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A Peres

Publications and source records attributed to A Peres.

At least 91 records · Page 5Linked to original sources
PubMed1986

Resting membrane potential and inward current properties of mouse ovarian oocytes and eggs.

The electrical properties of the membrane of the ovarian oocyte at the germinal vesicle (GV) stage and of the ovulated egg of the mouse have been studied using a two-microelectrode voltage-clamp technique. The stable resting potential measured with a single electrode was -38.2 +/- 2.8 mV SE (18 oocytes, 5 animals) and -27.8 +/- 1.4 mV SE (28 eggs, 8 animals) in a solution containing 20 mM [Ca2+]0. The lower values appear to be strongly affected by damage due to electrode insertion. However, there was no evidence of the resting potential being more negative than -40 to -50 mV. Voltage-dependent inward current could not be activated from a holding potential (Vh) close to the resting potential. When Vh was set at -90 mV, depolarizing pulses activated a transient inward current in both oocytes and eggs. The threshold voltage, peak voltage and inactivation vs potential curve were very similar in oocytes and eggs. On the other hand, the current amplitude appeared reduced in ovulated eggs, whilst times to peak and inactivation time constants in eggs were significantly longer than in oocytes. In oocytes the inward current was blocked by 10 mM Co2+ and decreased by lowering [Ca2+]0 to 5 mM similarly to the results reported for eggs. It therefore appears that GV ovarian oocytes possess Ca2+ channels which differ from those present in eggs mainly with respect to their kinetic properties. The physiological role of this inward current remains obscure in both preparations since they are almost completely inactivated at the resting potential.

Animals↗
PubMed1986

Membrane potential measurements of unfertilized and fertilized Xenopus laevis eggs are affected by damage caused by the electrode.

Upon penetration in an unfertilized Xenopus egg bathed in 1/10 Ringer, the voltage recorded by a microelectrode shows an abrupt jump to a negative voltage (Ep) followed by a rapid depolarization to a steady value (Er) (Ep = -39.4 +/- 1.9 mV and Er = -11.5 +/- 0.5 SE, 54 eggs from 9 females). The same is true for fertilized eggs impaled 16-35 min after insemination (Ep = -29.5 +/- 2.1 mV, Er = -11.5 +/- 0.9 mV, SE, 18 eggs from 3 females). The voltage recorded by a second microelectrode inserted into the same egg does not show the transient initial negativity. The stationary level of the membrane potential is close to the diffusion potential calculated from the Goldman equation with equal permeabilities for all the relevant ions. It is concluded that the low resting potentials measured in Xenopus eggs before and after fertilization are largely due to damage caused by the electrode. Using an upper limit of -39 mV for the true membrane potential and correlating the input resistance with the stationary membrane potential, a lower limit of 22 M omega (about 1 M omega cm2) for the membrane resistance can be obtained. Insertion of a microelectrode during the first 3 min after insemination shows a steady positive potential while, at later times (3-16 min post-insemination), a positive peak followed by a repolarization can be observed. This indicates that the measurement of the peak of the fertilization potential is not seriously affected by the electrode penetration while its time course after the first 3 min may be deformed by the presence of a large leakage conductance.

Animals↗
PubMed1986

The effects of polyinosinic: polycytidylic acid (pI:C) on the GVH reaction: immunopathological observations.

The effects of polyinosinic: polycytidylic acid (pI:C) on the graft-versus-host (GVH) reaction were studied. The drug pI:C rapidly and markedly induces interferon and augments natural killer (NK) cell activity. GVH reactions were induced by injecting parental lymphoid cells intravenously into F1 hybrid mice. The development of a GVH reaction was monitored by measuring the plaque-forming cell (PFC) response to sheep red blood cells (SRBC) and by histological examination. When 30 X 10(6) B6 lymphoid cells were injected into B6AF1 mice, the recipients developed profound immunosuppression by 10-12 days post-GVH induction. In addition, pathological changes indicative of GVH reactions were seen in the spleen, lymph nodes, thymus, liver, lung, pancreas, and salivary gland of these mice. However, the treatment of B6AF1 recipients with pI:C prior to parental cell transfer markedly reduced the degree of suppression of the immune response, as measured by the PFC response to SRBC. Also, such mice failed to demonstrate the histological lesions of GVH disease. Treatment of donor mice with pI:C had no effect in preventing either GVH-induced immunosuppression or pathological changes. This study suggests that a pI:C-induced mechanism, possibly involving NK cells, is capable of regulating the GVH reaction.

Animals↗
PubMed1986

Calcium current in mouse eggs recorded with the tight-seal, whole-cell voltage-clamp technique.

The tight-seal, whole-cell recording technique has been used to voltage-clamp unfertilized eggs of the mouse. Good seal formation was obtained in a solution containing 20 mM Ca2+ and the transient inward Ca2+ current recorded. This technique offers several advantages over the conventional, two-microelectrodes voltage-clamp: improved signal to noise ratio; larger membrane-pipette seal resistance; possibility of very stable, long duration, recordings and possibility of controlling the intracellular medium. The main disadvantage of the technique, namely the rundown of channels due to loss of intracellular components, was not encountered in this preparation.

Animals↗
PubMed1985

The effective membrane capacity of Xenopus eggs: its relations with membrane conductance and cortical granule exocytosis.

