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Biomedical subjects

C Hidalgo

Publications and source records attributed to C Hidalgo.

At least 19 recordsLinked to original sources
PubMed1992

[A 2-year follow-up of a program for the control of cardiovascular risk factors among asymptomatic workers].

In 1987, a cardiovascular risk profile was obtained on 836 workers of the National Electricity Co in Santiago. There were 714 males and 125 females, the mean age was 45 years (ES +/- 0.3). Hypertension (systolic pressure > 160 or diastolic > 90 mmHg) was present in 17% of subjects, hypercholesterolemia (> 240 mg/dl or > 220 mg/dl associated to 2 other risk factors) in 17%, obesity (> 20% above ideal weight) in 33% and 29% were smokers. An advice to stop smoking, changes in the casino menu and hypertension, obesity and hypercholesterolemia's control programs were offered. These were attended by 108 hypertensives, 141 subjects with hypercholesterolemia and 104 obese individuals with an attendance rate of 64%, 75 and 77% respectively. Measurements repeated 2 years later revealed a reduction in diastolic pressure of 3.3 +/- 1.1 mmHg (p < 0.004) only in adherent subjects. Cholesterol levels were reduced by 24 +/- 3 mg/dl (p < 0.001) with no differences for non participants, adherent and non adherent subjects. Adherent obese subjects reduced their weight by 2.2 +/- 0.4 kg (p < 0.001). There was no change in the number of smokers.

Cardiovascular Diseases↗
PubMed1991

Inositol 1,4,5-triphosphate phosphatase activity in membranes isolated from amphibian skeletal muscle [corrected].

The hydrolysis of [3H]inositol 1,4,5-trisphosphate by a soluble fraction and by isolated transverse tubule and sarcoplasmic reticulum membranes from frog skeletal muscle was studied. Transverse tubule membranes displayed rates of hydrolysis several-fold higher than those of sacroplasmic reticulum and soluble fraction; Km and Vmax were 25.2 microM and 44.1 nmol/mg/min, respectively. Transverse tubule membranes sequentially hydrolyzed inositol trisphosphate to inositol bisphosphate, inositol 1-phosphate and inositol, indicating that these membranes have inositol bis- and monophosphatases in addition to inositol trisphosphatase.

Animals↗
PubMed1991

[Method for direct determination of the rotational symmetry of thick muscle filaments by digital image processing].

We present a method based on digital image processing techniques that permits to determine directly the rotational symmetry of muscle thick filaments. Electron micrographs of transverse sections of relaxed muscle rapidly frozen against a copper block cooled with liquid helium were digitized, aligned to give maximal cross correlation and averaged. The final averaged image permits to determine directly the number of projections on the backbone surface.

Animals↗
PubMed1991

[Preventive medical examination in asymptomatic workers: design and initial outcome of an institutional program].

We have designed a preventive medical examination program for workers of an electric company in Santiago, Chile. The first stage, directed mainly to identification of cardiovascular risk factors was completed in 1987. 1006 males and 163 females with mean age 45 +/- 9.4 years (range 22-65) were screened. High blood pressure mainly of mild degree was detected in 17.6% of subjects (57% of them were new cases). Total cholesterol above 220 mg/dl and HDL cholesterol below 40 mg/dl were present in 33% and 22%, respectively. Obesity (body weight > 120% of ideal weight for height) was present in 19%, and body mass index was above 27 in 25% of subjects. 23% of males and 31% of females smoked 1 or more cigarettes a day and 2% had an abnormal non-fasting glucose level. A total of 750 workers have at least 1 risk factor that should be corrected. No cases of cancer were detected by Papanicolaou and mammography. A positive correlation was found among LDL cholesterol, age and triglyceride levels and HDL was negatively correlated to triglycerides, blood glucose and obesity. A multivariate analysis of these factors revealed that only age was related to LDL levels and triglycerides to HDL levels. This health prevention program may help a significant number of asymptomatic workers by detecting risk factors that need correction in order to decrease mortality and morbidity in this population.

Adult↗
PubMed1990

[Chronic neutrophilic leukemia: apropos of 2 cases and review of the literature].

Two patients with chronic neutrophilic leukemia, a rare myeloproliferative syndrome, are reported with a review of the literature. The major features of the 34 collected cases (including the two patients reported here) were persistent leukocytosis simulating a leukemoid reaction, hepatosplenomegaly, hyperuricemia, increased vitamin B12 blood level, increased leukocyte alkaline phosphatase and absence of the Philadelphia chromosome. Infection was the leading cause of death. Concomitant multiple myeloma was found in eight patients.

Adult↗
PubMed1989

Sodium-calcium exchange in transverse tubules isolated from frog skeletal muscle.

