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Biomedical subjects

J Alvarez

Publications and source records attributed to J Alvarez.

At least 199 records · Page 11Linked to original sources
PubMed1993

Control of Ca2+ entry into HL60 and U937 human leukaemia cells by the filling state of the intracellular Ca2+ stores.

Differentiation of HL60 cells by treatment with dimethyl sulphoxide induces the expression of membrane receptors for N-formylmethionyl-leucyl-phenylalanine (fMLP) and for platelet-activating factor (PAF). In these cells both agonists produced an increase in the cytosolic Ca2+ concentration ([Ca2+]i) by release of Ca2+ from the intracellular stores, followed shortly by an acceleration of the entry of Ca2+ or Mn2+, used here as a Ca2+ surrogate for Ca2+ channels. Cytochrome P-450 inhibitors blocked the agonist-induced entry of Ca2+ or Mn2+ with no modification of Ca2+ release from the stores. Emptying the intracellular Ca2+ stores either by treatments inducing no inositol phosphate production, such as prolonged incubation in Ca(2+)-free medium or treatment with the Ca2+ ionophore ionomycin, increased the plasma-membrane permeability to Ca2+ and Mn2+. This Ca(2+)-store-regulated Mn2+ entry was inhibited by Ni2+ and by cytochrome P-450 inhibitors. Refilling of the Ca2+ stores by incubation in Ca(2+)-containing medium restored low Mn2+ permeability. The same mechanism is present and functional in non-differentiated cells, before expression of membrane receptors for fMLP and PAF. These results suggest that agonist-induced Ca2+ (Mn2+) entry is secondary to the emptying of the intracellular Ca2+ stores, which in turn activates plasma-membrane channels by a mechanism involving cytochrome P-450.

Antifungal Agents↗
PubMed1993

Protein flexibility and aggregation state of human epidermal growth factor. A time-resolved fluorescence study of the native protein and engineered single-tryptophan mutants.

A time-resolved fluorescence spectroscopic study of the recombinant human epidermal growth factor (hEGF), a bis(tryptophan)-containing protein (Trp49-Trp50), and of the two single-tryptophan-containing engineered mutants with Trp49 or Trp50 replaced by Phe ([W49F]hEGF, [W50F]hEGF), was undertaken in order to gain insight into the conformational dynamics of the C-terminal region. Quite different position-dependent microenvironments for the two Trp residues are shown by comparing the fluorescence intensity decay of both mutants. Trp50 in the single-tryptophan mutant [W49F]EGF probably undergoes a dominant interaction with the solvent. A more heterogeneous environment of Trp49 in the [W50F]hEGF mutant is found. Moreover, the fluorescence decay of the native hEGF is not simply the additive result of the decays of both mutants: the Trp2 sequence confers a conformation of the C-terminal sequence which is more in contact with the rest of the protein molecule. By contrast, the fluorescence anisotropy decay of the native protein is quite similar to that of the single-tryptophan mutants. A high degree of rotational freedom in the C-terminal region of the protein is demonstrated. The resonance energy transfer, which could contribute to the anisotropy decay, appears therefore not to be highly efficient with respect to the depolarization motions. In addition to these local conformational and dynamic aspects of the hEGF C-terminal sequence, the fluorescence anisotropy decay data demonstrate the existence of a dimerization process of the native protein which is dependent on pH and protein concentration. This phenomenon influences the excited-state lifetime profiles and, therefore, the local conformational equilibrium of the C-terminal region.

Epidermal Growth Factor↗
PubMed1993

1 alpha,25-dihydroxyvitamin D3 up-regulates expression of the osteoclast integrin alpha v beta 3.

Osteoclast precursors selectively attach to bone and differentiate into multinucleated cells that function to remodel and resorb it. We have shown previously that attachment of osteoclasts to bone and subsequent resorption are mediated by the integrin alpha v beta 3. 1 alpha,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) enhances osteoclast precursor differentiation in vivo by mechanisms that are still not clearly understood but entail enhanced attachment of cells to bone. This observation raises the possibility that at least one component of vitamin D-induced osteoclast precursor differentiation involves modulation of integrin expression. To test if the steroid modulates the osteoclast integrin alpha v beta 3 (the vitronectin receptor), we examined the effects of 1,25-(OH)2D3 on transcription of the alpha v gene as well as surface expression and function of alpha v beta 3, in chicken osteoclast precursors. Treatment of the cells with 1,25-(OH)2D3 led to a progressive dose-dependent increase in steady state alpha v mRNA levels with enhanced expression evident within 24 h. The effect was receptor-mediated as indicated by the effects of other vitamin D analogs. The increase in alpha v mRNA levels did not reflect decreased message degradation but, as demonstrated by nuclear run-on experiments, was due to accelerated rates of transcription. Most importantly, induction of alpha v mRNA by 1,25-(OH)2D3 was mirrored by higher levels of expression of alpha v beta 3 on the cell surface, as well enhanced attachment to its substrate, vitronectin.

