Characterization of the egg vesicular components in the seaweed, Fucus serratus L. (Fucales, Phaeophyta), using enzyme histochemistry and vital staining: the search for a lysosome-like body

Fucus serratus eggs were examined for evidence of the existence of a lysosome-like body using enzyme histochemical and vital staining techniques. Simultaneous coupling azo-dye techniques for lysosomal acid phosphatase proved inappropriate owing to endogenous phenolic binding artefacts. The large number of alginate polysaccharide and polyphenolic egg vesicles interfered with vital staining techniques for lysosomes. Lysosomal esterase activity was detected in the abundant egg lipid bodies. The role of the egg lipid body as an equivalent lysosome-like body of higher plants, the spherosome, is discussed in relation to egg fertilization and early zygote development.

Ligand-induced regulation of glucagon-like peptide-I receptor function and expression in insulin-secreting beta cells

Glucagon-like peptide-I (GLP-I) is a potent incretin hormone and mediates its actions via the cyclic AMP (cAMP) pathway. The GLP-I receptor belongs to the family of seven-transmembrane domain receptors coupled to G proteins. We have analyzed the regulation of GLP-I receptor function and expression by its own ligand and the cAMP-dependent pathway in rat insulinoma-derived beta cells (RINm5F). The GLP-I receptor underwent rapid homologous desensitization, which occurred at the receptor level. This was characterized by a reduced binding capacity not mediated by protein kinase A (PKA). GLP-I receptor mRNA levels were down-regulated during incubation of cells by agents increasing cAMP levels including GLP-I itself. This effect was dependent upon time and concentration. Forskolin, the PKA activator 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole-3, 5-monophosphorothiotate, and GLP-I stabilized the GLP-I receptor mRNA. All induced down-regulation of the GLP-I receptor number within 3 h, a time point at which GLP-I receptor mRNA levels were not decreased. This effect was not influenced by cycloheximide. Therefore, in addition to transcriptional effects, posttranslational mechanisms exist to regulate GLP-I receptor numbers in insulin-secreting cells.

ACE inhibitor co-therapy in patients with heart failure: rationale for the Randomized Aldactone Evaluation Study (RALES)

Angiotensin converting enzyme (ACE) inhibitor therapy in conjunction with loop diuretics and, possibly, digoxin, is associated with a relatively high incidence of recurrent heart failure and death. Even high doses of ACE inhibitors may not completely suppress the renin-angiotensin-aldosterone system; aldosterone "escape' may occur through non-angiotensin II dependent mechanisms involving corticotropin, atrial natriuretic peptide, serum potassium, and deficient high-density lipoprotein cholesterol concentrations. Addition of spironolactone (an aldosterone receptor blocker) to an ACE inhibitor regimen causes marked diuresis and symptomatic improvement. The Randomized Aldactone Evaluation Study (RALES) was organized to explore the role of combination therapy with spironolactone in patients with heart failure. Patients with New York Heart Association Functional Class II-IV heart failure and left ventricular ejection fractions < or = 40% who were on regimens comprising an ACE inhibitor, loop diuretic, and, possibly, digoxin were randomized to receive placebo or spironolactone in doses of 12.5, 25, 50, or 75 mg per day. Eve at the lowest dose of spironolactone, a significant decrease in plasma N-terminal pro-atrial natriuretic peptide occurred, with concomitant increase in concentrations of plasma renin and urinary aldosterone. As prophylaxis for heart failure, a daily dose of 25 mg of spironolactone and monitoring of serum potassium concentrations are recommended; symptomatic therapy in refractory or severe heart failure may require doses as high as 100 mg b.i.d. The RALES Mortality Trial will follow up 1400 similar patients for 3 years to determine the effect of the addition of spironolactone on combined mortality and hospitalization for heart failure.

Normal MR appearance of the pituitary gland in the first 2 years of life

PURPOSE

To investigate changes in the size, shape, and signal intensity of the pituitary gland during the first 2 years of life.

METHODS

One hundred consecutive MR studies, spin-echo T1- and T2-weighted sequences, of children 0 to 2 years of age were analyzed. Signal intensity and shape of the gland were graded and its signal intensity measured.

RESULTS

There was a statistically significant difference in the signal intensity of both the anterior and posterior pituitary gland and in the shape between children younger than and older than 6 weeks of age and younger than and older than 27 weeks of age. There were definite trends in the size of the gland with age (decrease in height and increase in anteroposterior diameter and width).

CONCLUSIONS

There are changes in the pituitary gland in the newborn period that may reflect the ongoing changes in pituitary hormones reported to occur during this time.

