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Biomedical subjects

J M Fernandez

Publications and source records attributed to J M Fernandez.

At least 163 records · Page 9Linked to original sources
PubMed1986

The universal Rn wave. An approach.

A large set of hourly Rn atmospheric concentration data collected during 1976, 1978, 1979 and 1980 has been obtained. These data follow a log-normal distribution law. The Fourier analysis of the mean daily course of Rn by month (Rn wave) shows that to accurately represent such a wave two terms are sufficient. Assuming that with a great deal of data the influence of the meteorological variables is very low, the two terms have been interpreted taking into account only the atmospheric stability, which depends on the solar flux. By applying the same treatment to Rn concentration data from other sites it was found that: (a) the phase of the first harmonic is a constant, independent of the site; (b) the phase of the second harmonic is a linear function of the hourly difference between sunrise and sunset; (c) the amplitude of the first harmonic is a linear function of the solar flux; and (d) no reliable correlation was found for the amplitude of the second harmonic, for which reason a mean value was taken. The error obtained in the prediction of the Rn wave was tolerable.

Air Pollutants↗
PubMed1986

Axonal stimulation for end-plate jitter studies.

This single fibre EMG study compares the standard method of neuromuscular jitter measurement in voluntarily activated muscle to that by intramuscular electrical stimulation of motor axons in a group of normal subjects. The latter method avoids the interdischarge interval-dependent jitter, as well as a possible failure to recognise split muscle fibres. The mean MCD on axonal stimulation was only 5.2 microseconds less than in the voluntary activation study and was thus 8% more than theoretically expected for single motor end plates. The difference could be due to an axonal jitter and some other factors. Axonal stimulation has proved to be a relatively easy and reliable method for routine estimation of neuromuscular jitter, provided that the resolution of time measurement is better than 2 microseconds, so that low jitter due to occasional direct muscle fibre stimulation is not mistaken for a normal reading. The upper normal limits for the extensor digitorum communis muscle suggested by the present study are 40 microseconds (individual muscle fibres) and 25 microseconds (mean of 30 muscle fibres).

Adolescent↗
PubMed1986

Autoregulation of alimentary and hepatic ketogenesis in sheep.

To determine the mechanism of autoregulation of ketogenesis, beta-hydroxybutyrate was infused into 5 normal; 3 diabetic, insulin-treated; and 3 diabetic, untreated anesthetized sheep. Net flux of fatty acids, acetoacetate, beta-hydroxybutyrate, and insulin were measured across splanchnic tissues by multiplying venoarterial differences by blood flow. beta-hydroxybutyrate depressed fatty acid concentrations and hepatic uptake. This decrease in hepatic uptake was not due solely to decreased concentrations, because hepatic extraction decreased 40% in normal and insulin-treated sheep. Portal-drained visceral release of acetoacetate was increased by beta-hydroxybutyrate infusion in normal and insulin-treated sheep, but this was associated with even larger increases in hepatic uptake, resulting in decreased total splanchnic release. Portal-drained viscera switched from release to uptake of beta-hydroxybutyrate in both normal and insulin-treated animals, but hepatic release increased slightly in normal sheep. beta-hydroxybutyrate increased insulin concentration, pancreatic production, and hepatic uptake. Because effects of ketone infusion on net fluxes of fatty acids, acetoacetate, and beta-hydroxybutyrate were similar in normal and diabetic, insulin-treated sheep but were diminished or totally absent in diabetic, untreated animals, the mechanism of autoregulation of ketogenesis may be mediated at the insulin receptor or at the site of hepatic fatty acid uptake.

3-Hydroxybutyric Acid↗
PubMed1984

Membrane patches and whole-cell membranes: a comparison of electrical properties in rat clonal pituitary (GH3) cells.

A comparison has been made between the electrical properties of excised 'outside-out' patches and whole-cell membranes of GH3 cells using the patch-pipette technique. Despite a complicated surface morphology, which includes numerous microvilli, ruffles and blebs, high-resistance seals (typically greater than 10(11) omega) were consistently formed between patch pipettes and GH3 cell membranes. When the internal solution contained 120 mM-CsF, outward currents through K channels were blocked and large Na channel currents were consistently observed in the whole-cell recording mode. Using the same solutions, single Na channel currents were readily observed in outside-out patches. Averaging patch currents yielded macroscopic currents showing the same voltage-dependent kinetics as those observed for the whole-cell membrane. The current vs. voltage and inactivation time constant vs. voltage relationships for the Na channel shifted towards more negative potentials (25 mV or more) within approximately 30 min after going into the whole-cell recording mode. These same relationships could be measured for outside-out patches and their positions along the voltage axis coincided with the asymptotic values measured in the whole-cell mode. When the internal solution contained 120 mM-N-methylglucamine fluoride and the external solution contained 120 mM-Tris chloride, no ionic channel currents could be observed either for whole-cell or outside-out patch membranes. Under these conditions, displacement currents induced by tetraphenyl borate (TPB) were recorded in both types of membranes. The total charge moved showed a sigmoidal dependence upon the applied voltage for both whole-cell and outside-out patch membranes. The charge vs. voltage relationship showed a shift along the voltage axis similar to that observed for Na channels except that the magnitude of the shift was larger. A shift in this relationship was also observed for excised patches but the observable magnitude of the shift was smaller than that in the whole-cell recording mode. The asymptotic values of the charge vs. voltage relationship were similar for whole-cell and outside-out patches, as were the asymptotic values for the translocation time constants. It is concluded that there are no fundamental differences in the properties of ionic channel and displacement currents between whole-cell membranes and excised membrane patches.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Cephalic tetanus studied with single fibre EMG.

