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O Alvarez

Publications and source records attributed to O Alvarez.

At least 55 records · Page 3Linked to original sources
PubMed1987

Mechanisms of Cs+ blockade in a Ca2+-activated K+ channel from smooth muscle.

Large unitary conductance Ca2+-activated K+ channels from smooth muscle membrane were incorporated into phospholipid planar bilayers, and the blockade induced by internally and externally applied Cs+ was characterized. Internal Cs+ blockade is voltage dependent and can be explained on the basis of a Cs+ binding to a site that senses 54% of the applied voltage, with an apparent dissociation constant, Kd(0), of 70 mM. On the other hand, external Cs+ blocks the channel in micromolar amounts, and the voltage dependence of blockade is a function of Cs+ concentration. The fractional electrical distance can be as large as 1.4 at 10 mM Cs+. This last result suggests that the channel behaves as a multi-ion pore. At large negative voltages the I-V relationships in the presence of external Cs+ show an upturn, indicating relief of Cs+ block. External Cs+ blockade is relieved by increasing the internal K+ concentration, but can be enhanced by increasing the external K+. All the characteristics of external Cs+ block can be explained by a model that incorporates a "knock-on" of Cs+ by K+.

Animals↗
PubMed1986

Characterization of a calcium-activated potassium channel from rabbit intestinal smooth muscle incorporated into planar bilayers.

Interaction of vesicles from a microsomal fraction of rabbit intestinal smooth muscle with planar bilayers promotes the incorporation of a large conductance potassium-selective channel. The channel conductance fluctuates between two states: closed and open and the fraction of time the channel dwells in the open state is a function of the electric potential difference and the calcium concentrations. This channel seems to correspond to a Ca-activated K channel described by other authors in smooth muscle cells with the patch-clamp technique. Single-channel conductance is a saturating function of the potassium concentration. The relationship between conductance and concentration cannot be described by a hyperbolic function, suggesting multiple occupancy of the channel. The single-channel conductance is 230 pS in symmetrical 0.1 M KCl. Current is a linear function of the applied voltage in the range between -100 and +100 mV, at concentrations of 0.1 M KCl or higher. At lower concentrations, current-to-voltage curves bend symmetrically to the voltage axis. Sodium, lithium and cesium ions do not pass through the channel and the permeability for Rb is 66% that of potassium. All these alkali cations and Ca2+ block the channel in a voltage-dependent manner. A two-site three-barrier model on Eyring absolute reaction rate theory can account for the conduction and blocking characteristics.

Animals↗
PubMed1986

[Graphic representation on microcomputers. An example of interface construction].

Personal computers are generally used in laboratories as programmable calculators, data base organizers or word processors. With the addition of appropriate interfaces, they can also be used in data acquisition, analysis, and automatic control of experiments. In this paper the basic principles of operation of input and output devices are described, to serve as a guide to the construction of these interfaces. This description is specifically dedicated to the S-100 8-bit computer bus, with detailed explanation of the several signals involved in input-output machine cycles. Complete schematics and software driver for an interface to display analog signals on an oscilloscope or X-Y plotter is included as an example. Applications of this interface to the analysis of currents from membrane ionic channels are also discussed.

Automation↗
PubMed1985

Effect of phospholipid surface charge on the conductance and gating of a Ca2+-activated K+ channel in planar lipid bilayers.

A Ca-activated, K-selective channel from plasma membrane of rat skeletal muscle was studied in artificial lipid bilayers formed from either phosphatidylethanolamine (PE) or phosphatidylserine (PS). In PE, the single-channel conductance exhibited a complex dependence on symmetrical K+ concentration that could not be described by simple Michaelis-Menten saturation. At low K+ concentrations the channel conductance was higher in PS membranes, but approached the same conductance observed in PE above 0.4 m KCl. At the same Ca2+ concentration and voltage, the probability of channel opening was significantly greater in PS than PE. The differences in the conduction and gating, observed in the two lipids, can be explained by the negative surface charge of PS compared to the neutral PE membrane. Model calculations of the expected concentrations of K+ and Ca2+ at various distances from a PS membrane surface, using Gouy-Chapman-Stern theory, suggest that the K+-conduction and Ca2+-activation sites sense a similar fraction of the surface potential, equivalent to the local electrostatic potential at a distance of 9 A from the surface.