Transverse tubule vesicles isolated from frog skeletal muscle display sodium-calcium exchange activity, which was characterized measuring 45Ca influx in vesicles incubated with sodium. The initial rates of exchange varied as a function of the membrane diffusion potentials imposed across the membrane vesicles, increasing with positive intravesicular potentials according to an electrogenic exchange with a stoichiometry greater than 2 sodium ions per calcium ion transported. The exchange activity was a saturable function of extravesicular free calcium, with an apparent K0.5 value of 3 microM and maximal rates of exchange ranging from 3 to 5 nmol/mg protein per 5 s. The exchange rate increased when intravesicular sodium concentration was increased; saturation was approached when vesicles were incubated with concentrations of 160 mM sodium. The isolated transverse tubule vesicles, which are sealed with the cytoplasmic side out, had a luminal content of 112 +/- 39 nmol calcium per mg protein. In the absence of sodium, the exchanger carried out electroneutral calcium-calcium exchange, which was stimulated by increasing potassium concentrations in the intravesicular side. Calcium-calcium exchange showed an extravesicular calcium dependence similar to the calcium dependence of the sodium-calcium exchange, with an apparent K0.5 of 6 microM. Sodium-calcium and calcium-calcium exchange were both inhibited by amiloride. The sodium-calcium exchange system operated both in the forward and in the reverse mode; sodium, as well as calcium, induced calcium efflux from 45Ca-loaded vesicles. This system may play an important role in decreasing the intracellular calcium concentration in skeletal muscle following electrical stimulation.

Animals↗
PubMed1989

Inositol trisphosphate and excitation-contraction coupling in skeletal muscle.

The role of inositol trisphosphate as a chemical messenger in excitation-contraction coupling is discussed, both in terms of positive and negative results. The evidence presented includes experiments on the effect of inositol trisphosphate in intact and skinned fibers, in calcium release from isolated sarcoplasmic reticulum vesicles, in activation of single calcium release channels incorporated in planar bilayers, and biochemical experiments that have established the presence of all the intermediate steps involved in the metabolism of phosphoinositides, both in intact muscle and in isolated membranes. From these results, it is clear that a role for inositol triphosphate in skeletal muscle function is highly likely; whether this molecule is the physiological messenger in excitation-contraction coupling remains to be established.

Animals↗
PubMed1989

Activation of calcium channels in sarcoplasmic reticulum from frog muscle by nanomolar concentrations of ryanodine.

Sarcoplasmic reticulum vesicles isolated from fast-twitch frog skeletal muscle presented two classes of binding sites for ryanodine, one of high affinity (Kd1 = 1.7 nM, Bmax1 = 3.3 pmol per mg) and a second class with lower affinity (Kd2 = 90 nM, Bmax2 = 7.0 pmol per milligram). The calcium channels present in the sarcoplasmic reticulum membranes were studied in vesicles fused into lipid bilayers. Low concentrations of ryanodine (5 to 10 nM) activated a large conductance calcium channel after a short delay (5 to 10 min). The activation, which could be elicited from conditions of high or low fractional open time, was characterized by an increase in channel fractional open time without a change in conductance. The open and closed dwell time distributions were fitted with the sum of two exponentials in the range of 4 to 800 ms. The activating effect of ryanodine was due to an increase of both open time constants and a concomitant decrease in the closed time constants. Under conditions of low fractional open time (less than 0.1), the time spent in long closed periods (greater than 800 ms) between bursts was not affected by ryanodine. Higher concentrations of ryanodine (250 nM) locked the channel in a lower conductance level (approximately 40%) with a fractional open time near unity. These results suggest that the activating effects of nanomolar concentrations of ryanodine may arise from drug binding to high affinity sites. The expression of the lower conductance state obtained with higher concentrations of ryanodine may be associated with the low affinity binding sites observed in frog sarcoplasmic reticulum.

Alkaloids↗
PubMed1988

Calcium modulation of phosphoinositide kinases in transverse tubule vesicles from frog skeletal muscle.

