which, in turn, can affect its ability to sire mature seeds.     

A large, dominant pedigree of atrioventricular septal defect (AVSD): exclusion from the Down syndrome critical region on chromosome 21.

We describe a large pedigree of individuals with autosomal dominant atrioventricular septal defect (AVSD). The pedigree includes affected individuals and individuals who have transmitted the defect but are not clinically affected. AVSDs are a rare congenital heart malformation that occurs as only 2.8% of isolated cardiac lesions. They are the predominant heart defect in children with Down syndrome, making chromosome 21 a candidate for genes involved in atrioventricular septal development. We have carried out a linkage study in the pedigree by using 10 simple-sequence polymorphisms from chromosome 21. Multipoint linkage analysis gives lod scores of less than -2 for the region of trisomy 21 associated with heart defects, which excludes a locus within this region as the cause of the defect in this family.