Search PubMed⌕ Search

Biomedical subjects

J A Sanchez

Publications and source records attributed to J A Sanchez.

At least 37 records · Page 2Linked to original sources
PubMed1995

Extracellular heparin inhibits Ca2+ transients and contraction in mammalian cardiac myocytes.

The effect of heparin on Ca2+ transients and cell shortening was studied in isolated cardiac myocytes from rat and guinea-pig ventricles. Ca2+ signals were measured with the fluorescent indicator fura-2. Heparin reversibly decreased Ca2+ transients and cell shortening in a dose-dependent manner. Half and complete blockade were obtained with 50microg/ml and 200microg/ml heparin, respectively. The dihydropyridine agonist BAY K 8644 (50nM) antagonized the effects of heparin. However, Ca2+ release elicited by caffeine (10mM) was not affected by heparin. The actions of heparin were also studied in multicellular preparations. In papillary muscle, heparin (5mg/ml) reversibly reduced the amplitude of the plateau of the action potential and the associated peak tension. BAY K 8644 (500nM) also antagonized these effects. It is proposed that heparin interacts with dihydropyridine-sensitive Ca2+ channels to cause a decrease of Ca2+ transients and contractility in heart.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1995

Mapping of replication initiation sites in human ribosomal DNA by nascent-strand abundance analysis.

New techniques for mapping mammalian DNA replication origins are needed. We have modified the existing nascent-strand size analysis technique (L. Vassilev and E.M. Johnson, Nucleic Acids Res. 17:7693-7705, 1989) to provide an independent means of studying replication initiation sites. We call the new method nascent-strand abundance analysis. We confirmed the validity of this method with replicating simian virus 40 DNA as a model. We then applied nascent-strand abundance and nascent-strand size analyses to mapping of initiation sites in human (HeLa) ribosomal DNA (rDNA), a region previously examined exclusively by two-dimensional gel electrophoresis methods (R.D. Little, T.H.K. Platt, and C.L. Schildkraut, Mol. Cell. Biol. 13:6600-6613, 1993). Our results partly confirm those obtained by two-dimensional gel electrophoresis techniques. Both studies suggest that replication initiates at relatively high frequency a few kilobase pairs upstream of the transcribed region and that many additional low-frequency initiation sites are distributed through most of the remainder of the ribosomal DNA repeat unit.

Animals↗
PubMed1995

Efficient reactivation of Xenopus erythrocyte nuclei in Xenopus egg extracts.

Rapid genome replication is one of the hallmarks of the frog embryonic cell cycle. We report here that complete reactivation of quiescent somatic cell nuclei in Xenopus egg extracts depends on prior restructuring of the nuclear substrate and prior preparation of cytoplasmic extract with the highest capacity to initiate and sustain DNA synthesis. Nuclei from mature erythrocytes swell, replicate their DNA efficiently, and enter mitosis in frozen/thawed extracts prepared from activated Xenopus eggs, provided the nuclei are first treated with trypsin, heparin, and an extract prepared from unactivated, meiotically arrested, eggs. Optimal replicating extracts are prepared from large batches of unfertilized eggs that are synchronously activated into the cell cycle for 28 minutes (at 20 degrees C). Because the Xenopus cell cycle progresses so rapidly, extracts prepared just a few minutes before or after this time have substantially lower DNA synthetic capacities. At the optimal time and temperature, eggs have just reached the G1/S boundary of the first cell cycle. This fact was revealed by injecting and replicating an SV40 plasmid in intact unfertilized eggs as described previously. We estimate that under optimal conditions approximately 6.14 x 10(9) base pairs of DNA/per nucleus are synthesized in 30-40 minutes, a rate that rivals that observed in the zygotic nucleus. The findings reported here are one step in our long term effort to develop a new in vitro/in vivo approach to nuclear transplantation. Nuclear transplantation in amphibian embryos has been used to establish that the genomes of many types of differentiated somatic cells are pluripotent. But very few such nuclei have ever developed into advanced tadpoles or adult frogs, probably because somatic nuclei injected directly into activated eggs fail to reactivate quickly enough to avoid being damaged during first mitosis. We have already shown that unfertilized eggs can be injected prior to activation of the first cell cycle. Future experiments will reveal whether in vitro reactivated somatic cell nuclei transplanted into such eggs reliably reach advanced stages of development.

Animals↗
PubMed1994

Acute peripheral neuropathy due to hereditary coproporphyria.

A 23-year-old man with epilepsy and a past history of abdominal pain and ileus, developed hypertension and arm and bulbar weakness when valproic acid and carbamazepine were reinitiated. Electrophysiologic studies demonstrated a peripheral neuropathy with features of axonal degeneration and demyelination. Axonal degeneration was documented by sural nerve biopsy. Markedly elevated urinary delta-aminolevulinic acid and porphobilinogen indicated a diagnosis of acute porphyria. Other laboratory studies were most consistent with hereditary coproporphyria. Motor function improved considerably but incompletely over 1 year. An acute, primarily motor neuropathy can occur in several forms of porphyria, including acute intermittent porphyria, variegate porphyria, and hereditary coproporphyria, sometimes even in the absence of concomitant gastrointestinal symptoms.

