Sperm motility is dependent on a unique isoform of the Na,K-ATPase

Intracellular translocation and differential accumulation of cell-penetrating peptides in bovine spermatozoa: evaluation of efficient delivery vectors that do not compromise human sperm motility

STUDY QUESTION

Do cell penetrating peptides (CPPs) translocate into spermatozoa and, if so, could they be utilized to deliver a much larger protein cargo?

SUMMARY ANSWER

Chemically diverse polycationic CPPs rapidly and efficiently translocate into spermatozoa. They exhibit differential accumulation within intracellular compartments without detrimental influences upon cellular viability or motility but they are relatively ineffective in transporting larger proteins.

WHAT IS ALREADY KNOWN

Endocytosis, the prevalent route of protein internalization into eukaryotic cells, is severely compromised in mature spermatozoa. Thus, the translocation of many bioactive agents into sperm is relatively inefficient. However, the delivery of bioactive moieties into mature spermatozoa could be significantly improved by the identification and utility of an efficient and inert vectorial delivery technology.

STUDY DESIGN

CPP translocation efficacies, their subsequent differential intracellular distribution and the influence of peptides upon viability were determined in bovine spermatozoa. Temporal analyses of sperm motility in the presence of exogenously CPPs utilized normozoospermic human donor samples.

MATERIALS AND METHODS

CPPs were prepared by manual, automated and microwave-enhanced solid phase synthesis. Confocal fluorescence microscopy determined the intracellular distribution of rhodamine-conjugated CPPs in spermatozoa. Quantitative uptake and kinetic analyses compared the translocation efficacies of chemically diverse CPPs and conjugates of biotinylated CPPs and avidin. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) conversion assays were employed to analyse the influence of CPPs upon sperm cell viability and sperm class assays determined the impact of CPPs on motility in capacitated and non-capacitated human samples.

MAIN RESULTS

Chemically heterogeneous CPPs readily translocated into sperm to accumulate within discrete intracellular compartments. Mitoparan (INLKKLAKL(Aib)KKIL), for example, specifically accumulated within the mitochondria located in the sperm midpiece. The unique plasma membrane composition of sperm is a critical factor that directly influences the uptake efficacy of structurally diverse CPPs. No correlations in efficacies were observed when comparing CPP uptake into sperm with either uptake into fibroblasts or direct translocation across a phosphatidylcholine membrane. These comparative investigations identified C105Y (CSIPPEVKFNKPFVYLI) as a most efficient pharmacokinetic modifier for general applications in sperm biology. Significantly, CPP uptake induced no detrimental influence upon either bovine sperm viability or the motility of human sperm. As a consequence of the lack of endocytotic machinery, the CPP-mediated delivery of much larger protein complexes into sperm is relatively inefficient when compared with the similar process in fibroblasts.

LIMITATIONS, REASONS FOR CAUTION

It is possible that some CPPs could directly influence aspects of sperm biology and physiology that were not analysed in this study.

WIDER IMPLICATIONS OF THE FINDINGS

CPP technologies have significant potential to deliver selected bioactive moieties and so could modulate the biology and physiology of human sperm biology both prior- and post-fertilization.

Green fluorescence protein driven by the Na,K-ATPase α4 isoform promoter is expressed only in male germ cells of mouse testis

PURPOSE

Expression of the Na,K-ATPase α4 isoform is required for sperm motility and fertility and is controlled by the Atp1a4 promoter. Here, we have investigated the specific tissue, cell type and developmental regulation of expression mediated by the Atp1a4 promoter.

METHODS

We have inserted the green fluorescent protein (GFP), downstream of the endogenous Atp1a4 promoter, in place of the Na,K-ATPase α4 gene, and used it as a marker for α4 expression in mice (Atp1a4 ( null(GFP) ) mice).

RESULTS

Replacement of α4 by GFP completely disrupted α4 expression and activity, produced sperm morphological and functional abnormalities, and caused infertility of Atp1a4 ( null(GFP) ) male mice. Immunoblot analysis of Atp1a4 ( null(GFP) ) mouse tissues showed GFP expression in testis. This particular expression pattern was found in adult, but not in mouse embryos or in 7, 18 day old mice. In agreement with expression of GFP, adult Atp1a4 ( null(GFP) ) mouse testis displayed the typical fluorescence of GFP. Immunocytochemistry of testis identified GFP in more differentiated male germ cells, but not in spermatogonia, Leydig or Sertoli cells. Further analysis, using immunoblot of fluorescently sorted testis cells with cell specific markers, detected GFP only in spermatocytes, spermatids and spermatozoa. While epididymis showed GFP expression, this was confined to the spermatozoa within the epididymal tubules.

CONCLUSIONS

Our results show that the Atp1a4 promoter drives GFP expression exclusively in male germ cells of the testis, where it restricts it to post-meiotic stages of spermatogenesis. These findings highlight the exquisite spatial and temporal control of expression exerted by the Atp1a4 promoter on Na,K-ATPase α4, which is particularly well suited to fulfill the special functions of spermatozoa.

Na+/K+-ATPase α1 isoform mediates ouabain-induced expression of cyclin D1 and proliferation of rat sertoli cells

Novel roles for the interaction of cardiotonic steroids to Na(+)/K(+)-ATPase have been established in recent years. The aim of this study was to investigate the intracellular signaling events downstream the action of ouabain on Na(+)/K(+)-ATPase in Sertoli cell obtained from immature rats. Treatment of Sertoli cells with ouabain (1 μM) induced a rapid and transient increase in the extracellular signal-regulated kinase (ERK1/2 or MAPK3/1) and phosphatidylinositol 3-kinase (PI3K)/serine-threonine protein kinase (AKT) phosphorylation. Also, ouabain upregulated the expression of cyclin D1 and incorporation of [methyl-(3)H]thymidine, both of which were dependent on MAPK3/1 but not AKT intracellular cascade, as shown by pretreatment with MEK (MAP2K1/2) inhibitor U0126 and PI3K inhibitor wortmannin respectively. Moreover, the effect of ouabain on these proliferation parameters was completely prevented by phospho-cAMP response element-binding protein (CREB)/CREB-binding protein complex inhibitor KG501 and only partially by nuclear factor κB nuclear translocation inhibitor SN50. Pretreatment with estrogen receptor antagonist ICI 182780 showed that MAPK3/1 activation by ouabain does not involve this receptor. The Na(+)/K(+)-ATPase α1 isoform, but not α4, was detected in Sertoli cells, suggesting that ouabain effects in Sertoli cells are mediated via α1. Taken together, these results show a rapid ouabain action in the Sertoli cells, which in turn can modulate nuclear transcriptional events essential for Sertoli cell proliferation in a critical period of testicular development. Our findings are important to understand the role of ouabain in the testis and its possible implications in male infertility.

