Search PubMed⌕ Search

Biomedical subjects

A Molla

Publications and source records attributed to A Molla.

At least 109 records · Page 6Linked to original sources
PubMed1984

Ca2+-ATPase activity in pancreatic acinar plasma membranes. Regulation by calmodulin and acidic phospholipids.

A high degree of ATP hydrolytic activity present in purified rat pancreatic acinar cells was localized to plasma membranes. This activity was stimulated almost equally by Mg2+ or Ca2+. Kinetic analysis revealed that the enzyme had a higher affinity for Ca2+ (Kd = 1.73 microM) than Mg2+ (Kd = 2.98 microM) but a similar maximal rate of activity. A comparison of substrate requirements revealed very similar profiles for the Mg2+- and Ca2+-stimulated activities. Combinations of saturating concentrations of Mg2+ or Ca2+ produced the same degree of maximal activity. Investigation of the partial reactions of the ATPase activity revealed two phosphoprotein intermediates (Mr = 115,000 and 130,000) in the presence of Ca2+ and Mg2+. A significant stimulation of the Ca2+-ATPase activity by calmodulin was observed (Kd = 0.7 microM). Calmodulin increased the Ca2+-sensitivity of this enzyme system; Mg2+ appeared to be required for this effect. The Ca2+-ATPase activity was also stimulated by acidic phospholipids. Using an 125I-labeled calmodulin gel overlay technique, calmodulin was shown to bind in a Ca2+-dependent fashion to 133,000- and 230,000-dalton proteins present in the plasma membrane-enriched fraction. Under conditions that favor Ca2+-dependent kinase activity, calmodulin enhanced the phosphorylation of a 30,000- and 19,000-dalton protein. The major ATP hydrolytic activity in pancreatic acinar plasma membranes was present as an ectoenzyme.

Adenosine Triphosphatases↗
PubMed1984

Does calmodulin play a role in the regulation of cardiac sarcolemmal adenylate cyclase activity?

The recent suggestion that calmodulin (CaM) could mediate calcium inhibition of cardiac adenylate cyclase (AC) has been reassessed. Using a purified sarcolemmal preparation (SL), the influence of different concentrations of free Ca2+ (obtained using Ca2+-EGTA solutions) was studied on dog heart AC. From 10(-9) M to 10(-3) M Ca2+ reduced basal activity, as well as epinephrine (10(-4) M)- and trypsin (1.0 microgram/mL)-stimulated activities with, in the three cases, an identical IC50 of 10(-8) M. The amount of endogenous CaM in the SL, measured using a radioimmunoassay technique, was found to be 7.5 ng/mg protein. The resulting concentration of CaM in the final AC incubation medium was lower than 50 pM, indicating the lack of a significant role for endogenous CaM in the inhibition observed. The addition of exogenous CaM to the AC assay at a concentration sufficient to stimulate other CaM-dependent systems did not modify the Ca2+ inhibitory curves for basal, epinephrine (10(-4) M)-stimulated, or trypsin (1 microgram/mL)-stimulated activities. These results indicate that CaM does not play a significant role in the Ca2+ inhibition of cardiac AC and that trypsin stimulation of cardiac AC is not mediated through a CaM-dependent process.

Adenylyl Cyclases↗
PubMed1984

Effect of intravenous somatostatin on stool output in diarrhea due to Vibrio cholerae.

Somatostatin has been shown to inhibit intestinal secretion induced by a variety of secretagogues. The ability of somatostatin to reduce stool output in patients with cholera was therefore investigated in a double-blind randomized controlled trial. Twenty-two patients with severe purging due to infection with Vibrio cholerae (less than or equal to 12.5 ml/kg X h) received either somatostatin at a dose of 250 micrograms/h in saline (n = 12) or placebo (n = 10). The study drug was given for 12 h followed by a control period of the same duration. No difference in stool output was apparent between somatostatin- and placebo-treated groups. No side effects of somatostatin were observed. It is concluded that somatostatin is ineffective as an antidiarrheal agent in Asiatic cholera in humans.

