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Biomedical subjects

M Lucas

Publications and source records attributed to M Lucas.

At least 217 records · Page 12Linked to original sources
PubMed1982

Biological properties of a calcium-modulator protein from Phycomyces blakesleeanus.

1. A modulator protein having properties similar to calmodulin-like proteins could be detected in Phycomyces the first day of growth. 2. The modulator protein from Phycomyces was partially purified to a specific activity of 9,000 Units/mg protein. 3. The modulator protein was similar to calmodulin with respect to: (a) the ability to stimulate a calcium-plus-calmodulin-dependent cAMP phosphodiesterase from bovine brain; (b) the inhibitory effect of trifluoperazine in this process; (c) the stimulation of the [Ca2+ + Mg2+)-ATPase from human erythrocyte membranes. 4. Maximum effect of modulator protein in the above mentioned reactions was achieved at micromolar calcium concentrations.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1982

Extracellular calcium and glucose-induced insulin release during fasting in isolated perfused rat pancreas.

The effects of different concentrations of Ca2+ (2.5 or 7.5 mM) upon the kinetic and dynamic aspects of glucose-induced insulin release were investigated in the isolated perfused pancreas of fed and 4-day fasted rats. The curve relating the rate of insulin release to the glucose concentrations (2.75-33.4 mM) showed a sigmoidal shape and was similar at both Ca2+ concentrations in the fed state. Pancreas of fasted animals showed a diminished insulin secretion and the kinetic pattern was linear throughout the whole range of glucose concentrations studied at 2.5 mM Ca2+. Perfusion of pancreas from fasted rats with glucose at 7.5 mM Ca2+ resulted in an increase of insulin secretion but the kinetic behaviour continued to be linear. In contrast, pancreas of 4-day fasted plus 2-day refed rats showed a kinetic of glucose-induced insulin secretion with the cooperative mechanisms observed in fed control animals. It is concluded that changes in Ca2+ utilization by the pancreatic beta cell play little role in the decreased insulin release observed in the fasted state.

Animals↗
PubMed1981

Four years' experience of maternal alpha-fetoprotein screening and its effect on the pattern of antenatal care.

Estimation of alpha-fetoprotein (A.F.P.) in maternal serum was used as a screening method for the detection of fetal neural tube defect (N.T.D.) in 7315 women over a four year period. Of these, 5668 pregnancies were tested between 15 and 21 weeks. Action was advised in 129 patients (2.3 per cent). In 74 patients, the only action required was reviewing the notes, including the report of any ultrasound examination, and repeating the blood A.F.P. Detailed ultrasound including scanning the fetal spine was requested in 47 patients and amniocentesis was advised in 19 of these (0.33 per cent). In practice the incidence of amniocentesis was 0.28 per cent as three patients declined our advise. The programme gave detection rates between 15 and 21 weeks of 100 per cent and 75 per cent respectively for anencephaly and open spina bifida. A high fetal mortality was associated with persistently elevated blood A.F.P. levels whether amniocentesis was performed or not.

Amniocentesis↗
PubMed1981

Gastroesophageal reflux in infants: relation to apnea.

The temporal relationship between apnea and gastroesophageal reflux was examined in 14 infants with abnormal GER scores and histories of prolonged apnea. Simultaneous polysomnographic and intraesophageal pH recordings were performed for each infant. GER episodes were compared to control segments of the recording (without GER) for frequency and type of apnea. Apnea was equally likely to occur during the control segments as during the GER episodes. Brief obstructive apneic episodes were more common during the onset of GER episodes than the onset of control segments. GER duration appeared prolonged during sleep. GER and apnea were not temporally related in the majority of instances, and may be two manifestations of a more general developmental delay.

Apnea↗
PubMed1981

Can practice result in the ability to divide attention between two complex language tasks? Comment on Hirst et al.

Several studies at the beginning of the century demonstrated that extensive practice enables subjects to adequately perform two language tasks presented simultaneously. This result was recently confirmed by Hirst et al. These authors concluded that practice eventually results in the ability to attend to both tasks simultaneously, since evidence shows that both primary and secondary tasks are processed semantically. Two arguments are presented showing that this conclusion is questionable. First, the processing of category and semantic relationships between words and sentences can be automatic. Second, the conclusion that true divided attention is possible after training can only be made if evaluated against several criteria of automatic performance. Hirst et al. reported data pertaining to only one of these criteria. Therefore this study is inconclusive and fails to elucidate the nature of the changes in processing that occur.

Attention↗
PubMed1981

Effects of oxaloacetate and beta-hydroxybutyrate on rat liver mitochondrial calcium flow during starvation.