Subunit isoform selectivity in assembly of Na,K-ATPase α-β heterodimers

To catalyze ion transport, the Na,K-ATPase must contain one α and one β subunit. When expressed by transfection in various expression systems, each of the four α subunit isoforms can assemble with each of the three β subunit isoforms and form an active enzyme, suggesting the absence of selective α-β isoform assembly. However, it is unknown whether in vivo conditions the α-β assembly is random or isoform-specific. The α(2)-β(2) complex was selectively immunoprecipitated by both anti-α(2) and anti-β(2) antibodies from extracts of mouse brain, which contains cells co-expressing multiple Na,K-ATPase isoforms. Neither α(1)-β(2) nor α(2)-β(1) complexes were detected in the immunoprecipitates. Furthermore, in MDCK cells co-expressing α(1), β(1), and β(2) isoforms, a greater fraction of the β(2) subunits was unassembled with α(1) as compared with that of the β(1) subunits, indicating preferential association of the α(1) isoform with the β(1) isoform. In addition, the α(1)-β(2) complex was less resistant to various detergents than the α(1)-β(1) complex isolated from MDCK cells or the α(2)-β(2) complex isolated from mouse brain. Therefore, the diversity of the α-β Na,K-ATPase heterodimers in vivo is determined not only by cell-specific co-expression of particular isoforms, but also by selective association of the α and β subunit isoforms.

Immunolocalisation of 11β-HSD-1 and -2, glucocorticoid receptor, mineralocorticoid receptor and Na+ K+-ATPase during the postnatal development of the rat epididymis

Glucocorticoids have been implicated in male reproductive function and 11β-HSD-1 and -2, the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR), all of which are known to modulate glucocorticoid action, have been localised in the adult rat epididymis, but their developmental expression has not been investigated. Na(+)K(+)-ATPase activity, responsible for sodium transport, is induced by both mineralocorticoids and glucocorticoids in the kidney and colon, and has been localised in epididymal epithelium. This study examined the immunolocalisation of 11β-HSD-1 and -2, GR, MR and Na(+)K(+)-ATPase in rat epididymal epithelium (n = 5) at postnatal days (pnd) 1, 7, 15, 28, 40, 60, 75 and 104, and relative mRNA expression of 11β-HSD-1 and -2, and GR at pre-puberty (pnd 28) and post-puberty (pnd 75). 11β-HSD-1, GR and MR were localised in the epididymal epithelium from pnd 1, and 11β-HSD-2 and Na(+)K(+)-ATPase reactivity from pnd 15. At pnd 28 there was maximal immunoreactivity for both the GR and MR and 11β-HSD-1 and -2. 11β-HSD-1 mRNA expression in the caput increased from pre- to post-puberty, whereas 11β-HSD-2 mRNA expression fell over the same period (P < 0.01). GR mRNA expression was similar at pre- and post-puberty in both caput and cauda. Developmental changes in expression of 11β-HSD-1 and -2 suggest that overall exposure of the epididymis to glucocorticoids increases post-puberty, but cell-specific expression of the 11β-HSD enzymes still provides a capacity for intricate local control of glucocorticoid exposure.

Migraine- and dystonia-related disease-mutations of Na+/K+-ATPases: relevance of behavioral studies in mice to disease symptoms and neurological manifestations in humans

The two autosomal dominantly inherited neurological diseases: familial hemiplegic migraine type 2 (FHM2) and familial rapid-onset of dystonia-parkinsonism (Familial RDP) are caused by in vivo mutations of specific alpha subunits of the sodium-potassium pump (Na(+)/K(+)-ATPase). Intriguingly, patients with classical FHM2 and RDP symptoms additionally suffer from other manifestations, such as epilepsy/seizures and developmental disabilities. Recent studies of FHM2 and RDP mouse models provide valuable tools for dissecting the vital roles of the Na(+)/K(+)-ATPases, and we discuss their relevance to the complex patient symptoms and manifestations. Thus, it is interesting that mouse models targeting a specific α-isoform cause different, although still comparable, phenotypes consistent with classical symptoms and other manifestations observed in FHM2 and RDP patients. This review highlights that use of mouse models have broad potentials for future research concerning migraine and dystonia-related diseases, which will contribute towards understanding the, yet unknown, pathophysiologies.

The pumps that fuel a sperm's journey

The sole purpose of a sperm cell is to carry genetic information from a male to a female egg. In order to accomplish this quest, the sperm cell must travel a long distance through a constantly changing environment. The success of this journey depends on membrane proteins that are uniquely expressed in sperm cells. One of these proteins is the α4 isoform of the sodium pump. This pump is optimized to cope with the ionic environment characteristic of the female reproductive tract, and its activity may be tightly coupled with secondary transporters that maintain cytoplasmic pH. Pharmacological inhibition of α4 is sufficient to inhibit sperm motility, and significant differences around the inhibitor-binding site compared with the ubiquitous α1 isoform, make α4 a feasible target in rational drug development.

Expression of dysadherin in the human male reproductive tract and in spermatozoa

OBJECTIVE

To study expression of dysadherin in human testis, epididymis, and spermatozoa.

DESIGN

Prospective study.

SETTING

Basic research laboratory.

PATIENT(S)

Testis, epididymis, and testicular spermatozoa from patients under treatment and semen from volunteer donors.

INTERVENTION(S)

Reverse transcription-polymerase chain reaction, immunohistochemistry, immunocytochemistry, and Western immunoblotting.

MAIN OUTCOME MEASURE(S)

Dysadherin messenger RNA (mRNA) analysis in testis, epididymis, and ejaculated spermatozoa, immunohistochemistry of both tissues, Western immunoblotting of tissue/cell extracts, and immunocytochemistry of spermatozoa.

