The size and form of DNA molecules from microsporocytes of Lilium longiflorum at different stages of meiosis

DNA molecules from lysates of microsporocytes at different stages of meiosis of Lilium longiflorum were examined in the electron microscope. In all of the preparations, only linear (non-circular) molecules were found. They had a mean length of between 59 and 75 , and a range of lengths which varied from 1 to 115 , to 1 to 210 . From the data obtained, there was no indication of a change in molecular form or size of DNA molecules associated with the process of meiosis.     

Evidence for an efflux carrier system involved in the secretion of glutamate by Corynebacterium glutamicum

Corynebacterium glutamicum effectively secretes L-glutamate when growing under biotin limitation. The secretion of glutamate was studied with respect to kinetic and energetic parameters: rate of glutamate uptake and efflux, specificity of transport, dependence of efflux on the energy state of the cell, concentration gradient of glutamate and ions, and membrane potential. By comparing these parameters when measured in biotin-limited, i.e. producer cells, and biotin-supplemented, i.e. non-producer cells, respectively, the following conclusions could be drawn: 1. The efflux of L-glutamate in C. glutamicum cannot be explained by passive permeation of this amino acid through the plasma membrane, as it has been assumed in the generally accepted model of glutamate secretion in biotin-limited cells. 2. It is unlikely that the efflux of glutamate occurs via an inversion of the glutamate uptake system. 3. Based on our results concerning the specificity and the kinetics of glutamate transport as well as the observed regulation phenomena, we conclude that secretion of glutamate in C. glutamicum occurs by a special efflux carrier system.Abbreviations dw dry weight - OD optical density - TPP tetraphenyl phosphonium bromide     

Beobachtungen am Nest des Zwergschn?ppers(Muscicapa parva)

Zusammenfassung Im Buchenwald des Naturschutzgebietes Serrahn (Mecklenburg) achtete Verf. seit 1949 auf den Zwergschnäpper. 1956 und 1957 brüteten dort über 12 Paare.Ankunft frühestens am 9. Mai. Als Erste erscheinen vorwiegend ältere (rotkehlige) . Den ersten folgen sehr bald die ersten .Balzflug, Zeigen der Nisthöhle, Copula sowie Variationen des Neststandes werden beschrieben.Fast stets baute nur das , in einem Falle 3 Tage lang. Während der Bauzeit setzt das seine Singflüge eifrig fort. Gepaarte verstummen, sobald ihr begonnen hat, fest auf dem Gelege zu brüten. Nur Junggesellen singen den ganzen Sommer über.An einem günstig gelegenen Nest wurde das Verhalten des Paares vom 4.(?) Bruttag ab bis zum Ausfliegen der Jungen (im Alter von 13 Tagen) aus einem dicht davor angebrachten Schirm genau beobachtet und aufgezeichnet. Nach dem Verlassen des Nestes suchen die Jungen unter Führung ihrer Eltern die nächste Dickung auf. Sobald sie selbständig geworden sind, beginnt die Jugendmauser, 3 Wochen danach die Wanderung ins Winterquartier. Die letzten Zwergschnäpper verschwanden meist vor Mitte September.Angaben über Gesang, Bedeutung der Rufe, Nahrung.Attrappen-Versuche am Nest ergaben, daß die Eltern genau zwischen dem (gefährlichen) Sperber und dem (ungefährlichen) Kuckuck zu unterscheiden wußten und ihnen gegenüber unterschiedliche Alarmlaute brachten. Tannenhäher und Wacholderdrossel lösten keine Abwehr-Reaktion aus.     