Highly purified transverse tubule membranes isolated from frog skeletal muscle phosphorylate phosphatidylinositol to phosphatidylinositol 4-phosphate and phosphatidylinositol (4,5)-bisphosphate. The two phosphorylation reactions have different calcium requirements. Phosphorylation of phosphatidylinositol to phosphatidylinositol 4-phosphate, which takes place in both isolated transverse tubules and sarcoplasmic reticulum membrane, is independent of calcium in a range of concentrations from 10(-9) to 10(-6) M, and is progressively inhibited to 10% of the maximal values by increasing calcium to 10(-4) M or higher (K0.5 = 5 X 10(-6) M). In contrast, phosphorylation of phosphatidylinositol 4-phosphate to phosphatidylinositol (4,5)-bisphosphate, a reaction exclusively present in transverse tubule membranes, is maximal at calcium concentrations higher than 2 X 10(-6) M and decreases to 30% of maximal values at calcium concentrations of 2 X 10(-7) M or lower (K0.5 = 10(-6) M). Unlike frog membranes, transverse tubules from rabbit muscle need exogenous phosphatidylinositol 4-phosphate in order to produce the bisphosphate derivative in the same range of calcium concentrations. Inositol (1,4,5)-trisphosphate has been proposed recently as a chemical messenger in excitation-contraction coupling in skeletal muscle. Calcium regulation of the synthesis of phosphatidylinositol (4,5)-bisphosphate, the membrane-bound precursor of inositol (1,4,5)-trisphosphate, might have physiological implications regarding modulation of excitation-contraction coupling by intracellular calcium levels.

1-Phosphatidylinositol 4-Kinase↗
PubMed1988

Inositol (1,4,5)-trisphosphate activates a calcium channel in isolated sarcoplasmic reticulum membranes.

Sarcoplasmic reticulum membrane vesicles isolated from frog skeletal muscle display high conductance calcium channels when fused into phospholipid bilayers. The channels are selective for calcium and barium over Tris. The fractional open time was voltage-independent (-40 to +25 mV), but was steeply dependent on the free cis [Ca2+] (P0 = 0.02 at 10 microM cis Ca2+ and 0.77 at 150 microM Ca2+; estimated Hill coefficient: 1.6). Addition of ATP (1 mM; cis) further increased P0 from 0.77 to 0.94. Calcium activation was reversed by addition of EGTA to the cis compartment. Magnesium (2 mM) increased the frequency of rapid closures and 8 mM magnesium decreased the current amplitude from 3.4 to 1.2 pA at 0 mV, suggesting a reversible fast blockade. Addition of increasing concentrations of inositol (1, 4, 5)-triphosphate (cis), increased P0 from 0.10 +/- 0.01 (mean +/- SEM) in the control to 0.85 +/- 0.02 at 50 microM in an approximately sigmoidal fashion, with an apparent half-maximal activation at 15 microM inositol (1, 4, 5)-trisphosphate in the presence of 40 microM cis Ca2+. Lower concentrations of this agonist were required to produce a significant increase in P0 when 10 microM or less cis Ca2+ were used. The channel was blocked by the addition to the cis compartment of either 0.5 mM lanthanum, 0.5 microM ruthenium red, or 200 nM ryanodine, all known inhibitors of Ca2+ release from sarcoplasmic reticulum vesicles. These results demonstrate the presence of calcium channels in the sarcoplasmic reticulum from frog skeletal muscle with a pharmacological profile consistent with a role in excitation contraction coupling and with the hypothesis that inositol ( 1,4,5)-trisphosphate is a physiological agonist in this process.

Animals↗
PubMed1987

Lipid composition of purified transverse tubule membranes isolated from amphibian skeletal muscle.

The level and proportion of lipids and their fatty acid composition were analyzed in highly purified transverse tubule membranes of amphibian skeletal muscle. Tubule membranes show (a) a higher content of lipids, (b) a higher phospholipid/cholesterol ratio and (c) a different phospholipid composition from other subcellular fractions, such as the light and heavy membranes from sarcoplasmic reticulum, which are similar in lipid profile. Transverse tubule membranes are characterized by a high percentage of phosphatidylserine and sphingomyelin and a low proportion of phosphatidylcholine compared with the other membranes. All three show a high proportion of ethanolamine plasmalogens (50% of the total ethanolamine glycerophospholipid). Transverse tubule membrane lipids contain a high proportion of 20- and 22-carbon polyunsaturated fatty acids, predominantly 20:4, 20:5, 22:5 and 22:6. Arachidonate predominates in phosphatidylinositol, eicosapentaenoate and docosahexaenoate in ethanolamine and serine glycerophospholipids.

Animals↗
PubMed1987

Lupus erythematosus cells in serum and pleural fluid of a patient with negative fluorescent antinuclear antibody test.

The authors report here a 61-year-old male with anemia, arthritis, and pleural effusions who had lupus erythematosus (LE) cells in the pleural fluid and a strongly positive LE cell test in the blood. However, the fluorescent antinuclear antibody (FANA) assay performed repeatedly with the serum always had negative results, despite the use of various technics. The patient was considered to have systemic LE and responded well to treatment with corticosteroids. Although the authors could not explain the LE cell-FANA incongruity, they suggest that the LE test not be deleted from the clinical laboratories' tests.

