Sensitivity of erythrocyte acetycholinesterase to inhibition by linolenoyl sorbitol. Dependence on a transmembrane potential

Acetylcholinesterase activity of human erythrocytes is known to be inhibited by linolenoyl sorbitol, the inhibition being critically dependent on cell membrane intactness. The extent of enzyme inhibition by the added lipid is correlated with the magnitude of Cl^? gradient across the erythrocyte membrane, indicating that enzyme sensitivity is associated with a transmembrane potential. If linolenoyl sorbitol is allowed to interact with the erythrocytes while a Cl^? gradient exists, enzyme sensitivity can subsequently be demonstrated not only in the absence of a gradient but even when the cells are lyzed. It is concluded that the transmembrane potential determines the accessibility of a membrane component to the added lipid.     

Differentiation of cartilage cells studied by quantitative [3H]thymidine autoradiography in vitro

The apical segments of the mandibular condylar cartilage of newborn ICR mice, containing the intact zones of progenitor cells along with a few rows of chondroblasts were initially prelabelled in vitro with [3H]thymidine and were subsequently chased and cultured for as long as eight days. Such explants underwent a process of tissue regeneration, as after three days in culture they reconstituted the original structure of the organ, thus resembling the in vivo appearance of neonatal mandibular condylar cartilage. Cellular proliferation with subsequent differentiation in the regenerating tissue was followed by means of quantitative autoradiography. Immediately after labelling, the autoradiography-positive grains were confined exclusively to progenitor cells. The latter revealed a substantial ability to proliferate in vitro, a fact that was manifested by a progressive increase in the labelling index along the course of the culture. The latter process was followed by cellular differentiation thereby obtaining hypertrophic chondrocytes. The increase in the rate of labelling index and in the total number of [3H]thymidine-labelled cells was significantly correlated with the overall growth of the regenerating explants.     

Replication forks of Escherichia coli are not the preferred sites for lysogenic integration of bacteriophage Mu.

The question of whether bacteriophage Mu prefers replication forks for lysogenic integration into Escherichia coli chromosomes was tested by using two different systems. In the first, inactivation of genes was scored in synchronized cultures infected by Mu at various times. No increase in the mutation frequency of a gene was found after infection at the time of its replication. In the second, the composition of colonies formed by bacteria lysogenized by Mu was determined; the newly formed lysogens should give rise to mixed colonies (containing lysogenized as well as nonlysogenized bacteria), uniform colonies, or both, depending on the mode of integration. Both types of colonies were found, and the fraction of uniform colonies was proportional to the relative length of the unreplicated segment of an average chromosome in the culture. The results in both systems clearly preclude the possibility that a lysogenizing Mu integrates with high preference at the chromosome replication forks.     

Ligand-affected shift of Na+/H+ exchange pHi set point in human blood platelets, rapidly revealed by a novel approach.

The Na+/H+ exchange time-course of BCECF-loaded human platelets, suspended in isotonic media containing NaCl and sodium propionate and activated by intracellular acidification, was measured spectrofluorimetrically. Sequential alkalinization rates decline exponentially as a function of the changing intracellular pH (pHi) and its linear expression (log rate vs. pHi) extrapolates reproducibly to the pHi set point for the Na+/H+ exchange activation. The set point of control platelets (7.28 +/- 0.01) is shifted rapidly (discernibly less than or equal to 30 s) and markedly to alkaline pHi (7.62 +/- 0.03) by PMA, that activates protein kinase C and is shifted to acidic pHi (7.05 +/- 0.01) by staurosporine, which inhibits protein kinases. The addition of 5-N-(3-aminophenyl)amiloride reveals that the alkalinization measured is predominantly Na+/H+ exchange with only a minute contribution (delta pHi = 0.012 +/- 0.002 in 1 min) of an acid loading component, at pHi greater than 7.2. The results support recent studies concluding that the set point indeed reflects the phosphorylation state of the Na+/H+ exchanger.     

