Occurrence of Prorocentrum lima,a DSP toxin-producing species from the Atlantic coast of Canada

A species of Prorocentrum (Dinophyta, Prorocentrales), isolated from a phytoplankton net sample from the Atlantic coast of Nova Scotia, has been brought into unialgal culture. The sample was collected at an aquaculture site immediately following an incident of diarrhetic shellfish poisoning (DSP) due to the consumption of contaminated mussels. This clonal isolate has been identified as P. lima, based on its morphological characteristics. Analysis of the culture extract, using high performance liquid chromatography (HPLC) with fluorescence detection, indicated the presence of the DSP toxins, okadaic acid (OA) and dinophysistoxin-1 (DTX-1).     

-alkoxyphenol leukotriene B4 receptor antagonists

A series of -alkoxyphenols containing a tetrazole acid sidechain have been prepared as antagonists of leukotriene B₄ receptors. These compounds were tested as receptor antagonists of human neutrophil and guinea pig lung membrane leukotriene B₄ receptors. Compounds in this series were found to be up to 18-fold more potent than LY255283. These results indicate that the acyl group of the 1,2,4,5 substituted hydroxyacetophenone class of LTB₄ antagonists is not critical to antagonist potency.     

Charge balance in the alpha-hydroxyacid dehydrogenase vacuole: an acid test.

The proposal that the active site vacuole of NAD(+)-S-lactate dehydrogenase is unable to accommodate any imbalance in electrostatic charge was tested by genetically manipulating the cDNA coding for human muscle lactate dehydrogenase to make a protein with an aspartic acid introduced at position 140 instead of the wild-type asparagine. The Asn 140-Asp mutant enzyme has the same kcat as the wild type (Asn 140) at low pH (4.5), and at higher pH the Km for pyruvate increases 10-fold for each unit increase in pH up to pH 9. We conclude that the anion of Asp 140 is completely inactive and that it binds pyruvate with a Km that is over 1,000 times that of the Km of the neutral, protonated aspartic-140. Experimental results and molecular modeling studies indicate the pKa of the active site histidine-195 in the enzyme-NADH complex is raised to greater than 10 by the presence of the anion at position 140. Energy minimization and molecular dynamics studies over 36 ps suggest that the anion at position 140 promotes the opening of and the entry of mobile solvent beneath the polypeptide loop (98-110), which normally seals off the internal active site vacuole from external bulk solvent.     

Transgenic animals as a tool for studying the effect of the c-myc proto-oncogene on cardiac development

Transgenic animals provide a model system to elucidate the role of specific proteins in development. This model is now being used increasingly in the cardiovascular system to study cardiac growth and differentiation. During cardiac myocyte development a transition occurs from hyperplastic to hypertrophic growth. In the heart the switch from myocyte proliferation to terminal differentiation is synchronous with a decrease in c-myc mRNA abundance. To determine whether c-myc functions to regulate myocyte proliferation and/or differentiation, we examined the in vivo effect of increasing c-myc expression during fetal development and of preventing the decrease in c-myc mRNA expression that normally occurs during myocyte development. The model system used was a strain of transgenic mice exhibiting constitutive expression of c-myc mRNA in cardiac myocytes throughout development. Increased c-myc mRNA expression is associated with both atrial and ventricular enlargement in the transgenic mice. This increase in cardiac mass is secondary to myocyte hyperplasia, with the transgenic hearts containing greater than twice as many myocytes as nontransgenic hearts. The results of this study indicate that constitutive expression of c-myc mRNA in the heart during development results in enhanced hyperplastic growth, and suggest a regulatory role for the c-myc protooncogene in cardiac myogenesis.     

The effect of inhibition of cholesterol esterification on the fate of cholesterol derived from HDL in rat hepatocyte monolayers

Rat HDL2 is known to stimulate bile acid synthesis in rat hepatocyte monolayers. The intracellular fate of the cholesterol derived from the HDL2 was studied using the inhibitor of cholesterol esterification, Sandoz compound 58-035. Rat HDL2 added to rat hepatocyte monolayers caused a stimulation of cholesterol esterification of 32%. This stimulation could be inhibited by 58-035. A small significant increase in bile acid synthesis was also observed in cells in the presence of HDL2, confirming our earlier observations. 58-035 prevented this increase. These observations imply that cholesterol entering the cell from HDL2 is first esterified and can only enter the substrate pool for bile acid synthesis after subsequent intracellular hydrolysis.     

Actions of 17 beta-estradiol on gonadotropin release induced by drugs that activate intracellular signal transduction mechanisms in rat anterior pituitary cells

We studied the effects of 17 beta-estradiol (E2) on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release induced by drugs that activate different intracellular signal transduction mechanisms in rat anterior pituitary cells. Cells were pretreated with E2 (6 x 10(-10) M) or diluent for 24 h. Then, both E2- and diluent-pretreated cells were incubated for 4 h with E2 or diluent, respectively, with or without drugs, and in the presence or absence of gonadotropin-releasing hormone (GnRH). Media were assayed for LH and FSH by radioimmunoassays. E2 treatment had no effect on basal FSH release, but occasionally stimulated basal LH release. Phospholipase C (PLC), L-alpha-1,2-dioctanoyl glycerol (C8), veratridine, 8-bromo-cyclic adenosine 3',5'-monophosphate (8-Br-cAMP), melittin (a phospholipase A2 [PLA2] activator), arachidonic acid, PLA2, and GnRH all stimulated LH and FSH release in both E2- and diluent-treated cells. E2 treatment increased both LH and FSH release induced by GnRH, PLC, C8, veratridine, and 8-Br-cAMP, but not by melittin, arachidonic acid, and PLA2. Neither C8, PLA2, nor arachidonic acid in combination with a maximal dose of GnRH had additive effects on either LH or FSH release, whereas melittin increased the maximal response to GnRH in both E2- and diluent-treated cells. The effects of veratridine and 8-Br-cAMP depended on dose of GnRH and presence or absence of E2. These results suggest that E2 augments stimulus-coupled gonadotropin release by interacting with the Ca2+-, and/or diacylglycerol-, and cAMP-activated pathways, but not with the arachidonic acid-activated pathway.