Antibodies, Antinuclear↗
PubMed1987

Lipid-protein interactions and the function of the Ca2+-ATPase of sarcoplasmic reticulum.

Regardless of the nature of the protein constituents of membranes, the molecular arrangement of lipids interacting with them must satisfy hydrophobic, ionic, and steric requirements. Biological membranes have a great diversity of lipid constituents, and this diversity might have functional roles. It has been proposed, for example, that the hydrophobic regions of membrane proteins are stabilized in the membrane through interactions with lipids able to adopt configurations other than the bilayer structure. Progress in understanding at the molecular level how lipid-protein interactions control the properties of membrane proteins has been hindered by the lack of information concerning the structure of the hydrophobic regions of membrane proteins. Nevertheless, there are many examples in the literature describing how changes in the lipid environment affect physical and biochemical properties of membrane proteins. From these studies, discussed in this review, an overall picture of how lipids and proteins interact in membranes is beginning to emerge.

Amino Acid Sequence↗
PubMed1986

Phosphorylation of phosphatidylinositol by transverse tubule vesicles and its possible role in excitation-contraction coupling.

Phosphorylation of phosphatidylinositol to phosphatidylinositol 4-monophosphate and to phosphatidylinositol 4,5-bisphosphate was demonstrated in transverse-tubule membranes isolated from frog skeletal muscle using [gamma-32P]ATP as substrate. At millimolar concentrations of Mg2+ both phosphorylation reactions were completed within 15 s at 25 degrees C. Isolated sarcoplasmic reticulum vesicles phosphorylated phosphatidylinositol to phosphatidylinositol 4-phosphate with a lower specific activity than the transverse tubules, and lacked the ability to produce phosphatidylinositol 4,5-bisphosphate. These findings show, for the first time, that isolated transverse-tubule membranes carry out one of the steps required to sustain a role for inositol trisphosphate as the physiological messenger in excitation-contraction coupling in skeletal muscle. The finding that 0.5 mM tetracaine apparently inhibits the phosphorylation of phosphatidylinositol 4-phosphate to phosphatidylinositol 4,5-bisphosphate also supports a role for these intermediates in excitation-contraction coupling.

Animals↗
PubMed1986

Transverse tubules from frog skeletal muscle. Purification and properties of vesicles sealed with the inside-out orientation.

Transverse tubule vesicles were isolated from frog skeletal muscle by a procedure initially described by Rosemblatt et al. (J. Biol. Chem. 256, 8140-8148 (1981)) and later modified by Hidalgo et al. (J. Biol. Chem. 258, 13937-13945 (1983]. A large fraction of the isolated vesicles (80-90%) were sealed, as indicated by the detergent induced increase in (Na+ + K+)-ATPase activity and ATP-dependent ouabain binding. To determine the orientation of the sealed vesicles binding of digoxin, a lipid soluble derivative of ouabain, was measured. The same values of ATP-dependent digoxin binding were found with or without detergents, indicating that all the vesicles that are sealed have the ATP site accessible, and hence are sealed with the cytoplasmic side-out (inside-out orientation). The transverse tubule preparation isolated from frog muscle is highly purified, as indicated by its cholesterol content and its (Na+ + K+)-ATPase activity; negligible contamination with sarcoplasmic reticulum was observed, as indicated by the protein composition and the lack of measurable Ca2+-ATPase activity of the isolated transverse tubules. High initial rates of Mg2+-ATPase activity were found, with the peculiar property of being inhibited during the course of the reaction. Addition of lysophosphatidylcholine or saponin partially prevented the inhibition of Mg2+-ATPase activity during the reaction.

Animals↗
PubMed1986

Ion pathways in transverse tubules. Quantification of receptors in membranes isolated from frog and rabbit skeletal muscle.

The presence of four cation pathways in membrane vesicles isolated from transverse tubules of frog and rabbit skeletal muscle was studied by measuring binding of specific blockers. Transverse tubules purified from frog muscle have a maximal binding capacity for [3H]nitrendipine (a marker for voltage-dependent calcium channels) of 130 pmol/mg of protein; this binding is strongly dependent on temperature and, at 37 degrees C, on the presence of diltiazem. Receptors for [3H]ethylenediamine tetrodotoxin (a marker for voltage-dependent sodium channels) and for 125I-labeled alpha-bungarotoxin (a marker for acetylcholine-mediated channels) showed maximal binding values of about 5 pmol/mg. The number of sodium-pumping sites in the isolated tubule vesicles, inferred from [3H]ouabain binding, was 215 pmol/mg. The high purity of this preparation makes feasible the use of these values as a criterion to judge the degree of purity of isolated preparations, and it allows investigation of transverse tubule contamination in other muscle membrane fractions.

Acetylcholine↗