Adult↗
PubMed1983

Azidocalmodulin derivatives. Activation of, and binding to, three target proteins: aorta myosin light-chain kinase, erythrocyte (Mg2+ + Ca2+)-dependent ATPase and cardiac sarcoplasmic-reticulum kinase.

Different azidocalmodulin derivatives were synthesized by modification of either one carboxylic acid group or one or several arginine residues and their binding and activation capacity investigated in three target enzyme systems. The systems studied were smooth-muscle myosin light-chain kinase, cardiac sarcoplasmic-reticulum kinase and erythrocyte (Mg2+ + Ca2+)-dependent ATPase. The results indicated that the activation ability of each calmodulin derivative was different depending on the system studied. Binding studies carried out by the displacement of 125I-calmodulin indicated that the monosubstitutions did not greatly alter the apparent Kd of calmodulin for the enzymes but that the modification of four arginine residues caused a 4-8-fold increase in the apparent Kd in all systems. These results have shown that azidocalmodulin derivatives may have different degrees of usefulness in the study of calmodulin target proteins in different systems, with the behaviour of the derivatives not predictable on the basis of the nature (soluble or membrane-bound) or the type (ATPase or kinase) of enzyme system to be investigated. However, the monosubstituted calmodulin and, in particular, the carboxylic acid-group-modified derivative (where the modification was statistically dispersed over the protein chain) are good candidates for photolabelling calmodulin-binding proteins.

Amino Acids↗
PubMed1983

Planarian regeneration: in vivo and in vitro effects of calcium and calmodulin on DNA synthesis.

Regeneration does not occur when planarians are grown in Ca2+-free medium. The possible effect of calcium upon DNA synthesis was therefore studied using cultured planarian cells and regenerating planarian fragments. In the cultures, DNA synthesis was Ca2+-dependent and required a minimum of 10(-6) M Ca2+ in the medium. It was gradually decreased in cells grown in Ca2+-free medium. Addition of Ca2+ to these cultures raised DNA synthesis. The time lag between addition of Ca2+ and stimulation of DNA synthesis varied with culture age. The triggering effect of Ca2+ was amplified by ionophore A 23187. A calcium binding protein, ram testis calmodulin, intensified the stimulatory effect of calcium, but EGTA blocked this effect. In the presence of trifluoperazine (TFP), DNA synthesis was not stimulated by Ca2+. This inhibition by TFP was overcome by adding calmodulin to the medium. Ca2+ therefore triggered DNA synthesis in vitro, and this role might have been potentiated by calmodulin. In vivo, DNA synthesis was shown to be dependent on the Ca2+ concentration in the medium in which intact or regenerating planarians were grown. In 12-h regenerates, the Ca2+ concentration in the medium was no longer critical. Total calcium content decreased just after sectioning until completion of healing (at 6 h) and then rose significantly to a peak at 12 h which coincided with the first peak of DNA synthesis. The calmodulin content gradually diminished during the first 6 h after sectioning. After a transient rise at 12 h, calmodulin content further decreased until 48 h. The results demonstrate the crucial role of Ca2+ in triggering DNA synthesis in planarian cells in vitro and in regenerating fragments. Calmodulin, whose concentration is very low in planarians compared to vertebrates, might help to induce the first peak of DNA synthesis at 12 h after sectioning, but is probably not the main Ca2+-binding protein involved in the regeneration process.

Animals↗
PubMed1983

Whole-gut transit time and its relationship to absorption of macronutrients during diarrhoea and after recovery.

Whole gut transit time (TT) was measured in 68 children aged up to 5 years (29 cholera, 17 rotavirus, 13 enterotoxigenic Escherichia coli, and 9 Shigella) during acute stages of diarrhoea and 2 weeks after recovery. Absorption of calories, fat, protein, and carbohydrates contained in a normal Bangladeshi diet was studied for 72 h after the first appearance of a charcoal marker in the stool, both during acute diarrhoea and 2 weeks after recovery. Mean TT varied from 5.5 to 7.3 h during the acute stage and from 14.1 to 15.5 h during the recovery period of diarrhoea of all aetiologies; the increase in the TT was significant as expected (P less than 0.001). Correlation coefficients were calculated between TT and the coefficients for absorption of fat, nitrogen, calories, and carbohydrates in the acute and recovery stages of cholera, rotavirus, E. coli, and Shigella. No significant relation was found between TT and absorption of nutrients in any stage of diarrhoea of any aetiology. The results of this study suggest that the mechanism for absorption of nutrients is independent of the whole-gut transit time. Further studies are necessary to identify the role of transit of a meal and its absorption along the whole gut.

