Acrosomal reaction and early events at fertilization in Marthasterias glacialis (Echinodermata: Asteroidea)

When the spermatozoon of M glacialis contacts the mature oocyte jelly it adheres to it. Following this, there is a slight tumefaction of the acrosome, which is followed by the disruption of the apical acrosomal vesicle and cytoplasmic membranes. Acrosomal vesicle contents are liberated and spread along the outer surface of the oocyte jelly. Meanwhile, the acrosomal process begins to extend, penetrates all the jelly extension, then the vitelline layer, and finally contacts the cytoplasmic egg membrane. Nevertheless, the sperm cell continues lying at the outer border of the jelly. From the beginning of the acrosome reaction the dense and finely fibrillar subacrosomal material is connected, by some expansions, to the basal acrosomal vesicle membrane. Both nuclear and mitochondrial diameters have diminished.     

Effect of temperature and Zn2+ on isometric contractile properties and electrical phenomena of frog (Rana) and Xenopus skeletal muscle fibers

Effects of temperature and Zn2+ on the isometric contractile properties of toe muscle fibers of Rana catesbeiana and Xenopus laevis were studied. The maximum twitch tension almost doubled when the temperature was lowered from 20 to 4 degrees C in Rana muscles but not in Xenopus muscles, although the duration of action potential in Xenopus muscle was increased slightly more than that seen in the Rana species. The maximum rate of rise of tension was greater in Xenopus muscle than in the Rana muscle, at 20 degrees C. The prolongation of the time-to-peak tension following exposure to low temperature (4 degrees C) was more pronounced in Rana than in Xenopus muscles. These results suggest that the speed of release and reuptake of Ca2+ by the sarcoplasmic reticulum (SR) differs in Rana and Xenopus muscles and that these factors may be related to differences in the SR and the T-tubular morphology. In Rana muscles, Zn2+ prolonged the falling phase of the action potential and potentiated the twitch tension. In Xenopus muscles, Zn2+ marginally prolonged the duration of action potential and the twitch tension was not markedly potentiated. These results indicate that Zn2+ potentiates the twitch by prolonging the action potential and that Rana muscles are more sensitive to the effects of Zn2+.     

Differences in Ca2+ mobilization induced by alpha-adrenergic agonist and phosphatidic acid in cultured hepatocytes

In an attempt to elucidate the relationship between phosphatidylinositol breakdown and alpha-adrenergic responses, effects of phosphatidic acid and phosphatidylinositol related metabolites on Ca²⁺ mobilization and glucose output in cultured hepatocytes were examined. Norepinephrine induced the net ⁴⁵Ca²⁺ efflux from preloaded cells and stimulated glucose output via alpha-adrenergic receptor stimulation, whereas phosphatidic acid caused ⁴⁵Ca²⁺ uptake to cells and did not stimulate glucose output. Myo-inositol-monophosphate, diglyceride and arachidonic acid, which are released by phosphatidylinositol breakdown, had no effect on ⁴⁵Ca²⁺ efflux and glucose output in cells. These results suggest that phosphatidic acid and phosphatidylinositol related metabolites can not mimic the alpha-adrenergic actions in cultured hepatocytes.     

Infection and development of Nosema bombycis (Microsporida: Protozoa) in a cell line of Antheraea eucalypti

Spores of Nosema bombycis derived from diseased insects were highly purified by Urografin density gradient centrifugation. Antheraea eucalypti cells were inoculated with the purified spores primed with 0.1 n KOH solution to start a continuous propagation of N. bombycis in cell culture. The first increase in the number of infected A. eucalypti cells was observed at 48 hr postinoculation, and it was caused by the secondary infective forms of N. bombycis. The secondary infective forms were produced during the course of sporoblast differentiation. The parasites in cell cultures divided synchronously until 36 hr postinoculation. Mature spores were observed initially 6 days postinoculation at 27°C. The infected cultures were subcultured extensively for more than 1 year with the addition of healthy A. eucalypti cells.     