Modulation of GABAergic neurotransmission in the brain by dipeptides

The effects of endogenous and synthetic peptides containing GABA or its analogues on the GABA/benzodiazepine/chloride ionophore, complex, GABA_B receptor, Cl fluxes, GABA release and GABA uptake were studied using synaptic membranes, crude synaptoneurosomal preparations and slices prepared from the rat and mouse brain. The sodium-independent binding of GABA was strongly inhibited by GABA-histidine, followed by -glutamyl-homotaurine, GABA-glycine and -glutamyl-GABA. The binding of diazepam was slightly enhanced by the same peptides. The peptides alone had no effect on the chloride fluxes, but GABA-histidine, -glutamyl-GABA and GABA-glycine enhanced while -glutamyl-homotaurine and GABA-taurine inhibited GABA-stimulated chloride uptake. GABA-histidine was the most effective displacer of baclofen binding, but -glutamyl-homotaurine was entirely ineffective. The uptake of GABA was markedly inhibited in synaptosomal preparations by GABA-histidine, while all other peptides were less effective. -Glutamyl-taurine attenuated but -glutamyl-homotaurine and GABA-glycine enhanced the potassium-stimulated release of GABA. The present actions of GABA-histidine in vitro may be of significance for GABAergic neurotransmission in vivo.     

Mass spectrometric analysis of genetic and post-translational heterogeneity in the lectins Jacalin andMaclura pomifera agglutinin

Jacalin andM. pomifera agglutinin are T-antigen specific lectins with ₄₄ structures that show far greater microheterogeneity than plant lectins from other families, due to multiple genetic isoforms and post-translational processing. Electrospray mass spectrometry and combined liquid chromatography-electrospray mass spectrometry were used to characterize the various forms. For both lectins, the mass data were consistent with previous protein sequencing of the major -chain species of 133 residues and three -chain species of 20 or 21 residues. In addition, for jacalin the mass of one minor -chain species was consistent with a second of the four reported gene sequences. However, the glycopeptide -chain form and one -chain form did not match any of the genes, suggesting a fifth gene remains to be found. ForM. pomifera agglutinin, three more -chain forms were found, but all six could arise from only two genes, with additional post-translational proteolysis and post-translational substitution with an unidentified component of 106 Da creating the set of six forms. Only two -chain forms were found also, with no glycosylation.     

The effect of the polar moiety of lipids on the ion permeability of bilayer membranes

Summary Bilayer membranes were prepared with the negatively charged lipids phosphatidylglycerol and diphosphatidylglycerol, the positively charged lipid lysyl phosphatidylglycerol, the zwitterionic lipid phosphatidylethanolamine, and an uncharged glycolipid, diglucosyldiglyceride, all isolated from gram-positive bacteria. Bilayer membranes of all these lipids manifested specific resistances of 10⁷ to 10⁹ cm² and capacitances of 0.3 to 0.4 F cm^–2. The membrane potentials of these bilayers were measured as a function of the sodium chloride, potassium chloride, and hydrogen chloride transmembrane concentration gradients (0.01 to 0.10m) and were found to be linear with the logarithm of the salt activity gradients. Membranes made from lysyl phosphatidylglycerol (one net positive charge) were almost completely chloride selective, whereas membranes from phosphatidylglycerol and diphosphatidylglycerol (one and two net negative charges, respectively) were highly cation selective. Membranes prepared with either diglucosyldiglyceride or phosphatidylethanolamine showed only slight cation selectivity. These findings indicate that the charge on the polar head group of membrane lipids plays an important role in controlling the ion-selective permeability of the bilayer.     

Phylogenetic Analysis of Vertebrate Fibrillar Collagen Locates the Position of Zebrafish α3(I) and Suggests an Evolutionary Link Between Collagen α Chains and Hox Clusters