RESULT(S)

Dysadherin mRNA was found in testis, epididymis, and ejaculated spermatozoa. Whereas testis and spermatozoa exhibited a distinctive 91-kDa protein form, the epididymis showed a 50-kDa moiety, also found in MDA-MB-231 breast cancer cells. Nucleotide sequence analysis revealed >99% homology between testicular and somatic cell mRNA, suggesting differential protein glycosylation. Dysadherin was immunodetected in round spermatids and testicular/ejaculated spermatozoa. It localizes to the acrosomal region and flagellum and colocalized with E-cadherin in the head and with the Na(+),K(+)-ATPase α4 subunit in the flagellum.

CONCLUSION(S)

This is the first report on expression of dysadherin in the male gonad and in spermatozoa. Its colocalization with E-cadherin and Na(+),K(+)-ATPase leads us to postulate a role for dysadherin as a modulator of sperm function.

A structural overview of the plasma membrane Na+,K+-ATPase and H+-ATPase ion pumps

Plasma membrane ATPases are primary active transporters of cations that maintain steep concentration gradients. The ion gradients and membrane potentials derived from them form the basis for a range of essential cellular processes, in particular Na(+)-dependent and proton-dependent secondary transport systems that are responsible for uptake and extrusion of metabolites and other ions. The ion gradients are also both directly and indirectly used to control pH homeostasis and to regulate cell volume. The plasma membrane H(+)-ATPase maintains a proton gradient in plants and fungi and the Na(+),K(+)-ATPase maintains a Na(+) and K(+) gradient in animal cells. Structural information provides insight into the function of these two distinct but related P-type pumps.

Targeting the Na(+)/K(+)-ATPase alpha1 subunit of hepatoma HepG2 cell line to induce apoptosis and cell cycle arresting

Recent research has shown that the Na(+)/K(+)-ATPase alpha1 subunit is a novel anti-cancer target, which plays pivotal roles in malignant cell ion transport, metabolism, migration and signal transduction. The purpose of the present study was to investigate the anti-cancer effects of ouabain and Na(+)/K(+)-ATPase alpha1 small interfering ribonucleic acid (siRNA) on HepG2 cell proliferation, apoptosis and cell cycle, and to explore the molecular mechanisms. The expression of Na(+)/K(+)-ATPase alpha1 subunit in human hepatocellular carcinoma (HCC), normal liver tissues and human HCC line (HepG2, SMMC-7721 and Bel-7402) has been investigated. Using the ouabain and Na(+)/K(+)-ATPase alpha1 subunit siRNA, which target the Na(+)/K(+)-ATPase, we have evaluated the effects of inhibiting Na(+)/K(+)-ATPase alpha1 in human HepG2 cells with respect to cell proliferation, morphology, cell cycle, impact on intracellular Ca2++, reactive oxygen species (ROS) concentration, and correlated gene expression level on messenger ribonucleic acid (mRNA) and protein. Our data showed that the expression Na(+)/K(+)-ATPase alpha1 subunit in HCC tissues is higher than that in normal liver tissues. Ouabain and Na(+)/K(+)-ATPase alpha1 siRNA could inhibit HepG2 cell proliferation. Ouabain could induce HepG2 cell apoptosis and generate S phase arrest, and siRNA could enhance the anti-cancer effect of ouabain that induced HepG2 cells apoptosis via an intracellular Ca(2+) and ROS increase-mediated, and generated cell cycle S phase arresting by decreasing the CyclinA1/cyclin-dependent kinase 2 (CDK2)/proliferating cell nuclear antigen (PCNA) complex product and increasing the expression of cyclin-dependent kinase inhibitor 1A (P21(CIP1)). We believe that targeting of the Na(+)/K(+)-ATPase alpha1 subunit in human HCC cells could provide new sight into the treatment of HCC.

Na,K-ATPase alpha4 isoform is essential for sperm fertility

Regulation of ion balance in spermatozoa has been shown to be essential for sperm motility and fertility. Control of intracellular ion levels requires the function of distinct ion-transport mechanisms at the cell plasma membrane. Active Na(+) and K(+) exchange in sperm is under the control of the Na,K-ATPase. Two molecular variants of the catalytic subunit of the Na,K-ATPase, α1 and α4, coexist in sperm. These isoforms exhibit different biochemical properties; however, their function in sperm fertility is unknown. In this work, we show that Na,K-ATPase α4 is essential for sperm fertility. Knockout male mice lacking α4 are completely sterile and spermatozoa from these mice are unable of fertilizing eggs in vitro. Furthermore, α4 deletion results in severe reduction in sperm motility and hyperactivation typical of sperm capacitation. In addition, absence of α4 causes a characteristic bend in the sperm flagellum, indicative of abnormal sperm ion regulation. Accordingly, α4-null sperm present increased intracellular Na(+) and cell plasma membrane depolarization. These results are unique in demonstrating the absolute requirement of α4 for sperm fertility. Moreover, the inability of α1 to compensate for α4 suggests that α4 is the Na,K-ATPase-α isoform directly involved in sperm fertility. Our findings show α4 as an attractive target for male contraception and open the possibility for the potential use of this Na,K-ATPase isoform as a biomarker for male fertility.

Role and regulation of EGFR in actin remodeling in sperm capacitation and the acrosome reaction

To bind and fertilize the egg, the spermatozoon should undergo few biochemical and motility changes in the female reproductive tract collectively called capacitation. The capacitated spermatozoon binds to the egg zona pellucida, and then undergoes the acrosome reaction (AR), which allows its penetration into the egg. The mechanisms regulating sperm capacitation and the AR are not completely understood. In the present review, we summarize some data regarding the role and regulation of the epidermal growth factor receptor (EGFR) in these processes. In the capacitation process, the EGFR is partially activated by protein kinase A (PKA), resulting in phospholipase D (PLD) activation and actin polymerization. Protein kinase C alpha (PKCα), which is already activated at the beginning of the capacitation, also participates in PLD activation. Further activation of the EGFR at the end of the capacitation enhances intracellular Ca(2+) concentration leading to F-actin breakdown and allows the AR to take place. Under in vivo conditions, the EGFR can be directly activated by its known ligand epidermal growth factor (EGF), and indirectly by activating PKA or by transactivation mediated by G protein-coupled receptors (GPCRs) activation or by ouabain. Under physiological conditions, sperm PKA is activated mainly by bicarbonate, which activates the soluble adenylyl cyclase to produce cyclic adenosine monophosphate (cAMP), the activator of PKA. The GPCR activators angiotensin II or lysophosphatidic acid, as well as ouabain and EGF are physiological components present in the female reproductive tract.