Animals↗
PubMed1993

The pathway for refilling intracellular Ca2+ stores passes through the cytosol in human leukaemia cells.

The pathway for refilling the intracellular Ca2+ stores of HL60 and U937 human leukaemia cells loaded with fura-2 has been investigated. On addition of external Ca2+ to cells with empty stores there was an increase in the cytosolic Ca2+ concentration ([Ca2+]i) which preceded the refilling of the stores. The increase in [Ca2+]i was faster than the refilling, by 3- to 15-fold, depending on the cell type. In measurements in single HL60 cells we found that the refilling of the stores correlated with the extent of the [Ca2+]i increase on addition of external Ca2+. The cells showing no [Ca2+]i increase were unable to refill their stores. The addition of Ni2+ to the extracellular medium prevented both the [Ca2+]i increase and the refilling of the stores. These results indicate that the limiting step for store refilling is the entry of Ca2+ from the extracellular medium to the cytosol. Hence, we conclude that extracellular Ca2+ cannot gain access directly to the intracellular Ca2+ stores in these cells, but must first enter the cytosol and be taken up from there into the stores.

Calcium↗
PubMed1993

Modulation of L-type Ca channel activity by P2-purinergic agonist in cardiac cells.

The mechanism of enhancement of the L-type Ca current by a P2-purinergic agonist adenosine-5'-O-(3-thiotriphosphate) (ATP gamma S) was studied by recording single channel activity from cell-attached patches on rat isolated ventricular cells using patch pipettes containing 110 mM Ba2+. The application of ATP gamma S to the patch membrane through the pipette solution did not affect single channel activity. The addition of ATP gamma S to the bath containing a depolarizing solution was ineffective due to the voltage dependence of the purinergic stimulation. Bath application of ATP gamma S (100 microM) to control 4-(2-hydroxyethyl)-1-piperazine-ethanesulphonic acid (HEPES) solution increased the amplitude of ensemble average currents both by decreasing the probability of a blank sweep occurring and by increasing the number of openings per non-blank sweep. The single channel conductance (17 pS) was not changed by ATP gamma S. Both activation and inactivation curves were shifted towards hyperpolarized potentials by about 10 mV under P2-purinergic stimulation. Since ATP gamma S increased channel activity when applied via the bath, it must be supposed that a diffusible messenger is involved.

Adenosine Triphosphate↗
PubMed1993

Binding of osteopontin to the osteoclast integrin alpha v beta 3.

Occupancy of the chicken osteoclast alpha v beta 3 integrin stimulates immediate cell signals. Peptides from osteopontin containing Arg-Gly-Asp and peptides from the osteopontin and bone sialoprotein sequences containing Arg-Gly-Asp stimulated immediate reductions in osteoclast cytosolic Ca2+. The changes in cytosolic Ca2+ required the Arg-Gly-Asp sequence, and were blocked by LM609, a monoclonal antibody to the alpha v beta 3 integrin. Osteoclast stimulation by the proteins through the integrin did not require immobilization since soluble peptides produced changes in cytosolic Ca2+ and inhibited osteoclast binding to bone particles and bone resorption. The decrease in cytosolic Ca2+ stimulated by osteopontin and related peptides was due to activation of a plasma membrane Ca(2+)-ATPase. Thus, the data suggest that ligand binding to the osteoclast alpha v beta 3 integrin results in a reduction in cytosolic Ca2+ which participates in regulation of osteoclast function.

Animals↗
PubMed1993

The incidence of obstructive apneas in preterm infants with and without bronchopulmonary dysplasia.

