A unifying model of the cell proliferation emphasizing plasma membrane fluxes.

The regulation of cellular growth and proliferation is perhaps the most investigated and elusive problem in cell biology and seems to be possible to solve from almost any angle of study chosen. Among the non-systemic factors that have been discussed are genetic damage, genomic control, regulation by stimulatory and inhibitory peptide factors such as EGF, chalones, and fibronectin, protein kinase activation with tyrosine phosphorylation, adenylylcyclase and cAMP, cGMP, membrane perturbations and specifically in tumours the failure of the Pasteur effect in control of glycolysis, excessive membrane ATPase activity, and excessive hydrolytic and proteolytic activities at the cell surface. This article focuses on the central role of fluxes within the plasma membrane and re-examines the possibility that changes of flux of metabolites, ions, and reducing equivalents may be the common denominator regulating cellular proliferation.

Metabolic iteration, evolution and cognition in cellular proliferation.

A model for cellular proliferation is described according to which proliferation ensues when metabolism evolves towards commitment to DNA synthesis, and inhibition of proliferation occurs when enzymic interactions are iterated within a few metabolic pathways, another limiting factor being the supply of metabolites. The model successfully describes cellular growth and division as a 'cognitive process' based on interaction within enzymic elements and the genome, and affords an explanation in these terms of some empirical phenomena which have previously been understood only as isolated observations.

A mathematical approach to cognitive processes.

A mathematical formalization of cognitive processes based on concepts previously given in Experientia is presented. Cognitive processes are described as a set of exponentially decaying interaction probabilities determined by previous interactions between different elements and an association parameter, the inverse of the cognitive stability. The interactions occur in a 'cognitive string' surrounded by a 'cognitive plasma' which carries the contextual information. The 'complexity' of a cognitive process is proportional to time.

Facilitation of actin polymerization by interfilamentous factors.

The polymerization of actin in low ionic strength buffer at 0 degrees C in the presence of 0.25 mM Mg2+ was studied by viscometry, turbidity and absorbance at 232 nm. Under these conditions, significant polymerization occurred only in the viscometer and not in isotropic mixtures. The polymerization rate with 0.25 mM MgCl2, as judged from shear viscosity, was equal to or greater than that observed with 0.1 M KCl and 0.25 mM MgCl2 at 0 degrees C, and was characterized by a longer nucleation period. Measurements of the turbidity at 350 nm (detecting filament formation and aggregation) and the absorbance at 232 nm (detecting conformational changes of the G-F transition) showed no evidence for polymerization or nucleation in a bulk solution at 0 degrees C when Mg2+ was added to 0.25 mM and, furthermore, F-actin nuclei were ineffective as seeds under these conditions. However, nucleation and polymerization by these criteria could be induced by raising the temperature to 20 degrees C. These results demonstrate the existence of narrow conditions when elongation of F-actin is dissociated from nucleation of oligomeric acceptor nuclei, even if monitored on the sub-molecular level (absorbance at 232 nm). Under these conditions, elongation appears to require anisotropic F-actin, i.e. that filaments are ordered by laminar flow.

Validity of Hill's equation in an artificial actomyosin streaming system.

The rotation of an actomyosin motor, assembled from blades, one side onto which F-actin of uniform polarity was attached, suspended in a solution of heavy meromyosin (HMM), was modelled as due to sliding of HMM over the margins of the blades, whereby the work resulting from ATPase activity is used for pushing bulk fluid containing HMM from the leading surface of the blade over the force-generating filaments to the back surface, which leads to increased sliding velocity. The amount of HMM contributing to force-generation is divided into one component perpendicular to the filaments, which is diffusion-limited and regulated by a component parallel to the filaments, represented by the movement of the bulk fluid, the supply of new HMM and the observable velocity of rotation of the blade. Using Hill's equation which essentially states that the product of a virtual force and a virtual velocity is constant within the range of observable forces and velocities, the force can be expressed as velocity, giving a simple first order differential equation. A solution to this equation can be fitted to the observed data with physically meaningful constants in terms of mass, viscosity, the force-velocity constant and a constant expressing the quality of the preparation. Control experiments were performed, using fixed blades. In these experiments, bulk flow around the margins did not increase as a result of ATPase activity and no movement or streaming was observed. The results show that Hill's equation may be applicable to streaming caused by actomyosin irrespective of its confinement to skeletal muscle and independently of preferred molecular model, and leads to several verifiable predictions.

