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G M Oliveira-Castro

Publications and source records attributed to G M Oliveira-Castro.

13 recordsLinked to original sources
PubMed1997

Outward potassium current oscillations in macrophage polykaryons: extracellular calcium entry and calcium-induced calcium release.

Outward current oscillations associated with transient membrane hyperpolarizations were induced in murine macrophage polykaryons by membrane depolarization in the absence of external Na+. Oscillations corresponded to a cyclic activation of Ca(2+)-dependent K+ currents (IKCa) probably correlated with variations in intracellular Ca2+ concentration. Addition of external Na+ (8 mM) immediately abolished the outward current oscillations, suggesting that the absence of the cation is necessary not only for their induction but also for their maintenance. Oscillations were completely blocked by nisoldipine. Ruthenium red and ryanodine reduced the number of outward current cycles in each episode, whereas quercetin prolonged the hyperpolarization 2- to 15-fold. Neither low molecular weight heparin nor the absence of a Na+ gradient across the membrane had any influence on oscillations. The evidence suggests that Ca2+ entry through a pathway sensitive to Ca2+ channel blockers is elicited by membrane depolarization in Na(+)-free medium and is essential to initiate oscillations, which are also dependent on the cyclic release of Ca2+ from intracellular Ca(2+)-sensitive stores; Ca2+ ATPase acts by reducing intracellular Ca2+, thus allowing slow deactivation of IKCa. Evidence is presented that neither a Na+/Ca2+ antiporter nor Ca2+ release from IP3-sensitive Ca2+ stores participate directly in the mechanism of oscillation.

Animals↗
PubMed1993

ATP- and UTP-induced currents in macrophages and macrophage polykaryons.

We have investigated the currents induced by extracellular ATP (ATPo), extra-cellular UTP, and other related compounds in macrophages. At potentials of -20 to -60 mV, a typical response to ATPo puffs consists of a fast-activating inward current followed by a transient outward current. The phenomenon lasts 5-20 s, but for sustained exposure to ATP the inward current persists for up to 10 min (our longest recording time). Both currents are inhibited by Mg2+, suggesting that the phenomenon is mediated by ATP4-. The outward current can be ascribed to a Ca(2+)-dependent K+ conductance, and release of Ca2+ from intracellular stores is at least in part responsible for this current. The inward current has a reversal potential of approximately 0 mV, and it is nonspecific for monovalent cations. UTP, a nucleotide that induces an increase in the cytoplasmic concentration of free Ca2+ but does not permeabilize macrophages, and ATP-gamma-S can also induce inward and outward current similar to those described for ATP, but higher doses are required. Adenosine and AMP produce no detectable effect, whereas ADP induces a small outward current. The implications of these results to the phenomenon of ATPo-induced permeabilization of macrophage membranes to large molecules are discussed.

Adenosine↗
PubMed1987

Electrophysiology of phagocytic membranes: intracellular K+ activity and K+ equilibrium potential in macrophage polykaryons.

The role of K+ as current carrier during the slow membrane hyperpolarizations (SH) elicited by iontophoretic Ca2+ injections into macrophage polykaryons is studied. The intracellular K+ activity (ak) and the K+ equilibrium potential (Ek) are measured using ion-sensitive microelectrodes. The mean value of ak is 84 +/- 5 mM in a culture medium containing 5.3 mM K+, but increases to 100 +/- 8 mM when the extracellular K+ concentration is raised to 30.3 mM. Under the same conditions the values of Ek obtained from the Nernst equation are -81 +/- 2 mV and -40 +/- 2 mV, respectively. The reversal potentials (ER) of the SH are calculated from changes observed in transmembrane potential and input resistance, according to an equivalent model based only on passive ionic fluxes. The mean ER values obtained are -74 +/- 8 mV in the presence of low K+ concentration and -37 +/- 3 mV for the high K+ medium. These values are significantly smaller than the estimated Ek for the corresponding situations. Evidence for the existence of an electrogenic (Na+ + K+)-ATPase activity is also presented. The evidence indicates that an increase in the membrane potassium permeability can account for about 90% of the total permeability change occurring during the SH.

