Biomedical subjects

S Rubinstein

Publications and source records attributed to S Rubinstein.

At least 19 recordsLinked to original sources

PubMed2006

Sperm capacitation is regulated by the crosstalk between protein kinase A and C.

The binding of capacitated sperm to the egg's zona pellucida stimulates it to undergo the acrosome reaction, a process which enables the sperm to penetrate the egg. Mammalian sperm capacitation and the acrosome reaction require remodeling of actin filaments. An increase in phospholipase D (PLD)-dependent actin polymerization occurs during capacitation whereas the increase in sperm intracellular calcium after its binding to the egg causes very fast actin depolymerization prior to the acrosome reaction. Protein kinase A (PKA) and C (PKC) can both activate sperm PLD and actin polymerization under in vitro incubation, however under physiological conditions, actin polymerization depends primarily on PKA activity. We suggest that PKA indirectly activates phosphatidylinositol 4-kinase to produce phosphatidylinositol 4,5-bisphosphate which is a cofactor for PLD activation. In addition, activation of PKA during capacitation inactivates phospholipase C resulting in preventing PKC activation. It appears that PKA activation promotes sperm capacitation whereas too early activation of PKC during capacitation would jeopardize this process. Thus, a refined balance between the two pathways is required for optimal and sustained activation during sperm capacitation.

Animals↗

PubMed2004

Crosstalk between protein kinase A and C regulates phospholipase D and F-actin formation during sperm capacitation.

Mammalian spermatozoa should reside in the female reproductive tract for a certain time before gaining the ability to fertilize. During this time, the spermatozoa undergo a series of biochemical processes collectively called capacitation. We recently demonstrated that actin polymerization is a necessary step in the cascade leading to capacitation. We demonstrate here for the first time a role for phospholipase D (PLD) in the induction of actin polymerization and capacitation in spermatozoa. The involvement of PLD is supported by specific inhibition of F-actin formation during sperm capacitation by PLD inhibitors and the stimulation of fast F-actin formation by exogenous PLD or phosphatidic acid (PA). Moreover, PLD activity is enhanced during capacitation before actin polymerization. Protein kinase A (PKA), known to be active in sperm capacitation, and protein kinase C (PKC), involved in the acrosome reaction, can both activate PLD and actin polymerization. We suggest that PKA- and PKC-dependent signal transduction pathways can potentially lead to PLD activation; however, under physiological conditions, actin polymerization depends primarily on PKA activity. Activation of PKA during capacitation causes inactivation of phospholipase C, and as a result, PKC activation is prevented. It appears that PKA activation promotes sperm capacitation whereas early activation of PKC during capacitation would jeopardize this process.

Actins↗

PubMed2003

Role of hydrogen peroxide in sperm capacitation and acrosome reaction.

The generation of reactive oxygen species (ROS) has been implicated in the regulation of sperm capacitation and acrosome reaction; however, the mechanisms underlying this regulation remain unclear. To examine the cellular processes involved, we studied the effect of different concentrations of hydrogen peroxide (H(2)O(2)) on protein tyrosine phosphorylation under various conditions. Treatment of spermatozoa with H(2)O(2) in medium without heparin caused a time- and dose-dependent increase in protein tyrosine phosphorylation of at least six proteins in which maximal effect was seen after 2 h of incubation with 50 microM H(2)O(2). At much higher concentrations of H(2)O(2) (0.5 mM), there is significant reduction in the phosphorylation level, and no protein tyrosine phosphorylation is observed at 5 mM H(2)O(2) after 4 h of incubation. Exogenous NADPH enhanced protein tyrosine phosphorylation similarly to H(2)O(2). These two agents, but not heparin, induced Ca(2+)-dependent tyrosine phosphorylation of an 80-kDa protein. Treatment with H(2)O(2) (50 microM) caused approximately a twofold increase in cAMP, which is comparable to the effect of bicarbonate, a known activator of soluble adenylyl cyclase in sperm. This report suggests that relatively low concentrations of H(2)O(2) are beneficial for sperm capacitation, but that too high a concentration inhibits this process. We also conclude that H(2)O(2) activates adenylyl cyclase to produce cAMP, leading to protein kinase A-dependent protein tyrosine phosphorylation.