Type I collagen in tetrapods is usually a heterotrimeric molecule composed of two 1 and one 2 chains. In some teleosts, a third chain has been identified by chromatography, suggesting that type I collagen should also exist as an 1(I)2(I)3(I) heterotrimer. We prepared, from zebrafish, three distinct cDNAs identified to be those of the collagen 1(I), 2(I), and 3(I) chains. In this study on the evolution of fibrillar collagen chains and their relationships, an exhaustive phylogenetic analysis, using vertebrate fibrillar collagen sequences, showed that each chain constitutes a monophyletic cluster. Results obtained with the newly isolated sequences of the zebrafish showed that the 3(I) chain is phylogenetically close to the 1(I) chain and support the hypothesis that the 3(I) chain arose from a duplication of the 1(I) gene. The duplication might occur during the duplication of the actinopterygian genome, soon after the divergence of actinopterygians and sarcopterygians, a hypothesis supported by the demonstration of a syntenic evolution between a set of fibrillar collagen genes and Hox clusters in mammals. An evolutionary scenario is proposed in which phylogenetic relationships of the chains of fibrillar collagens of vertebrates could be related to Hox cluster history. Present address (Laure Bonnaud): Institut Jacques Monod, Tour 43, CNRS, Universités Paris 6 et 7, Equipe Evolution du Développement des Nématodes, 2 place Jussieu, 75005 Paris, France     

Zur Dynamik der Selbststeuerung bei Anpassungsvorgängen

Zusammenfassung Die vorliegende Arbeit ist die 2. einer Reihe, deren Ziel die vergleichend-physiologische Untersuchung der Dynamik zentralnervöser Selbststeuerungssysteme sein soll. Die bei Anpassungsvorgängen auftretenden Änderungen des motorischen Verhaltens der Lebewesen werden als Schwingungsvorgänge im mathematischen Sinne aufgefaßt. Die Güte der Anpassung wird definiert als die zu der Einschwingungskurve gehörige Fläche.Ebenso wie die in der I. Mitteilung untersuchten Axolotl (Amblystoma) zeigen auch die hier benutzten Tische (Carassius carassius) periodisch gedämpften Einschwingungstyp. Dieser scheint bei niederen Wirbeltieren häufig zu sein (verbunden mit relativ großer Fläche, d. h. geringer Güte), während bei höheren Wirbeltieren, besonders beim Menschen, aperiodische Einschwingung (mit nahezu minimaler Fläche, also optimaler Güte) vorherrscht.Die Versuche bezogen sich hier nicht (wie bei der I. Mitteilung) auf die Anpassungsleistung von Einzeltieren, sondern auf die Verhaltensänderung eines Kollektivs. Da es sich bei diesen Fischen um ausgesprochene Schwarm-Tiere handelt, erschien dieser Weg als der biologisch richtigere.     

Effects of GABA antagonists,SR 95531 and bicuculline,on GABAA receptor-regulated chloride flux in rat cortical synaptoneurosomes

Synaptoneurosomes isolated from cerebral cortices of male Sprague-Dawley rats were used for studying GABA_A receptor-regulated chloride influx. The in vitro effects of GABA antagonists, SR 95531 (a pyridazinyl GABA derivative) and bicuculline, on pentobarbital-stimulated, muscimol-stimulated or flunitrazepam-enhanced, muscimol-stimulated chloride uptake were studied. The chloride uptake was determined at 30°C, for 5 sec. Pentobarbital and muscimol produced a maximal stimulation of chloride uptake in cortical synaptoneurosomes at 500 M and 50M, respectively. SR 95531 as well as bicuculline had no effect on the basal uptake of chloride. Whereas, SR 95531 (0.3–30 M) and bicuculline (0.1–100 M), when added 5 min before muscimol (50 M), produced a significant concentration-dependent inhibition of muscimol (50 M)-stimulated chloride uptake (IC₅₀ s of 0.89±0.11 M and 13.45±2.10M, respectively). In studies of the inhibitory effects of SR 95531 and bicuculline on pentobarbital (500 M)-stimulated chloride uptake, the IC₅₀ s were 0.81±0.12 M and 3.86±1.14 M, respectively. SR 95531 exhibited a more potent inhibitory effect than bicuculline on flunitrazepam-enhanced, muscimol-stimulated chloride uptake. The results revealed that SR 95531 has a more potent antagonistic effect than bicuculline on GABA_A-regulated chloride flux.     