Calcium homeostasis, signalling and protein phosphorylation during calcium-induced conidiation in Penicillium notatum

Cytosolic free calcium concentration [Ca2+]c of protoplasts from Penicillium notatum was measured using the permeant acetoxy ester (quin-2-AM) of the calcium-chelating fluorescent dye quin-2. Low uptake of the ester occurred at pH 5.8-7.0 and its subsequent hydrolysis was low. Uptake was promoted by an external pH of 5.0 and significant hydrolysis to quin-2 achieved by adjustment of the internal pH to 7.2, which was near the optimum of the carboxylic esterases responsible for the hydrolysis. Uptake of Ca2+ was biphasic with the average cell calcium concentration of protoplasts increasing from an initial value of 2 mumol to 50 mumol (kg cell water)-1, during attainment of the steady state after 30 min, at which time [Ca2+]c was unchanged at 20 nM but increased to 182 nM at 2-6 h exposure to 2.5 mM-Ca2+. Broadly similar changes in [Ca2+]c were found in protoplasts derived from mycelium samples exposed to Ca2+ over the same period of time. The location of Ca2+ was determined in subfractionated organelles and characterized using enzyme markers and electron microscopy. In 32 h mycelium preloaded with Ca2+ for 6 h, Ca2+ was located principally in the mitochondria with lower concentrations associated with the endoplasmic reticulum, Golgi, vacuoles and plasma membrane components. Calcium was not released by inositol 1,4,5-trisphosphate or the calcium ionophore A23187 from any subcellular fractions obtained from mycelium on Percoll gradients, nor from preparations of vacuoles or plasmalemma vesicles, except in the case of mitochondria where rapid release of the ion was achieved by the addition of 2-5 microM-A23187. The anti-calmodulin agent calmidazolium (R24571) greatly reduced sporulation when addition preceded that of Ca2+. Calcium-induced cultures showed massive novel protein phosphorylation 2 h after addition of the ion which was virtually eliminated by R24571, whilst 1 h and 4-6 h protein phosphorylations, which were also present to some degree in vegetative controls, were substantially reduced. Two-dimensional SDS-PAGE analysis of phosphoproteins confirmed that Ca(2+)-induced mycelium had enhanced capacity for calmodulin-mediated phosphorylation relative to corresponding vegetative cells and that complex differential changes in such phosphorylations occurred during Ca(2+)-induction of the sporulation process.

Preparation of right-side-out plasma membrane vesicles from Penicillium cyclopium: a critical assessment of markers

A plasma membrane fraction was obtained by the combined use of differential centrifugation and aqueous polymer two-phase partitioning techniques. Vanadate-inhibited ATPase and glucan synthase activities were highly enriched in this fraction, although the presence of ATPase activity which was not inhibited by vanadate, nitrate, molybdate, anyimycin A or azide was also detected. Other intracellular membrane marker activities were present at very low or undetectable levels. A further separation step using Percoll density gradient centrifugation resulted in the separation of a fraction which exclusively contained vanadate-inhibited ATPase activity, and was enriched with silicotungstic-acid-staining membrane material. Latency tests performed on the plasma membrane markers showed that the membrane vesicles were in the right-side-out orientation.

Calcium binding and induction of conidiation in protoplasts of Penicillium cyclopium

Cell wall-free protoplasts of P. cyclopium could regenerate a cell wall and form mycelia in liquid culture with high rates of viability. When calcium was added to the medium, protoplasts displayed biphasic accumulation with an immediate metabolism-independent adsorption phase, followed by slow metabolism-dependent uptake. Exposure of the protoplasts to Ca2+ for periods of 2 min, followed by incubation in calcium-free medium for 24 hours, was sufficient to induce conidiation with morphogenetic events parallel to those found in cultures containing calcium throughout the incubation period, and similar to those reported in cultures inoculated from conidia. The conidiation event caused by short exposure to calcium could be reversed, within 2 hours of Ca2+ addition, by a brief treatment with the specific calcium chelating agent BAPTA (100 microM), which removed 65 to 75% of the total cell calcium. The results implicate the membrane-bound calcium fraction in the process of conidiation induction.

Adenine and pyridine nucleotide levels during calcium-induced conidiation in Penicillium notatum

Concentrations of adenine and pyridine nucleotides and the associated charge values were examined in extracts of mycelium of Penicillium notatum during vegetative growth and reproductive development promoted by the addition of Ca2+ (10 mmol dm-3). The significant increase in adenylate energy charge promoted by Ca2+ was due to a fall in intracellular AMP and a concomitant rise in ATP concentration. Intracellular concentrations of NADH and NAD fell within 1 h of the addition of Ca2+. The catabolic reduction charge was unchanged by Ca2+ whilst the anabolic reduction charge increased in Ca2+-induced mycelium due to lowered intracellular NADP concentration. Reduced concentration of NADPH in Ca2+-induced mycelium, relative to the vegetative controls, lowered the phosphorylated nucleotide fraction. The results are discussed in relation to metabolic economy during morphogenesis in P. notatum.

