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1.
The role of anion channels in the mechanism of acrosome reaction in bull spermatozoa. 总被引:3,自引:0,他引:3
The involvement of anion channels in the mechanism of the acrosome reaction (AR) was investigated. The AR was induced by Ca2+ or by addition of the Ca2+ ionophore A23187. The occurrence of AR was determined by following the release of acrosin from the cells. In order to investigate the role of anion channels in the AR, several anion-channel inhibitors were tested, mainly DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid). Other blockers, like SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid), furosemide, probenecid and pyridoxal 5-phosphate, were also tested. We found that DIDS binds covalently to sperm plasma membrane in a time- and concentration-dependent manner. Maximal binding occurs after 2 h with 0.3 mM DIDS. DIDS and SITS inhibit AR in a concentration-dependent manner. The IC50 of DIDS and SITS in the presence of A23187 is 0.15 and 0.22 mM, respectively. Tributyltin chloride (TBTC), an Cl-/OH- exchanger, partially overcomes DIDS inhibition of the AR. HCO3- is required for a maximal acrosin release and Ca(2+)-uptake, in the presence or absence of A23187. It is known that HCO3- activates adenylate cyclase and therefore, increases the intracellular level of cAMP. The inhibition of the AR by DIDS decreases from 95 to 50% when (dibutyryl cyclic AMP (dbcAMP) was added, i.e., HCO3- is no longer required while elevating the level of cAMP in an alternative way. Moreover, we show that the stimulatory effect of HCO3- on Ca(2+)-uptake is completely inhibited by DIDS. We conclude that DIDS inhibits AR by blocking anion channels, including those that transport HCO3- into the cell. 相似文献
2.
NAD metabolism in Salmonella typhimurium: isolation of pyridine analogue supersensitive (pas) and pas suppressor mutants 总被引:1,自引:0,他引:1
Mutants of Salmonella typhimurium supersensitive to the nicotinic acid analogue 6-amino-nicotinic acid (6ANA) were isolated as unable to grow on what are normally subinhibitory concentrations of the analogue. The mutations were classified on the basis of their map positions as pasA (89-92 units), pasB (66-69 units), pasC (18-22 units), pasD (18 units) and pasE (55 units). The mutants exhibited a wide range of minimal inhibitory concentrations towards 6ANA, and several were affected in terms of growth. The data suggest that most of the mutations probably reside in genes whose products utilize nicotinamide adenine dinucleotide (NAD) as a cofactor, the altered gene products being more sensitive to internal 6-amino NAD concentrations. Secondary mutations which suppress the Pas- phenotype were found to reside in the following NAD-related loci; pncB, nadB and nadD. Two of the pncB mutants appear to be affected in the expression of NAPRTase while several of the nadB mutants are apparently insensitive to feedback inhibition by internal NAD concentrations. 相似文献
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4.
Suresh Anand Sadananthan Mya Thway Tint Navin Michael Izzuddin M. Aris See Ling Loy Kuan Jin Lee Lynette Pei‐Chi Shek Fabian Kok Peng Yap Kok Hian Tan Keith M. Godfrey Melvin Khee‐Shing Leow Yung Seng Lee Michael S. Kramer Peter D. Gluckman Yap Seng Chong Neerja Karnani Christiani Jeyakumar Henry Marielle Valerie Fortier S. Sendhil Velan 《Obesity (Silver Spring, Md.)》2019,27(3):470-478
5.
Remodeling of the actin cytoskeleton during mammalian sperm capacitation and acrosome reaction 总被引:7,自引:0,他引:7
Brener E Rubinstein S Cohen G Shternall K Rivlin J Breitbart H 《Biology of reproduction》2003,68(3):837-845
The sperm acrosome reaction and penetration of the egg follow zona pellucida binding only if the sperm has previously undergone the poorly understood maturation process known as capacitation. We demonstrate here that in vitro capacitation of bull, ram, mouse, and human sperm was accompanied by a time-dependent increase in actin polymerization. Induction of the acrosome reaction in capacitated cells initiated fast F-actin breakdown. Incubation of sperm in media lacking BSA or methyl-beta-cyclodextrin, Ca(2+), or NaHCO(3), components that are all required for capacitation, prevented actin polymerization as well as capacitation, as assessed by the ability of the cells to undergo the acrosome reaction. Inhibition of F-actin formation by cytochalasin D blocked sperm capacitation and reduced the in vitro fertilization rate of metaphase II-arrested mouse eggs. It has been suggested that protein tyrosine phosphorylation may represent an important regulatory pathway that is associated with sperm capacitation. We show here that factors known to stimulate sperm protein tyrosine phosphorylation (i.e., NaHCO(3), cAMP, epidermal growth factor, H(2)O(2), and sodium vanadate) were able to enhance actin polymerization, whereas inhibition of tyrosine kinases prevented F-actin formation. These data suggest that actin polymerization may represent an important regulatory pathway in with sperm capacitation, whereas F-actin breakdown occurs before the acrosome reaction. 相似文献
6.
