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S Citi

Publications and source records attributed to S Citi.

47 records · Page 3Linked to original sources
PubMed1988

Modulation of cellular morphology and locomotory activity by antibodies against myosin.

Three monoclonal antibodies directed against chicken brush border myosin were used to study the possible function of myosin in microfilament organization and locomotion of chicken fibroblasts. These antibodies bind to distinct and separate epitopes on the heavy chain of chicken nonmuscle myosin and display differential effects of myosin filament formation and actin-myosin interaction (Citi, S., and J. Kendrick-Jones. 1988. J. Musc. Res. Cell Motil. 9: 306-319). When injected into chicken fibroblasts, all antibodies induced breakdown of stress fibers. Concomitantly, a large proportion of the cells developed extensive lamellae which altered their morphology drastically. These cells showed also increased locomotory activity. All effects were concentration dependent and reversible. The most drastic alterations were observed with cells injected with antibody quantities exceeding the quantity of cellular myosin (molar ratios of antibody to myosin greater than 3:1). The finding that antibodies with different effects on myosin filament formation in vitro all induce similar intracellular processes suggests that it is the antibody-induced decrease in functional myosin that triggers an increase in plasma membrane dynamics and locomotory activity, rather than differences in myosin filament length or conformation.

Actin Cytoskeleton↗
PubMed1987

Polymerization of vertebrate non-muscle and smooth muscle myosins.

We investigated how light chain phosphorylation controls the stability of filaments of vertebrate non-muscle myosins (from bovine thymocytes and chicken intestine epithelial brush border cells) and smooth muscle myosin (from chicken gizzard) in vitro. Using a sedimentation assay, the solubilities of the myosins were determined by measuring the amounts of myosin monomers (Cm) and filaments (Cp) present under a given set of conditions as a function of the total myosin concentration (Ct). Below 200 mM-NaCl, each myosin displayed distinct "critical monomer concentrations" (Cc) for polymerization, which were dependent on the salt concentration, the state of light chain phosphorylation and the presence of MgATP. At 150 mM-NaCl, MgATP increased the Cc of non-phosphorylated brush border myosin approximately five to tenfold, thymus myosin approximately 10 to 15-fold, and gizzard myosin approximately 25 to 50-fold. When these myosins were phosphorylated, MgATP had little effect on their solubilities, and their Cc values remained low. Analytical ultracentrifugation and electron microscopy demonstrated that the myosins were present in three different conformational states under the conditions used in the sedimentation assays, i.e. filaments, extended monomer (6 S) and folded monomer (10 S). Since at equilibrium only filaments and monomers were observed, we suggest that the polymerization pathway for these myosins can be analysed in terms of a dynamic monomer-polymer equilibrium (polymer in equilibrium 6 S monomer in equilibrium 10 S monomer). At roughly physiological ionic strength, light chain dephosphorylation (in the presence of MgATP) promotes the folded state (10 S), whereas phosphorylation promotes the extended state (6 S), and thereby favours filament assembly. The relevance of the monomer-polymer equilibrium to the state of organization of the myosin in vivo is discussed.

Animals↗
PubMed1987

Effects of light chain phosphorylation and skeletal myosin on the stability of non-muscle myosin filaments.

The effect of light chain phosphorylation and the presence of skeletal muscle myosin on the stability of non-phosphorylated non-muscle myosin filaments was investigated. Purified skeletal, brush border and thymus myosins were assembled in vitro into hybrid filaments consisting of varying proportions of (1) non-muscle and skeletal myosins, or (2) phosphorylated and non-phosphorylated non-muscle myosins. The stability of these hetero- and homopolymers in the presence of MgATP was determined using sedimentation, gel electrophoresis and immunochemical techniques. In addition, the effect of a monoclonal antibody, binding to the tip of brush border myosin tail, on the assembly of the homo- and heteropolymers, was tested. Filamentous non-phosphorylated non-muscle myosin was disassembled by MgATP to the same extent whether in homo- or heteropolymers, indicating that skeletal myosin has no stabilising effect on the hybrid filaments. The presence of small amounts of phosphorylated non-muscle myosin was, however, found to prevent the complete disassembly by MgATP of non-phosphorylated non-muscle myosin filaments, indicating that light chain phosphorylation stabilizes co-operatively non-muscle myosin filaments. The monoclonal antibody prevented the assembly of brush border myosin into both homo- and heteropolymers, and its effect on the filaments was compared with that of MgATP.

Adenosine Triphosphate↗
PubMed1987

Studies on the structure and conformation of brush border myosin using monoclonal antibodies.

We have produced and characterised five monoclonal antibodies against myosin isolated from chicken intestinal epithelial brush border cells. The binding sites of the antibodies on the rod portion of brush border myosin were localised using rotary shadowing/electron microscopy of myosin-antibody complexes. Two antibodies were shown to bind to the tip of the myosin tail, two antibodies to sites about two thirds down the length of the rod, and one antibody about one third down the length of the rod. Brush border myosin was digested with papain, trypsin and alpha-chymotrypsin, and they myosin fragments obtained were analysed by western blots with the monoclonal antibodies and polyclonal antiserum, and by gel overlay with 125I-labelled light chains. Using this approach we were able to identify and map the protease cleavage sites and thus characterise the proteolytic substructure of brush border myosin. Solid-phase assays, western blots and immunofluorescence were used to study the cross-reactivity of these monoclonal antibodies against a variety of myosins from different species and cell types, to assess the immunological relatedness between brush border myosin and homologous molecules present in different tissues and species. Finally, we used a competitive solid-phase assay to measure the 'relative affinities' of the antibodies towards the three possible conformational states of brush border myosin, i.e. filament, extended monomer and folded monomer.