Animals↗
PubMed1985

Antibodies to Bartonella bacilliformis as determined by fluorescence antibody test, indirect haemagglutination and ELISA.

Two strains of Bartonella bacilliformis were cultured on Columbia agar supplemented with 5% defibrinated human blood. Antigens prepared from these cultures were used for determination of antibodies by fluorescence antibody test (FAT) indirect haemagglutination (IHA) and an enzyme immunoassay (ELISA). One hundred and eighty-seven human sera from B. bacilliformis-endemic areas of Peru were tested of which 63.6% were reactive. ELISA was the most sensitive test, followed by FAT and IHA. IgM antibody was determined by FAT with the IgM fraction of test sera. It was present not only in patients with Oroya fever but also in some healthy individuals as well as in one patient with chronic bartonellosis (verruga peruana). Substantial differences in antigenic activity between the two strains of B. bacilliformis were not observed. Cross reactivity with sera containing antibodies to bacteria other than B. bacilliformis was not noted. For identification of Oroya fever patients in the field, an eosin/thiazine stain of blood smears was found to be appropriate.

Antibodies, Bacterial↗
PubMed1984

Alkali metal ion selectivity of the hemocyanin channel.

The selectivity of the hemocyanin channel was measured for alkali metal ions and ammonium. Permeability ratios relative to K+ measured from biionic potentials were: NH4+ (1.52) greater than Rb+ (1.05) greater than K+ (1.0) greater than Cs+ (0.89) greater than Na+ (0.81) greater than Li+ (0.35). Single-channel ion conductance was a saturating function of ion concentration regardless of the cation present in the bathing medium. Maximal conductances were 270, 267, 215, 176, 170 and 37 ps for K+, Rb+, NH4+, Cs+, Na+ and Li+, respectively. Current-voltage curves for the different monovalent cations were measured and described using a three-barrier model previously used to explain the voltage dependence of the "instantaneous" channel conductance (Cecchi, Alvarez & Latorre, 1981). In this way, binding and peak energies were estimated for the different ions. Considering the energy peaks as transition states between the ion and the channel, it is concluded that they follow Eisenman's selectivity sequences XI (cis peak, i.e., Li+ greater than Na+ greater than K+ greater than Rb+ greater than Cs+; highest field strength), VII (central peak) and II (trans peak). The cis side was that to which hemocyanin was added and was electrically ground. The binding energies, on the other hand, follow Eisenman's series XI for strong electric field sites. Binding of NH4+ to the cis-well suggests that the orientation of the ligands in the site is tetrahedric.

Hemocyanins↗
PubMed1984

Aortic collagenase activity as affected by laparotomy, cecal resection, aortic mobilization, and aortotomy in rats.

Recent biochemical evidence that aneurysm formation may be related to higher activated collagenase levels within aneurysmal aortic walls in association with reports of asymptomatic aneurysm rupture after laparotomy has led to speculation that operative trauma unrelated to direct aortic injury may increase the chance of aneurysm rupture by inducing collagenase activation within the aortic wall. The purpose of this study was to determine whether aortic collagenase can be activated by distant operative trauma and the kinetics of activation after injury. Ninety-six rats were divided into four groups: group 1--laparotomy alone; group 2--cecal resection; group 3--aortic mobilization; and group 4--aortotomy and repair. Animals within each group were sacrificed 1,3, and 6 hours and 1,2,3,4, and 5 days after surgery. The abdominal aortas were removed and assayed for collagenase activity by incubation with and digestion of tritium-labeled collagen. Collagenase activity was significantly elevated up to 6 hours after direct aortic injury (p less than 0.05) and decreased to normal levels within 2 days. Laparotomy, colon resection, and aortic mobilization had no significant effect on aortic collagenase activity compared to the controls. These data suggest that collagenase activity is a local phenomenon related to wound healing at the site of initial injury. Operative trauma without direct aortic injury had no effect on aortic collagenase activity.

Animals↗
PubMed1983

Large divalent cations and electrostatic potentials adjacent to membranes. Experimental results with hexamethonium.