Simulation of cellular compaction and internalization in mammalian embryo development as driven by minimization of surface energy

A model based upon minimization of surface energy is proposed as an explanation for compaction and internalization of cells during mammalian embryo development. The model is used to simulate and graphically display these phenomena on a computer.     

In vitro release of growth hormone-releasing factor from rat hypothalamus: effect of insulin-like growth factor-1

The release of growth hormone-releasing factor (GHRF) from rat hypothalamus was investigated in vitro. After 60 min preincubation the released GHRF from sliced rat hypothalamic fragments during 60 min incubation was detected by a highly specific and sensitive radioimmunoassay for rat GHRF. The release of GHRF was Ca2+-dependent and enhanced by high concentration of K+. Insulin-like growth factor-1 (IGF-1) significantly decreased GHRF release to 65% and 84% of the control at concentrations of 10(-8) M and 10(-7) M, respectively. These results suggest that this in vitro system is useful for the investigation of the mechanism of GHRF release from the hypothalamus and that IGF-1 is probably involved in the feedback inhibition of growth hormone secretion by attenuating GHRF release from the hypothalamus besides countering the effect of GHRF on the pituitary.     

Manganese-histidine cluster as the functional center of the water oxidation complex in photosynthesis

The recent model of Kambara and Govindjee for water oxidation [Kambara T. and Govindjee (1985) Proc. Natl. Acad. Sci. U.S.A., 82:6119–6123] has been extended in this paper by examining all the data in order to identify the most likely candidate for the redox-active ligand (RAL), suggested to operate between the water oxidizing complex (WOC) and Z, the electron donor to the reaction center P680. We have concluded that a very suitable candidate for RAL is the imidazole moiety of a histidine residue. The electrochemical data available on imidazole derivatives play heavily in this identification of RAL. Thus, we suggest that histidine might play the role of an electron mediator between the WOC and Z. A model of S-states in terms of their plausible chemical identity is presented here.Abbreviations J electronic spin of ion - P680 reaction center chlorophyll - RAL Redox active ligand - S_n state of the oxygen-evolving system - WOC water oxidation complex - Z electron donor to P680 Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement     

Molecular characterization of mutant actin genes which induce heat-shock proteins in Drosophila flight muscles

Heat-shock proteins (hsps) are constitutively induced by the mutant actins in the Drosophila indirect flight muscles (IFM). We compared primary structures of the mutant actin genes (KM75 and HH5) which induce hsps and of the non-inducing alleles (KM129 and KM88). The KM75 actin has lost 20 amino acids at the C-terminus. The HH5 actin has only one amino acid substitution, from Gly-336 to Ser. In KM129, the C-terminal part of actin is replaced by novel amino acids. KM88 is a null allele, with an amber mutation early in the coding region of the mutated actin gene. Although all of the KM75, HH5 and KM129 actins have defects near the C-terminus, only hsp-inducing mutant actins cause enlargement of the IFM nuclei as well as a disruption of myofibrils even in the presence of two copies of the normal genes. We further consider the underlying mechanisms linking these features of the hsp-inducing alleles.     

In vitro modification of Candida albicans invasiveness

Candida albicans produces germ-tubes (GT) when it is incubated in animal or human serum. This dimorphism is responsible for its invasive ability.The purpose of the present paper is (1) to evaluate the ability of rat peritoneal macrophages to inhibit GT production of ingested Candida albicans, obtained from immunized rats and then activated in vitro with Candida-induced lymphokines; (2) to determinate any possible alteration of phagocytic and candidacidal activities.The phagocytes were obtained from rats immunized with viable C. albicans. Some of them were exposed to Candida-induced lymphokines in order to activate the macrophages in vitro. The monolayers of activated, immune and normal macrophages were infected with a C. albicans suspension during 4 hr.Activated macrophages presented not only the highest phagocytic and candidacidal activities but a noticeable inhibition of GT formation and incremented candidacidal activity.