Animals↗
PubMed1986

Regulation in vitro of brush border myosin by light chain phosphorylation.

Myosin was purified from chicken brush border cells to greater than 95% homogeneity and in a predominantly non-phosphorylated state. The effects of light chain phosphorylation by a Ca2+-calmodulin-dependent myosin light chain kinase on the conformational, enzymatic and filament assembly properties of this myosin were investigated. The actin-activated MgATPase activity of the non-phosphorylated myosin was low, and upon light chain phosphorylation an eight- to ninefold increase in this activity was observed, which was further potentiated by tropomyosin. Light chain phosphorylation was shown to control the assembly and disassembly of brush border myosin filaments. For example, turbidity measurements and electron microscopy demonstrated that MgATP disassembled non-phosphorylated myosin filaments; the disassembled myosin could reassemble when the light chains were phosphorylated, and could be disassembled again by dephosphorylating the light chains with phosphatase. In the electron microscope, the disassembled non-phosphorylated myosin molecules appeared in a folded conformation, and they were extended when phosphorylated. Proteolytic digestion was used to probe further the conformation of these folded and extended molecules, and their subunit organizations were characterized by a gel overlay technique. Quantitative analysis further demonstrated that light chain phosphorylation alters dramatically the monomer/polymer equilibrium of brush border myosin, shifting it towards filament formation. Comparison of analogous data for myosin from gizzard and thymus shows that each myosin has distinct solubility properties.

Animals↗
PubMed1986

Relationship between systolic time intervals and arterial blood pressure.

It has been suggested that systolic time intervals (STI) can be used to monitor the cardiac effects of antihypertensive treatments and also to evaluate hypertensive patients. STI changes observed in hypertensives have been ascribed to myocardial disease, although they could be due to the existence of a relationship between STI and blood pressure. A group of 37 subjects (18 normotensives and 19 hypertensives) with no signs of heart failure and left ventricular dysfunction were studied to examine the relationship of STI to blood pressure. Pacing with an external battery pulse generator was performed at the rate of 95 beats/min in order to eliminate differences in heart rate. STI were measured from good quality high speed (100 mm/s) recordings and the average value of 10 consecutive cardiac cycles was used for statistical analysis. Normal subjects showed significantly lower values of pre-ejection period (PEP), electromechanical systole (QS2), and pre-ejection period/left ventricular ejection time ratio (PEP/LVET). Moreover, a significant inverse relationship between diastolic pressure and LVET and significant direct relationships between diastolic pressure and PEP, systolic pressure and PEP, diastolic pressure and PEP/LVET, and between systolic pressure and PEP/LVET were demonstrated. We suggest to consider the relation of STI to blood pressure to provide regression equations to best appreciate and use STI.

Adult↗
PubMed1984

Computerized M-mode echocardiography in the assessment of cardiovascular effects during intravenous administration of amiodarone.

Antianginal and antiarrhythmic long term therapy with amiodarone may be associated with side effects, therefore it should be used mainly in short term treatment of severe arrhythmias and acute coronary insufficiency. It is important to assess if any inotropic effect may be produced after intravenous administration of this drug in commonly accepted therapeutic doses (5 mg/kg body weight). To investigate this possibility we studied the effects of amiodarone on blood pressure (BP), on heart rate (HR) and on the maximal velocity of circumferential fiber shortening (Vcf Max). Simultaneous echocardiogram (UCG), electrocardiogram (lead DII) (ECG) and BP cuff measurement were performed on 12 subjects without cardiomegaly and clinical evidence of heart failure, immediately before a 30 second intravenous injection of amiodarone and every 30 seconds over a period of 6 minutes after drug administration. Amiodarone administration markedly raised HR within the first 30 seconds from the beginning of the injection and concomitantly decreased diastolic BP. No significant lowering of systolic BP was observed. Vcf Max (circ/sec) raised during the test concomitantly with HR increase, showing a significant relationship between left ventricular performance and HR. The same was also true during atrial pacing performed on one subject. No significant changes in any of the parameters studied were demonstrated after placebo (saline solution) administration to two presumable healthy subjects. Amiodarone does not seem to have any positive or negative intrinsic inotropic effect when administered intravenously at a dose of 5 mg/kg body weight.

Adolescent↗
PubMed1983

Circadian rhythms in dynamic electrocardiography.

A group of ten healthy subjects aged 32-58 years was studied by dynamic electrocardiography. An electrocardiogram (ECG) was recorded on CM 5 lead for 14 seconds every 15 minutes during the 24 hours. All the subjects were under a similar nyctohemeral schedule, sleeping between 23.30 and 06.45, and all followed their spontaneous diet without any restriction. "Mean Cosinor" analysis of the data revealed statistically significant circadian rhythms of heart rate (HR), R and T-wave voltages, duration of the QT interval and ST segment displacement, but not of the duration of the corrected QT (QTc).

Adult↗