Acute Disease↗
PubMed1982

Rice-powder electrolyte solution as oral-therapy in diarrhoea due to Vibrio cholerae and Escherichia coli.

124 patients with acute diarrhoea due to Vibrio cholerae or Escherichia coli were treated with either the standard sucrose-electrolyte solution or a cereal-based electrolyte solution, containing 30 g rice powder per litre and electrolytes as recommended by the World Health Organisation. The treatments were compared by measuring the rate of purging, change in body weight, serum specific gravity, urine output, and post-hydrolysis sugar content in the stool. The proportions of successfully treated patients in the rice-powder group were 80% for cholera patients and 88% for E. coli patients--no different from those in patients receiving the sucrose-electrolyte solution. Failure was due to rates of purging that exceeded the patient's ability to drink enough replacement solution. This study suggests that a rice-powder electrolyte solution is efficient and safe to use as a rehydrating oral fluid in acute diarrhoea.

Adult↗
PubMed1982

Subcellular localization of myosin light chain kinase in skeletal, cardiac, and smooth muscles.

Antibodies were elicited against turkey gizzard myosin light chain kinase (MLCK), purified by affinity chromatography on the enzyme bound to Sepharose, and used to localize myosin kinase--in rabbit fast skeletal, slow skeletal, cardiac, and smooth muscles--by indirect immunofluorescence. When studied on nitrocellulose replicas of NaDodSO4/polyacrylamide gel electrophoretograms, antibodies were specific for the Mr 140,000 MLCK of gizzard smooth muscle. By using the same technique, they were shown to recognize the Mr 140,000 MLCK and a Mr 75,000 polypeptide--presumably derived from the former by proteolysis--in rat arterial and stomach smooth muscle as well as in rat thyroid cells. The same antibodies reacted only with a Mr approximately equal to 75,000 protein from rat cardiac and skeletal muscle. Antibodies inhibited the activity of smooth and skeletal myosin kinases in an in vitro assay with approximately equal to 11 mole of antibody needed for 50% inhibition of 1 mole of gizzard enzyme. The antibodies stain vascular and gizzard smooth muscle cells with no apparent segregation of the enzyme in a specific part of the cell. In contrast, sarcomeric muscles exhibit a striated staining pattern, superimposable to the staining by antiactin antibodies. This shows that (i) antibodies are not species- or tissue-specific, (ii) they recognize kinases that differ in their molecular weight and ability to be phosphorylated, probably at the level of their common catalytic and calmodulin-binding domains, and (iii) sarcomeric muscle kinases are at least in part bound to the contractile apparatus and their distribution is restricted to a specific part of the sarcomere. This raises the possibility that myosin phosphorylation may be controlled not only by the Ca2+ concentration but also by actin-myosin interaction.

Animals↗
PubMed1982

Carbohydrate malabsorption in infants with rotavirus diarrhea.

We studied a group of patients with rotavirus diarrhea to determine the association of carbohydrate malabsorption during diarrhea with the degree of acidosis and severity of purging. Unlike enterotoxigenic diarrhea in which the metabolic acidosis is due to loss of bicarbonate in an alkaline stool, patients with rotavirus develop a metabolic acidosis while passing an acid stool with little detectable bicarbonate. Also unlike enterotoxigenic diarrhea, rotavirus stool contains large quantities of reducing substances suggesting significant carbohydrate malabsorption. Our findings are consistent with the hypothesis that carbohydrate malabsorption is an important secondary pathophysiological mechanism in the rotavirus diarrhea syndrome. This model for rotavirus diarrhea helps to explain the electrolyte and acid-base pattern of the rotavirus stool and stresses the importance of further nutrition balance studies to determine the optimal dietary management of patients with rotavirus diarrhea.