Acute Disease↗
PubMed1994

The aortic bodice: a life-saving maneuver.

A technique is described for control of bleeding from the site of aortic cannulation after removal of the cannula. The technique employs a Dacron graft wrapped under some tension around the site.

Aorta↗
PubMed1994

Modulation of Ca2+ transients by photorelease of caged nucleotides in frog skeletal muscle fibers.

Action potentials and intracellular Ca2+ transients were monitored in current-clamped segments of frog skeletal muscle fibers using the triple vaseline-gap technique. Calcium signals were measured with the fluorescent indicator rhod 2. Action potentials produced a transient increase in intracellular Ca2+ that was estimated, by deconvolution of the fluorescence signals, to range between 3 and 12 microM. The comparative effects of flash photolysis of caged adenosine 3',5'-cyclic monophosphate (cAMP) and caged ATP on action potentials and Ca signals in muscle were investigated. The photorelease of both nucleotides produced a reduction in the amplitude of the afterpotential that follows the spike. Photorelease of cAMP and ATP prolonged the rate of decay of the Ca signals. No changes in either the rate of rise or in the latent period between stimulation and onset of the Ca signal were observed. Release of cAMP reduced the amplitude of Ca signals, whereas release of ATP had the opposite effect. Our results show that cAMP and ATP, released above their endogenous levels, modulate intracellular Ca2+ release. The cAMP modulation is more significant and may be of physiological importance.

Action Potentials↗
PubMed1993

Characterization of stretch-activated ion channels in cultured astrocytes.

The presence of a stretch-activated channel in rat cerebellar astrocytes in culture is described. This stretch-sensitive channel is K(+)-selective and its open probability increases with suction following a Boltzmann-like distribution with half activation at 45 mm Hg. Kinetic analysis of the single-channel data indicated that there are two open and two closed states and that the shortest time constants of both open and closed states are the most sensitive to suction. A symmetrical two-barrier-one-site permeation model can quantitatively describe the inward rectification of the single-channel current to voltage relations. It is suggested that this stretch-activated channel plays a role in the regulatory volume response of astrocytes to hyposmotic conditions.

Animals↗
PubMed1993

Immunohistochemical localization of laminin in the hearts of patients with chronic chagasic cardiomyopathy: relationship to thickening of basement membranes.

Histologic, ultrastructural, and immunohistochemical studies were made of endomyocardial biopsy specimens from 10 patients with chronic chagasic cardiomyopathy. Histologic and electron microscopic observation disclosed marked thickening of the basement membranes of the myocytes, endothelial cells, and vascular smooth muscle cells in all patients. Light (peroxidase-labeled antibodies) and electron (gold-conjugated antibody) microscopic immunohistochemical methods revealed a positive reaction for laminin in these thickened basement membranes. This thickening of basement membranes may develop as a consequence of: (1) an immunologic reaction that is triggered by the presence of a laminin-like molecule on the surfaces of Trypanosoma cruzi amastigotes and trypomastigotes; (2) an immunologic response to direct injury of basement membranes causing some of their components to become antigenic; (3) myocardial fibrosis, with synthesis of new connective tissue components; and (4) a combination of the preceding factors. The relationship of these changes to antilaminin antibodies requires clarification.

Adult↗
PubMed1993

Malignant melanoma.

Malignant melanoma is the most rapidly increasing cancer in Caucasians throughout the world. The increased incidence is due to greater sun exposure arising from changes in clothing habits and life-styles over the past fifty years. Most melanomas arise in preexisting moles in sun-exposed sites and may spread rapidly via the vascular system if not detected and removed early. Treatment of disseminated disease is unsatisfactory, with most patients dying of refractory brain metastases.

Humans↗
PubMed1993

Influence of calcium intake on calcitriol levels in idiopathic hypercalciuria in children.

Twenty-four children with idiopathic absorptive hypercalciuria (IAH) and a control group (CG) of 11 healthy children were studied. Plasma 1,25-hydroxyvitamin D3 (calcitriol), parathyroid hormone (PTH), calcium (Ca) and phosphate (P) levels were measured during dietary manipulation. The three diets analyzed were: (A) calcium-restrictive diet (400 mg/1.73 m2/day) for 7 days; (B) supplemented diet (1,000 mg/1.73 m2/day) for 3 days; (C) supplemented diet continued for 15 days. The IAH group had higher levels of serum calcitriol than the control group for all three diets. Serum calcitriol levels in the IAH group decreased in diet B compared to diet A, and returned to levels observed with diet A during diet C. Serum Ca, P and plasma PTH levels did not vary throughout the study in either group. In IAH, two subgroups were observed. In one, serum calcitriol levels were elevated and in the other, serum calcitriol levels were not different from the controls. This second group had a lower P and maximum rate of tubular reabsorption of phosphate per 100 ml of glomerular filtrate than the IAH group with elevated serum calcitriol levels and the control group. These results suggest that IAH in children may be related both to increased serum calcitriol levels and to an altered Tmp/GFR.

