Physiological actions of taurine

Cyclodextrin Drug Carrier Systems.

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Degradable Controlled-Release Polymers and Polymeric Nanoparticles: Mechanisms of Controlling Drug Release

T-type Ca2+ channels were originally called low-voltage-activated (LVA) channels because they can be activated by small depolarizations of the plasma membrane. In many neurons Ca2+ influx through L...

Molecular Physiology of Low-Voltage-Activated T-type Calcium Channels

Capacitation of bovine sperm was evaluated by determining the ability of sperm to fertilize bovine oocytes in vitro and to undergo an acrosome reaction upon exposure to lysophosphatidylcholine (LC). Incubation of sperm with heparin (10 micrograms/ml) increased the percentage of oocytes fertilized, but this required exposing sperm to heparin for at least 4 h before adding them to oocytes. There was no effect on the percentage of motile or acrosome-reacted sperm after exposure of noncapacitated sperm to 100 micrograms/ml LC for 15 min. When sperm were incubated for 4 h with heparin, exposure to 100 micrograms/ml LC for 15 min had no effect on the percentage of sperm that were motile, but the percentage of acrosome-reacted sperm increased from less than 10% to over 70%. The acrosome reactions (ARs) induced by LC were synchronous, reached maximal levels within 15 min, and differed (p less than 0.001) between sperm incubated under capacitating (with heparin) and noncapacitating conditions (without heparin). The time course required for heparin to capacitate sperm as judged by in vitro fertilization and to render sperm sensitive to LC induction of the AR were found to be similar. The percentage of ARs induced by LC and percentage of oocytes fertilized by sperm were found to be heparin-dose-dependent, with the maximum responses occurring at 5-10 micrograms/ml heparin. The correlation between the mean fertilization and LC-induced AR percentages was 0.997 (p less than 0.01). These studies demonstrate capacitation of bovine sperm by heparin requires at least a 4-h exposure of sperm to heparin and suggest that plasma membrane changes prior to an AR can be detected by exposure of bovine sperm to LC.

Capacitation of bovine sperm by heparin.

Steroid induced exocytosis: the human sperm acrosome reaction.

Hydrolysis of the phospholipid phosphatidylinositol 4,5-bisphosphate is thought to be intimately involved in agonist-induced changes in intracellular Ca2+ levels Recently we have shown that human preovulatory follicular fluid, which induces exocytosis in human sperm, can stimulate a rapid, transient increase in sperm cytosolic [Ca2+] [Thomas & Meizel (1988) Gamete Res 20, 397-411] We report here that both a Sephadex G-75 column fraction, derived from follicular fluid, and progesterone (a component of both the G-75 fraction and whole follicular fluid) stimulate rapid hydrolysis of PtdIns(4,5)P2 and PtdIns4P in human sperm We also report that progesterone stimulates a rapid influx of Ca2+ in human sperm Human spermatozoa were labelled for 24 h with myo-[3H]inositol and then treated with either the G-75 fraction or progesterone A 30-65% loss of label was detected in PtdIns(4,5)P2 and PtdIns4P within 15 s of stimulus addition; no changes were observed in PtdIns during 2 min of treatment The loss of label from both lipids was accompanied by an increase in water-soluble inositol phosphates Production of both InsP3 and InsP2 was seen within 10 s; however, InsP3 was rapidly removed and had reached control levels by 1 min Similarly, formation of InsP2 reached a peak by 30 s and then began a decline accompanied by a corresponding increase in InsP No increases in InsP4 were seen in sperm treated in this fashion Stimulated hydrolysis of the phosphoinositides and release of inositol phosphates were both blocked by the Ca2+ antagonist La3+ Likewise, the progesterone-induced increase in intracellular Ca2+ was inhibited by La3+, and phosphoinositide hydrolysis stimulated by this hormone was dependent upon the presence of extracellular Ca2+

Phosphatidylinositol 4,5-bisphosphate hydrolysis in human sperm stimulated with follicular fluid or progesterone is dependent upon Ca2+ influx

Human ejaculated spermatozoa were washed through a Percoll gradient, preincubated for 10 hr in a defined medium containing serum albumin, and then induced to undergo rapid acrosome reactions by addition of human follicular fluid or a Sephadex G-75 column fraction of the fluid. Induction by follicular fluid did not occur when the spermatozoa were preincubated for only 0 or 5 hr. The reactions were detected by indirect immunofluorescence using a monoclonal antibody directed against the human sperm acrosomal region. The percentage of acrosomal loss counted by transmission electron microscopy agreed with that counted by immunofluorescence. The apparent molecular weight of the Sephadex G-75 fraction containing the peak of acrosome reaction-inducing activity was 45,000 ± 4,200 (SD). The occurrence of physiological acrosome reactions was supported by: assessing motility (no significant loss of motility occurred during the treatment period when sperm were preincubated with bovine serum albumin), transmission electron microscopy (the ultrastructural criteria for the acrosome reaction were met), and zona-free hamster oocyte binding and penetration (spermatozoa pretreated with the active fraction of follicular fluid, then washed and incubated with oocytes, showed significantly greater binding to and penetration of oocytes). The stimulation of the acrosome reaction by follicular fluid is apparently not due to blood serum contamination; treatment of preincubated spermatozoa with sera from the follicular fluid donors had no effect on the spermatozoa. The nature of the active component(s) in that fraction is currently being investigated.

Induction of the acrosome reaction in human spermatozoa by a fraction of human follicular fluid

A full understanding of the acrosome reaction is central to understanding sperm function. Acrosomal status can be determined on living, motile sperm in only a few mammalian species. For other species, many light microscopic methods have been developed, including colored stains for bright-field microscopy, and probes for fluorescence microscopy. We review the existing methods and the criteria that should be considered in the choice of an assay.

Methods for evaluating the acrosomal status of mammalian sperm.

This review deals with exogenous molecules that stimulate the acrosome reaction (AR) of mammalian sperm in vitro, presumably by acting at the sperm surface. Such molecules may exert their effect(s) by stimulating capacitation and/or by stimulation or initiation of the AR, and they are probably present at one of three putative in vivo sites (also discussed here) for the AR of a fertilizing sperm: the oviductal fluid, the cumulus oophorus matrix, and the zona pellucida. The molecules discussed include serum albumin, hydrolytic enzymes (particularly proteases); hormones including biogenic amines, estradiol, and arachiodonic acid metabolites; sulfur-containing β-amino acids; glycosaminoglycans such as hyaluronic acid; and a zona pellucida glycoprotein. Possible mechanisms to explain the effects of these molecules are also discussed. Several conclusions and suggestions are offered in this review: (1) There is more than one site for the AR of a fertilizing sperm in vitro, depending on experimental conditions and species, but the site(s) at which the AR of a fertilizing sperm occur(s) in vivo is/are still a matter of disagreement; (2) there are a number of molecules that can stimulate or initiate the AR in vitro, and such molecular duplication may also exist in vivo to ensure fertility; and (3) synergistic interaction between some of those exogenous molecules may occur in the stimulation of capacitation and the stimulation or initiation of the AR.

Stanley Meizel

Papers

Steroid induced exocytosis: the human sperm acrosome reaction.

Phosphatidylinositol 4,5-bisphosphate hydrolysis in human sperm stimulated with follicular fluid or progesterone is dependent upon Ca2+ influx

Induction of the acrosome reaction in human spermatozoa by a fraction of human follicular fluid

Methods for evaluating the acrosomal status of mammalian sperm.

Molecules that initiate or help stimulate the acrosome reaction by their interaction with the mammalian sperm surface.