Rat liver mitochondria accumulate calcium from the incubation medium both in the presence of ATP and of succinate with rotenone. Lowering free calcium concentration by means of EGTA leads to a reduction of maximum transport capacity to less than 25% of the total added calcium. Under these conditions addition of oxaloacetate inhibits calcium uptake, an effect which is blocked by equimolar concentrations of beta-hydroxybutyrate. Oxaloacetate and acetoacetate induce an efflux of previously accumulated mitochondrial calcium. These effects appear to be independent of free calcium concentration and of whether the mitochondria were obtained from fed rats or rats fasted for 16 h or 4 days.

Acetoacetates↗
PubMed1981

Experimental Escherichia coli and rotavirus infection in lambs.

Colostrum-deprived lambs were infected with either enteropathogenic Escherichia coli(O9:K30:K99) or rotavirus or a mixture of the E coli and rotavirus. E coli doses of 10(6) and above consistently produced diarrhoea, as did experimental rotavirus infection. When both of the agents were administered, the mortality rate was higher, although the duration of diarrhoea was no greater than that observed when either of the two agents was administered alone.

Animals↗
PubMed1980

Irreversible inactivation of beta-adrenergic receptors of C6 glioma cells. Synthesis and study of a thiol derivative of propranolol.

The beta-adrenergic receptor of C6 glioma cells contains a disulfide bridge which can be reduced by dithiothreitol (DTT). On intact cells, N-ethylmaleimide (NEM) (5 mM) does not change the affinity of [3H] H2-alprenolol ([3H] DHA) but reduces the total number of beta-adrenergic cell receptors by 21 +/- 3 per cent ; (N = 3). After receptor reduction by DTT, NEM irreversibly blocks the accessibility of the beta-adrenergic receptors to [3H]DHA. On isolated membranes, incubation in the presence of either NEM (5 mM) or isoproterenol (5.10(-7) M) does not significantly modify the total number of beta-adrenergic receptors accessible to [3H]DHA. Incubation of membranes with both NEM and isoproterenol reduces the number of binding sites by 33 +/- 2 per cent ; (N = 3). A thiol derivative of propranolol was synthetized. Its affinity is 10 times lower than that of propranolol. This sulfur derivative reduces the total number of beta-adrenergic receptors by 22 +/- 3 per cent (N = 3) when incubated with the native receptor and by 55 +/- 4 per cent (N = 4) when incubated with the reduced receptor. DTT does not significantly reverse the blockade induced by propranolol-SH. A model is proposed for explaining these results.

Adenylyl Cyclases↗
PubMed1980

Effect of phosphoenolpyruvate on liver mitochondrial calcium retention from fed and fasted rats.

Rat liver mitochondria from fed and 4-day-fasted rats are able to accumulate calcium supported by ATP (energy-driven calcium uptake) or by succinate (respiration-driven calcium uptake). Phosphoenolpyruvate decreases the amount of calcium accumulated in both ways, whether the rats were fasted or fed ad libitum. Phosphoenolpyruvate induces a net calcium efflux from mitochondria. The effect of phosphoenolpyruvate is partially reversed by ADP. Phosphoenolpyruvate is also able to inhibit the ATP-driven calcium accumulation in the absence of exogenously added respiratory substrates.

Adenosine Diphosphate↗
PubMed1978

Calcium metabolism and enzyme secretion in guinea pig pancreas. Uptake, storage and release of calcium in whole cells and mitochondrial and microsomal fractions.

In isolated pancreatic acinar cells from the guinea pig stimulation of enzyme secretion by carbamoylcholine is slightly diminished in the absence of extracellular Ca. LaCl3 in a concentration, which does not influence the secretory response to carbamoylcholine, nearly completely abolishes 45Ca uptake by cells, indicating that Ca uptake is not necessary for secretion. In cells preloaded with 45CaCl2, addition of carbamoylcholine leads to an immediate release of 45Ca, which can be blocked by atropine or 8-(N,N-diethylamino)-octyl 3,4,5-trimethoxybenzoate and is not influences by LaCl3 in concentrations, which do not inhibit secretion. A similar release of 45CaCl2 from preloaded cells is obtained by addition of the mitochondrial inhibitors antimycin A, carbonylcyanide p trifluoromethoxyphenylhydrazone (FCCP), and oligomycin. Possibly due to markedly diminished ATP levels, neither antimycin A nor FCCP act as secretagogues, both compounds being inhibitors of secretion. Oligomycin, which decreases ATP levels only to 20%, stimulates secretion. Mitochondria and microsomes from pancreatic tissue are able to accumulate 45Ca. Mitochondrial 45Ca uptake can be driven by ATP or active respiration and is inhibited by NaN3, oligomycin, antimycin A or FCCP. Microsomal 45Ca uptake is ATP-dependent. NaN3 and mitochondrial inhibitors have no influence on microsomal 45Ca uptake, which is stimulated several-fold by oxalate. The results support the assumption, that in the guinea pig pancreas Ca mobilization from intracellular stores is necessary to initiate secretion. Due to their ability for an active accumulation of45Ca both mitochondria and microsomes could serve as intracellular calcium stores.

Amylases↗