Ionenverhältnisse und die Besiedlung hyperhaliner Gewässer,besonders durch Insekten

Zusammenfassung Die Besiedlung hyperhaliner Gewässer ist nur den Tieren möglich, die eine ausgeprägte Osmoregulation haben. In einem kurzen Überblick über die wichtigsten Ionenwirkungen wird die Bedeutung der einzelnen Ionen auf die Osmoregulation dargelegt. Dabei wird vor allem auf die Wirkung der gemeinsamen Einwirkung mehrerer Ionen hingewiesen. Im ökologischen Teil wird auf die Besiedlungsbedingungen hyperhaliner Gewässer und die im Freiland beobachtete Verteilung der Organismen in Gewässern mit unbalanziertem Ionenmilieu eingegangen. Um die an derartige Ionenverhältnisse gebundenen Tiere und ihre Lebensbedingungen zu charakterisieren wird der Ausdruck Kairie vorgeschlagen und diskutiert, der eine Erweiterung des Rapie-Begriffes vonPora darstellt. Ein stenokairischer Organismus stellt sehr enge Bedingungen an die ionale Zusammensetzung des Aussenmilieus, ein eurykairischer Organismus vermag Gewässer verschiedenster ionaler Zusammensetzung zu besiedeln.     

The appearance of exo-α-mannosidase in cultures of Penicillium charlessi

Summary Growth of the fungus Penicillium charlesii G. Smith on glucose, minimal salts medium results in the appearance of -d-mannopyranosidase activity capable of hydrolyzing p-nitrophenyl--d-mannopyranoside. No activity is found until depletion of the carbon source, after which the enzyme activity rapidly increases in the mycelium. Prolonged incubation of the culture results in the appearance of small amounts of -mannosidase activity in the growth medium. The initial release of a mannose-containing polysaccharide into the medium precedes the appearance of -mannosidase by several days.     

Spin-labelling studies of fragmented sarcoplasmic reticulum

Vesicular fragments of sarcoplasmic reticulum (SR) were spin labelled with 2,2,6,6-tetramethyl, 4-isothiocyanate piperidine-1-oxyl (probe A) and 2,2,6,6-tetramethyl, 4-amino (N-iodoacetamide) piperidine-1-oxyl (probe B). Two to five moles of probe A or B were covalently bound to 10⁶g of membrane protein, with minimal loss of activity (ATPase, Ca²⁺, uptake). The EPR spectra of labelled SR were then studied in various experimental conditions.Strongly acid or alkaline pH, protein denaturation with ura, and membrane solubilization with deoxycholate produced marked alterations of the EPR spectra of spin-labelled SR, indicating changes in the local environment surrounding the probes, and the occurrence of conformational changes.A reversible modification of the EPR spectra of probe A and an accelerated efflux of accumulated Ca²⁺ were produced by increasing the temperature of SR suspensions from 30° to 40° C. Such a parallel behavior indicates that reversible structural transitions may control membrane permeability and Ca²⁺ efflux.ATP modifies the EPR spectra of probe B, suggesting that ATP binding to the membrane induces a structural change involving the local environment of certain sulfhydryl groups. The ATP concentration required for this effect is comparable to that requied for activation of ATPase. ADP and ITP are also effective, while pyrophosphate, AMP, and cyclic AMP are not. The effect of ATP is reversible.In other experiments, 2,2,6,6-tetramethylpiperidine-1-oxyl (probeC) was equilibrated with concentrated suspensions of SR. The EPR spectra obtained thereafter indicate that probe C binds to the membrane fragments, still maintaining a high degree of motional freedom. These spectra were markedly changed by deoxycholate solubilization of the membrane fragments, while they were little affected by protein denaturation with guanidine. These results confirm the hypothesis that the region of distribution of probe C into SR, is prevalently constituted by low-viscosity lipids.Supported by research grants from USPHS (HE 09878), the American Heart Association (66742), and the Muscular Distrophy Association of America.     