Acidosis↗
PubMed1981

Cyclic adenosine 3',5'-monophosphate-dependent regulation of purified bovine aortic calcium/calmodulin-dependent myosin light chain kinase.

Myosin light chain kinase was extracted from bovine aortic muscularis by a low ionic strength buffer containing 50% glycerol. It was purified 130-fold with a 10% yield by anion-exchange chromatography followed by affinity chromatography on calmodulin-Sepharose. The enzyme was 95% calcium/calmodulin-dependent and exhibited a specific activity of 2-6 mumol/min per mg. It phosphorylated the myosin regulatory light chain exclusively. The apparent Kd for calmodulin was 6.3 nM. Upon phosphorylation of the enzyme by the catalytic subunit of cyclic AMP-dependent protein kinase, its affinity for calmodulin decreased 4-fold, without alteration of the V. When examined by SDS-polyacrylamide gel electrophoresis, the purified enzyme was made up of two major peptides (Mr 142 000 and 131 000, respectively), with a minor 80 000 dalton peptide. All these peptides were 32P-labeled after incubation with [gamma-32P]ATP and the catalytic subunit of cyclic AMP-dependent protein kinase. Also, after non-denaturing polyacrylamide gel electrophoresis, they all exhibited myosin light chain kinase activity, suggesting that the 131 000 and 80 000 dalton species are proteolytic products of the native enzyme of Mr 142 000. Vascular smooth muscle myosin light chain kinase is therefore soluble, calcium/calmodulin dependent and phosphorylatable by cyclic AMP-dependent protein kinase with concomitant decrease in its affinity for calmodulin. These features account for the beta-adrenergic relaxation of vascular smooth muscle.

Animals↗
PubMed1981

Octopus calmodulin. The trimethyllysyl residue is not required for myosin light chain kinase activation.

Octopus calmodulin was purified to homogeneity and shown to contain 0.1 residue each of epsilon-N-monomethyl-lysine, epsilon-N-dimethyllysine, and epsilon-N-trimethyllysine/mol. With the exception of this partial methylation and of a single tyrosyl residue, it shared all the characteristic properties of mammalian calmodulin in terms of molecular weight, amino acid composition, electrophoretic behavior in the presence or absence of Ca2+ ions, and activation of calcium/calmodulin-dependent myosin light chain kinase. In fact, Octopus calmodulin proved to be slightly more effective than ram testis calmodulin in activating both skeletal and smooth muscle myosin light chain kinases in the presence of Ca2+. This provides conclusive evidence that (a) stoichiometric trimethylation of lysine 115 is not required for enzyme activation, and (b) the inability of troponin C to activate myosin light chain kinase (Walsh, M. P., Vallet, B., Cavadore, J. C., and Demaille, J. G.

Adenosine Triphosphatases↗
PubMed1981

Stool electrolyte content and purging rates in diarrhea caused by rotavirus, enterotoxigenic E. coli, and V. cholerae in children.

One hundred twenty children below 5 years of age with diarrhea caused by Vibrio cholerae, enterotoxigenic Escherichia coli, or rotavirus were studied for stool electrolyte composition and purging rates. The mean purging rate in cholera was 60.1 ml, in ETEC 39.2 ml, and in rotavirus infection 31.4 ml/kg/8 hour. The mean stool sodium concentration in cholera was 88.9 mMol/L, in ETEC 53.7 mMol/L, and in rotavirus infection 37.2 mMol/L. Stool potassium concentration did not show much variation, Mean CO2 concentration in rotavirus infection was 6 mMol/L, significantly lower than in cholera and in ETEC diarrhea. In cholera, stool sodium concentration increased significantly with increase in purging rates; the same was not true in rotavirus and ETEC diarrhea. These differences are considered important factors in formulating replacement therapy in diarrhea.

Child, Preschool↗