Acrosome Reaction↗

PubMed2001

Involvement of MEK-mitogen-activated protein kinase pathway in follicle-stimulating hormone-induced but not spontaneous meiotic resumption of mouse oocytes.

Mitogen-activated protein (MAP) kinase has been reported to be activated during oocyte meiotic maturation in a variety of mammalian species. However, the mechanism(s) responsible for MAP kinase activation and the consequence of its premature activation during gonadotropin-induced oocyte meiotic resumption have not been examined. The present experiments were conducted to investigate the possible role of MAP kinase in FSH-induced and spontaneous oocyte meiotic resumption in the mouse. MAP kinase kinase (MAPKK, MEK) inhibitor, PD98059 or U0126, produced a dose-dependent inhibitory effect on both FSH-induced oocyte meiotic resumption and MAP kinase activation in the oocytes. However, the same inhibitor did not block spontaneous meiotic resumption of either denuded or cumulus cell-enclosed mouse oocytes, despite the activity of MAP kinase being totally inhibited. Immunoblotting the oocytes and the cumulus cells with the anti-active MAP kinase antibody showed that MAP kinase activity in the oocytes was detected at 8 h of FSH treatment, prior to germinal vesicle breakdown and increased as maturation progressed in the following culture period. In the cumulus cells, MAP kinase was activated even faster, its activity was detected at 1 h of FSH stimulation and increased gradually until 8 h of FSH treatment, then decreased and diminished after 12 h of FSH action. These data demonstrated that the MEK-MAP kinase pathway is implicated in FSH-induced but not spontaneous oocyte meiotic resumption.

Animals↗

PubMed2000

Chiropractic patients in the Netherlands: a descriptive study.

BACKGROUND: Despite the worldwide popularity of chiropractic, there is still relatively little known about the patients who visit chiropractors in the Netherlands and other European countries. OBJECTIVE: To describe in-depth the patient population of new patients to chiropractors in the Netherlands. DESIGN: Study population consisted of 10 consecutive new patients per participating chiropractor. A retrospective-type questionnaire was used. SETTING: Private practice. OUTCOME MEASURES: Mode of referral, area, and nature of the complaints; related to the chief complaint: previous treatments, examinations, type of referral, days lost at work, level of pain, and treatment expectations. RESULTS: Of the 130 chiropractors registered with the Netherlands Chiropractors'Association, 94 chiropractors(78%) participated. Eight hundred thirty-three patients (89%) returned questionnaires. By far, the greatest reason that patients visit chiropractors in the Netherlands is for neuromusculoskeletal (NMS) complaints. At the time of examination, 86% of the patients had spinal-related complaints, of which 12% involved multiple areas of the spine. Non-NMS complaints are minimal (<2%). Seventy-seven percent of patients with NMS complaints have chronic complaints (>12 weeks). Three-quarters of these patients have undergone previous conservative therapy for their complaint, which includes physical and manual therapy, postural correction, and exercise therapy. Despite the chronic nature of their complaints, patients have high expectations that their treatment will be effective. CONCLUSIONS: Most patients who see chiropractors in the Netherlands have chronic NMS-related complaints. Chiropractors are not a part of the normal referral system in this country, with the result that the patients have rather long histories, including previous evaluations by medical specialists and other previous forms of (conservative) care.

Adolescent↗

PubMed2000

Differential localization of conventional protein kinase C isoforms during mouse oocyte development.