Animals↗
PubMed1987

Reception-mediated phagocytosis of yeast by macrophage polykarions.

1. The phagocytic capacity of polynuclear macrophages (PNM) produced by intraperitoneal implants in mice was analyzed and compared with that of the mononuclear macrophage (M luminal diameter). The ability of PNM and M luminal diameter to interiorize aldehyde-fixed Saccharomyces cerevisiae is described. 2. PNM containing two to five nuclei and M luminal diameter exhibited a similar time course of phagocytosis. The phagocytic index reached a plateau from 30 to 60 min after exposure to yeast. 3. Mannose, mannan extracted from yeast and horseradish peroxidase inhibited yeast phagocytosis by PNM and M luminal diameter subpopulations to a similar extent. 4. Amino sugars (glucosamine, N-acetylglucosamine, galactosamine and N-acetylgalactosamine) caused similar reductions in the phagocytic indices of PNM and M luminal diameter. 5. The presence of monosaccharides (glucose, galactose, fructose and mannitol) did not alter the phagocytic capacity of either type of phagocyte. 6. Neither opsonin-dependent ingestion of sheep red blood cells nor ingestion of aldehyde-fixed cells by PNM or M luminal diameter is affected by mannose, suggesting that these processes involve internalization pathways different from the mannose-hexosamine recognition system. 7. Trypsin sensitivity, temperature dependence and divalent cation requirements for PNM phagocytosis were comparable to those of the M luminal diameter. 8. The similarities of the PNM to their mononuclear precursors suggest that the mannose-hexosamine receptor was preserved after polykaryon formation.

Animals↗
PubMed1986

Electrophysiology of phagocytic membranes. Role of divalent cations in membrane hyperpolarizations of macrophage polykaryons.

The electrophysiological properties of the membrane of mouse peritoneal macrophage polykaryons are studied. Slow hyperpolarizations can be elicited by iontophoretic injections of either Ca2+ or Sr2+ into the cytoplasm. The effect of both cations is identical, since: it is invariably triggered by the cation injection, the amplitude is dependent on the K+ gradient, quinine blocks reversibly the response to both cation injections. Mg2+, Ba2+ and Mn2+ did not elicit responses when injected into the cytoplasm. Ca2+ induced slow hyperpolarizations were reversibly blocked by the addition of Ba2+ to the external saline, but were not affected by the presence of external tetraethylammonium chloride. Cells maintained in saline containing high concentrations of Ca2+, Sr2+ or Mn2+ exhibited sustained hyperpolarizations. Quinine blocked the hyperpolarization induced by high Ca2+ or Sr2+, but was ineffective for the case of Mn2+. Cells hyperpolarized by external Mn2+ frequently exhibited nonlinear, voltage-current characteristics. Similar patterns could also be observed in a small fraction (less than 10%) of the cells in control conditions. Current-induced shifts between two stable membrane potentials were seen either in high Ca2+ or normal medium. The great variability of the responses described for this phagocytic membrane is discussed. The evidence supports the assumption that Ca2+ and Sr2+ can induce transient or persistent hyperpolarized states by activating a potassium permeability. External Mn2+ may act in part by reducing impalement-related current leakage from the phagocytic membrane.

Animals↗
PubMed1983

Ca2+-sensitive K+ channels in phagocytic cell membranes.

