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G Bernardini

Publications and source records attributed to G Bernardini.

At least 55 records · Page 3Linked to original sources
PubMed1990

Spermiogenesis in Xenopus laevis: from late spermatids to spermatozoa.

Spermatogenesis is a complex morphogenetic process in which microfilaments and microtubules have been shown to play an important role. The last steps of Xenopus spermatogenesis, i.e., the corkscrew shaping of the sperm head, have been followed to study actin and microtubule distribution by conventional and immunoelectron microscopy. During sperm head morphogenesis, actin is absent in the elongating spermatids, but it is present in the Sertoli cells where results localized at the periphery of their cytoplasm that surrounds the developing germ cells. Sertoli cell actin and microtubules may assist the elongation and the shaping of the spermatids and function in maintaining the Sertoli-spermatid association.

Actins↗
PubMed1990

Anionic versus cationic immunoglobulin clearance in normal subjects: a novel approach to the evaluation of charge permselectivity.

The excretion of proteins differing in charge (the different immunoglobulin subclasses) and/or size (albumin, immunoglobulins) were investigated in normal subjects in a number of physiological conditions aiming at the evaluation of renal charge permselectivity. In 101 randomly selected normal subjects the urinary excretion rates of albumin, IgG4 (anionic proteins) and of total IgG (mostly cationic) were evaluated in basal conditions; the protein/creatinine urinary ratio and protein clearances were assessed in part of them. In addition, the intra- and interday variations of protein excretion were evaluated. Protein clearances were measured in a sample group after standardized physical exercise, after an amino acid load, and in orthostatism. Albumin, IgG4 and IgG were assayed using sensitive methods developed in our laboratories. The excretion rate values of albumin, IgG4 and total IgG (median, interquartile range) were 4.36 micrograms/min, (2.58-6.59), 4.25 ng/min (2.6-7.6), and 1.47 micrograms/min (0.85-2.44), respectively. The clearances of the three proteins (mean +/- SD) were 0.13 +/- 0.07, 0.017 +/- 0.012 and 0.14 +/- 0.08 ml/min x 10(-3), respectively. The IgG4/IgG ratio averaged 0.1 and was always below 0.25. Protein excretion rates showed a noticeable variation during the day and from day to day. Physical exercise, the change of posture and the amino acid load significantly increased proteinuria but did not significantly modify the anionic/cationic immunoglobulin ratio. Thus, the anionic/cationic immunoglobulin ratio of about one tenth, substantially stable during dynamic tests, in normal subjects may be considered an index of physiological renal protein charge permselectivity.

Adolescent↗
PubMed1989

The plasma membrane of Xenopus laevis spermatozoon.

Xenopus laevis sperm plasma membrane ultrastructure has been studied by means of freeze-fracture, deep-etching, and lectin-gold binding. Xenopus spermatozoa differ from those of other species in that their plasma membrane does not exhibit topographical domains. In fact, no geometric arrangement or characteristic array of particles is present on fractured plasma membrane. Fractures rarely occur in acrosomal or nuclear membranes. Wheat germ agglutinin receptors are distributed homogeneously on the plasma membrane of the sperm head and tail.

Animals↗
PubMed1988

Xenopus spermatozoon: correlation between shape and motility.

Xenopus spermatozoa have a characteristic corkscrew-shaped head and a flagellum with a conventional "9 + 2" structure (Bernardini et al.: J Ultrastruct Md Struct Res: 94:188-194. They are motile in water and media of low osmolarities, but not in media of osmolarities higher than 200 mosm/liter, regardless of the ionic composition. External calcium and pH are not involved in the inhibition of sperm movement at high osmolarities. The duration of sperm motion was less than 10 min, and both flagellar beat frequencies and sperm velocities declined progressively. However, in demembranated and reactivated tails, flagellar beating was sustained for longer times. Flagella propagated three-dimensional waves that induced a spinning motion of the whole spermatozoon. This pattern of movement is not dependent on the shape of the sperm head, since isolated, reactivated flagella exhibited three-dimensional waves.

Animals↗
PubMed1988

Xenopus spermatozoon: is there any correlation between motility and oxygen consumption?

The motility status of Xenopus laevis spermatozoa does not affect their respiration rate. Oxygen consumption for 10(9) spermatozoa is approximately 0.4 mumol/minute. Oxygen consumption is not increased by gramicidin D, an uncoupler, and it is not blocked by KCN or NaN3. The adenosine triphosphate (ATP) content of spermatozoa that have been activated is definitely less than that in the spermatozoa that remained immotile. Incubation in KCN, NaN3, and gramicidin decreases the ATP content and impairs motility. The conclusions of the present study are that in Xenopus spermatozoa motility and oxygen consumption are not correlated, and the composition of the respiratory chain of these spermatozoa presents noteworthy peculiarities.

Adenosine Triphosphate↗
PubMed1987

Fertilization induces endocytosis in Xenopus eggs.

Fertilization-induced endocytosis in Xenopus eggs was shown by direct visualization of fluorescent dye in semithin sections. The eggs were incubated in a medium containing 0.1% Lucifer yellow CH for 20 min before, during and after fertilization and then fixed at different times after fertilization. The eggs incubated during or immediately after fertilization contained fluorescent vesicles in the cortex. These vesicles were mainly distributed in the animal hemisphere.

Animals↗
PubMed1987

Ofloxacin vs. cotrimoxazole in patients with complicated urinary tract infections.

A simple open randomized study was performed to evaluate the comparative efficacy and safety of ofloxacin and cotrimoxazole in 40 patients with complicated urinary tract infections. In these patients ofloxacin produced better clinical results than cotrimoxazole. The results were also excellent when cotrimoxazole-resistant strains were involved, even in immunocompromised hosts.

