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Biomedical subjects

C Hidalgo

Publications and source records attributed to C Hidalgo.

At least 55 records · Page 3Linked to original sources
PubMed1994

[Influence of body fat and its distribution on cardiovascular risk factors in healthy subjects].

The aim of this work was to study the association between obesity and body fat distribution with known cardiovascular risk factors. Seven hundred eighty two healthy individuals, 634 men and 148 female age 44 +/- 10 years were studied. Multiple stepwise regression models were performed in which cardiovascular risk factors (total, LDL and HDL cholesterol, triglycerides, fasting and postprandial blood glucose, systolic and diastolic blood pressure) were considered as the dependent variable and age, sex, smoking habits, body mass index (BMI), waist circumference (WC), waist hip ratio (WHR), subscapular/tricipital skinfold ratio (STR) and percentage of total body fat (%BF), derived from the sum of four skinfolds, as the independent variables. Among anthropometric variables, WC was the principal predictor of total cholesterol and basal blood glucose, WHR was the principal predictor of HDL cholesterol (inverse relationship) and triglycerides; BMI was the principal predictor of systolic and diastolic blood pressure; %BF was the principal predictor of post prandial blood glucose. Performing the same analysis in a subgroup of patients with a BMI between 21 and 24, measures of fat distribution continued to be predictors of cardiovascular risk factors. It is concluded that both total body fat and its distribution are related to cardiovascular risk factors and, in some cases, may have an additive effect and should be measured in preventive medical examinations.

Adipose Tissue↗
PubMed1993

pH-sensitive calcium release in triads from frog skeletal muscle. Rapid filtration studies.

Triad vesicles from frog skeletal muscle exhibited calcium-induced calcium release highly sensitive to extravesicular pH; calcium induced release at pH > 7.4 but not at pH 6.8. In contrast, triads isolated from rabbit skeletal muscle exhibited significant calcium-induced calcium release at pH 6.8. At pH 7.4, there was no stimulation of calcium release in triads from frog at pCa 7, maximum stimulation at pCa 5, and complete inhibition at pCa 3. Addition of ATP at pCa 5, pH 6.8, induced calcium release with the same high rate constants in both preparations. In triads from frog, ATP-induced calcium release at pCa 5 had the same kinetics at pH 6.8 and 7.4, whereas ATP-induced calcium release at pCa > 8, pH 6.8, was partial, with a decrease in the amounts released but not in rate constants. In contrast, triads from rabbit displayed the opposite behavior, with a decrease in rate constants but not in the amounts of calcium released at pCa > 8, pH 6.8. In triads from frog ATP-induced calcium release decreased at pCa < 4, to reach total inhibition at pCa 2; addition of magnesium (free > 0.5 mM) completely abolished ATP-induced calcium release at pH 6.8, pCa 7 or 5. The potential physiological relevance of these results is discussed.

Adenosine Triphosphate↗
PubMed1993

Phospholipase C activity in membranes and a soluble fraction isolated from frog skeletal muscle.

Highly purified triads and transverse tubules, as well as soluble fraction isolated from frog skeletal muscle, hydrolyze exogenous phosphatidylinositol 4,5-bisphosphate forming inositol 1,4,5-trisphosphate with maximal rates in the range 0.5-1 nmol/mg per min at pCa 3. Sarcoplasmic reticulum membranes present a minor activity. The hydrolysis rates in triads were 0.072 +/- 0.015 nmol/mg per min at pCa 7, increasing to 0.263 +/- 0.026 nmol/mg per min at pCa 5 with 1.0 mM Mg and 0.1 mM substrate. The phospholipase C activity of isolated transverse tubules at pCa 3 was 0.570 +/- 0.032 nmol/mg per min. Since triads contain 10% transverse tubules, and correcting for the small contribution of sarcoplasmic reticulum, the calculated phospholipase C activity of transverse tubules at pCa 3 is about 10-times higher than the observed values, suggesting loss of activity during isolation. The activation by calcium was also observed in a soluble fraction and was neither replaced nor inhibited by magnesium. No effect of GTP analogs on phospholipase C activity was detected.

Animals↗
PubMed1993

Triads and transverse tubules isolated from skeletal muscle contain high levels of inositol 1,4,5-trisphosphate.

We measured the content of inositol 1,4,5-trisphosphate in sarcoplasmic reticulum, transverse tubules, and triads isolated from frog skeletal muscle, as well as in triads isolated from rabbit skeletal muscle. We found that acid extracts of both transverse tubules and triads contained significant amounts of inositol 1,4,5-trisphosphate, in the range of 300-400 pmol/mg of protein as determined by a radioreceptor assay, whereas no detectable amounts were found in sarcoplasmic reticulum vesicles. The identity of inositol 1,4,5-trisphosphate in the extracts was confirmed by comigration with [3H]inositol 1,4,5-trisphosphate on polyethyleneimine-cellulose plates, and by phosphorylation to inositol 1,3,4,5-tetrakisphosphate using the inositol 1,4,5-trisphosphate 3-kinase present in muscle extracts. These findings may have important physiological implications. First, the results indicate that the muscle plasma membrane regions differentiated as transverse tubules contain high amounts of inositol 1,4,5-trisphosphate, suggesting that they might possess a high density of binding sites for this compound. Second, since inositol 1,4,5-trisphosphate has been proposed as a chemical transmitter in excitation-contraction coupling in skeletal muscle, our finding that this second messenger is present in high density at the site of coupling may contribute to the understanding of its role in this process.

Animals↗
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↗