A simple extension of the Gouy-Chapman theory predicts that the ability of a divalent cation to screen charges at a membrane-solution interface decreases significantly if the distance between the charges on the cation is comparable with the Debye length. We tested this prediction by investigating the effect of hexamethonium on the electrostatic potential adjacent to negatively charged phospholipid bilayer membranes. The distance between the two charges of an extended hexamethonium molecule is approximately 1 nm, which is the Debye length in the 0.1 M monovalent salt solutions used in these experiments. Six different experimental approaches were utilized. We measured the electrophoretic mobility of multilamellar vesicles to determine the zeta potential, the line width of the 31P nuclear magnetic resonance (NMR) signal from sonicated vesicles to calculate the change in potential at the phosphodiester moiety of the lipid, and the conductance of planar bilayer membranes exposed to either carriers (nonactin) or pore formers (gramicidin) to estimate the change in potential within the membrane. We also measured directly the effect of hexamethonium on the potential above a monolayer formed from negative lipids, and attempted to calculate the change in the surface potential of a bilayer membrane from capacitance measurements. With the exception of the capacitance calculations, each of the techniques gave comparable results: hexamethonium exerts a smaller effect on the potential than that predicted by the classic screening theory. The results are consistent with the predictions of the extended Gouy-Chapman theory and are relevant to the interpretation of physiological and pharmacological experiments that utilize hexamethonium and other large divalent cations.

Animals↗
PubMed1982

Probing the pore size of the hemocyanin channel.

We have studied single-channel conductance for different monovalent cations and streaming potentials caused by osmotic gradients of non-electrolytes in hemocyanin-treated membranes. We have found that the smaller ion, which cannot pass through the channel, is tetramethylammonium and that acetamide is the smaller non-electrolyte excluded from the pore. From the streaming potentials measured, we calculated that no more than three water molecules can accompany the ion through the channel in a row. From these results we conclude that the hemocyanin channel has in its structure a narrow portion which can be represented as a cylinder 6 A long and 5 A in diameter.

Animals↗
PubMed1981

A three-barrier model for the hemocyanin channel.

Keyhole limpet hemocyanin forms ion-conducting channels in planar lipid bilayer membranes. Ionic current through the open hemocyanin channel presents the following characteristics: (a) it is carried mainly by cations; (b) it is a nonlinear function of membrane potential; (c) channel conductance is a saturating function of ion activity; (d) it shows ionic competition. A model for the open hemocyanin channel is developed from absolute reaction rate theory. The model calls for three energy barriers in the channel. Two energy barriers represent the entrance and exit of the ion into and out of the channel. The third barrier separates two energy minima that represent two binding sites. Furthermore, only one ion is allowed inside the channel at a given time. This model is able to recreate all the hemocyanin characteristics found experimentally in negatively charged and neutral membranes.

Hemocyanins↗
PubMed1981

Venezuelan equine encephalitis virus: horse virulence of P-676 and MF-8 small and minute plaques.

The P-676 and MF-8 epizootic strains of Venezuelan equine encephalitis (VEE) virus were found to contain a minute plaque (MP), different from the predominant small plaque (SP) present in these virus strains. The MP and SP were stable after passages in Vero cells, mice, or horses. Equines were inoculated with the SP or MP of the P-676 and MF-8 strains. Inoculation of either P-676 SP or MP into horses induced high fever and viremia but no signs of encephalitis or death. Four horses infected with MF-8 SP became very ill, with high fever and viremia; three of the inoculated animals died. Four horses were infected with MF-8 MP; only showed viremia but appeared asymptomatic and afebrile. Neutralization tests with immune sera from the infected equines showed that the P-676 SP and MP appear distinct, while a clear difference cannot be observed with MF-8 SP and MP.

Animals↗
PubMed1980

Transplacental transmission of Venezuelan equine encephalitis virus in horses.

Transplacental passage of Venezuelan equine encephalitis virus, epizootic strain P-676, occurred in four of nine fetuses studied. The mares were infected near term. Virus was recovered in high titer from fetal blood and organs, while no virus was detected in maternal blood but neutralizing antibodies were present. No evidence of in utero infection was found in two fetuses from mares infected with MF-8, another epizootic strain of Venezuelan equine encephalitis virus.

Animals↗