Increased expression of the Na,K-ATPase alpha4 isoform enhances sperm motility in transgenic mice

The Na,K-ATPase alpha4 (ATP1A4) isoform is specifically expressed in male germ cells and is highly prevalent in spermatozoa. Although selective inhibition of alpha4 activity with ouabain has been shown to affect sperm motility, a more direct analysis of the role of this isoform in sperm movement has not yet been demonstrated. To establish this, we engineered transgenic mice that express the rat alpha4 isoform fused to green fluorescent protein in male germ cells, under the control of the mouse protamine 1 promoter. We showed that the rat Atp1a4 transgene is expressed in mouse spermatozoa and that it is localized to the sperm flagellum. In agreement with increased expression of the alpha4 isoform, sperm from transgenic mice displayed higher alpha4-specific Na,K-ATPase activity and binding of fluorescently labeled ouabain than wild-type mice. In contrast, expression and activity of ATP1A1 (alpha1), the other Na,K-ATPase alpha isoform present in sperm, remained unchanged. Similar to wild-type mice, mice expressing the alpha4 transgene exhibited normal testis and sperm morphology and no differences in fertility. However, compared to wild-type mice, sperm from transgenic mice displayed plasma membrane hyperpolarization and higher total and progressive motility. Other parameters of motility also increased, including straight-line, curvilinear, and average path velocities and amplitude of lateral head displacement. In addition, sperm from the transgenic mice showed enhanced sperm hyperactive motility, but no changes in progesterone-induced acrosome reaction. Altogether, these results provide new genetic evidence for the role of the ATP1A4 isoform in sperm motility, under both noncapacitating and capacitating conditions.

The physiological significance of the cardiotonic steroid/ouabain-binding site of the Na,K-ATPase

The Na,K-ATPase is the membrane "pump" that generates the Na(+) and K(+) gradients across the plasma membrane that drives many physiological processes. This enzyme is highly sensitive to inhibition by cardiotonic steroids, most notably the digitalis/ouabain class of compounds, which have been used for centuries to treat congestive heart failure and arrhythmias. The amino acids that constitute the ouabain-binding site are highly conserved across the evolutionary spectrum. This could be fortuitous or could result from this site being conserved because it has an important biological function. New physiological approaches using genetically engineered mice are being used to define the biological significance of the "receptor function" of the Na,K-ATPase and its regulation by potential endogenous cardiotonic steroid-like compounds. These studies extend the reach of earlier studies involving the biochemical purification of endogenous regulatory ligands.

Activity of the Na,K-ATPase alpha4 isoform is important for membrane potential, intracellular Ca2+, and pH to maintain motility in rat spermatozoa

While the function of the ubiquitous Na,K-ATPase alpha1 subunit has been well documented, the role of the sperm-specific alpha4 isoform of this ion transporter is less known. We have explored the importance of alpha4 in rat sperm physiology by taking advantage of the high sensitivity of this isoform for the inhibitor ouabain. Using concentrations that selectively block alpha4 activity, we found ouabain to reduce not only sperm total motility, but also multiple parameters of sperm movement, including progressive motility, straight line, curvilinear, and average path velocities, lateral head displacement, beat cross frequency, and linearity. According to a direct role of alpha4 in Na(+) transport, ouabain inhibition of alpha4 increased [Na(+)](i) in the male gametes. In addition, interference of alpha4 activity with ouabain produced cell membrane depolarization, diminished pH, and increased [Ca(2)(+)](i) in spermatozoa. Inhibition of alpha4 was sufficient to cause all these effects and additional blockage of alpha1, the other Na,K-ATPase alpha isoform expressed in sperm, and higher doses of ouabain did not result in further changes in the cell parameters studied. These results show that alpha4 is the Na,K-ATPase isoform primarily involved in controlling the transmembrane Na(+) gradient in sperm, and that alpha4 activity is necessary for maintaining membrane potential, [Ca(2)(+)](i), and [H(+)](i) in the cells. The high dependence of sperm motility on membrane excitability, [Ca(2)(+)](i), and acid-base balance suggests that their regulation is the mechanism by which alpha4 maintains motility of the male gametes.

The structure of the Na+,K+-ATPase and mapping of isoform differences and disease-related mutations

The Na+,K+-ATPase transforms the energy of ATP to the maintenance of steep electrochemical gradients for sodium and potassium across the plasma membrane. This activity is tissue specific, in particular due to variations in the expressions of the alpha subunit isoforms one through four. Several mutations in alpha2 and 3 have been identified that link the specific function of the Na+,K+-ATPase to the pathophysiology of neurological diseases such as rapid-onset dystonia parkinsonism and familial hemiplegic migraine type 2. We show a mapping of the isoform differences and the disease-related mutations on the recently determined crystal structure of the pig renal Na+,K+-ATPase and a structural comparison to Ca2+-ATPase. Furthermore, we present new experimental data that address the role of a stretch of three conserved arginines near the C-terminus of the alpha subunit (Arg1003-Arg1005).

Expression of Atp8b3 in murine testis and its characterization as a testis specific P-type ATPase

Spermatogenesis is a complex process that produces haploid motile sperms from diploid spermatogonia through dramatic morphological and biochemical changes. P-type ATPases, which support a variety of cellular processes, have been shown to play a role in the functioning of sperm. In this study, we isolated one putative androgen-regulated gene, which is the previously reported sperm-specific aminophospholipid transporter (Atp8b3, previously known as Saplt), and explored its expression pattern in murine testis and its biochemical characteristics as a P-type ATPase. Atp8b3 is exclusively expressed in the testis and its expression is developmentally regulated during testicular development. Immunohistochemistry of the testis reveals that Atp8b3 is expressed only in germ cells, especially haploid spermatids, and the protein is localized in developing acrosomes. As expected, from its primary amino acid sequence, ATP8B3 has an ATPase activity and is phosphorylated by an ATP-producing acylphosphate intermediate, which is a signature property of the P-Type ATPases. Together, ATP8B3 may play a role in acrosome development and/or in sperm function during fertilization.

