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Biomedical subjects

V Taglietti

Publications and source records attributed to V Taglietti.

At least 55 records · Page 3Linked to original sources
PubMed1984

Maturation involves suppression of voltage-gated currents in the frog oocyte.

Voltage- and time-dependent currents having slow kinetics have been studied in plasma membranes of immature oocytes of the european frog, Rana esculenta. IK, corresponding to an outward flow of K+, is activated at potentials more positive than about -40 mV, and subserves outward rectification; Iir, corresponding to an outward flow of Cl-, is activated at potentials more negative than about -80 mV and subserves inward rectification. Such currents can act as negative feedback mechanisms in the control of membrane potential in the immature oocyte and limit to a somewhat restricted range its possible deviations from resting values. Besides IK, membrane depolarizations to potentials more positive than about +30 mV are capable of activating INa, corresponding to outflow of Na+. By contrast, the frog mature egg-cell has a single voltage- and time-dependent current, IM, activated at potentials more positive than +30 mV, with properties similar to INa. The disappearance of IK and Iir along with remarkable reduction in leakage lowers impedance in the egg membrane. It seems reasonable to suggest that the observed changes in membrane permeability reflect changes which have taken place along the maturation process and are of importance for successful fertilization.

Animals↗
PubMed1983

[Electrophysiological study of the frog egg at various stages of development. IV. Changes associated with the maturation process].

The I/V relationship of frog oocytes is markedly modified following maturation, lacking the mature unfertilized egg cell membrane of K-selective channels and the leakage being strongly reduced. The only kind of voltage-dependent channels still present in this membrane are activated by depolarizing steps to potentials more positive than 30-40 mV; the current flowing through these channels is carried at least partly by Na+. At difference with the immature oocyte, where several ionic mechanisms are oriented to maintain the membrane potential at a constant level, the mature egg-cell admits considerable voltage deflections. The observed variations in membrane properties could be of importance in allowing the maturation process and/or in preparing the mature egg-cell to successful fertilization.

Animals↗
PubMed1983

[Electrophysiological study of frog eggs at different stages of development. II) Outward rectification in oocytes at the final stage of vitellogenesis].

Voltage-clamp experiments in full-grown frog oocytes, in a range of membrane potentials from 90 mV negative to 30 mV positive, have revealed the presence of voltage-dependent channels selective for K+, blocked by extracellular TEA. The percentage of open K+-channels increases with membrane depolarizations over a range from -40 mV to +10 mV, thus supporting the outward rectification in the I/V relationship. The current transport through the K+-channels open at different potential levels and in various [K+]o takes place in accordance with the constant-field assumptions. The leakage current of the oocyte membrane was found to be considerable large.

Animals↗
PubMed1983

[Electrophysiological study of frog eggs at different stages of development. III) Ionic currents activated by intense hyperpolarization and depolarization of the oocyte at the final stage of vitellogenesis].

In addition to K-selective channels, two kinds of voltage-dependent channels are present in the membrane of full-grown frog oocytes: 1) non-selective channels, activated by hyperpolarizing steps to potentials more negative than -80, -90 mV; 2) cationic channels, activated by depolarizing steps to potentials more positive than +30, +40 mV. The former are related to the inward rectification; the latter could contribute to the outward rectification of the I/V relationship. Therefore the membrane potential in full-grown oocytes tends to be maintained at a constant value due to the changes of permeability that follow possible potential variations occurring in both directions.

Animals↗
PubMed1983

[Electrophysiological study of frog eggs at different stages of development. I) Membrane potential and I/V relationship in the oocyte at the final stage of vitellogenesis].

Variations of [K+]o have been found to influence the membrane potential in frog full-grown oocytes at a greater extent than other modifications in extracellular medium composition; however, the relationship between membrane potential and [K+]o was far from that expected for an ideal K electrode. The I/V relationship, as determined in current clamp conditions, displays an evident "inward-going" rectification at potentials more negative than -80, -90 mV as well as an evident "outward-going" rectification at potentials more positive than -20, -10 mV, thus suggesting the presence of voltage-dependent channels in this membrane. In the linearity range of the I/V relationship, Rm was found to be about 3 + 15 K omega cm2 and Cm about 20 + 30 microF/cm2.

Animals↗
PubMed1982

Noise analysis of acetylcholine induced current at neuromuscular junctions of the mouse diaphragm.

Miniature end-plate currents (mepcs) and membrane noise elicited by acetylcholine (ACh) iontophoresis were investigated at neuromuscular junctions of the mouse diaphragm. All the experiments were performed at a holding potential of -70 mV at a temperature of 19 degrees C. The equilibrium potential of the ACh response was estimated to be near zero; the mepcs displayed a peak amplitude of 2.46 +/- 0.13 nA (mean +/- S.E.) and relaxed exponentially with a time constant to 1.63 +/- 0.11 msec. Single ACh-activated channels had a conductance of 26.5 +/- 1.5 pS and a mean life time of 1.69 +/0- 0.13 msec.

Acetylcholine↗
PubMed1977

Adaptive distortions in the generator potential of semicircular canal sensory afferents.

The generator potential in sensory afferents of frog crista ampullaris was extracellularly recorded from the cut end of the posterior ampullary nerve by means of suction electrodes. A servocontrolled turntable allowed suitable rotatary stimulations. The analysis of the recorded generator potential revealed a different time course from that predicted on the basis of the pendulum model. Adaptation and undershoots in the responses to velocity ramps, steps and sinusoids, were mainly responsible for the deviations, which became very evident only when fairly high acceleration rates were applied. Both adaptation and undershoots were produced presumably by the activation of an electrogenic pump, probably located in nerv terminals contacting the hair cells. In fact, the time course of the generator potential became much more consistent with the predictions from the pendulum model under treatments capable of hindering the ion pump activity.

Acceleration↗
PubMed1976

Effects of Ba ions on frog's isolated muscle spindle.

Dilute solutions of Barium Chloride have been tested on frog's isolated muscle spindles with the aim of clarifying the processes leading to the afferent discharge. In the presence of Ba++ the spindle properties are modified as follows: 1. The discharge of slack spindles increases and becomes extremely regular. 2. The phasic response to stretching is enhanced, the tonic responses being on the contrary virtually suppressed. Under Ba-treatment therefore the spindle changes from a phasic-tonic receptor to a merely phasic receptor. 3. The "silent period" following every propagated spike is prolonged while the safety margin of the "abortive" into propagated spike conversion becomes maximal under Ba-treatment. Additionally, this analysis showed that, when a "true" action potential arises in the spindle, it propagates not only to the stem fibre, but also to all the sensory endings in the spindle intracapsular network. Comparison between the effects of Ba++ and those produced by TEA and ouabain indicates that the action of Ba++ on muscle spindles results from conjunction of two factors : a) reduction of K permeability, and b) enhanced efficiency of an electrogenic Na/K-pump in spindle nerve membranes.

Action Potentials↗