1,721,026 research outputs found
Electrical events during gamete maturation and fertilization in animals and humans
No full textGamete cells are electrogenic, i.e. capable of responding to electrical stimuli and modifying their electrical properties
during the crucial periods of maturation and fertilization. Ion channels have been widely demonstrated on the
plasma membrane of the oocyte and spermatozoon in all animals studied, and electrical modifications in gametes
are due to ion currents that are modulated via these ion channels. The modification of intracellular calcium levels in
gametes has been extensively studied, and these modifications are recognized to be a second messenger system for
gamete maturation and fertilization. Other ions also move through the plasma membrane, either in association with
or independent of calcium, and these generate typical features such as fertilization currents and oscillation of resting
potential. These modifications were first studied in marine invertebrates, and the observations subsequently compared
with mammalian systems, including human. The precise role played by these currents in the processes of maturation
and fertilization is still poorly understood; however, recent research opens new frontiers for their clinical
and technological application
Calcium current activity decreases during meiotic progression in bovine oocytes.
No full textBy using the whole cell voltage-clamp
technique, we studied changes in plasma membrane permeability
at different meiotic stages of bovine oocytes. Follicular
oocytes were matured in vitro and activated by Ca2+ ionophore.
Oocytes at germinal vesicle (GV), germinal vesicle
breakdown (GVBD), metaphase I (MI), metaphase II (MII),
and meiosis exit were used for electrophysiological recording.
By clamping the oocytes at -30 mV, we found that the L-type
voltage-dependent Ca2+ channels were active at the GV
stage and that their activity decreased after the GVBD stage.
Furthermore, the resting potential decreased from the GV to
the MI stage and increased again at MII. A significant decrease
of the steady-state conductance occurred from the GV
to the MI stage, followed by a sharp increase at the MII stage.
With the addition of organic L-type Ca2+ channel blockers
(nifedipine and verapamil), we inhibited the Ca2+ currents.
However, only in the case of verapamil was there a decrease
of in vitro maturation efficiency. Our results suggest that, in
addition to the cumulus-oocyte junctions, the plasma membrane
channels provide another mode of Ca2+ entry into
bovine oocytes during meiosis
Fertilization and activation currents in bovine oocytes.
No full textOne of the first events that occurs at fertilization is a
transient modification of the electrical properties of the
oocyte plasma membrane. The whole-cell voltage clamp
technique was used to demonstrate an outward ion current
and a hyperpolarization of the plasma membrane after
fertilization in bovine oocytes. These electrical events,
together with measurement of internal calcium concentrations,
were also recorded after injection with sperm
factor and exposure to parthenogenetic activators, such as
Ca2+ ionophore, ethanol and thapsigargin. Experiments
were carried out simultaneously in immature and in vitro
matured oocytes. Significant differences were recorded
in the activation current and hyperpolarization among
oocyte activators and between immature and matured
oocytes. However, outward ion current and Ca2+ release
showed similar dynamics. The injection of the calcium
chelator EGTA completely abolished both ion current and
hyperpolarization, indicating that these electrical events
are calcium dependent. Addition of specific calcium
releasers, such as 1,4,5-inositol trisphosphate (IP3) and
caffeine, triggered ion activation current and hyperpolarization
indicating that IP3 and ryanodine receptors are
active in both immature and matured oocytes. Different
ion channel inhibitors were used to characterize the
channels underlying outward currents. Only addition of
rIberiotoxin caused a complete inhibition of the current,
indicating the involvement of high conductance Ca2+-
activated K+ channels in generating activation current. In
conclusion, these findings provide evidence that bovine
oocyte activation is associated with Ca2+-dependent
electrical events. Oocytes have the potential to react to
different activators even when immature; however, oocyte
maturation seems to increase sensitivity to physiological
activators, such as spermatozoa and sperm factor, and
chemicals, such as ethanol
Gamete quality in a multistressor environment
Full text linkOver the past few decades, accumulated evidence confirms that the global environment conditions are changing rapidly. Urban industrialization, agriculture and globalization have generated water, air and soil pollution, giving rise to an environment with a growing number of stress factors, which has a serious impact on the fitness, reproduction and survival of living organisms. The issue raises considerable concern on biodiversity conservation, which is now at risk: it is estimated that a number of species will be extinct in the near future. Sexual reproduction is the process that allows the formation of a new individual and is underpinned by gamete quality defined as the ability of spermatozoa and oocytes to interact during fertilization leading to the creation and development of a normal embryo.