Protein kinase C (PKC), the major cell target for tumor-promoting phorbol esters, plays a central role in signal transduction pathways. In many biological systems where Ca(2+) serves as a second messenger, regulatory control is mediated by PKC. The activation of PKC depends on its binding to RACK1 receptor, which is an intracellular protein anchor for activated PKC. We demonstrate that the conventional PKC (cPKC) isoforms, PKC-alpha, PKC-betaI, and PKC-betaII, as well as RACK1, are expressed in mouse oocytes (germinal vesicle [GV]) and mature eggs (metaphase II [MII]). In GV oocytes, PKC-alpha, PKC-betaII, and RACK1 were uniformly distributed in the cytoplasm, while PKC-betaI was localized in the cytoplasm and in the plasma membrane as well. Treatment of GV oocytes with the biologically active phorbol ester, 12-o-tetradecanoyl phorbol-13-acetate (TPA), resulted in a rapid translocation of the cytosolic PKC-alpha, but not PKC-betaI, PKC-betaII, or RACK1, to the plasma membrane. This was associated with inhibition of GV breakdown. In MII eggs (17 h post-hCG), PKC-alpha was uniformly distributed in the cytoplasm while PKC-betaI and -betaII were distributed in the cytoplasm and in the plasma membrane as well. Treatment with TPA resulted in a rapid translocation of PKC-alpha from the cytoplasm to the plasma membrane and a significant decrease of PKC-betaI throughout the cytoplasm, while it also remained in the cell periphery. No change in the distribution of PKC-betaII or RACK1 was observed. TPA also induced pronucleus formation. Physiological activation of MII eggs by sperm induced cortical granule exocytosis associated with significant translocation of PKC-alpha and -betaI, but not -betaII, to the plasma membrane. Overall, these results suggest a possible involvement of cPKC isoforms in the mechanism of mouse oocyte maturation and egg activation.

Animals↗

PubMed2000

Activation of protein kinase calpha in the lysophosphatidic acid-induced bovine sperm acrosome reaction and phospholipase D1 regulation.

Protein kinase C (PKC) has been implicated in the sperm acrosome reaction. In the present study, we demonstrate induction of the acrosome reaction and activation of sperm PKCalpha by lysophosphatidic acid (LPA), which is known to induce signal transduction cascades in many cell types via binding to specific cell-surface receptors. Under conditions by which LPA activates PKCalpha, there is significant stimulation of the acrosome reaction, which is inhibited by PKC inhibitors. Protein kinase Calpha belongs to the Ca(2+)-dependent classical PKC family of isoforms, and indeed we show that its activation depends upon the presence of Ca(2+) in the incubation medium. Protein kinase Calpha is a known regulator of phospholipase D (PLD). We investigated the possible regulatory relationships between PKCalpha and PLD1. Using specific antibodies against PLD1, we demonstrate for the first time its presence in bovine sperm. Furthermore, PLD1 coimmunoprecipitates with PKCalpha and the PKCalpha-PLD1 complex decomposes after treatment of the cells with LPA or 12-O:-tetradecanoyl phorbol-13-acetate, resulting in the translocation of PKCalpha to the plasma membrane and translocation of PLD1 to the particulate fraction. A possible bilateral regulation of PKCalpha and PLD1 activation during the sperm acrosome reaction is suggested.

Acrosome Reaction↗

PubMed1999

MAP kinase activity is downregulated by phorbol ester during mouse oocyte maturation and egg activation in vitro.

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.

Animals↗

PubMed1999

Mitogen-activated protein kinase in human eggs.

Mitogen-activated protein (MAP) kinase in human eggs has been investigated by using immunoblotting with both anti-Active MAPK and anti-ERK2 antibodies. The results showed that the main form of MAP kinase was p42ERK2. It was in a dephosphorylated form in oocytes at the germinal vesicle stage, but fully phosphorylated in unfertilised mature eggs. MAP kinase phosphorylation was significantly decreased when pronuclei were formed after intracytoplasmic sperm injection. Neither MAP kinase expression nor activity was detected in morphologically degenerated eggs. Although MAP kinase still existed in early embryos arrested at the 8-cell or morula stages, little, if any, activity could be detected. These data suggest that MAP kinase may play an important role in the cell cycle regulation of human eggs, as in other mammalian species.