Adolescent↗
PubMed1993

Protection by alpha-tocopherol against skin necrosis induced by doxorubicin hydrochloride.

Extravasation of doxorubicin hydrochloride during i.v. infusions can cause serious local complications due to the action of free radicals which are produced as a result of this leakage. An experiment was carried out using female Wistar rats to study the protective effect of alpha-tocopherol against the tissular necrosis produced by 0.05 mg of doxorubicin hydrochloride. alpha-Tocopherol was administered by two vehicles, one emulsified and the other gelled, with butylated hydroxytoluene and ascorbic acid used as antioxidants, respectively. No differences were observed in the diameters of the ulcers with each treatment in the various groups of animals relative to the control group. Conversely, differences were found (p < 0.05) in the period of chronic lesion between the animals treated with alpha-tocopherol and those used as a control group, irrespective of the vehicle used. These results lead to the conclusion that accidental toxicity resulting from the leakage of doxorubicin hydrochloride in the skin can be mitigated by applying alpha-tocopherol topically, due to its regenerating action in the damaged cutaneous zones. This effect is independent of the vehicle used and also of the antioxidant employed in the elaboration of the formulas.

Animals↗
PubMed1993

Improved ultrastructural lung preservation with prostaglandin E1 as donor pretreatment in a primate model of heart-lung transplantation.

Donor pretreatment with prostaglandin E1 as a pulmonary vasodilator has developed as a simple, effective means to provide excellent preservation in heart-lung transplantation. This study was undertaken to investigate the degree of ultrastructural preservation of the lung with prostaglandin E1 and other pulmonary vasodilators in a primate heart-lung transplantation model. Heart-lung transplantation was performed in 14 African green monkeys. Donor cardiac preservation was achieved with cold crystalloid cardioplegic solution (10 ml/kg). Lung preservation was achieved with cold, modified Euro-Collins solution delivered into the main pulmonary artery (60 ml/kg total). Vasodilator agents were administered intravenously 15 minutes before aortic crossclamping. The heart-lung grafts were stored at 4 degrees C for 6 hours. Three groups of animals were studied: five donors with prostaglandin E1 (0.1 to 4.0 micrograms/kg per minute), five donors with prostacyclin (0.1 to 0.35 micrograms/kg per minute), and four donors with nitroprusside (0.8 to 5.0 micrograms/kg per minute). After transplantation, arterial blood gas measurements and lung biopsies were performed at 1- and 3-hour intervals. Five formalin blocks per specimen were sectioned for hematoxylin and eosin staining. Cellular preservation and endothelial cell swelling were evaluated with electron microscopy. The specimens were graded for alveolar hemorrhage, endothelial cell swelling, and cellular preservation (grade 0, minimal, to grade 3, severe) and a mean score was obtained for each preservative agent. Prostaglandin E1-treated specimens demonstrated the least amount of endothelial swelling (mean score of 1.0) compared with prostacyclin- and nitroprusside-treated specimens (mean scores of 1.4 and 2.7, respectively). All nitroprusside-treated specimens demonstrated moderate to severe endothelial cell swelling. Interstitial and alveolar hemorrhage was noted in poorly preserved specimens, but there were no significant differences between groups. We conclude that prostaglandin E1 provides improved cellular preservation by decreasing the extent of endothelial cell swelling as observed on electron microscopy.

Alprostadil↗
PubMed1992

Mechanical circulatory support decreases neurologic complications in the treatment of traumatic injuries of the thoracic aorta.

The surgical treatment of traumatic injuries of the thoracic aorta is controversial because a number of technical approaches have been recommended. Despite the technique employed, spinal cord ischemia continues to be a persistent problem. Nineteen patients with confirmed aortic injuries secondary to blunt trauma were treated at the Yale-New Haven (Conn) Medical Center from 1984 to 1991. The patients were analyzed in two groups: group 1 (n = 10) underwent repair using mechanical circulatory support and group 2 (n = 9) underwent repair without mechanical circulatory support. Sixteen patients survived. Three patients died of complications of multiple trauma. The groups were comparable with respect to aortic cross-clamp time, preoperative systolic blood pressure, and Injury Severity Score. Three patients in the nonmechanical support group developed neurologic complications (P less than .05). No patient in the mechanical support group had a neurologic complication. We believe that mechanical circulatory support reduces the incidence of neurologic complications following traumatic injuries of the thoracic aorta and should be used whenever clinically feasible.

