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Biomedical subjects

J Alvarez

Publications and source records attributed to J Alvarez.

At least 271 records · Page 15Linked to original sources
PubMed1989

Effects of manganese chloride, verapamil, and hypoxia on the rate-dependent increase in internal longitudinal resistance of rabbit myocardium.

The effects of high rates of stimulation on the internal longitudinal restivity (Ri) and conduction velocity (theta) were studied on rabbit papillary muscle preparations using a silicon-oil chamber. Increasing the rate from 75 to 150/min caused Ri to rise and theta to decrease. The maximum rate of depolarization and action potential duration were also decreased. At a rate of 300/min the effects were more pronounced. Blockade of the slow inward current (Isi) and of the Na-Ca exchange by MnCl2 (5 mmol/L) did not prevent rate-induced changes in these variable. Verapamil (0.02 mmol/L) was also ineffective. Hypoxia (PO2 = 5.3 kPa) at 75/min induced changes in Ri and theta which were similar to those recorded at 150/min under aerobic conditions. The effects of high rates of stimulation were potentiated under hypoxia. From the present results it is suggested that Isi and the Na-Ca exchange are not the main determinants of the rate-induced increase in Ri, which could be determined by other intracellular Ca-release mechanisms or by a decrease in myoplasmic pH.

Animals↗
PubMed1988

Do axons grow during adulthood? A study of caliber and microtubules of sural nerve axons in young, mature, and aging rats.

Calibers and microtubules of sural nerve axons were studied in young (6-week-old), mature (14-week-old), and aging (2-year-old) rats. The mean cross-sectional area of nonmedullated fibers was about 0.50 micron 2 (range: 0.47-0.52) in the three age groups. Their caliber spectra were also similar. In contrast, myelinated axons grew from 6.6 to 16.7 micron 2 between the sixth and 14th week of age. The increase of cross-sectional area was greater, the greater the initial caliber of axon (range 44-154%). No further change of caliber was observed in the aging rat. The cross-sectional area of nerve allotted per myelinated fiber was 42, 66, and 97 micron 2 in young, mature, and aging rats, respectively. The fraction of nerve tissue occupied by the axoplasm, though, did not change substantially; it was 20, 28, and 21%, respectively. The microtubular density of 3-micron myelinated axons had a general average of 21 microtubules/micron 2. Differences between groups were not significant. In nonmedullated fibers, the microtubular density decreased as the size of the axon increased. No differences were observed between age groups. We conclude that nonmedullated fibers of the sural nerve stop growing before the sixth week whereas myelinated fibers keep growing until the 14th week of age. The correlation between microtubular content and axonal caliber is a lifelong feature of axons.

Aging↗
PubMed1988

Axons grow in the aging rat but fast transport and acetylcholinesterase content remain unchanged.

Caliber and microtubular density of myelinated fibers, acetylcholinesterase (AChE) content and its accumulation at a ligature were studied in the phrenic nerve of mature (3-4 months) and aging (2-year-old) rats. The number of axons remained constant. The cross-sectional area of the nerve was 67% greater in the older group; the axoplasm, though, constituted about 20% of the nerve tissue irrespective of age. The mean cross-sectional area of myelinated axons was twice as big in aging compared to mature rats. All axons grew in the same proportion irrespective of their original caliber. The microtubular density of 3-microns axons was about 22 microtubules/micron2 in mature and aging rats. The AChE activity of aging rats was half as much as that of mature rats if it was expressed per wet weight of nerve tissue but did not change if it was expressed per nerve fiber. Twenty-four hours after ligation of the nerve, total AChE activity rose in mature and aging rats by ca. 168%; the molecular forms--asymmetric and globular--accumulated in the same proportion in both age groups. We conclude that myelinated axons grow in the adult stage of life but the structure of axoplasm, content of AChE per axon, and rate of fast transport remain lifelong features of nerve fibers.

Acetylcholinesterase↗
PubMed1988

All or none cell responses of Ca2+-dependent K channels elicited by calcium or lead in human red cells can be explained by heterogeneity of agonist distribution.