The alpha1 isoform of the Na+/K+ ATPase is up-regulated in dedifferentiated progenitor cells that mediate lens and retina regeneration in adult newts

Adult newts are able to regenerate their retina and lens after injury or complete removal through transdifferentiation of the pigmented epithelial tissues of the eye. This process needs to be tightly controlled, and several different mechanisms are likely to be recruited for this function. The Na(+)/K(+) ATPase is a transmembrane protein that establishes electrochemical gradients through the transport of Na(+) and K(+) and has been implicated in the modulation of key cellular processes such as cell division, migration and adhesion. Even though it is expressed in all cells, its isoform composition varies with cell type and is tightly controlled during development and regeneration. In the present study we characterize the expression pattern of Na(+)/K(+) ATPase alpha1 in the adult newt eye and during the process of lens and retina regeneration. We show that this isoform is up-regulated in undifferentiated cells during transdifferentiation. Such change in composition could be one of the mechanisms that newt cells utilize to modulate this process.

Na,K-ATPase and the role of alpha isoforms in behavior

The Na,K-ATPase is composed of multiple isoforms and the isoform distribution varies with the tissue and during development. The alpha1 isoform for example, is the major isoform in the kidney and many other tissues, while the alpha2 isoform is the predominate one in skeletal muscle. All three isoforms are found in the brain although in adult rodent brain, the alpha 3 isoform is located essentially in neurons while the alpha2 isoform is found in astrocytes and some limited neuronal populations. Interestingly the alpha 4 isoform is found exclusively in the mid region of the sperm tail. The distribution of the isoforms of the Na,K-ATPase has been extensively studied in many tissues and during development. The examples cited above provide some indication to the diversity of Na,K-ATPase isoform expression. In order to understand the significance of this distribution, we have developed animals which lack the alpha1, alpha2, and alpha 3 isoforms. It is anticipated that these studies will provide insight into the role that these isoforms play in driving various biological processes in specific tissues. Here we describe some of our studies which deal with the behavioral aspects of the alpha1, alpha2, and alpha 3 deficient mice, particularly those that are haploinsufficient in one isoform i.e. lacking one functional gene for the alpha1, alpha2, or alpha 3 isoforms. Such studies are important as two human diseases are associated with deficiency in the alpha2 and alpha 3 isoforms. These are Familial Hemiplegic Migraine type 2 and Rapid-Onset Dystonia Parkinsonism, these diseases result from alpha2 and alpha 3 isoform haploinsufficiency, respectively. We find that the haploinsufficiency of both alpha2 and alpha 3 isoforms result in behavioral defects.

Coulter counter-based evaluation of sperm volume to assess sperm viability of bull semen and application to X/Y sperm sorting

The Coulter Counter Hypo-Osmotic Swelling test (CC-HOS) was developed to provide insight into the membrane integrity (relative volume shift Vr) of sperm necessary for fertilization, and to identify the optimum buffer needed for the X/Y chromosome sorting process. Using the CC-HOS test on neat bovine semen, the mean relative volume shift Vr for July and August was 1.20 and 1.14, respectively, whereas mean Vr values ranged from 1.32 to 1.41 during September to November. There was an inverse relationship between Vr magnitude and environmental temperature; we inferred that this enhanced sperm viability during autumn relative to summer. A method was developed to measure the dynamics of volume change of sperm in the buffer (pH 6.5) used for the X/Y chromosome sorting process. When exposed to the buffer (4 mM K+, 153 mM Na+, 140 mM Cl(-)), sperm from Bull C had a mean modal volume of 22.8+/-0.2 fL during a 0-300 s time interval, which did not significantly vary from sperm volumes (21.88+/-0.66 fL for Bull A and 22.46+/-0.38 fL for Bull B) noted in isotonic Isoton II solution. However, when exposed to lower ionic concentrations (2 mM K+, 62 mM Na+, 47 mM Cl-), the mean volume of Bull C sperm increased to 29.2+/-1.5 fL and exhibited slower rates toward stabilized volumes relative to higher ionic concentration buffers. Utilization of volume swelling measurements for measuring the impact of ion concentrations in X/Y chromosome sorting process buffers illustrated the importance of its application for emerging sperm-based biotechnologies.

Adverse effects of cadmium on bull spermatozoa

Cadmium (Cd) is a widespread environmental pollutant. Because of its long biological half-life (10-30 years in humans), Cd accumulates in the biological systems such as gonads. The present study was designed to evaluate the effect of Cd in the concentration range 50-750 micromol/L, in vitro, on the membrane integrity, motility and acrosomal status of bull spermatozoa. The samples were processed for sperm analyses using semen-diluting fluid (phosphate-buffered saline, pH 7.2). A significant elevation in the malondialdehyde level/lipid peroxidation (LPO) rate and a decrease in the spermatocrit values, particularly at a concentration of 750 micromol/L Cd, indicated the deleterious effect of Cd on sperm membrane integrity. There was also a negative correlation between LPO rate and percentage of motile spermatozoa (r = 0.992). The gelatin test indicates that Cd may alter the integrity of acrosomal membranes and shows an abnormal acrosome reaction. In this regard, a strong negative correlation was found between LPO rate and % halos (bright clear zone around sperm heads after gelatin digestion) (r = 0.990). Taking the results together, Cd proved to be a potential toxicant in the category of environmental factors that induce membrane impairment, lower motility, and decrease the rate of acrosome reactions, leading to male infertility. Apparently, the presence of Cd in the environment and seminal plasma exerts a toxic effect on sperm cells.

The influence of fluorides on mouse sperm capacitation

Increasing infertility, due to pathological changes on sperm, has become a serious issue. Eco-toxicological effect of rising concentration of fluorides can be enhanced in the presence of aluminium ions by forming fluorometallic complexes, analogues of phosphate groups that interfere with the activity of G-proteins and P-type ATPases, which are part of several signalling pathways during sperm maturation. In order for sperm to gain fertilizing ability, they must undergo in the female reproductive tract, capacitation that includes tyrosine phosphorylation and consequent actin polymerization. The present paper reports the findings of 3-month oral toxicity in mice of fluorides at the concentrations 0, 1, 10, and 100ppm and their synergic action with aluminium at dose of 10ppm. There were no mortalities, clinical signs of discomfort or body weight loss during the experiment. The analysis revealed, for the concentrations of 10 and 100ppm, abnormalities of spermatogenesis and ability of epididymal spermatozoa to capacitate in vitro, as the result of decreased sperm head tyrosine phosphorylation and actin polymerization. The enhancing overload caused by fluorides represents a potential factor, having an impact on function of sperm, hence contributing to a growing infertility in the human population.