Academic Medical Centers↗
PubMed1992

Sulfhydryl alkylating agents induce calcium current in skeletal muscle fibers of a crustacean (Atya lanipes).

Voltage-clamp experiments using the three-microelectrode voltage clamp technique were performed on ventroabdominal flexor muscles of the crustacean Atya lanipes. Potassium and chloride currents were found to underlie the normal, passive response of the muscle. Blocking potassium currents with tetraethylammonium and replacing chloride ions with methanesulfonate did not unmask an inward current. By treating the muscle with the sulfhydryl-alkylating agent 4-cyclopentene-1,3-dione an inward current was detected. The current induced by the agent is carried by Ca2+, since it is abolished in Ca(2+)-free solutions. The induced Ca2+ current is detected at about -40 mV and reaches a mean maximum value of -78 microA/cm2 at ca. -10 mV. At this potential the time to peak is close to 15 msec. The induced Ca2+ current inactivated with 1-sec prepulses which did not elicit detectable Ca2+ current; the fitted hx curve had a midpoint of -38 mV and a steepness of 5.0 mV. Measurements of isometric tension were performed in small bundles of fibers, and the effects of the sulfhydryl-alkylating agents 4-cyclopentene-1,3-dione and N-ethylmaleimide were investigated. Tetanic tension was enhanced in a strictly Ca(2+)-dependent manner by 4-cyclopentene-1,3-dione. The amplitude of K+ contractures increased after treatment with N-ethylmaleimide. It is concluded that Ca2+ channels are made functional by the sulfhydryl-specific reagents and that the increase in tension is probably mediated by an increase in Ca2+ influx through the chemically induced Ca2+ channels.

Animals↗
PubMed1992

Effect of sodium deprivation on contraction and charge movement in frog skeletal muscle fibres.

Measurements of isometric tension were performed in single twitch skeletal muscle fibres and the effect of extracellular Na+ removal on contraction was investigated. Na+ withdrawal brought about an increase in the amplitude of K+ contractures and their time course became faster. The potentiation of K+ contractures depended strongly on extracellular Ca2+ and developed slowly following an exponential time course with a time constant of approximately 8 min. Removal of extracellular Na+ greatly increased the amplitude of caffeine contractures and lowered its threshold: caffeine (0.5 mM) had no effect on resting tension in Ringer's but produced contractures in Na(+)-free solutions. Intramembrane charge movement (charge 1) was monitored in contracting voltage-clamped segments of frog skeletal muscle fibres using the triple-Vaseline-gap technique. Movement of charge 1 did not depend on the presence of extracellular Na+. However, the mechanical threshold decreased by approximately 10 mV at several pulse durations and the charge which produced just detectable contractions decreased by approximately 5 nC microF-1 in the absence of extracellular Na+. Intracellular heparin (40 mg ml-1) increased the mechanical threshold by approximately 20 mV without affecting the movement of charge 1. The effect of Na(+)-free solutions on the mechanical threshold was additive to that of heparin. It is concluded that the effects of Na(+)-withdrawal on contraction take place at a location beyond the voltage sensor of excitation-contraction coupling.

Action Potentials↗
PubMed1992

Normal bronchial healing without bronchial wrapping in canine lung transplantation.

The deleterious effect of steroids on bronchial healing in lung transplantation has led to the development of techniques to protect the anastomosis and to the exclusion of steroid-dependent patients from transplantation. The effect of steroids on bronchial healing was tested in a canine single-lung allotransplantation model. Twenty size-matched mongrel dogs (20 to 30 kg) underwent left lung transplantation without anastomotic wrap or direct revascularization. Postoperatively, all received daily doses of cyclosporine (15 mg/kg) and azathioprine (1 mg/kg) and were subdivided into three steroid dosage groups. Group A (n = 10) animals received 1.5 mg/kg of prednisone per day whereas groups B (n = 5) and C (n = 5) received 5.0 mg/kg of prednisone per day for 28 postoperative days. In addition, group C received prednisone (5.0 mg.kg-1.day-1) for 1 month preoperatively. In group A, 8 of 10 dogs survived 28 days without evidence of respiratory compromise, with anastomotic bursting pressure greater than 510 mm Hg. In group B, all 5 dogs survived to 28 days without evidence of respiratory compromise and with intact bronchial anastomoses (bursting pressures greater than 510 mm Hg). In group C, 3 of 5 animals survived to 28 days with intact anastomoses. Histological examination demonstrated normal bronchial healing in all anastomoses. These data suggest that preoperative steroid dependence should not be a contraindication to lung transplantation and that bronchial anastomotic wrapping with vascular tissue may not be essential.

Anastomosis, Surgical↗