In phagocytic cells evidence for properties of Ca2+-sensitive K+-selective channels comes mostly from electrophysiological studies. Macrophages and macrophage-like cells are compared with fibroblasts (L-cells) where the Ca+-dependent K+ conductance is better understood. This model shares a mesenchymal origin and an accessory phagocytic capacity with the professional phagocytes. In macrophages several values of transmembrane potentials have been measured by different groups, using various techniques. Microelectrode measurements have demonstrated a voltage-dependent K+ conductance involved in transition from low to high membrane potentials. Current-voltage relationships in mouse peritoneal exudate cells have revealed a region of negative slope resistance. Slow calcium spikes were found in a subpopulation of cells from human dialysis fluid that appear to be distinct from typical macrophages. Action potentials have been recorded from human monocyte-derived macrophages. Their ionic mechanism has not yet been established. Spontaneous and electrically elicited slow membrane hyperpolarizations have been described in macrophages and macrophage-like cells. Similar activity is well known in L-cells and in both cases it is possible to identify a Ca2+-sensitive K+ conductance as the underlying mechanism. Phagocytosis is a cell function that has been related to membrane hyperpolarization and to slow hyperpolarizing activity. In some cases no changes of electrical activity have been observed during the phagocytic process. Chemotactic factors induce membrane hyperpolarizations in macrophages, but the relation between electrical change and cell motility has not been established. Exocytosis, a is another Ca2+ sensitive cell function that awaits correlation with electrochemical changes. The evidences accumulated to date are compatible with several models for gating and modulation of the voltage-independent K+ conductance by Ca2+. The use of higher resolution techniques, such as patch-clamp, with well defined subpopulations of phagocytic cells may produce the missing link in the transduction of membrane signals into the specifically targeted cell functions.

Animals↗
PubMed1981

Electrophysiology of phagocytic membranes. III. Evidence for a calcium-dependent potassium permeability change during slow hyperpolarizations of activated macrophages.

The roles of potassium and calcium in the slow hyperpolarizations of membranes of activated macrophages are investigated using standard intracellular electrical recording techniques. The amplitude of spontaneous slow hyperpolarizations decreases as a logarithmic function of the external potassium concentration in the culture medium. Similar dependence on the potassium gradient is observed when different levels of membrane potentials are imposed by constant current injection. The reversal potential for electrically evoked slow hyperpolarizations is -90 mV. A 10-fold increase in external potassium concentration causes a 60 mV shift of the reversal potential towards zero. Divalent cation ionophores (A23187 and X537A) can induce slow hyperpolarization responses in quiescent cells or permanent hyperpolarization in spontaneously active cells. The amplitude of the ionophore-induced hyperpolarizations is reduced by an increase in external potassium concentration in a manner consistent with data on slow hyperpolarization responses in the absence of ionophore. The calcium antagonist, verapamil, depresses the slow hyperpolarization responses at the concentration of 10(-5) M. It is suggested that the development of the hyperpolarizing response is due to a calcium-dependent potassium channel. The data support the assumption that spontaneous and artificially elicited slow hyperpolarization responses share a common calcium-dependent mechanism.

Animals↗
PubMed1979

Electrophysiology of phagocytic membranes. II. Membrane potential and induction of slow hyperpolarizations in activated macrophages.

The potential differences measured on the cell surface and after penetration into the cytoplasm of activated macrophages are described. Linear regressions are made of the measured potential differences as functions of the tip potential of each microelectrode. The surface potential of the macrophage is not significantly different from zero. Mouse macrophages have a transmembrane potential of--26 mV, whereas in guinea-pig cells this value is--18 mV. The input resistances of guinea-pig cells are higher than those of mouse macrophages. The cytoplasmic location of the electrode was characterized both by fluorescent dye injection and by electric criteria. Slow membrane hyperpolarizations are directly elicited by mechanical stimulation. Electric responses evoked by current pulses were further characterized. Our results lead to the extablishment of objective criteria to validate intracellular recordings from macrophage.

Animals↗
PubMed1977

Electrophysiology of phagocytic membranes. I. Potassium-dependent slow membrane hyperpolarizations in mice macrophages.

Electrophysiological properties of activated mouse macrophages cultured in vitro were studied using microelectrode techniques. In a high percentage of the individual cells analysed a slow hyperpolarization (SH) was observed with a concomitant decrease (2--4 times) of the input resistance. Increasing doses of tetraethyl ammonium progressively reduce the amplitude of the SH and at a concentration of 15 mM complete blockade of the phenomena is observed. Valinomycin, at a concentration of 10(-7) M produces rapid and permanent hyperpolarization, with a shift in the membrane potential to about --50 mV. These data strongly support the previously proposed hypothesis that the development of SH is due to an increase in the membrane permeability to potassium ions.

Animals↗