Adult↗

PubMed1999

Intracellular Ca(2+)-Mg(2+)-ATPase regulates calcium influx and acrosomal exocytosis in bull and ram spermatozoa.

Calcium influx is required for the mammalian sperm acrosome reaction (AR), an exocytotic event occurring in the sperm head prior to fertilization. We show here that thapsigargin, a highly specific inhibitor of the microsomal Ca(2+)-Mg(2+)-ATPase (Ca(2+) pump), can initiate acrosomal exocytosis in capacitated bovine and ram spermatozoa. Initiation of acrosomal exocytosis by thapsigargin requires an influx of Ca(2+), since incubation of cells in the absence of added Ca(2+) or in the presence of the calcium channel blocker, La(3+), completely inhibited thapsigargin-induced acrosomal exocytosis. ATP-Dependent calcium accumulation into nonmitochondrial stores was detected in permeabilized sperm in the presence of ATP and mitochondrial uncoupler. This activity was inhibited by thapsigargin. Thapsigargin elevated the intracellular Ca(2+) concentration ([Ca(2+)](i)), and this increase was inhibited when extracellular Ca(2+) was chelated by EGTA, indicating that this rise in Ca(2+) is derived from the external medium. This rise of [Ca(2+)](i) took place first in the head and later in the midpiece of the spermatozoon. However, immunostaining using a polyclonal antibody directed against the purified inositol 1,4,5-tris-phosphate receptor (IP(3)-R) identified specific staining in the acrosome region, in the postacrosome, and along the tail, but not in the midpiece region. No staining in the acrosome region was observed in sperm without acrosome, indicating that the acrosome cap was stained in intact sperm. The presence of IP(3)-R in the anterior acrosomal region as well as the induction, by thapsigargin, of intracellular Ca(2+) elevation in the acrosomal region and acrosomal exocytosis, implicates the acrosome as a potential cellular Ca(2+) store. We suggest here that the cytosolic Ca(2+) is actively transported into the acrosome by an ATP-dependent, thapsigargin-sensitive Ca(2+) pump and that the accumulated Ca(2+) is released from the acrosome via an IP(3)-gated calcium channel. The ability of thapsigargin to increase [Ca(2+)](i) could be due to depletion of Ca(2+) in the acrosome, resulting in the opening of a capacitative calcium entry channel in the plasma membrane. The effect of thapsigargin on elevated [Ca(2+)](i) in capacitated cells was 2-fold higher than that in noncapacitated sperm, suggesting that the intracellular Ca pump is active during capacitation and that this pump may have a role in regulating [Ca(2+)](i) during capacitation and the AR.

Acrosome↗

PubMed1998

Protein kinase inhibitors induce the interphase transition by inactivating mitogen-activated protein kinase in mouse eggs.

The role of mitogen-activated protein (MAP) kinase in mouse egg activation induced by protein kinase inhibitors and a protein tyrosine kinase (PTK) inhibitor was investigated. Separated egg proteins were first probed with anti-Active MAP kinase antibody and then re-probed with anti-ERK2 antibody. Staurosporine and Ro-31-8220, at concentrations that normally inhibit protein kinase C, did not affect egg activation or MAP kinase activity, while higher dosages caused egg activation. Staurosporine at 2 microM induced the metaphase-interphase transition without emission of the second polar body (PB2), while Ro-31-8220 at 40 microM induced PB2 emission, first cleavage, and then the transition to interphase. Half the eggs were also activated by the PTK inhibitor genistein. In each treatment, the proportion of eggs that entered interphase was well correlated with the degree of MAP kinase inactivation. Artificial activation of this kinase by okadaic acid overcame the interphase transition. These data suggest that protein kinase inhibitors and a protein tyrosine kinase inhibitor induce the interphase transition by inactivating MAP kinase in mouse eggs.