We have studied the all or none cell response of Ca2+-dependent K+ channels to added Ca in human red cells depleted of ATP by incubation with iodoacetate and inosine. A procedure was used which allows separation and differential analysis of responding and nonresponding cells. Responding (H for heavy) cells incubated in medium containing 5 mM K lose KCl and water and increase their density to the point of sinking on diethylphthalate (specific gravity = 1.12) on centrifugation. Nonresponding (L for light) cells do not lose KCl at all. There is no intermediate behavior. Increasing the Ca concentration in the medium increases the fraction of cells which become H. No differences in the sensitivity to Ca2+ of the individual K+ channels were detected in inside-out vesicles prepared either from H or from L cells. The Ca content of H cells was higher than that of L cells. Cells depleted of ATP by incubation with iodoacetate and inosine sustain pump-leak Ca fluxes of about 15 mumol/liter cells per hour. ATP seems to be resynthesized in these cells at the expense of cell 2,3-diphosphoglycerate stores at a rate of about 150 mumol/liter cells per hour. Inhibition of 2,3-diphosphoglycerate phosphatase by tetrathionate increased 6-8 times the measured rate of uptake of external 45Ca. This was accompanied by an increase in the fraction of H cells. All or none cell responses of Ca2+-dependent K channels have also been evidenced in intact human red cells on addition of Pb. They have the same characteristics as those in responding and nonresponding cells. The detailed study of the kinetics of Pb-induced shrinkage of red cells suspended in medium containing 5 mM K showed that changes of Pb concentration changed not only the fraction of H cells but also the rate of shrinkage of responding cells. H cells generated by Pb treatment contained significantly more lead than L cells. The above results suggest that the two all or none cell responses studied here can be explained by heterogeneity of agonist distribution among cells. Since pump-leak fluxes exist in both cases, differences of agonist distribution could be generated by heterogeneity of pumping among cells. This interpretation turns interest from K channels to Ca pumps to explain the heterogeneous behavior of red cells in response to a uniform stimulus.

Adenosine Triphosphate↗
PubMed1988

Biliary and pancreatic obstruction during gallstone migration.

A prospective study on biliary and pancreatic obstruction during gallstone migration was performed in patients without acute pancreatitis. From January to October 1986, 125 patients with upper abdominal pain due to cholelithiasis were admitted to the hospital. Ultrasonography performed in all patients at admission demonstrated a distal bile duct measuring 7 mm or more in 39 patients, who were monitored for diameter changes of the biliary and pancreatic duct every 24 h and their stools screened for gallstones. Patients underwent surgery at least 8 days after admission. Gallstone migration was found preoperatively in 10 patients, of whom 6 had total serum bilirubin values lower than 2 mg/100 ml. Migration time was accurately determined by the sudden decrease in bile duct caliber. Simultaneous dilatation of biliary and pancreatic duct was found in 4 out of 10 patients with migrating gallstones and in 7 out of 23 patients without gallstone migration, though differences proved non-significant. Acute pancreatitis developed in 2 patients with lithiasis of the distal bile duct who ingested a fatty meal against medical advice. Gallstone migration, even of small stones, was preceded by a period of biliary obstruction. Pain and jaundice before migration were not as frequent as expected.

Acute Disease↗
PubMed1988

Hemodynamic and morphologic alterations after experimental administration of protamine sulfate.

The hemodynamic, hematologic, and morphologic effects induced by protamine sulfate have been studied in 28 dogs divided into 6 groups. All of the groups were given heparin (3 mg/kg body weight) and Groups I, II, III, and IV were given protamine (5 mg/kg body weight). Group I (control group) was not subjected to extracorporeal circulation. The other groups had the following interventions: Group II, cardiopulmonary bypass without aortic clamp, hypothermia, or cardioplegia; Groups III and V, hypothermia of 25 degrees C, aortic clamping for 25 minutes, administration of cardioplegic solution, and slow rewarming; and Groups IV and VI, the same as Groups III and V, but with rapid rewarming. After injection of protamine sulfate, there was a decrease in mean arterial pressure due to peripheral vasodilation and an increase in the mean pulmonary pressure due to increased pulmonary vascular resistance; marked diminution of the number of circulating platelets aside from the extracorporeal circulation; a decrease in the contractility of both ventricles with augmented right ventricular work and decreased cardiac output; and right ventricular edema in Groups I, II, III, and IV. These alterations were most evident in Groups III and IV.

Animals↗
PubMed1988

Acute respiratory arrest due to hypokalemia.