Plasma membrane vesicles, isolated from ejaculated ram sperm, were found to contain Ca2+-activated Mg2+-ATPase and Ca2+ transport activities. Membrane vesicles that were exposed to oxalate as a Ca2+-trapping agent accumulated Ca2+ in the presence of Mg2+ and ATP. The for Ca2+ uptake was 33 nmol/mg protein per h, and the values for Ca2+ and ATP were 2.5 μM and 45 μM, respectively. 1 μM of the Ca2+ ionophore A23187, added initially, completely inhibited net Ca2+ uptake and, if added later, caused the release of Ca2+ previously accumulated. A Ca2+-activated ATPase was present in the same membrane vesicles which had a of 1.5 μmol/mg protein per h at free Ca2+ concentration of 10 μM. This Ca2+-ATPase had values of 4.5 μM and 110 μM for Ca2+ and ATP, respectively. This kinetic parameter was similar to that observed for uptake of Ca2+ by the vesicles. The Ca2+-ATPase activity was insensitive to ouabain. Both Ca2+ transport and Ca2+-ATPase activity were inhibited by the flavonoid quercetin. Thus, ram spermatozoa plasma membranes have both a Ca2+ transport activity and a Ca2+-stimulated ATPase activity with similar substrate affinities and specificities and similar sensitivity to quercetin. 相似文献
7.
Heard but not seen: an acoustic survey of the African forest elephant population at Kakum Conservation Area, Ghana 总被引:1,自引:0,他引:1
Mya E. Thompson Steven J. Schwager Katharine B. Payne 《African Journal of Ecology》2010,48(1):224-231
This study, designed to survey forest elephants ( Loxodonta africana cyclotis ) at Kakum Conservation Area, Ghana, is the first to apply acoustic methods to elephant abundance estimation and to compare results with independent survey estimates. Nine acoustic sensors gathered sound continuously for 38 days. Low-frequency calling rates have been established as useful elephant abundance indices at a Namibian watering hole and a central African forest clearing. In this study, we estimated elephant population size by applying an abundance index model and detection function developed in central Africa to data from simultaneous sampling periods on Kakum sensors. The sensor array recorded an average of 1.81 calls per 20-min sampling period from an effective detection area averaging 10.27 km2 . The resulting estimate of 294 elephants (95% CI: 259–329) falls within confidence bounds of recent dung-based surveys. An extended acoustic model, estimating the frequency with which elephants are silent when present, yields an estimate of 350 elephants (95% CI: 315–384). Acoustic survey confidence intervals are at least half as wide as those from dung-based surveys. This study demonstrates that acoustic surveying is a valuable tool for estimating elephant abundance, as well as for detecting other vocal species and anthropogenic noises that may be associated with poaching. 相似文献
8.
The effects of protein kinase C (PKC) stimulator, phorbol 12-myriatate 13-acetate (PMA), on meiotic cell cycle regulation and mitogen-activated protein (MAP) kinase changes have been studied in mouse oocytes and eggs. The results showed that MAP kinase activation itself was not necessary for germinal vesicle breakdown (GVBD), but the ability of the ooplasm to phosphorylate MAP kinase was a prerequisite for this event. At concentrations of 1.6 nM, PMA effectively inhibited GVBD and MAP kinase activation, suggesting that PMA inhibits GVBD by inhibiting molecule(s) upstream to MAP kinase. At concentrations of 16.2 nM, PMA induced metaphase-interphase transition more effectively in eggs collected 19 hr after human chorionic gonadotropin (hCG) administration than in those collected 15 hr after hCG administration. The degree of MAP kinase activity decrease was well correlated with the time course and proportion of pronuclear formation. On the other hand, when the effect of PMA on cell cycle progression was abolished by protein phosphatase inhibitor, okadaic acid, MAP kinase was superactivated. The biologically inactive 4 alpha-phorbol 12,13-didecanoate (4 alpha-PDD) had no evident effects on either GVBD and interphase transition or on MAP kinase activity. Furthermore, the effects of PMA on oocyte GVBD, egg activation, and MAP kinase activity could be overcome by the specific PKC inhibitor, calphostin C, suggesting the possible involvement of this enzyme in the regulation of MAP kinase activity. The results suggest that activation of PKC by PMA entrains a cascade of events that ultimately inhibits MAP kinase activation and GVBD in mouse oocytes and induces MAP kinase inactivation and metaphase-interphase transition in mouse eggs. 相似文献
9.
Morikawa A Koide N Sugiyama T Mu MM Hassan F Islam S Ito H Mori I Yoshida T Yokochi T 《FEMS immunology and medical microbiology》2004,41(3):211-218
The effect of D-galactosamine (D-GalN) on nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells was examined. D-GalN augmented the production of NO, but not tumor necrosis factor (TNF)-alpha in LPS-stimulated RAW 264.7 cells. Pretreatment of D-GalN augmented the NO production whereas its post-treatment did not. D-GalN augmented the NO production in RAW 264.7 cells stimulated with either TNF-alpha and interferon-gamma. The augmentation of LPS-induced NO production by D-GalN was due to enhanced expressions of an inducible type of NO synthase mRNA and proteins. Intracellular reactive oxygen species (ROS) were exclusively generated in RAW 264.7 cells stimulated with D-GalN and LPS. Scavenging of intracellular ROS abrogated the augmentation of NO production. It was therefore suggested that D-GalN might augment LPS-induced NO production through the generation of intracellular ROS. 相似文献
10.
Phages, the most abundant biological entities on the planet, play important roles in biogeochemical cycling, horizontal gene transfer, and defining microbial community composition. However, very little is known about phage diversity or biogeography, and there has not yet been a systematic effort to compare the phages found in different ecosystems. Here, we report that T7-like Podophage DNA polymerase sequences occur in every major biome investigated, including marine, freshwater, sediment, terrestrial, extreme, and metazoan-associated. The majority of these sequences belong to a unique clade that is only distantly related to cultured isolates. Some identical T7-like phage-encoded DNA polymerase genes from this clade were >99% conserved at the nucleotide level in multiple different environments, suggesting that these phages are moving between biomes in recent evolutionary time and that the global genomic pool for T7-like phages may be smaller than previously hypothesized. 相似文献