Interactions betweenAulonium ruficorne [Coleoptera: Colydiidae] and other natural enemies of bark beetles [Coleoptera: Scolytidae]

The within tree distribution of some common natural enemies of bark beetles in pine plantations in Israel and some aspects of their feeding habits were studied with special emphasis on the potential impact on the predatorAulonium ruficorne Olivier. A total of 12 predators and 2 parasite species were found associated withA. ruficorne in the natural enemy complex of bark beetles on pines. No secondary parasites were detected. The anthocoridScoloposcelis pulchella (Zetterstedt) and the dipteranMedetera striata Parent were observed feeding on immature stages ofA. ruficorne in the absence of scolytids. The associated Coleoptea:Nemosema elongatum F.,Rhizophagus bipustulatus L.,Corticeus spp.,Plastysoma spp. andPlegaderus discisus Erickson are thought to compete withA. ruficorne on larvae and pupae of bark beetles when the latter are in limited quantities (especially in the lower section of the tree). The parasites, mainlyMetacolus unifasciatuss Forster andDendrosoter caenopachoides Ruschka are assumed to compete withA. ruficorne during the larval period in the smooth bark section of the stem. Competition might occur mainly during spring and fall. Deutonymphs of the miteIpiduropoda sellnicki were detected on the abdomen ofA. ruficorne adults. Larvae of the predator were rarely infected in the field by the bacteriaSerratia sp. while laboratory cultures suffered high rate of mortality caused by this pathogen.      

Erythrocyte Lii-Nao countertransport system Inhibition by N-ethylmaleimide probes for a conformational change of the transport system

Human erythrocytes were treated by a series of SH-reagents, including maleimides, iodo compounds, mercurials and oxidizing agents. Rates of Li efflux into Na-rich medium, Li leak and Li_i-Na_o countertransport were then determined. Of the 13 different reagents studied, only N-ethylmaleimide, iodoacetamide and iodoacetate inhibited selectively the countertransport activity. The effect of the various reagents indicates that the sensitive SH-groups of the countertransport system are not externally exposed. N-Ethylmaleimide was used to probe for changes elicited by substrate cations in Li_i-Na_o countertransport. In Na- and Li-free medium, inhibition of Li_i-Na_o countertransport by N-ethylmaleimide of 35% was reached within 2 s. In Na or Li medium, maximal inhibition was twice as great, but was attained much more slowly, within 10 min. Kinetic data and Hill plot analysis indicate the involvement of two classes of SH-groups: one expressed in the various media with and without substrate cations, and an additional one, which becomes specifically available to N-ethylmaleimide in the presence of external Na or Li. The affinity of Na to the site promoting inhibition by N-ethylmaleimide (apparent K_m  12 mM) is higher than the affinity of Na to its external countertransport site (apparent K_m  25 mM), as reported by Sarakadi, B., Alifimoff, J.K., Gunn, R.B. and Tosteson, D.C. (1978) J. Gen. Physiol. 72, 249–265). Reactivity of $\text{N-}\text{ethyl}\text{[}{}^{14}\text{C}\text{]}\text{maleimide}$ was not modified by the media tested. It is concluded that external Na and Li cause a conformational change in the protein(s) of the countertransport system in human erythrocytes.     

The effect of a moving foveal target on the subjective sensation of motion

In this paper, we report on two experiments concerning the effect of the visual field of fovea on the subjective estimation of angular velocity. Experiment 1 investigates the effect of a slow moving target on the perception of self motion. The result of this experiment can be summarized as follows: a slow moving target seen in the visual field of fovea by a stationary person generates in this person a sensation of self rotation in the same direction as the motion of the target. This phenomenon will be called foveal induced ego motion. Experiment 2 investigates the latency for the detection of a self angular acceleration when the person focusses his fovea on a slowly moving target. From the results of this experiment we conclude that the latency for detection of a small self angular acceleration is shorter if the person sees a small foveal target moving with respect to the person in the direction of self rotation than if that small foveal target is moving (with respect to the person) in the opposite direction. The results of these experiments help us in refining existing models of visual-vestibular interaction, by providing a model which accounts for the phenomenon of oculogyral illusion.This research was conducted while serving as a Visiting Professor at the Man Vehicle Laboratory, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA     

The Na+/H+ exchanger is phosphorylated in human platelets in response to activating agents.

alpha-Thrombin, phorbol esters (PMA) and 1,2-diacylglycerol (DAG), three activators of the amiloride-sensitive Na+/H+ exchange in human platelets, rapidly increase the intracellular pH and the level of phosphorylation of the Na+/H+ exchange protein (NHE1). This stimulatory effect is suppressed by staurosporine, a potent kinase inhibitor, and increased by okadaic acid, a potent inhibitor of phosphatase 1 and 2A. The modulations of NHE1 phosphorylation by these factors correlate well with their effects on platelet pH. Thus, we conclude that in platelets (i) Na+/H+ exchange is mediated by NHE1, and (ii) platelet activating agents stimulate NHE1 via the modulation of the kinase/phosphatase equilibrium.