In vitro mercury exposure on spermatozoa from normospermic individuals

Epidemiological evidence suggests that exposure to industrial metal aerosols is detrimental to the male reproductive system. Oxidative stress has been identified as a crucial factor leading to male factor infertility largely due to peroxidative damage to the sperm cell membrane. The objectives of the present study were to test the effect of mercury in the concentration range from 50 to 800 micromol(-1), in vitro, on the sperm membrane and DNA integrity, motility and acrosomal status of human spermatozoa. We found a significant increase in the Lipo Per Oxidation (LPO) indicating the deleterious effect of mercury on the sperm membrane integrity. This effect was prominent at the concentration of 800 microM mercury. There was also a strong negative correlation between LPO rate and percentage of viable spermatozoa (r = -0.941, p<0.001). Data obtained from SCGE assay technique revealed that mercury is capable of inducing DNA breaks in the sperm nuclei. Almost, 88% of DNA breaks were of double-stranded. The correlation between LPO rate and percentage of DNA breaks was found to be 0.918 (p<0.001). Performing the gelatin digestion test indicates that mercury was able to alter the integrity of acrosomal membranes showing an abnormal acrosome reaction. In this regard, a strong correlation was found between LPO rate and percentage of halos (r = -0.893, p<0.001). Taken together, mercury induced membrane impairments, lowered sperm viability, DNA breaks and a decreased rate in the acrosome reaction of human spermatozoa leading to sperm dysfunction. Entering mercury in the male gonads and seminal plasma may exert deleterious effects on the human spermatozoa. Hence, considering the wide spread use of mercury and its compounds, these metals should regarded with more concern.

Effects of vanadate on male rat reproductive tract histology, oxidative stress markers and androgenic enzyme activities

Vanadium has been recognized as industrial hazards that adversely affect male reproductive systems of humans and animals. However, less information is available concerning the underlying mechanism in the pathogenesis of male reproductive dysfunction. The present study investigated the possible involvement of oxidative stress to induce oxidative deterioration of testicular functions in adult rats. The results of in vitro and in vivo studies demonstrate that vanadium treatment resulted in a significant dose- and time-dependent increase in the testicular lipid peroxidation, marked inhibition in the level of superoxide dismutase and catalase activities, decreased sperm counts, and substantially inhibited the activities of Delta(5)3beta- and 17beta-hydroxysteroid dehydrogenase as well as serum testosterone level. Histopathological examination revealed inhibition of spermatogenesis and the preferential loss of maturing and elongated spermatids along with increased percent of abnormal sperm. Taken together, the results suggest that an increase in free radical formation relative to loss of antioxidant defense system during vanadium exposure may render testis more susceptible to oxidative damage leading to their functional inactivation. Thus the toxic effects of vanadium are cumulative and that vanadium produced damages in testes are dose- and time-dependent.

The transcription factor CREMtau and cAMP regulate promoter activity of the Na,K-ATPase alpha4 isoform

The Na,K-ATPase is an essential enzyme of the plasma membrane that plays a key role in numerous cell processes that depend on the transcellular gradients of Na(+) and K(+). Among the various isoforms of the catalytic subunit of the Na,K-ATPase, alpha4 exhibits the most limited pattern of expression, being restricted to male germ cells. Activity of alpha4 is essential for sperm function, and alpha4 is upregulated during spermatogenesis. The present study addressed the transcriptional control of the human Na,K-ATPase alpha4 gene, ATP1A4. We describe that a 5' untranslated region of the ATP1A4 gene (designated -339/+480 based on the ATP1A4 transcription initiation site) has promoter activity in luciferase reporter assays. Computer analysis of this promoter region revealed consensus sites (CRE) for the cyclic AMP (cAMP) response element modulator (CREM). Accordingly, dibutyryl cAMP (db-cAMP) and ectopic expression of CREMtau, a testis specific splice variant of CREM were able to activate the ATP1A4 promoter driven expression of luciferase in HEK 293 T, JEG-3 and GC-1 cells. Further characterization of the effect of db-cAMP and CREMtau on deleted constructs of the ATP1A4 promoter (-339/+80, and +25/+480), and on the -339/+480 region carrying mutations in the CRE sites showed that db-cAMP and CREMtau effect required the CRE motif located 263 bp upstream the transcription initiation site. EMSA experiments confirmed the CRE sequence as a bonafide CREMtau binding site. These results constitute the first demonstration of the transcriptional control of ATP1A4 gene expression by cAMP and by CREMtau, a transcription factor essential for male germ cell gene expression.

Gene transposition as a cause of hybrid sterility in Drosophila

We describe reproductive isolation caused by a gene transposition. In certain Drosophila melanogaster-D. simulans hybrids, hybrid male sterility is caused by the lack of a single-copy gene essential for male fertility, JYAlpha. This gene is located on the fourth chromosome of D. melanogaster but on the third chromosome of D. simulans. Genomic and molecular analyses show that JYAlpha transposed to the third chromosome during the evolutionary history of the D. simulans lineage. Because of this transposition, a fraction of hybrids completely lack JYAlpha and are sterile, representing reproductive isolation without sequence evolution.