In a case of cephalic tetanus with left facial spasms and trismus, the repetitive stimulation of the left facial nerve at 3, 10 and 20 Hz showed no facilitation or decrement. The amplitudes of the blink reflex were 50% lower on the affected side. The silent period of the masseter muscles was shortened. Concentric needle examination of the masseters and left facial EMG of the left frontalis muscle showed increased jitter and blocking in a significant proportion of the recorded potentials. Both jitter and blocking improved on higher innervation rates. All electrophysiological findings were normal on the second examination when the patient was asymptomatic. The single fibre EMG findings point to a presynaptic defect in the neuromuscular transmission in human tetanus.

Diagnosis, Differential↗
PubMed1981

A low-cost method for rapid transfer function measurements with direct application to biological impedance analysis.

The measurement of the linear transfer function of a biological system has found wide use in the characterization of the system's input/output properties, and in the separation and measurement of the properties of the different subelements that make up the system. Unfortunately sophisticated and expensive instrumentation has traditionally been required to make these measurements. In this paper, we present detailed design specifications of a low-cost instrument that is capable of yielding transfer function measurements with a high degree of accuracy and speed. The instrument is comprised of a pseudo-random binary sequence signal generator with precise date acquisition synchronization circuits, interfaced to a general-purpose mini-or microcomputer system common to many laboratory environments. The instrument is capable of measuring the transfer function of an arbitrary biological system up to a bandwidth of 8.3 KHz, with a frequency resolution of 425 points. In cases where the biological measurements are not contaminated with experimental noise, the transfer function can be determined in as little as 47 ms of data collection. In the case where experimental noise is present in the biological measurements, a simple averaging method is described which results in an effective increase in the signal-to-noise ratio, thereby yielding accurate transfer function estimates. The instrument is especially well suited to the measurement of transfer functions of biological systems, where experimental noise is a problem and where only limited time is available to acquire stable measurements.

Costs and Cost Analysis↗
PubMed1975

A new method for ventriculocentesis.

A new, safe, simple technique for percutaneous ventriculocentesis has been devised and used in 15 consecutive patients with excellent results and no complications. This method allows rapid access to the ventricular system for diagnostic and therapeutic purposes.

Cerebral Ventricles↗
PubMedDate not supplied

Determination of sertaconazole nitrate, a new imidazole antifungal, by high-performance liquid chromatography.

A high-performance liquid chromatographic method is developed for the determination of bulk sertaconazole nitrate and related compounds (potential impurities and degradation products) as well as a sertaconazole nitrate cream formulation. A 10-microns Spherisorb CN column is used along with a mobile phase consisting of acetonitrile and aqueous 0.01 M sodium phosphate (37:63, v/v). The sertaconazole nitrate peak is monitored at a wavelength of 260 nm; the retention time being 19.3 min. The detector response for sertaconazole nitrate is linear over the concentration range from 64 to 96 micrograms ml-1. The method is found to be sufficiently selective for the reliable determination of related compounds, FI-7001, FI-7009 and FI-7011, as indicated by same-day and between-day relative standard deviations (RSD) for replicate assays of 1.72% (n = 9) and 2.17% (n = 24), respectively. The application of this method to a cream formulation of sertaconazole nitrate is found to give a mean percentage recovery of 99.4% with RSD of 1.14% (n = 9); none of the cream vehicle peaks are found to interfere with the determination of sertaconazole nitrate.

Antifungal Agents↗
PubMedDate not supplied

Capacitance measurements reveal stepwise fusion events in degranulating mast cells.