An uncommon but treatable etiology of acute respiratory failure is hypokalemia. A 36-year-old woman with previously undiagnosed distal renal tubular acidosis presented with foot and ankle swelling that was being treated with furosemide. She had been seen by three physicians within 24 hours and was diagnosed as having depression or hysterical conversion reaction. Her symptoms progressed to respiratory arrest. Initial treatment consisted of administering 40 mEq of KCl over one hour through a central venous line. The patient recovered rapidly and was weaned off a respirator within 24 hours of admission.

Acute Disease↗
PubMed1988

Central pontine and extrapontine myelinolysis following correction of severe hyponatremia.

A chronically hyponatremic patient developed neurological features of pontine level disconnection following the raising of serum sodium. At autopsy histopathological examination confirmed the presence of myelinolysis in the central pons and similar symmetrical lesions in the thalamus. In chronic hyponatremic patients, more than the rapidity of correction, the magnitude of the osmolar change may predispose to development of these lesions.

Demyelinating Diseases↗
PubMed1987

Investigation of the structure and function of the human erythrocyte glucose transporter by proteolytic dissection.

Tryptic and papain digestion have been employed to investigate the structure and function of the human erythrocyte glucose transporter. Trypsin cleaves the native protein into two large, membrane-embedded fragments and a number of small peptides that are released from the membrane. These fragments have been isolated and located within the transporter sequence by fast atom bombardment mass spectrometry and amino acid analysis. The results indicate that the segments of the sequence comprising residues 213-269 and 457-492 are cleaved from the cytoplasmic surface of the membrane by trypsin treatment. These findings are compatible with a model previously proposed for the arrangement of the polypeptide in the membrane (Mueckler, M., et al. (1985) Science 229, 941-945). Despite the loss of these 93 residues, the portion of the protein remaining embedded in the membrane is still able to bind cytochalasin B. This binding is inhibited by D-glucose, indicating that the membrane-embedded fragments retain the substrate-binding site. Fourier transform infrared spectroscopic analysis of the protein before and after proteolytic digestion shows that the intramembranous part of the protein is largely alpha-helical, although some beta-sheet structure appears also to be present. The spectroscopic findings also indicate that the extramembranous, cytoplasmic domain of the transporter, which is removed by trypsin, contains alpha-helical structure.

Amino Acid Sequence↗
PubMed1987

Conformational changes in concanavalin A associated with demetallization and alpha-methylmannose binding studied by Fourier transform infrared spectroscopy.

Infrared spectra of concanavalin A have been obtained both in the absence and in the presence of the metal ions, Mn2+ and Ca2+, and the saccharide, alpha-methylmannose. Second derivative calculations have been used to determine the frequencies of the different amide I and II components. In the demetallized protein dissolved in H2O buffer, absorptions in the amide I, II and III regions at 1695 and 1634, 1532 and 1237 cm-1, respectively, are assigned to beta-structure, while absorptions at 1563 and both 1318 and 1343 cm-1 are assigned to turns and bends. After deuterium exchange, the residual amide II maximum in the difference spectrum shifts from 1538 to 1563 cm-1, indicating that exchange is faster in the beta-structure than in the turns. In the presence of Mn2+ and Ca2+, the amide II band component at 1532 cm-1 shifts 4-6 cm-1 to higher wavenumbers, and the amide I band component at 1634 shifts 1 cm-1 in the same direction, both in H2O and 2H2O buffers, suggesting changes in the hydrogen-bonding network of a large portion of the protein, particularly in the beta-sheet regions. The addition of alpha-methylmannose increases the magnitude of exchange from 55% to above 90%. Comparison with existing X-ray crystallographic data has been made, and the usefulness of FT-IR to complement this technique is discussed.

Calcium↗
PubMed1987

An estimate of the number of Ca2+-dependent K+ channels in the human red cell.

An original approach has been designed to count Ca2+-dependent K+ channels in the human red cell using a preparation of inside-out vesicles. The relative frequency of vesicles having no K+ channels is estimated from the fraction of 42K+ (or 86Rb+) which is not released from loaded vesicles on maximal stimulation with Ca2+. The mean number of channels per vesicle is then calculated from this figure assuming a Poisson distribution for the K+ channels. From this value and the mean vesicular radius, computed from the volume/surface ratio, the mean number of channels per cell can be estimated. A value of 142 +/- 27 (mean +/- S.E.) was obtained, which is well above that estimated by comparison of unitary conductance and tracer equilibration rate measurements (about 10 channels/cell, Grygorczyk, R. Schwarz, W. and Passow, H. (1984) Biophys. J. 45, 693-698), but compares favourably with the channel density inferred from comparison with the number of Na+ pumps in a similar preparation of inside-out vesicles (100-200/cell, Lew, V.L., Muallem, S. and Seymour, C.A. (1982) Nature 296, 742-744). The procedure described here can be considered for general application as an alternative to other known procedures.