Determination of sialic acid residues in transferrin by oxidative-reductive immunoassay.

A method is described for the determination of sialic acid residues in glycoproteins displaying microheterogeneity in the sugar residue. The new method is based on combining an oxidative-reductive step with binding of the glycoprotein to an immunoadsorbent. After a mild oxidation with sodium metaperiodate the sugar is reduced with labeled sodiumborotritide. The chemical modification of the sugar residues does not seem to impair the binding of glycoprotein to the immunoadsorbent. The procedure, which has been elaborated for human transferrin, can be carried out in the presence of other substances in body fluids.

On the stability of cognitive processes.

An empirical and mathematical model for self-organization is proposed, based on elemental properties, on unique interaction and on the combination of hierarchical elements. In the model, higher elements are stabilized by the 'cognitive' (strong) interaction of subelements, disregarding intermediate elements. This is called 'elementary reductionism' and is illustrated by the sequence quarks-elementary particles-atoms-molecules-cells-organisms- societies. Optimal dynamic interaction of nonidentical elements is called 'cognitive stability'. This is compared with thermodynamic equilibrium. The principal differences are outlined.

Ethanol in preweanling rats with dams: body temperature unaffected.

At an ambient temperature of 24 degrees C, the neonatal rat was found to exhibit poikilothermic characteristics if separated from the dam. On day one after birth, at one hour after separation from dams, the body temperature in rat pups was found to be identical with ambient temperature. Preweanling pups, under these circumstances, were unable to maintain a constant body temperature prior to day 19 postnatally. No differences were observed in body temperatures of rat pups treated chronically (days 6-16 postnatally) with ethanol 4 g/kg body weight (in two 2 g/kg doses three hours apart), as compared with isocaloric isovolumetric milk-, or sham-treated control groups. A significantly lower temperature was observed only at 105 minutes after the first treatment in a group of rats acutely treated (one day only) with ethanol on day 22 postnatally as compared with an isovolumetric water control group. In adult rats, also treated acutely with ethanol, a significant hypothermic response occurred at 105 minutes after the first 2 g/kg dose and persisted during the remainder of the observation period. This study shows that body temperature was unaffected in neonatal Sprague-Dawley rats left with their dams after intubation with ethanol 4 g/kg body weight. Therefore any brain biochemical and/or structural alterations resulting from ethanol exposure, using this animal model, are not due to an ethanol induced hypothermic response.

The effects of ethanol exposure during the brain growth spurt in rats.

The purpose of this study was to determine whether micromorphological changes occur at a low level of ethanol exposure previously shown by us to induce alterations in synaptosomal biochemistry. The results suggest that 4 g ethanol per kg body weight daily throughout the brain growth spurt causes no significant structural changes in the cerebellum, lobule IX, at the light and electron microscopic levels. Although ethanol- and isocaloric sucrose-treated groups did not differ from each other in cumulative percent body weight gain throughout the treatment period, both groups differed significantly in this parameter from isocaloric milk-treated and "handled" control groups. On the day following completion of the treatment period, brain weight in the ethanol-treated group was significantly less than that of all other groups. Further, the results indicate that isocaloric sucrose "pair feeding" is contraindicated in postnatal studies and that nutritional status is better controlled by daily gavage of neonates than by other methods currently used in ethanol studies in postnatal animals.

Effect of ethanol on synaptosomal sialic acid metabolism in the developing rat brain.

The total, glycoprotein-bound and glycolipid-bound sialic acid concentration, ad the activities of ecto-sialyltransferase and neuraminidase were determined in synaptosomes from preweanling ethanol-treated and control rats. The period of treatment corresponded to that of maximal synaptogenesis and peak synthesis of sialoglycocompounds (days 27-37 postconception). The average of the peak blood ethanol concentration was 271 mg/100 ml. In the ethanol-treated animals the sialic acid concentration was significantly reduced (approximately 20%) with an equally distributed decrease of glycoprotein- and glycolipid-bound sialic acid. The activity of ecto-sialyltransferase with asialofetuin as exogeneous acceptor was significantly diminished (about 30%) in the ethanol-treated pups. Neuraminidase showed an unchanged activity after correction for the reduction of endogeneous sialic acid substrate concentration. The total protein and lipid concentrations of the synaptosomal preparations did not differ between the groups. These results suggest that ethanol treatment during on of the vulnerable periods of brain development causes an inhibition of the incorporation of sialic acid into synaptosomal membrane-bound sialoglycocompounds. Such an effect of ethanol exposure might disturb intercellular interactions and the functional performance of the membrane during development, and could be of importance in the pathogenesis of the central nervous system manifestations of the fetal alcohol syndrome.