Animals↗

PubMed1998

Angiotensin II induces acrosomal exocytosis in bovine spermatozoa.

Ejaculated mammalian spermatozoa must reside in the female genital tract for some time before gaining the ability to fertilize the egg. During this time, spermatozoa undergo some physiological changes that collectively are called capacitation. Capacitation of mammalian spermatozoa is a prerequisite for acrosome reaction, which is an exocytotic event occurring before fertilization. The specific biophysical and biochemical changes that accompany sperm capacitation and the agonists inducing acrosome reaction are not fully understood. Using SDS-gel electrophoresis and immunoblotting, we demonstrate the existence of a class of angiotensin receptors (AT1) in bovine spermatozoa. In capacitated sperm, we show that angiotensin II (ANG II) AT1 receptors are localized in the head and tail, whereas in noncapacitated cells the receptors are localized in the tail only. We find that ANG II markedly stimulates acrosomal exocytosis of capacitated bovine spermatozoa in vitro in a concentration range of 0.1-10 nM. No effect of ANG II was found in noncapacitated cells. The ability of ANG II to stimulate the acrosome reaction depends on the presence of calcium ions in the incubation medium. The ANG II-induced acrosome reaction was markedly inhibited by a selective AT1 receptor antagonist, losartan (DUP 753). PD-123319, a selective antagonist of the ANG II AT2 receptor, had no effect on the ANG II-induced acrosome reaction. Thus ANG II via activation of AT1 receptors may play a regulatory role in the induction of the acrosome reaction.

Acrosin↗

PubMed1998

Light irradiation of mouse spermatozoa: stimulation of in vitro fertilization and calcium signals.

Irradiation of mouse spermatozoa by 630 nm He-Ne laser was found to enhance the intracellular calcium levels and fertilizing potential of these cells. The effect of light on calcium transport and on fertilization rate was abrogated in the absence of Ca2+ during the irradiation time, indicating that the effect of light is Ca2+ dependent. The stimulatory effect of light on Ca2+ uptake was abolished in the presence of a voltage-dependent Ca(2+)-channel inhibitor nifedipine, indicating the involvement of a plasma membrane voltage-dependent Ca2+ channel. Furthermore, the stimulatory effect of light was completely inhibited by the mitochondrial uncoupler FCCP, indicating that laser irradiation might affect the mitochondrial Ca2+ transport mechanisms. A causal association between laser irradiation, reactive oxygen species (ROS) generation and sperm function was indicated by studies with ROS scavengers, superoxide dismutase (SOD) and catalase, and exogenous hydrogen peroxide. The SOD treatment, which enhanced H2O2 production, resulted in increased Ca2+ uptake and enhanced fertilization rate. On the other hand, catalase, which decomposes H2O2, impaired the light-induced stimulation in Ca2+ uptake and the fertilization rate. Taken together, the data suggest that H2O2 might be involved in the irradiation effects, and indeed laser irradiation enhances the production of H2O2 by spermatozoa. These results indicate that the effect of 630 nm He-Ne laser irradiation is mediated through the generation of H2O2 by the spermatozoa and that this effect plays a significant role in the augmentation of the sperm cells' capability to fertilize metaphase II-arrested eggs in vitro.

Animals↗

PubMed1997

Synthesis of 2-oxacortexone and its effect on Ca2+ uptake in bovine spermatozoa.