Na+/K+ATPase as a Signaling Molecule During Bovine Sperm Capacitation1

A heteromeric integral membrane protein, Na+/K+ATPase is composed of two polypeptides, alpha and beta, and is active in many cell types, including testis and spermatozoa. It is a well-known ion transporter, but binding of ouabain, a specific inhibitor of Na+/K+ATPase, to Na+/K+ATPase in somatic cells initiates responses that are similar to signaling events associated with bovine sperm capacitation. The objectives of the present study were to demonstrate the presence of Na+/K+ATPase in bovine sperm and to investigate its role in the regulation of bovine sperm capacitation. The presence of Na+/K+ATPase in sperm from mature Holstein bulls was demonstrated by immunoblotting and immunocytochemistry using a monoclonal antibody developed in mouse against the beta 1 polypeptide of Na+/K+ATPase. Binding of ouabain to Na+/K+ATPase inhibited motility (decreased progressive motility, average path velocity, and curvilinear velocity) and induced tyrosine phosphorylation and capacitation but did not increase intracellular calcium levels in spermatozoa. Furthermore, binding of ouabain to Na+/K+ATPase induced depolarization of sperm plasma membrane. Therefore, binding of ouabain to Na+/K+ATPase induced sperm capacitation through depolarization of sperm plasma membrane and signaling via the tyrosine phosphorylation pathway without an appreciable increase in intracellular calcium. To our knowledge, this is the first report concerning the signaling role of Na+/K+ATPase in mammalian sperm capacitation.

The Na,K-ATPase alpha4 isoform from humans has distinct enzymatic properties and is important for sperm motility

In the rat, the Na,K-ATPase alpha4 isoform exhibits unique enzymatic characteristics and is important for sperm motility. In this work, we studied expression, localization and function of alpha4 in human spermatozoa. We show two catalytically active Na,K-ATPase alpha polypeptides with different ouabain affinity and identified expression of alpha1, alpha4, beta1 and beta3 isoforms in the gametes. In addition, human sperm presented two Na,K-ATPases composed of alpha4, alpha4beta1 and alpha4beta3. Kinetic analysis of these isozymes produced in insect cells showed that, compared with human alpha1beta1, alpha4beta1 and alpha4beta3 exhibit higher Na(+) and lower K(+) affinity and higher sensitivity to ouabain. These particular enzymatic properties suggested a role for alpha4 in sperm function. Using computer-assisted sperm analysis (CASA), we found that ouabain inhibition of alpha4 significantly decreased percentage sperm motility. In contrast, ouabain did not affect linearity of forward progression, amplitude of lateral head displacement, beat cross frequency and sperm straight-line, curvilinear or average path velocities. This suggests a primary role of alpha4 in flagellar motility. Accordingly, we found alpha4 in the sperm tail, predominating in the mid-piece of the flagellum. Therefore, similar to the rat ortholog, human Na,K-ATPase alpha4 isoform has a distinct activity that is essential for sperm function.

An N-terminal Sequence Targets and Tethers Na+ Pump α2 Subunits to Specialized Plasma Membrane Microdomains

Sodium pumps (alphabeta dimers) with the alpha1 isoform of the catalytic (alpha) subunit are expressed in all cells. Additionally, most cells express Na+ pumps with a second alpha isoform. For example, astrocytes and arterial myocytes also express Na+ pumps with the alpha2 isoform. The alpha2 pumps localize to plasma membrane (PM) microdomains overlying "junctional" sarco-/endoplasmic reticulum (S/ER), but the alpha1 pumps are more uniformly distributed. To study alpha2 targeting, we expressed alpha1/alpha2 and alpha2/alpha1 chimeras and 1-90 and 1-120 amino acid N-terminal peptides in primary cultured mouse astrocytes. Immunocytochemistry revealed that alpha2/alpha1 (but not alpha1/alpha2) chimeras markedly reduced native alpha2 (i.e. were "dominant negatives"). N-terminal (1-120 and 1-90 amino acids) alpha2 (and alpha3), but not alpha1 peptides also targeted to the PM-S/ER junctions and were dominant negative for native alpha2 in astrocytes and arterial myocytes. Thus alpha2 and alpha3 have the same targeting sequence. Ca2+ (fura-2) signals in astrocytes expressing the 1-90 alpha2 peptide were comparable to signals in cells from alpha2 null mutants (i.e. functionally dominant negative): 1 microM ATP-evoked Ca2+ transients were augmented, and 100 nM ouabain-induced amplification was abolished. Amino acid substitutions in the 1-120 alpha1 and alpha2 constructs, and in full-length alpha1, revealed that Leu-27 and Ala-35 are essential for targeting/tethering the constructs to PM-S/ER junctions.

Physiological role of the α1- and α2-isoforms of the Na+-K+-ATPase and biological significance of their cardiac glycoside binding site

An interesting feature of Na+-K+-ATPase is that it contains four isoforms of the catalytic α-subunit, each with a tissue-specific distribution. Our laboratory has used gene targeting to define the functional role of the α1- and α2-isoforms. While knockout mice demonstrated the importance of the α1- and α2-isoforms for survival, the knockin mice, in which each isoform can be individually inhibited by ouabain and its function determined, demonstrated that both isoforms are regulators of cardiac muscle contractility. Another intriguing aspect of the Na+-K+-ATPase is that it contains a binding site for cardiac glycosides, such as digoxin. Conservation of this site suggests that it may have an in vivo role and that a natural ligand must exist to interact with this site. In fact, cardiac glycoside-like compounds have been observed in mammals. Our recent study demonstrates that the cardiac glycoside binding site of the Na+-K+-ATPase plays a role in the regulation of blood pressure and that it mediates both ouabain-induced and ACTH-induced hypertension in mice. Whereas chronic administration of ouabain or ACTH caused hypertension in wild-type mice, it had no effect on blood pressure in mice with a ouabain-resistant α2-isoform of Na+-K+-ATPase. Interestingly, animals with the ouabain-sensitive α1-isoform and a ouabain-resistant α2-isoform develop ACTH-induced hypertension to a greater extent than wild-type animals. Taken together, these results demonstrate that the cardiac glycoside binding of the Na+-K+-ATPase has a physiological role and suggests a function for a naturally occurring ligand that is stimulated by administration of ACTH.