The use of con A Sepharose as an affinity adsorbent in a simple assay of serum sialyl and fucosyltransferase and its application in tumour diagnosis.

A considerably simplified assay for recording sialyl- and fucosyltransferase in human serum is presented. Serum samples incubated with labeled nucleotide-sugar and glycosylated endogenous acceptor molecules were adsorbed to Con A Sepharose and quantitated by scintillation counting. The results correlated with those of a much more time consuming acid precipition method, and displayed a higher diagnostic sensitivity due to the improved specificity of the method and the combined recording of the two activities. A correlation between serum sialyl- and fucosyltransferase activities as well as quantitative agreement between the amount of incorporated sialic acid and fucose indicated that rhe endogenous acceptor molecules were rate-limiting for transfer and may themselves have diagnostic potential.

The plasma membrane consists of two polar-nonpolar-polar leaflets.

The implications of a double polar-nonpolar-polar leaflet construction of the plasma membrane are investigated. Experimental data from transmission electron microscopic and enzymologic characterization of plasma membranes are advantageously interpreted in these terms compared to interpretation in terms of lipid bilayer. X-ray diffraction and electron spin resonance studies do not differentiate between the present and previous models for the structure of plasma membranes but electron spin resonance data that fail to indicate a statistical distribution of spin labels also fail to support the fluid mosaic model for cell membranes. Results from experiments involving vectorial digestion and labelling of plasma membranes as well as freeze fracture electron microscopic data are compatible with the present model. The molecular composition of the human erythrocyte membrane is investigated whereby the band III protein and glycophorin are suggested to be the structural proteins of the outer leaflet and the spectrins those of the inner leaflet.

The migrating thermodynamic quantum hypothesis for cytoplasmic streaming, sodium pumping and other cell biological phenomena, deduced from biofunctional considerations of the ultrastructure of brush border microvilli.

An attempt is made to reconcile experimental data dealing with, inter alia, cytoplasmic streaming in Characean algae, contraction in actomyosin systems. Na+- and -K+-simtulated ATPase activity and the ultrastructure of brush border microvilli. It is postulated that myosin molecules transfer energy from ATP to an actin-containing filament and that a high energy conformation is subsequently propagated along the filament. At regularly spaced intervals corresponding to the length of an actin-tropomyosin subunit, the propagation of high energy involves rejection of a pressure pulse in the direction of cytoplasmic streaming. Proteins in solution capable of storing the thermodynamic energy represented by the pressure pulse will either migrate in the opposite direction or conserve the quantized cytoplasmic flow generated by the actin-containing filaments. At sites where actin filaments are attached to the plasma membrane the high energy is propagated in another direction leading to expulsion of sodium ions and neutralization of the vectorial pressure pulse.

The fluid double polar-nonpolar-polar leaflet model for biological membranes.

A model for biological membranes is proposed according to which the plasma membrane consists of two functionally different polar-nonpolar-polar leaflets separated by a polar space. The binding of water-soluble proteins, integral lipoproteins and spanning proteins to a biological membrane as well as possible conformations of interphase peptides partitioned between polar and nonpolar layers are discussed. A model for the diffusion of water soluble proteins across nonpolar layers of a membrane is described. Three complete biological membranes containing two leaflets and an inter-leaflet space are defined. These are: 1: The inner nuclear membrane + the perinuclear space and the endoplasmatic cisternae + the outer nuclear membrane and the endoplasmatic reticulum, 2: the innner mitochondrial membrane + the mitochondrial intermembraneous space + the outer mitochondrial membrane and 3: the cytoplasmic leaflet of the plasma membrane + an intramembraneous space in the plasma membrane + the outer leaflet of the plasma membrane.