Properties of mitochondria from Penicillium cyclopium and their response to calcium and other divalent cations

The respiratory properties of isolated mitochondria from P. cyclopium were studied with particular attention to their response to calcium ions. The results obtained indicate concentration dependent stimulation of NADH oxidation by calcium ions. Similar effects could also be obtained with other divalent cations.

Oxidation of carbon sources via the tricarboxylic acid cycle during calcium-induced conidiation of Penicillium notatum

The TCA cycle was examined during Ca2+-induced conidiation in Penicillium notatum over the 12-h period after addition of Ca2+ to vegetative cultures. Conidiation was independent of Ca2+ when certain intermediates and derivatives of the TCA cycle served as sole carbon sources. Arsenite and malonate augmented the effect of Ca2+ on conidiation but did not substitute for it. Mitochondria from vegetative cells had low rates of oxidation of TCA cycle intermediates and, with the exception of pyruvate, aconitate and glutamate, these were poorly linked to phosphorylation processes. Calcium ions affected mitochondrial function causing reduced oxidation of oxoglutarate, elimination of pyruvate oxidation and a decline in respiratory control of these substrates with increased oxidation of NADH and NADPH. Radiorespirometric studies and enzyme searches revealed a complete but weakly oxidative TCA cycle in vegetative cells. In Ca2+-induced cells oxoglutarate dehydrogenase activity was deleted within 6.5 h of Ca2+ addition and this was accompanied by establishment of an 'incomplete Krebs cycle'. Calcium-induced conidiation was associated with increased capacity for acetate and glutamate metabolism involving an activated glyoxylate shunt which may be related to enhanced biosynthetic demand. The metabolic basis of the Ca2+ effect on conidiation is discussed in connection with previous findings.

Enzymes of gluconate metabolism and glycolysis in Penicillium notatum

In addition to the ability of Penicillium notatum to grow on sucrose, glucose, fructose and gluconate, substantial growth occurred on 2-ketogluconate and 5-ketogluconate thereby indicating a diverse sugar metabolism. Cell-free extracts contained all the enzymes of the Embden-Meyerhof-Parnas pathway and for both oxidative and non-oxidative pentose phosphate metabolism. Despite inconsistencies in results between different assay methods for the conventional Entner-Doudoroff (ED) enzymes, the data indicated the route was enzymatically possible. Demonstrations of the activities of the enzymes of the non-phosphorylative equivalent of the ED pathway were achieved. No evidence was found of a phosphorylative linking enzyme between the two pathways. Both 2- and 5-ketogluconate reductases were detected along with gluconate dehydrogenase which suggested interconvertibility between the ketogluconates and gluconate. However, ketogluconokinase, responsible for the conversion of ketogluconate to 2-keto-6-phosphogluconate, was not detected. A scheme for the interrelationships of routes of gluconate metabolism is discussed.

Pathways of glucose catabolism and the origin and metabolism of pyruvate during calcium-induced conidiation of Penicillium notatum

Experiments examined the metabolic basis of Ca2+-induced conidiation during the 12-h period following the addition of Ca2+ to 40-h vegetative cultures of Penicillium notatum. Vegetative mycelium had enzymic capacity for three routes of glucose catabolism viz. the Embden-Meyerhof-Parnas (EMP), pentose phosphate (PP) and the Entner-Doudoroff (ED) sequences. Inhibitors of EMP enzymes restricted vegetative growth more than that associated with conidiation whilst arsenate augmented the limited capacity of lower levels of Ca2+ to promote conidiation. Arsenite (5.6 mmol . l-1) partially blocked the metabolism of pyruvate and caused its accumulation, which was also promoted by Ca2+ alone. Arsenite did not induce conidiation in vegetative cultures but when combined with Ca2+ it enhanced conidiation. Radiorespirometry and the analysis of accumulated pyruvate, promoted by arsenite, indicated that approximately 54% of carbon was catabolized via combined EMP/ED routes and 46% by the PP pathway and subsequently via a weakly functional TCA cycle. Calcium-induced cultures swung to a primarily ED (25%) and PP (75%) based catabolism with low substrate level phosphorylation, including a facility for a non-phosphorylative ED route, and further diminished oxidative TCA capacity. Pyruvate accumulation in Ca2+-induced cultures coincided with the decline in activity of pyruvate dehydrogenase and a reduced capacity for gluconeogenesis, with other enzymes of pyruvate metabolism showing altered activities. These changes in enzyme activities, pyruvate accumulation and its subsequent metabolism were related to growth rate and the developmental cycle, and are discussed in conjunction with the regulatory role of calcium.