The effective membrane capacity (Ceff) of the Xenopus egg has been measured integrating the membrane current transients in response to small voltage-clamp pulses. Before activation Ceff has a value of 1.34 +/- SE. 0.13 microF/cm2 (apparent surface area, 13 eggs from 3 females) and is essentially constant over the voltage range between - 30 and + 60 mV. During artificial activation of the eggs by pricking or by addition of Ca2+ ionophore A23187, Ceff increases by about 60% in 2-3 min and then slowly decreases returning to near the initial value in 15-20 min. Electron microscopic observations of the egg surface at different times reveal that the capacity time course parallels the changes in plasma membrane area due to cortical granule exocytosis and to a later reduction of microvillar extension. Simultaneous measurements of capacity and conductance show that the capacity changes are slower and delayed in comparison with the transient development of the chloride conductance responsible for the activation potential. In CO2-treated eggs the cortical granule exocytosis is prevented and, correspondingly, the transient capacity increase is strongly reduced or absent, but the development of the chloride conductance remains normal. This technique gives a method to electrophysiologically monitor the cortical granule exocytosis; moreover our results show that the exocytotic process can be blocked without affecting the membrane conductance changes.

Animals↗
PubMed1985

A voltage-dependent K+ channel controlling the membrane potential in frog oocytes.

Full-grown frog ovarian oocytes (Rana esculenta), were voltage clamped with a conventional two-microelectrode system. Depolarizations from a holding potential of--60 mV produced slowly developing outward currents. Two-step clamp experiments showed that, in Ringer's solution, this current has a reversal potential at about--84 mV. Substitution of either sodium or chloride with impermeant ions in the external solution did not alter significantly the activation of the current nor its reversal potential. Increasing the potassium ions concentration caused a shift on the reversal potential in the positive direction with a slope of about 48 mV per decade. The presence of TEA ions (50 mM) in the external solution partially reduced the current. It is concluded that the membrane of full-grown frog ovarian oocytes possesses voltage-dependent ionic channels permeated mainly by potassium. They appear to play an important role in the control of membrane potential.

Animals↗
PubMed1985

Sodium conductance and the activation potential in Xenopus laevis eggs.

Experiments have been performed to identify the membrane permeability changes causing activation potential in Xenopus eggs. The eggs were artificially activated either by pricking or by addition of the Ca2+ ionophore A23187 to the bath. Two different ionic currents appear to control the activation potential: (i) a chloride current which develops after a delay of 30 s to 5 min from the activating stimulus and which, in low external chloride, produces a depolarization and, (ii) a voltage-dependent outward current which begins to flow when the membrane potential is more positive than about +20 mV and tends to hyperpolarize the membrane. The chloride current lasts about 3-4 min; the voltage-dependent outward current is present before activation and disappears more slowly than the Cl- current. Changes in external sodium concentration affect the reversal potential of the outward current before and after the development of the inward Cl- current. We suggest that the chloride current has the role of producing a rapid depolarization necessary to block polyspermy, while the voltage-dependent sodium outward current might prevent the depolarization from reaching excessively high values and help the repolarization phase.

Animals↗
PubMed1985

Interleukin-1 and interleukin-2 defects associated with murine graft-versus-host-induced immunodeficiency.

In this study we investigated the mechanism, or mechanisms, involved in graft-versus-host (GVH)-induced T cell immunodeficiency. Chronic GVH reactions were induced in normal CBA X A F1 (BAF1) hybrid mice by the injection of parental A strain lymphoid cells. At various times (43-91 days) after GVH induction, the functional status of GVH T cells was assessed using interleukin-1 (IL-1) and interleukin-2 (IL-2) as probes. The response of GVH thymocytes to IL-1 was depressed when compared with normal thymocytes. Although GVH peanut-agglutinin-negative (PNA-) thymocytes did respond to IL-2 alone or IL-2 plus phytohemagglutinin (PHA), this response was significantly lower than the response of PNA- thymocytes from normal mice. In addition, GVH spleen cells failed to produce significant amounts of IL-2 when stimulated with concanavalin A. These results suggest that the long term immunosuppression associated with murine chronic GVH disease is due, at least in part, to a decrease in the responsiveness to IL-1 and IL-2, and to a marked deficiency in IL-2 production.

Animals↗
PubMed1984

Analysis of lumped and distributed elements models of cut muscle fibers in vaseline or sucrose gap preparations.

A general method of finding the time course and the steady state distribution of potential in Vaseline or sucrose gap preparations is given by making use of the linear cable equation. The general solution has been found analytically in terms of its Laplace transform and then numerically inverted. Two particular experimental situations, namely the single gap and the double gap preparations, have been analyzed. The results have been compared with the solutions of the commonly used lumped elements models. While for the double gap no large errors are introduced by the lumped model, for the single gap there are significant differences. The dependence of the voltage distribution on various electrical and geometrical parameters has been examined. It is suggested that the proposed mathematical treatment might be used by experimenters as a reference to assess the validity of simplified lumped models.

Animals↗
PubMed1983

A hyperpolarization-activated chloride current in Xenopus laevis oocytes under voltage-clamp.

Voltage-clamp experiments have been performed on ovulated Xenopus laevis oocytes. Two kinds of oocytes were studied: mature oocytes presenting the white spot due to germinal vesicle breakdown (GVBD) were found to be essentially unexcitable; oocytes without the white spot appeared to possess ionic channels which open transiently on hyperpolarization. The current is carried by chloride ions and, in Holtfreter's solution, has a reversal potential at approximately - 15 mV.

Animals↗