This review aimed to provide the current state of knowledge regarding the impact of a broad spectrum of environmental stressors on diverse parameters used to estimate and evaluate gamete quality in humans and in canonical animal models used for experimental research.
Effects of metals, biocides, herbicides, nanoparticles, plastics, temperature rise, ocean acidification, air pollution and lifestyle on the physiological parameters that underlie gamete fertilization competence are described supporting the concept that environmental stressors represent a serious hazard to gamete quality with reproductive
disorders and living organism failure. Although clear evidence is still limited, gamete capacity to maintain and/or recover physiological conditions is recently demonstrated providing further clues about the plasticity of organisms and their tolerance to the pressures of pollution that may facilitate the reproduction and the persistence of species within the scenario of global change.
Changes in the global environment must be urgently placed at the forefront of public attention, with a massive effort invested in further studies aimed towards implementing current knowledge and identifying new methodologies and markers to predict impairment of gamete quality
Developmental potential in bovine oocytes is related to cumulus-oocyte complex grade, calcium current activity, and calcium stores.
No full textA morphological classification of the immature cumulus-oocyte
complex (COC), which grossly resembled the atresia grade
of its follicle source, was used in bovine oocytes to determine
1) the developmental potential by either in vitro fertilization or
parthenogenetic activation, 2) the calcium current activity by
whole-cell voltage clamp technique, and 3) the intracytoplasmic
calcium stores by microfluorimetric evaluation. The COC classification
took into account some cumulus and ooplasm features,
designated as follows: A) presence of a clear and compact
cumulus and translucent ooplasm, B) dark and compact cumulus
and dark ooplasm, and C) dark and expanded cumulus and dark
ooplasm. We found no difference between in vitro fertilization
and parthenogenetically activated oocytes in terms of cleavage
rate and blastocyst production. Both protocols indicated a significant
variability between the three compared COC categories.
The B-COCs showed the highest embryo production efficiency
as well as the greatest Ca2+ current activity, whereas ACOCs
showed an opposite pattern. The C-COCs, mostly attributed
to atretic and heavily atretic follicles, showed
morphological characteristics between those of A- and B-COCs.
Stores of Ca2+ were significantly greater in A-COCs than in B- and
C-COCs in the case of immature oocytes, and greater in B-COCs
than in C-and A-COCs in the case of in vitro-matured
oocytes. These results demonstrate that in the bovine 1) the considered
morphological criteria for oocyte classification are related
to developmental competence, 2) plasma membrane Ca2+
current in the immature oocyte is related to developmental potential,
and 3) calcium stores are related to morphological quality
in immature oocytes and to developmental competence in
mature oocytes
Electrophysiology and Fluorescence Spectroscopy Approaches for Evaluating Gamete and Embryo Functionality in Animals and Humans
Full text linkThis review has examined two of the techniques most used by our research group for evaluating gamete and embryo functionality in animal species, ranging from marine invertebrates to humans. Electrophysiology has given access to fundamental information on some mechanisms underpinning the biology of reproduction. This technique demonstrates the involvement of ion channels in multiple physiological mechanisms, the achievement of homeostasis conditions, and the triggering of profound metabolic modifications, often functioning as amplification signals of cellular communication. Fluorescence spectrometry using fluorescent probes to mark specific cell structures allows detailed information to be obtained on the functional characteristics of the cell populations examined. The simple and rapid execution of this methodology allowed us to establish a panel helpful in elucidating functional features in living cells in a simultaneous and multi-parameter way in order to acquire overall drafting of gamete and embryo functionality
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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