We tested the hypotheses that (1) preterm infants with bronchopulmonary dysplasia (BPD) have an increased incidence of obstructive apneas as compared to those without BPD (control) and (2) the respiratory pattern during obstructive apneas may be associated with more pronounced hypoventilation. Ventilation was measured with a flow-through system. We examined 2929 total apneas in 12 infants with BPD and 4366 apneas in 12 control infants matched for study weight (1.51 +/- 0.11 kg in the BPD group and 1.62 +/- 0.12 kg in the control group, P = 0.6) and for postconceptional age (33.3 +/- 0.8 weeks in the BPD group compared with 33.4 +/- 0.7 weeks in the control group, P = 0.6). The incidence of central apneas predominated in the BPD group (2551/2929, 87%) and in the control group (4188/4366, 96%). Obstructive apneas were more frequent in the BPD group (378/2929, 13%) than in the control group (178/4366, 4%, P = 0.004). The increased incidence of obstructive apneas in infants with BPD was observed in Quiet sleep (9.1 vs. 1.6%, P = 0.03) and in REM sleep (14.2 vs. 3.6%, P = 0.009). This increased incidence of obstructive apneas was applicable to short apneas (< 10 s, 10.9 vs. 2.7%, P = 0.003) and long apneas (> 10 s, 27.5 vs. 16.4%, P = 0.01). There were no significant changes in ventilatory pattern that could be uniquely attributed to one type of apnea. The findings suggest: (1) the great variability in the incidence of obstructive apneas reported in the literature relates, at least in part, to the clinical status of the infants and (2) ventilatory pattern is not a useful predictor of either type of apnea.

Apnea↗
PubMed1993

Haemodynamic effects of propofol during coronary artery bypass surgery.

We have studied the haemodynamic effects of a bolus injection of propofol 2 mg kg-1 in 20 patients with good ventricular function undergoing aortocoronary bypass surgery. Heart rate and systolic and diastolic systemic (SAP, DAP) and pulmonary arterial pressures, central venous pressure, pulmonary artery wedge pressure, cardiac output (CO), right ventricular ejection fraction, systemic (SVR) and pulmonary vascular resistances and left ventricular stroke work index (LVSWI) were measured before and at 1, 3, 5, 10, 20 and 30 min after the administration of propofol. At 1 min, maximum decreases were detected in SAP (-26%, P < 0.001), DAP (-17%, P < 0.001), SVR (-22% P < 0.001) and LVSWI (-23%, P < 0.001). The other variables studied showed no significant variations at any time during the study. We conclude that propofol reduces systemic arterial pressure by a decrease in SVR, but not in CO or ventricular filling pressures.

Adult↗
PubMed1993

Effects of propofol on mean arterial pressure and systemic vascular resistance during cardiopulmonary bypass.

This study was designed to evaluate the effects of propofol on mean arterial pressure (MAP) and systemic vascular resistance (SVR) during cardiopulmonary bypass (CPB). Twenty patients were divided randomly for administration of 2 mg.kg-1 propofol (group Propofol, n = 10) or 0.9% saline solution (group Control, n = 10) during CPB. The two groups were comparable with respect to sex, age, height, type of surgery (valvular or coronary), arterial hypertension and preoperative antihypertensive treatment. Only their weight and body surface area were significantly different (control group vs propofol group, respectively: 78.5 +/- 14.4 vs 64.7 +/- 7.7 kg, P < 0.05; and 1.85 +/- 0.2 vs 1.68 +/- 0.13 m2, P < 0.05). MAP, SVR and SVR index were significantly lower in the propofol group than in the control group at 10, 15 and 20 min of study, suggesting that the hypotensive effect of a bolus injection of propofol is due, at least in part, to a direct decrease in the SVR.

Aged↗
PubMed1993

Linear and whorled nevoid hypermelanosis.

A case of hyperpigmentation distributed in streaks and whorls was recently delineated and separated from a confusing number of pigmentary disorders. A 13-year-old boy had hyperpigmented, reticulate spots on his trunk and neck in a linear and whorled distribution following the lines of Blaschko. Onset was at age 1 year. Histologically, the spots showed increased melanin in the basal layer of the epidermis, but no increase in melanocytes, incontinence of pigment, or melanophages were seen in the dermis. The karyotype was 46,XY and there was no evidence of chromosomal mosaicism or chimerism. This entity represents a disorder separated recently from other pigmentary alterations that follow Blaschko lines, such as Bloch-Sulzberger incontinentia pigmenti, hypomelanosis of Ito, early systematized epidermal nevus, and chimerism.

Adolescent↗
PubMed1993

Spirometry and maximal respiratory pressures in patients with facial paralysis.

The study included 17 patients with facial paralysis (FP) (10 male, 7 female) aged 47.6 +/- 21.0 years. Twelve of the 17 patients had Bell's palsy. The other causes of FP were as follows: one, polyradiculoneuritis; one, war injury; one, cerebrovascular accident; one, sarcoidosis; and one, dermatomyositis. Spirometry and maximal respiratory pressures (PImax and PEmax) were performed with three different techniques: without holding the lips, with patient holding lips, and with technician holding lips. We observed significant differences for PImax and PEmax among the three methods. There were no differences for spirometric values. In nine of the patients with Bell's palsy, PImax, PEmax, and spirometry tests were repeated two months after the first determination. With respect to the first determination, the values of Pmax-w/v holding lips increased, yet spirometric values were similar. In conclusion, PImax and PEmax can be an index of clinical FP evolution. Spirometric maneuvers can be performed with either patient or technician holding lips to ensure a perfect seal between lips and mouthpiece.