An Electrogenic Ionic Pump Derived from an Ionotropic Receptor: Assessment of a Candidate

1.Data obtained studying permeability characteristics of single Deiters' membranes in a microchamber system show that intracellular GABA can activate chloride in out passage with a GABA_A pharmacology.2.The overall data suggest the presence of a chloride extrusion pump in these neurons based on intracellular GABA activated chloride channels.3.This conclusion takes up a previous theoretical suggestion that ionic channels could work as ionic pumps provided an energy input modifies the energy profile along the permeation path.4.According to our quantitative evaluation, this pumping mechanism works with a low yield and along a cycle with a strongly asymmetric behavior, being far from equilibrium due to powerful leakage pathways for chloride in these neurons.     

Austausch-Mechanismus des Ionentransports in Pflanzen am Beispiel des Phosphat- und Chloridtransports bei Maiswurzeln

Zusammenfassung Der Efflux von Phosphat und Chlorid aus Maiswurzeln in Abhängigkeit von der Außenkonzentration dieser Ionen wurde durch Schütteln der Maiswurzeln in Erlenmeyer-Kolben mit PO₄ ^-oder KCl-Lösungen verschiedener Konzentration untersucht.Es wurde gefunden, daß der Efflux (bei höheren Außenkonzentrationen) eine Funktion der Außenkonzentration ist. Die Stimulierung des Efflux ist spezifisch und währt mindestens 8 Std. Bei niederen Außenkonzentrationen (unter ungefähr 10^-5 M) verschwindet der spezifische Einfluß externer Ionen auf den Efflux.Es wird wie früher (Weigl, 1967a) angenommen, daß die Stimulierung des Efflux durch Ionenaustausch in einer Membran zustandekommt und daß sich die Austauschstellen (Bindungsstellen) an Membraneinheiten befinden, durch deren Bewegung sie durch die Diffusionsschranke geführt werden. Die Gründe für diese Annahme werden erörtert. Eine alternative Theorie wäre, daß das Protoplasma als ganzes als Ionen-Carrier mit vielen spezifischen Bindungsstellen fungiert. Diese Theorie, die die Rolle von Membranen einschränkt, wird gegenwärtig von wenigen Forschern verfochten (Overstreet, 1957; Bange und Meijer, 1966).

---

Exchange mechanism of ion transport in corn roots

Summary The effect of the external anion concentration on the rate of efflux of anions from corn roots was investigated by following the efflux of labeled anions in shaken solutions of different concentrations of unlabeled anions.Rates of efflux of phosphate and chloride from corn roots are rather independent of external concentrations of the anions as long as these concentrations are low.Rates of efflux of phosphate and chloride from corn roots at high external concentrations of these ions were found to be a function of the external concentrations.Stimulation of efflux is specific: phosphate efflux is stimulated only by phosphate and not by chloride in the medium and vice versa. Since it appears unlikely that this effect is due to specific changes in the permeability of the membranes, it may by concluded that the specific stimulation of efflux by external ions as observed in this investigation is caused by ion exchange at mobile membrane units (Weigl, 1967a). Reasons for this hypothesis are discussed and alternative hypotheses such as that calling for the protoplasm to function as ion exchanger with various specific binding sites are examined. The latter hypothesis remembers to the theory that the ion carrier is the protoplasm itself (Overstreet, 1957; Bange and Meijer, 1966), which diminishes the importance of membranes as limiting boundaries.

     

Effects of Biogenic Amines and Polypeptide Hormones on Protein Kinase A and Adenylyl Cyclase Activities in Muscles of the Mollusc Anodonta cygnea

