Structure de la paroi de Aremoricanium rigaudae Deunff, 1955 (Acritarche,Ordovicien)

The wall of Aremoricanium rigaudaeDeunff, 1955, type-species by original designation of the genus AremoricaniumDeunff, 1955, is composed of two layers: the internal one has a circular opening while the second is the only one which develops the processes and a tubular expansion.     

Synaptic modulation by substance P.

The phrase "synaptic modulation," to describe a role of neurotropic peptides, has been used in a number of different ways by a number of different investigators. Using the phrase in its original context, i.e. altered (increased or decreased) synaptic excitability without reference to site or mode of action, evidence is presented that substance P modulates synaptic transmission of cat alpha-motoneurons. The effect appears to be biphasic, with low doses inhibiting, and high doses facilitating synaptic transmission.     

Behavioral changes in bluegill (Lepomis macrochirus) as indicators of sublethal effects of metals

Synopsis The development of rapid, yet sensitive toxicity testing methods is needed for the establishment of water quality standards to protect aquatic life. A technique using changes in the behavior of bluegill (Lepomis macrochirus) was utilized to evaluate the impact of five sublethal levels of a cadmium (Cd) and zinc (Zn) mixture. The technique proved very sensitive and various changes in behavior occurred at the lowest metal levels used; 21 ug Cd per liter and 99 ug Zn per liter. Coughs, yawns, partial jerks and jerk swimming were especially sensitive indicators of elevated metal levels. The frequency, but not the form, of eight of the nine behaviors quantified changed significantly with increasing metal levels.     

Reconstituted low density lipoprotein: A vehicle for the delivery of hydrophobic fluorescent probes to cells

Previous studies have shown that the cholesteryl ester core of plasma low density lipoprotein (LDL) can be extracted with heptane and replaced with a variety of hydrophobic molecules. In the present report we use this reconstitution technique to incorporate two fluorescent probes, 3-pyrenemethyl-23, 24-dinor-5-cholen-22-oate-3β-yl oleate (PMCA oleate) and dioleyl fluorescein, into heptane-extracted LDL. Both fluorescent lipoprotein preparations were shown to be useful probes for visualizing the receptor-mediated endocytosis of LDL in cultured human fibroblasts. When normal fibroblasts were incubated at 37°C with either of the fluorescent LDL preparations, fluorescent granules accumulated in the perinuclear region of the cell. In contrast, fibroblasts from patients with the homozygous form of familial hypercholesterolemia (FH) that lack functional LDL receptors did not accumulate visible fluorescent granules when incubated with the fluorescent reconstituted LDL. A fluorescence-activated cell sorter was used to quantify the fluorescence intensity of individual cells that had been incubated with LDL reconstituted with dioleyl fluorescein. With this technique a population of normal fibroblasts could be distinguished from a population of FH fibroblasts. The current studies demonstrate the feasibility of using fluorescent reconstituted LDL in conjunction with the cell sorter to isolate mutant cells lacking functional LDL receptors.     

Control of the Ca2+-triggered bioluminescence of Veretillum cynomorium lumisomes

Calcium ions can trigger an emission of light from Veretillum cynomorium lumisomes (bioluminescent vesicles) under conditions where they are not lysed. This process does not require a metabolically-linked source of energy, but is dependent upon the nature of the ions present inside and outside the vesicles. The Ca²⁺-triggered bioluminescence is stimulated by an asymmetrical distribution of cations or anions. Either high internal sodium or high external chloride is required for the maximal effect. When sodium is present outside the structure and potassium inside, the slow inward diffusion of calcium is decreased. Unbalanced diffusion of internal cations also stimulates the bioluminescence, suggesting control of the calcium influx by an electrochemical gradient. It is assumed that rapid outward diffusion of sodium or inward diffusion of chloride generates an electrical potential difference (inside negative) which drives the Ca²⁺-influx. With purified lumisomes it has been shown that Ca²⁺-triggered bioluminescence and calcium uptake (presumably net uptake) were correlated. In two instances uptake of the lipophilic cation dibenzyldimethylammonium has given direct evidence for the existence of a potential difference. With NaCl-loaded vesicles, it has not been possible to demonstrate an uptake of lipophilic cations but experiments with ²²Na and ⁴²K indicated a higher rate of sodium efflux, in accord with the proposed hypothesis.     

Interaction of alcohols with proteins

The kinetics of denaturation of egg albumin have been determined for methanol, ethanol, propanol, and butanol. The reactions are first order in respect to protein but between 11th and 18th order for the alcohols. The denaturation reaction is characterized by a large temperature coefficient with little or no dependence on pH. There is a marked change of pH when proteins are denatured. A series of eight proteins has been studied. There is surprisingly little difference in susceptibility to alcohol denaturation between the various proteins. Methanol, ethanol, propanol, and butanol are strongly bound to egg albumin—butanol being the most strongly bound. The binding of alcohol is probably accompanied by protein dehydration. The polyhydric alcohols' behavior is much different. These alcohols do not denature proteins and the protein is hydrated. Sucrose produces the greatest degree of hydration.     

Antinociceptive effects of intrathecally administered human beta-endorphin in the rat and cat

Rats chronically implanted with intrathecal catheters displayed a dose-dependent increase in the hot-plate and tail-flick response latencies following the injection of human beta-endorphin into the lumbar spinal subarachnoid space through the indwelling catheter. beta-Endorphin was approximately 25 times more potent than morphine on a molar basis. Matching morphine and beta-endorphin doses such that approximately equal submaximal submaximal effects occurred, it was observed that the antinociception produced by beta-endorphin lasted approximately three times longer than that produced by morphine. Experiments with intrathecal injection of beta-endorphin into the spinal subarachnoid space of cats fitted with intrathecal catheters also revealed a potent antinociceptive effect which was completely antagonized by naloxone. In the rats, naloxone administered systemically in doses of 10--100 microgram/kg produced a parallel shift in the dose-response curves of both nociceptive measures suggesting a competitive antagonism. Using a dose ratio analysis, an in vivo pA2 of 7.1 for naloxone was obtained. These data and those derived from previous work based on the pA2 suggest that the interaction of morphine, certain pentapeptides, and beta-endorphin is the same with regard to the spinal opiate receptor population mediating behaviorally defined analgesia.