Adult↗
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↗
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

Lens junctions are communicating junctions.

Lens fibers are electrically coupled with each other and directly exchange dyes and metabolites. In most cells, this form of communication is mediated by gap junctions. Lens fibers lack typical gap junctions. The lens junctions, although morphologically similar to gap junctions, differ from them structurally, chemically and immunologically. Nevertheless, recent evidence suggests that indeed lens junctions are communicating junctions. The lens junction protein, MIP26, displays structural characteristics similar to other channel proteins. Once incorporated into liposomes it forms channels permeable to molecules as heavy as 1.5 kDa. Like other communicating junctions, lens junctions assume crystalline arrays and uncouple with Ca++. The liposome incorporated channels close with Ca++ and H+ in the presence of calmodulin (CaM). Partial loss of gating competency occurs after proteolytic cleavage of the C-terminal arm of MIP26. The need for a unique type of communicating junction in lens is unclear. A possibility is that this tissue has some special cell-to-cell transport requirements, in terms of size and/or charge of permeants, not shared by coupled cells of other tissues.

Animals↗
PubMed1984

Segmented and "equivalent" representation of the cable equation.

The linear cable theory has been applied to a modular structure consisting of n repeating units each composed of two subunits with different values of resistance and capacitance. For n going to infinity, i.e., for infinite cables, we have derived analytically the Laplace transform of the solution by making use of a difference method and we have inverted it by means of a numerical procedure. The results have been compared with those obtained by the direct application of the cable equation to a simplified nonmodular model with "equivalent" electrical parameters. The implication of our work in the analysis of the time and space course of the potential of real fibers has been discussed. In particular, we have shown that the simplified ("equivalent") model is a very good representation of the segmented model for the nodal regions of myelinated fibers in a steady situation and in every condition for muscle fibers. An approximate solution for the steady potential of myelinated fibers has been derived for both nodal and internodal regions. The applications of our work to other cases dealing with repeating structures, such as earthworm giant fibers, have been discussed and our results have been compared with other attempts to solve similar problems.

Action Potentials↗
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↗
PubMed1984

Gap junction structure and cell-to-cell coupling regulation: is there a calmodulin involvement?

In most tissues neighboring cells communicate directly with each other by exchanging ions and small metabolites via cell-to-cell channels located at the intermembrane particles of gap junctions. Evidence indicates that the channels close when the [Ca2+]i or [H+]i increases. The channel occlusion (cell-to-cell uncoupling) is mainly a safety device by which cells can isolate themselves from damaged neighboring cells ("healing-over" process). Despite our knowledge of uncoupling agents, the uncoupling mechanism is still poorly understood. Uncoupling treatments have been shown to cause structural changes in gap junctions, characterized by an increase in tightness and regularity (crystallization) of particle packing and a decrease in particle size. Recently these changes have been shown to be induced by Ca2+ or H+ in isolated lens junctions and by Ca2+ in liver junctions, which suggests a close relationship between structural changes and uncoupling, but preliminary studies indicate that the junctional changes may not be synchronous with uncoupling but may lag behind it. However, recent X-ray diffraction data show that the channels of crystalline gap junctions (typical of uncoupled cells) are indeed closed, because they are inaccessible to sucrose (a gap junction permeant). Thus it seems that crystalline junctions are indeed in a non-permeable state, but the occlusion of the channels may precede the crystallization process. In the lens, junction crystallization is inhibited by a calmodulin (CaM) inhibitor, trifluoperazine (TFP). Is CaM involved in the uncoupling mechanism? To test this hypothesis, TFP and calmidazolium (CDZ), the most specific CaM inhibitor, were used on amphibian embryonic cells electrically uncoupled by CO2. Both TFP and CDZ effectively protect the cells from uncoupling, which suggests that CaM participates in the process. As a hypothesis, we propose that channel occlusion follows a CaM-mediated conformational change in the junctional protein. Particle crystallization may follow the conformational changes and result from a modification in electrostatic repulsion among the particles.

Animals↗
PubMed1984

Reversible effects of heptanol on gap junction structure and cell-to-cell electrical coupling.

It has been shown that certain alkanols such as heptanol and octanol reversibly uncouple crayfish axons. We have studied the effects of heptanol on the electrical coupling in Xenopus embryo cells and on the gap junction particle distribution of stomach and pancreas epithelia. Cell-to-cell electrical communication in Xenopus embryos reversibly decreases 10-15 min after the beginning of heptanol superfusion to reach values of coupling ratio lower than 0.05. Particle density of rat stomach and pancreas gap junction reversibly increases after exposure to heptanol-Tyrode's solutions. In stomach, gap junction particles from isles with hexagonal patterns after 10 to 15 min; in pancreas crystallization occurs after 20 to 30 min. Optical diffractions are used to average particle spacings in treated and control junctions of pancreas.

Alcohols↗
PubMed1983

Is calmodulin involved in the regulation of gap junction permeability?

The cell-to-cell channels of gap junctions mediate the direct exchange of ions and small metabolites between neighboring cells. A number of studies have shown that these channels close when the intracellular free calcium or hydrogen concentration increases, the result being cell-to-cell uncoupling. Since most of the calcium-activated biological phenomena are mediated by calmodulin (CaM), an obvious question is whether or not CaM is involved in the mechanism of cell coupling regulation. Data from the present study, showing the inhibitory effects of a calmodulin blocker on electrical uncoupling in Xenopus embryo cells, suggest a possible CaM participation in the uncoupling mechanism.

Animals↗