The effects of biogenic amines, glucagon, and insulin on the cAMP-dependent protein kinase A (PKA) activity have been studied in the muscle tissue of the freshwater bivalve mollusc Anodonta cygnea. It was shown that serotonin, glucagon, and insulin both in vivo and in vitro stimulated PKA activity, whereas isoproterenol inhibited it. The stimulating effect of serotonin and inhibiting effect of isoproterenol was blocked by serotoninergic (cyproheptadine) and adrenergic (propranolol) inhibitors, which confirms specificity of the effect of biogenic amines on the PKA activity. Taking into account participation of adenylyl cyclase system in action of the above hormones, the revealed hormonal effects on the PKA activity produce metabolic effects via the following chain reaction. In the case of serotonin and glucagon: receptor G_s-protein AC cAMP PKA phosphorylation of glycogen synthase (GS) and glucose-6-phosphate dehydrogenase (G6PDH) and inhibition of their activity; in the case of isoproterenol: -adrenoreceptor G_i-protein AC inhibition decreasing PKA inhibition of phosphorylase and stimulation of GSI and G6PDH. A participation is suggested of the insulin-stimulated AC signaling system in the mechanism of the mitogenic insulin effect mediated, as shown in this work, via the PKA activation, but not of the metabolic effect of insulin.     

Taurine and β-alanine uptake in primary astrocytes differentiating in culture: Effects of ions

The effects of ions on taurine and -alanine uptake were studied in astrocytes during cellular differentiation in primary cultures. The uptakes were strictly Na⁺-dependent and also inhibited by the omission of K⁺ and in the presence of ouabain suggesting that their transport is fuelled mainly by these cation gradients. Two sodium ions were associated in the transport of one taurine and -alanine molecule across cell membranes. A reduction in Cl^– concentration also markedly inhibited the uptake of both amino acids, indicating that this anion is of importance in the transport processes. The similar ion dependency profiles of taurine and -alanine uptake corroborate the assumption that the uptake of these amino acids in astrocytes is mediated by the same carrier. In Na⁺- and K⁺-free media both taurine and -alanine uptakes were reduced significantly more in 14-day-old or older than in 7-day-old cultures. No significant changes occurred in the coupling ratio between Na⁺ and taurine or -alanine as a function of spontaneous cellular differentiation or upon dBcAMP treatment. These results suggest that the uptake systems of these structurally related amino acids in astrocytes have reached a relatively high degree of functional maturity by two weeks in culture.     

Monocarboxylic acid permeation through lipid bilayer membranes

Summary The membrane permeability coefficients for the homologous monocarboxylic acids, formic through hexanoic, as well as benzoic and salicylic, were determined for egg phosphatidylcholine-decane planar bilayer membranes. The permeabilities of formic, acetic and propionic acid were also determined for solvent-free phosphatidylethanolamine bilayers. Permeability coefficients were calculated from tracer fluxes measured under otherwise symmetrical conditions, and precautions were taken to ensure that the values were not underestimated due to unstirred layer effects. The relation between the nonionic (HA) permeability (P ^m ) and the hexadecane/water partition coefficient (K _p ) was: log ^m =0.90 log K_p+0.87 (correlation coefficient=0.996). Formic acid was excluded from the analysis because its permeability was sixfold higher than predicted by the other acids. The permeabilities for solvent-free membranes were similar to those for decanecontaining membranes. The exceptionally high permeability of formic acid and the high correlation of the other permeabilities to the hexadecane/water partition coefficient is a pattern that conforms with other nonelectrolyte permeabilities through bilayers. Similarly, the mean incremental free energy change per methylene group (G-CH₂-) was –764 cal mol^–1, similar to other homologous solutes in other membrane systems. However, much less negative G values (–120, to –400 cal mol^–1) were previously reported for fatty acids permeating bilayers and biological membranes. These values are due primarily to unstirred layer effects, metabolism and binding to membranes and other cell components.     