Low temperature base catalyzed autoxidation (BCA) of the A-ring of 21-acetoxypregn-5-ene-3,20-dione 20-ethylene ketal (7) resulted in the saponification of the ester with the concomitant formation of 2,21-dihydroxypregna-1,4-diene-3,20-dione 20-ethylene ketal (8). Continued BCA at ambient temperature, converts the latter to 1,21-dihydroxy-2-oxaprogesterone 20-ethylene ketal (9), which is reduced by NaBH4 to the 2-oxasteroid, 21-hydroxy-2-oxaprogesterone 20-ethylene ketal (10). Treatment of enol 8, lactol 9, and lactone 10 with aqueous acid generates the corresponding deprotected analogs 2,21-dihydroxypregna-1,4-diene-3,20-dione (enol 11), 1,21-dihydroxy-2-oxaprogesterone (lactol 12), and 2-oxacortexone (2-oxadesoxycorticosterone, 21-hydroxy-2-oxaprogesterone, lactone 13). In bovine spermatozoa, neither 2-oxasteroid ketal 10 nor its deprotected analog 13 stimulated Ca2+ uptake. In high concentration (0.5 mM), the inhibition of Ca2+ uptake is only 37% for 13, as compared to 83% found with the parent steroid, cortexone (desoxycorticosterone, 21-hydroxyprogesterone, 5). The difference in molecular structure between 13 and 5 indicates the importance of the oxygen atom in ring A in achieving the protective effect of the steroid. Ketalization of the C-20 carbonyl is not important for protection. Thus it seems that by replacing C-2 by an oxygen atom we can reduce the biological damage caused by relatively high concentrations of steroid treatment. These results are highly significant when treatment of patients with high doses of steroids is considered.

Animals↗

PubMed1997

Subcellular distribution of protein kinase C alpha and betaI in bovine spermatozoa, and their regulation by calcium and phorbol esters.

Protein kinase C (PKC), the major cell target for tumor-promoting phorbol esters, is central to many signal transduction pathways. Previously we have demonstrated the presence of PKC in ram and bovine spermatozoa. However, the relative distribution of various PKC isozymes in the cytosolic and membrane fractions and their regulation by calcium and phorbol esters have not been elucidated. Immunocytochemical studies and Western blotting with antibodies specific for individual isoforms revealed that at least two PKC isoforms, cPKC alpha and cPKC betaI, are found in bovine sperm cells. We demonstrate, by Western blotting analysis, that both PKC isozymes were predominantly localized in the cytosol when subcellular fractionation was carried out in the presence of EGTA. When cell lysis was carried out in the presence of Ca2+, most PKC alpha and PKC betaI redistributed to the particulate fraction. Treatment of sperm cells with the biologically active phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) resulted in a rapid and extensive translocation of cytosolic PKC alpha and cytosolic PKC betaI to the membrane fraction within 1 min. Furthermore, PKC's total activity was measured as a calcium- and phospholipid-dependent phosphorylation of a synthetic peptide in the cytosolic and membrane fractions derived from control and TPA-treated spermatozoa. TPA evoked a decrease in cytosolic PKC activity, accompanied by an increase in the activity associated with the plasma membrane fraction. This translocation of PKC enzymes may ensure their binding to intracellular receptor proteins ("RACKs") and the phosphorylation of specific substrates, which appears to determine their physiological function. The presence of RACK in the membrane fraction of bovine sperm cells was confirmed with use of an antibody directed against the RACK protein. Previously we demonstrated the involvement of PKC in sperm acrosomal exocytosis, a process induced by signal transduction events. Thus, our results suggest that the rapid association of PKC alpha and PKC betaI with the sperm plasma membrane, as shown in the present work for the first time, may be an early event in sperm cell regulation, leading to acrosomal exocytosis and fertilization.

Acrosome↗

PubMed1997

Regulatory mechanisms in acrosomal exocytosis.