Adult↗
PubMed1993

[The nutritional evaluation of cooking fats and oils].

Fatty acids content of locally obtained margarines, shortenings and cooking oils from businesses in Panama were determined by gas chromatographic method. The results found show that all of these oils have a high nutritional value, because of their high unsaturated fatty acid content. The soya oil group is characterized by its high content of linolenic acid (w3), for this reason they are preferably recommended as edible oils. Margarines were classified as "saturated" (high in palmitic acid) and "unsaturated" (high in linoleic acid). Saturated margarines are not very recommendable as edible fats since the high palmitic acid content is a hypercholesterolemic agent. The majority of the shortenings are also rich in palmitic acid.

Chromatography, Gas↗
PubMed1993

[Cardiovascular risk factors in peripheral arterial disease. A study of 403 cases].

We studied the prevalence of risk factors and related cardiovascular complications in 403 patients with periferal arterial disease (PAD) arising from atherosclerosis. The control group was made up of 126 patients of the same age and sex and without PAD. The average age was 66.9 +/- 12 years, and the percentage of men was 80%. Among the male subjects, smoking, the presence of diabetes, total cholesterol count, and age were the prevalent risk factors, even after logistic regression analysis. Among women, only smoking and diabetes showed significant differences. Among both sexes, the prevalence of arterial hypertension was similar to that of the controls. Greater prevalence of related cardiovascular complications was found only in men. We conclude that for PAD, smoking and diabetes are the most important cardiovascular risk factors, with total cholesterol level being an important additional factor in men.

Adult↗
PubMed1992

Assembly and disassembly of axonal microtubules of the toad Xenopus laevis under the effect of temperature.

In toads Xenopus laevis living at 11 degrees (winter), the microtubular density of 4-microns myelinated axons of lumbosacral nerves was assessed with the electron microscope. In controls, the density was 11.2 microtubules/microns2. In nerves incubated at 0 degrees, microtubules decreased following a simple exponential curve with a half time of 4.7 min (k = 0.149 min-1); residual microtubules were 4.5%. After rewarming, the full complement of microtubules reappeared within 60 min. In steady state, the microtubular density exhibited a linear relationship with temperature (range: 0-22 degrees; slope 0.94 microtubules/microns 2 per degree; r, 0.96). After heating the nerve by 11 degrees above the physiological temperature, microtubules increased by 83%, whereby the pool of unpolymerized tubulin was at least 2.7 mg/ml of axoplasm. A seasonal variation of the microtubular density was observed which accorded with the environmental temperature. The macroscopic kinetics of microtubule disassembly in the axoplasm is similar to that reported for purified tubulin but that of assembly is slower. Microtubules of peripheral axons of Xenopus are cold-labile and vary during the annual cycle.

Animals↗
PubMed1992

Control of plasma-membrane Ca2+ entry by the intracellular Ca2+ stores. Kinetic evidence for a short-lived mediator.

We have studied the correlation between the degree of filling of the intracellular Ca2+ stores and the plasma-membrane permeability to Mn2+, a Ca2+ surrogate for plasma-membrane Ca2+ channels, in human neutrophils loaded with fura-2. Refilling of the stores of cells previously depleted of Ca2+ decreased the entry of Mn2+, but the magnitude of this effect depended on the refilling protocol. When refilling was allowed to proceed to steady-state levels by a 3 min incubation with different external Ca2+ concentrations (0.05-1 mM), almost complete inhibition of Mn2+ entry was observed at 40% of maximum refilling. In contrast, when different degrees of store refilling were attained by incubation with 1 mM-Ca2+ for short periods (10-40 s), inhibition of Mn2+ entry was smaller at comparable degrees of refilling. When quick refilling was allowed to proceed up to 40% (about 20 s at 37 degrees C) and then stopped at this level by removal of external Ca2+, the rate of Mn2+ uptake was high just after refilling and then decreased with time within the next few seconds (half-times approximately 7 s at 37 degrees C and approximately 20 s at 25 degrees C). We have proposed previously that the Ca2+ stores, when emptied of Ca2+, may generate a second messenger able to open the plasma-membrane Ca2+ channels by a mechanism involving cytochrome P-450. The results here are consistent with the existence of such a messenger and suggest that it is cleared from the cytoplasm with a half-time of about 7 s at 37 degrees C. In addition, inhibition of Mn2+ entry in cells with empty Ca2+ stores by cytochrome P-450 inhibitors showed a time lag consistent with the clearance kinetics proposed above.

Calcium↗