Regulation of auxin transport in pea (Pisum sativum L.) by phenylacetic acid: effects on the components of transmembrane transport of indol-3yl-acetic acid

Phenylacetic acid (PAA), a naturally-occurring acidic plant growth substance, was readily taken up by pea (Pisum sativum L. cv. Alderman) stem segments from buffered external solutions by a pH-dependent, non-mediated diffusion. Net uptake from a 0.2 M solution at pH 4.5 proceeded at a constant rate for at least 60 min and, up to approx. 100 M, the rate of uptake was directly proportional to the external concentration of the compound. The net rate of uptake of PAA was not affected by the inclusion of indol-3yl-acetic acid (IAA) in the uptake medium (up to approx. 30 M) and, unlike the net uptake of IAA, was not stimulated by N-1-naphthylphthalamic acid (NPA) or 2,3,5-triiodobenzoic acid. At an external concentration of 0.2 M and pH 4.5, the net rate of uptake of PAA was about twice that of IAA. It was concluded that the uptake of PAA did not involve the participation of carriers and that PAA was not a transported substrate for the carriers involved in the uptake and polar transport of IAA. Nevertheless, the inclusion of 3–100 M unlabelled PAA in the external medium greatly stimulated the uptake by pea stem segments of [1-¹⁴C]IAA (external concentration 0.2 M). It was concluded that whilst PAA was not a transported substrate for the NPA-sensitive IAA efflux carrier, it interacted with this carrier to inhibit IAA efflux from cells. Over the concentration range 3–100 M, PAA progressively reduced the stimulatory effect of NPA on IAA uptake, indicating that PAA also inhibited carrier-mediated uptake of IAA. The consequences of these observations for the regulation of polar auxin transport are discussed.Abbreviations IAA indol-3yl-acetic acid - DMO 5,5-dimethyloxazolidine-2,4-dione - NPA N-1-naphthylphthalamic acid - PAA phenylacetic acid - TIBA 2,3,5-triiodobenzoic acid     

Permeability change in transformed mouse fibroblasts caused by ionophores,and its relationship to membrane permeabilization by exogenous ATP

Summary Electrogenic ionophores have been found to induce membrane permeabilization in Swiss mouse 3T3 cells that had undergone spontaneous transformation (3T6 cells). Cells attached to plastic dishes were loaded with [³H] uridine, and then the medium was replaced by buffered salt solution at pH 7.8. The enhancement of membrane permeability was assayed by following the efflux of uridine nucleotides, normally impermeant substances. Titration with electrogenic ionophores, such as carbonylcyanidem-chlorophenylhydrazone (CCCP), SF-6847 and gramicidin D, markedly increased the membrane permeability within a very narrow range of ionophore concentration. Nonelectrogenic ionophores, such as monensin and nigericin, did not affect membrane permeability. Measurements of the distribution of the lipophilic cation tetraphenylphosphonium (TPP⁺) between the cells and their environment implied that the remarkable increase in permeability took place within a narrow range of membrane potential (). The data could be explaine by a threshold value, under which aqueous channels are opened in the plasma membrane. The effects exerted by electrogenic ionophores on the plasma membrane were found to be similar to those induced by exogenous ATP. In both cases rapid efflux of K⁺, influx of Na⁺ and reduction of preceded membrane permeabilization to low molecular weight, charged molecules, such as nucleotides. It is suggested that dissipation of induces conformational alterations in membranal components, and/or topological changes, such as aggregation of protein molecules, to form membranal aqueous channels. Electrogenic ionophores permeabilize both normal (3T3) and transformed (3T6) mouse fibroblasts, whereas ATP effects are specific for transformed cells. Thus, it is postulated that ATP actsvia specific sites on the surface of transformed cells.     

Ultrastructural analysis of mineralized matrix from human osteoblastic cells: Effect of tumor necrosis factor-alpha

The study, addressed to understand whether or not human platelets possess a unique thiol-oxidase whose activity could be modulated by signalling pathway initiated upon the activation of Receptor-C_k revealed the existence of disulphide-dependent oxidation within these cells and this phenomenon was regulated by Receptor-C_k-dependent generation of second messengers especially phosphatidic acid (PA); cAMP and cGMP. Purification of this activity revealed the existence of 47 kDa protein having thiol-oxidase activity. Keeping in view these results we propose that the existence of this novel 47 kDa Thiol-oxidase within human platelets may provide a crucial switch for the regulation of Receptor-C_k-dependent mevalonate pathway in human platelets.