Calcimycin↗
PubMed1987

Alteration of uptake and distribution of eicosanoid precursor fatty acids by aspirin.

Aspirin is an important drug in the treatment of numerous disorders, especially rheumatic diseases. Its several mechanisms of action include inhibition of prostaglandin production by acetylation of prostaglandin synthetase. To explore further the modulatory effect of aspirin on eicosanoid production, we examined its effect on uptake and incorporation of fatty acids into phospholipids of human peripheral blood monocytes. Aspirin ingestion by normal volunteers inhibited uptake of arachidonic acid and linoleic acid in monocytes cultured for 3 days. Similar inhibition was observed when cultured normal human peritoneal macrophages were treated with aspirin for 3 days. In contrast, monocytes cultured for 12 days from both normal volunteers who had ingested aspirin and normal cells treated with aspirin in vitro for the first 3 days of a 12-day culture period expressed an increased uptake of both arachidonic and linoleic acids. Similarly, incorporation of fatty acid into phosphatidylcholine was depressed in 3-day cultured cells but was increased in 12-day cultured cells. Thus, aspirin, whether administered in vivo or added in vitro, modulates cellular uptake and incorporation of eicosanoid precursor fatty acids and their insertion into membrane phospholipids in cultured human monocytes and macrophages.

Arachidonic Acid↗
PubMed1987

Fourier transform infrared spectroscopic study of the structure and conformational changes of the human erythrocyte glucose transporter.

Fourier transform infrared spectroscopy has been used to study the secondary structure of the human erythrocyte glucose transporter after purification and reconstitution in erythrocyte lipids. The spectra indicate that the glucose transporter contains, in addition to the predominant alpha-helical structure, an appreciable amount of beta-structure and random coil conformation. A study of the time dependency of H-2H exchange revealed that more than 80% of the polypeptide backbone is readily accessible to the solvent. This result indicates that a portion of the intramembrane-spanning region of the membrane protein is exposed to the solvent, suggesting the existence of an intraprotein aqueous channel. The residual (10-20%) portion of the protein which exchanges slowly includes some alpha-helical structure, probably situated in a hydrophobic environment inside the membrane. The infrared spectra of transporter preparations were also examined after incubation with substrate and substrate analogues. Compared with the spectra recorded under conditions in which the "inward-facing" form predominates, a small but reproducible shift in the bands assigned to alpha-helical and beta-strand structures is observed after incubation with 4,6-O-ethylidene-D-glucose, which largely fixes the transporter in the "outward-facing" conformation. An increase of temperature, which is known to increase the proportion of transporter in the outward-facing conformation, results in a similar shift in this alpha-helical absorption band.

Erythrocyte Membrane↗
PubMed1987

Intravitreal vancomycin. Retinal toxicity, clearance, and interaction with gentamicin.

Some of the gram-positive isolates from exogenous bacterial endophthalmitis cases treated at our institution have been found to be resistant to either cefazolin sodium, gentamicin sulfate, or both. However, all of these isolates have been sensitive to vancomycin. These findings prompted us to reevaluate the retinal toxicity and clearance of intravitreal vancomycin in pigmented rabbits. Doses up to 2 mg were found to be nontoxic in phakic and aphakic-vitrectomized eyes. Clearance was determined in phakic and aphakic-vitrectomized rabbit eyes with or without intact lens capsules. The antibiotic was cleared most slowly in phakic eyes. Aphakic-vitrectomized eyes without an intact lens capsule cleared antibiotic most rapidly, while aphakic-vitrectomized eyes with intact capsules exhibited an intermediate clearance rate. In addition, the interaction between vancomycin and gentamicin on gram-positive endophthalmitis isolates was found to be additive or synergistic depending on the bacterial species. Based on these data, we recommend the combination of vancomycin and an aminoglycoside as the initial antibiotic therapy for exogenous bacterial endophthalmitis.

Animals↗