Search PubMed⌕ Search

Biomedical subjects

J Alvarez

Publications and source records attributed to J Alvarez.

At least 343 records · Page 19Linked to original sources
PubMed1979

Axonal microtubules: their regulation by the electrical activity of the nerve.

The effect of nerve impulses upon the axonal microtubules was studied in the sural nerve of the cat. We showed that a sustained activity (40 impulses/sec for 2 h) determines a difference in microtubule counts: the active nerve exhibited 24% more profiles than the resting one. In addition, microtubules of the active nerve appear to be less sensitive to the depolymerizing action of colchicine. We propose that the action potential leads to a decrease of the disassembly rate constant of microtubules.

Action Potentials↗
PubMed1979

Evidence that natural cytotoxicity and antibody-dependent cellular cytotoxicity are mediated in humans by the same effector cell populations.

The present study strongly suggests that, in humans, natural killer (NK) activity and antibody-dependent cell-mediated cytotoxicity (ADCC) are mediated by the same effector cell population. This is supported by two different experimental approaches. First, competition for NK effector cells was accompanied by simultaneous inhibition of ADCC activity. Target cells sensitive to NK activity were capable of inhibiting specifically an ADCC assay in cold target competition experiments. Second, specific removal of NK cells on monolayers formed by target cells sensitive to NK activity caused simultaneous depletion of ADCC effector cells. In association with the removal on the monolayers of effector cells for ADCC as well as NK activity, we also found a significant depletion of cells bearing Fc gamma receptors.

Antibody Specificity↗
PubMed1979

[Design of a course in physiology for medical training].

This article describes a course in general physiology and neurophysiology being offered at the School of Medicine of the Catholic University in Chile since 1971. The course was designed to provide the student skills in the planning, performance, and analysis of experimental problems. An account is given of the changes made in the course in response to annual evaluations over seven years. The procedures for grading student progress in developing critical judgment, handling information, and solving problems are analyzed. The authors are of the view that a course of this kind helps improve the ability to judge problems beyond the course curriculum. The describe the advantage of such courses for the training of physicians and recommend that activities that could be continued throughout medical training be designed and evaluated to stimulate the development of the students' critical faculties.

Chile↗
PubMed1979

Rate-dependent action potential changes in rat atrium.

Experiments in isolated left atria from rat hearts were performed in order to study the effects of stimulation rate on the transmembrane action potential. 1. Two components (fast and slow) of the action potential upstroke could be differentiated by adding MnCl2 to the perfusion solution. 2. With the increase in rate of stimulation over the control cycle length (500 msec), amplitude, Vmax and action potential duration at 80% of repolarization (D80) diminished in normal Krebs. In Mn-containing Krebs, only a slight reduction in amplitude was recorded. Resting potential and action potential duration at 20% (D20) and 50% (D50) of repolarization were only slightly affected in normal Krebs and not at all in Mn-Krebs. 3. Low rates of stimulation in normal Krebs increased D50 only slightly; however, D80 increased significantly while other parameters remained constant. No effects were seen in Mn-Krebs. 4. The results with Mn-Krebs indicate the importance of slow inward current on changes induced by stimulation rates. A possible mechanism relating intracellular calcium concentration and the outward K current, depending on the rate of stimulation, is discussed.

Animals↗
PubMed1979

Comparison of the cytotoxic activities of different human lymphoid tissues.

Normal human lymphoid cells from peripheral blood, spleen, tonsils and thymus were examined for their ability to mediate three different cytotoxic effector cell functions: antibody-dependent cellular cytotoxicity (ADCC); lectin-induced cellular cytotoxicity (LICC) and natural killer activity (NK), against 51Cr labelled erythroid and tumor target cells. We found a hierarchy of cytotoxic activities in the different lymphoid tissues. Peripheral blood and spleen cells were able to mediate LICC, ADCC and NK activities. Tonsil cells showed a natural segregation of the different cytotoxic functions: NK and ADCC activity against tumor target cells were absent, whereas LICC activity was fully present. With respect to ADCC activity against erythroid targets, tonsil cells showed low, but significant, cytotoxicity. Thymus cells had no detectable ADCC, NK and LICC activities. Correlation in the different lymphoid tissues between cytotoxic activities and cell surface marker studies revealed: (a) that the presence of E-SRBC rosette forming cells was not always associated with the detection of LICC activity, as is the case with the thymus; (b) that, in the absence of detectable Eox-7S rosette forming cells (thymus and tonsils), NK and ADCC activities against tumor cells were always absent, but LICC was observed (tonsils), indicating that the presence of this Fc(7S) receptor bearing cells is strongly associated with the expression of NK and ADCC but not with LICC.

Antibody-Dependent Cell Cytotoxicity↗
PubMed1978

Effects of atrial premature stimulation on sinus node function in isolated rabbit atria.

The effects of premature atrial depolarizations (PADs) on the sinus node function were studied in isolated rabbit atria by using simultaneous intracellular recordings in the sinus node and adjacent regions. Late PADs (test cycle 85% or more of the basic cycle) did not capture the sinus node, blocking somewhere between this structure and the crista terminalis, inducing however a shortening of action potential, an increased rate of rise (Vmax) and amplitude of phase 0, and a variable depression of phase 4 depolarization on sinus node fibres. These effects were attributed to electrotonic interactions. Earlier PADs (test cycle 45--85% of the basic cycle) penetrated and captured the sinus node, changing its action potential shape, depending on the prematurity of the response. Two major effects were demonstrated: 1) a reduction in the maximum diastolic potential; 2) a linearly-related (p less than 0.001) decrease of the slope of phase 4 depolarization. These effects resulted in a depression of sinus node automaticity that was inversely-related to the test cycle length. Dominant pacemaker shifts within the sinus node were frequently observed with early as well as with late PADs resulting in a change of the basic cycle by as much as 90 msec. It is concluded that the use of the technique of premature atrial stimulation may not permit precise evaluation of sinoatrial conduction time.

Action Potentials↗
PubMed1976

Possible role of extracellular matrix vesicles in initial calcification of healing rachitic cartilage.

Fluid (20-30 nl) was aspirated by a modified renal micropuncture technique from vitamin D-, phosphate-deficient rats. The fluid revealed a mineral forming agent which could be sedimented at 140,000 X g for 8 hours, was resistant to acid demineralization, but was destroyed by heating, freezing and thawing as well as sonication, and blocked by phospholipase A at 10-5 M but not at 10-7 M. Electron microscopic study of the fluid sediment revealed images consistent with matrix vesicles. These data are consonant with the view that matrix vesicles, their remnants, or closely associated structures comprised the mineral forming agent.

Animals↗
PubMed1976

Ambient temperature of hypoxia: a differential study of liver catalase and cytochrome oxidase in guinea pig.

The activities of liver catalase and cytochrome oxidase have been determined in sea-level and high-altitude native guinea pigs exposed to different ambient temperatures. The activities of both of these enzymatic systems have been found to increase as ambient temperature is reduced, and this occurs in the sea-level and the high-altitude animals. At equal temperatures, cytochrome oxidase activity is identical in the liver of guinea pigs from sea-level and high-altitude. Catalase activity is approximately 50% lower in the high-altitude animals than in the sea-level ones maintained at the same ambient temperature. It is necessary to reassess current data on hypoxia-induced enzymatic and hormonal changes measured under conditions where the ambient temperature was not controlled, especially in those cases involving volunteer human subjects.

Altitude↗