Mast cells undergo an extensive and violent morphological transformation on stimulation. Here we describe the dynamics of fusion of the secretory granules in individual mast cells during exocytosis. The cell membrane capacitance (proportional to the cell surface area) was measured using the whole-cell patch-pipette technique, in which the intracellular space is dialysed with the solutions used to fill the patch pipette. Our results show that degranulation occurs spontaneously and reproducibly if the GTP analogue, GTP-gamma-S, and Mg-ATP are present in the pipette filling solution. Contrary to previous reports, in these conditions Ca2+ (and/or Ca2+ buffers) is not required for degranulation. Although electrogenic Ca2+ entry was not detected before or during degranulation and membrane conductance remained low, the capacitance, and by implication the area of the membrane of degranulating cells, increased sigmoidally and stepwise. We conclude that stepwise increases of capacitance are due to the fusion of individual secretory granules with the plasma membrane, and that guanine nucleotide regulatory proteins are involved in the control of this process.

Animals↗
PubMedDate not supplied

IgE-mediated degranulation of mast cells does not require opening of ion channels.

Rat peritoneal mast cells respond to antigenic stimulation by releasing histamine through exocytosis. The dynamics of exocytosis can be investigated by dialysing single cells with patch pipettes using the whole-cell recording configuration of the patch-clamp technique. However, dialysed cells fail to respond to external stimuli such as compound 48/80 or antigens, suggesting that essential cytoplasmic components have been washed out. We have developed a new patch-clamp configuration in which the patch under the pipette tip is not disrupted but instead permeabilized, preventing the diffusion of large molecules out of the cell. In this configuration the cell responds to external stimulation, and the capacitance as well as the conductance of the cell membrane can be recorded during degranulation. On antigenic stimulation, the cell capacitance (proportional to plasma membrane area), after an initial delay, increases by a factor of about 3. This increase in capacitance is often preceded by a transient increase in conductance. Agents that block Ca-activated channels inhibit this conductance change without affecting the amplitude and time course of degranulation. We therefore conclude that, in contrast to excitable secretory cells such as chromaffin cells, mast cells do not use ion channels in stimulus-secretion coupling.

Animals↗
PubMedDate not supplied

The exocytotic fusion pore interface: a model of the site of neurotransmitter release.

Ultrastructural techniques have shown that an early event in the exocytotic fusion of a secretory vesicle is the formation of a narrow, water-filled pore spanning both the vesicle and plasma membranes and connecting the lumen of the secretory vesicle to the extracellular environment. Smaller precursors of the exocytotic fusion pore have been detected using electrophysiological techniques, which reveal a dynamic fusion pore that quickly expands to the size of the pores seen with electron microscopy. While it is clear that in the latter stages of expansion, when the size of the fusion pore is several orders of magnitude bigger than any known macromolecule, the fusion pore must be mainly made of lipids, the structure of the smaller precursors is unknown. Patch-clamp measurements of the activity of individual fusion pores in mast cells have shown that the fusion pore has some unusual and unexpected properties, namely that there is a large flux of lipid through the pore and the rate of pore closure has a discontinuous temperature dependency, suggesting a purely lipidic fusion pore. Moreover, comparisons of experimental data with theoretical fusion pores and with breakdown pores support the view that the fusion pore is initially a pore through a single bilayer, as would be expected for membrane fusion proceeding through a hemifusion mechanism. Based on these observations we present a model where the fusion pore is initially a pore through a single bilayer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Peptide YY administration decreases brain aluminum in the Ts65Dn Down syndrome mouse model.

We have previously reported the Ts65Dn (Ts) mouse has impaired intestinal absorptive function and amino acid metabolism. Peptide YY (PYY) has enhanced glucose absorption in mice and turkeys. Other studies have reported that persons with Down syndrome have increased intestinal absorption of aluminum. Alzheimer's-like lesions have been reported in Ts mice. Trial 1 of this study examined brain Al concentrations, plasma metabolites and intestinal metabolism of 40 control and 40 Ts mice administered 300microg PYY/kg body weight or 0.9% saline for 3d. Trial 2 examined nutrient digestibility of 12 C and 12 Ts given PYY or saline for 14d. In Trial 1, PYY lowered (p<0.05) the brain Al pool (mg/g FBW) in both C and Ts mice by 80% compared to saline. Ts mice had increased plasma NH3 (329 vs. 269 microM, p<0.05), decreased plasma glucose (7.4 vs. 8.4 mM, p<0.01), elevated apparent energetic efficiency of jejunal glucose uptake (p<0.01) and elevated brain Al pool (0.41 vs. 0.12 microg, p=0.06) compared to C mice. In Trial 2, PYY increased small intestinal density (mg/cm) 12% in both genotypes (p<0.05), but did not alter nutrient digestibility. Brain Al accretion and hyperammonemia are proposed risk factors for Alzheimer's disease (AD). Ts mice and PYY appear to be suitable models for the study of metabolic and neurological anomalies in Down syndrome and AD.

Aluminum↗