Acrosomal exocytosis occurs after the binding of the spermatozoon to the zona pellucida of the oocyte via specific receptors. We suggest that the zona pellucida binds to at least two different receptors in the plasma membrane. One (R) is a Gi-coupled receptor that activates phospholipase C beta 1. The other (TK) is a tyrosine kinase receptor coupled to phospholipase C gamma. Binding to R would regulate adenylyl cyclase leading to an increase in cyclic adenosine monophosphate and protein kinase A activation. The protein kinase A activates a voltage-dependent Ca2+ channel in the outer acrosomal membrane that releases Ca2+ from the interior of the acrosome to the cytosol. This is the first (I), relatively small, rise in intracellular Ca2+ which leads to activation of the phospholipase C gamma. The products of phosphatidyl-inositol bisphosphate hydrolysis by phospholipase C, diacylglycerol and inositol-trisphosphate lead to protein kinase C translocation to the plasma membrane and its activation. Protein kinase C opens a voltage-dependent Ca2+ channel (L) in the plasma membrane, leading to the second (II), higher, increase in intracellular Ca2+ leading to acrosomal exocytosis. Spermine, a physiological constituent of the seminal plasma regulates sperm acrosomal exocytosis by modulating intracellular Ca2+ binding sites and phospholipase C activity. Spermine is rapidly incorporated into the sperm cells during ejaculation and temporarily inhibits premature capacitation and acrosome reaction. During the passage of the spermatozoon through the female genital tract, there is a progressive depletion of spermine from spermatozoa, so that capacitation and consequently the acrosomal exocytosis take place at the appropriate time, when the spermatozoon reaches the vicinity of the egg.

Acrosome↗

PubMed1997

Environmental factors affecting nutritional status in urban areas of developing countries.

The demographic and economic transition that many developing countries are undergoing is producing important changes in diet and lifestyle that greatly impact on disease risks. Among the risk behaviors associated with socioeconomic transition and urbanization are excessive dietary fat intake, sedentary lifestyle, smoking, and environmental contamination. Combined with a reduced infant mortality and increased life expectancy, those risk factors lead to an increasing prevalence of chronic disease like non-insulin dependent diabetes and coronary heart disease. This disease. This disease profile is a relatively new phenomenon in developing countries, where health programs have traditionally focused on "acute" interventions such as immunization or oral rehydration. A new approach will be needed to address chronic diseases, which frequently demand a life-long and technically complex medical management, and may have significant impact on the quality of life and productivity of the population. Efforts to address this situation should focus on a) expanding the information base on diet, nutritional status and lifestyle changes in populations migrating to urban areas; b) developing and evaluating approaches for improving diet quality in urban populations, including fortification and community-based supplementation programs; c) understanding better the social and behavioral determinants of nutritional status in the urban poor; and d) defining the role of the food industry and of agricultural production for improving the quality of the food supply in urban areas.

Asia↗

PubMed1996

Calcium efflux mechanism in sperm mitochondria.

This paper reports an investigation on calcium efflux mechanism in ram sperm mitochondria. Energized sperm mitochondria take up Ca2+ via the ruthenium-red sensitive uniporter, and possess a ruthenium-red insensitive efflux mechanism. Extramitochondrial Na+ did not affect the rate of Ca2+ efflux indicating that Na+/Ca2+ exchange mechanism is not involved. Depolarization of inner mitochondrial membrane induced by the uncoupler carbonylcyanide-p-trifluoromethoxyphenyl hydrazone (FCCP) or by the organomercurial SH-reagent mersalyl, causes high stimulation in Ca2+ efflux. This stimulated Ca2+ efflux determined in the presence of ruthenium-red and phosphate, is not inhibited by cyclosporin A (CSA), indicating that mitochondrial permeability transition pore (MTP) is not involved in this Ca2+ efflux mechanism. The stimulated Ca2+ efflux is inhibited by ADP or atractyloside suggesting that the Ca2+ transport mechanism might be intrinsic to the ADP/ATP carrier (AAC). Thus, the data indicate that sperm mitochondria contain a Ca2+ efflux mechanism operated via AAC and regulated by mitochondrial membrane potential and by ADP concentration.

Adenosine Diphosphate↗