Different expression and activity of the alpha1 and alpha4 isoforms of the Na,K-ATPase during rat male germ cell ontogeny

Two catalytic isoforms of the Na,K-ATPase, alpha1 and alpha4, are present in testis. While alpha1 is ubiquitously expressed in tissues, alpha4 predominates in male germ cells. Each isoform has distinct enzymatic properties and appears to play specific roles. To gain insight into the relevance of the Na,K-ATPase alpha isoforms in male germ cell biology, we have studied the expression and activity of alpha1 and alpha4 during spermatogenesis and epididymal maturation. This was explored in rat testes at different ages, in isolated spermatogenic cells and in spermatozoa from the caput and caudal regions of the epididymis. Our results show that alpha1 and alpha4 undergo differential regulation during development. Whereas alpha1 exhibits only modest changes, alpha4 increases with gamete differentiation. The most drastic changes for alpha4 take place in spermatocytes at the mRNA level, and with the transition of round spermatids into spermatozoa for expression and activity of the protein. No further changes are detected during transit of spermatozoa through the epididymis. In addition, the cellular distribution of alpha4 is modified with development, being diffusely expressed at the plasma membrane and intracellular compartments of immature cells, finally to localize to the midregion of the spermatozoon flagellum. In contrast, the alpha1 isoform is evenly present along the plasma membrane of the developing and mature gametes. In conclusion, the Na,K-ATPase alpha1 and alpha4 isoforms are functional in diploid, meiotic and haploid male germ cells, alpha4 being significantly upregulated during spermatogenesis. These results support the importance of alpha4 in male gamete differentiation and function.

Mammalian sperm translate nuclear-encoded proteins by mitochondrial-type ribosomes

It is widely accepted that spermatozoa are translationally silent. The present study demonstrates, for the first time, incorporation of labeled amino acids into polypeptides during sperm capacitation, which was completely inhibited by mitochondrial translation inhibitors but not by the cytoplasmic translation inhibitor. Unlike 80S cytoplasmic ribosomes, 55S mitochondrial ribosomes were present in polysomal fractions, indicating that these ribosomes are actively involved in protein translation in spermatozoa. Inhibition of protein translation significantly reduced sperm motility, capacitation and in vitro fertilization rate. Thus, contrary to the accepted dogma, nuclear genes are expressed as proteins in sperm during their residence in the female reproductive tract until fertilization.

Multiple functions of Na,K-ATPase in epithelial cells

The Na,K-adenosine triphosphatase (ATPase), or sodium pump, has been well studied for its role in the regulation of ion homeostasis in mammalian cells. Recent studies suggest that Na,K-ATPase might have multiple functions such as a role in the regulation of tight junction structure and function, induction of polarity, regulation of actin dynamics, control of cell movement, and cell signaling. These functions appear to be modulated by Na,K-ATPase enzyme activity as well as protein-protein interactions of the alpha and beta subunits. In this review we attempt to differentiate functions associated with enzyme activity and subunit interactions. In addition, the consequence of impaired Na,K-ATPase function or reduced subunit expression levels in kidney diseases such as cancer, tubulointerstitial fibrosis, and ischemic nephropathy are discussed.

Sodium/potasium ATPase (Na+, K+-ATPase) and ouabain/related cardiac glycosides: a new paradigm for development of anti- breast cancer drugs?

Prolonged exposure to 17beta-estradiol (E2) is a key etiological factor for human breast cancer. The biological effects and carcinogenic effects of E2 are mediated via estrogen receptors (ERs), ERalpha and ERbeta. Anti-estrogens, e.g. tamoxifen, and aromatase inhibitors have been used to treat ER-positive breast cancer. While anti-estrogen therapy is initially successful, a major problem is that most tumors develop resistance and the disease ultimately progresses, pointing to the need of developing alternative drugs targeting to other critical targets in breast cancer cells. We have identified that Na+, K+-ATPase, a plasma membrane ion pump, has unique/valuable properties that could be used as a potentially important target for breast cancer treatment: (a) it is a key player of cell adhesion and is involved in cancer progression; (b) it serves as a versatile signal transducer and is a target for a number of hormones including estrogens and (d) its aberrant expression and activity are implicated in the development and progression of breast cancer. There are several lines of evidence indicating that ouabain and related digitalis (the potent inhibitors of Na+, K+-ATPase) possess potent anti-breast cancer activity. While it is not clear how the suggested anti-cancer activity of these drugs work, several observations point to ouabain and digitalis as being potential ER antagonists. We critically reviewed many lines of evidence and postulated a novel concept that Na+, K+-ATPase in combination with ERs could be important targets of anti-breast cancer drugs. Modulators, e.g. ouabain and related digitalis could be useful to develop valuable anti-breast cancer drugs as both Na+, K+-ATPase inhibitors and ER antagonists.

The highly conserved cardiac glycoside binding site of Na,K-ATPase plays a role in blood pressure regulation

The Na,K-ATPase contains a binding site for cardiac glycosides, such as ouabain, digoxin, and digitoxin, which is highly conserved among species ranging from Drosophila to humans. Although advantage has been taken of this site to treat congestive heart failure with drugs such as digoxin, it is unknown whether this site has a natural function in vivo. Here we show that this site plays an important role in the regulation of blood pressure, and it specifically mediates adrenocorticotropic hormone (ACTH)-induced hypertension in mice. We used genetically engineered mice in which the Na,K-ATPase alpha2 isoform, which is normally sensitive to cardiac glycosides, was made resistant to these compounds. Chronic administration of ACTH caused hypertension in WT mice but not in mice with an ouabain-resistant alpha2 isoform of Na,K-ATPase. This finding demonstrates that the cardiac glycoside binding site of the Na,K-ATPase plays an important role in blood pressure regulation, most likely by responding to a naturally occurring ligand. Because the alpha1 isoform is sensitive to cardiac glycosides in humans, we developed mice in which the naturally occurring ouabain-resistant alpha1 isoform was made ouabain-sensitive. Mice with the ouabain-sensitive "human-like" alpha1 isoform and an ouabain-resistant alpha2 isoform developed ACTH-induced hypertension to greater extent than WT animals. This result indicates that the cardiac glycoside binding site of the alpha1 isoform can also mediate ACTH-induced hypertension. Taken together these results demonstrate that the cardiac glycoside binding site of the alpha isoforms of the Na,K-ATPase have a physiological function and supports the hypothesis for a role of the endogenous cardiac glycosides.

Na,K-ATPase Subunit Heterogeneity as a Mechanism for Tissue-Specific Ion Regulation

The Na,K-ATPase comprises a family of isozymes that catalyze the active transport of cytoplasmic Na+ for extracellular K+ at the plasma membrane of cells. Isozyme diversity for the Na,K-ATPase results from the association of different molecular forms of the alpha (alpha1, alpha2, alpha3, and alpha4) and beta (beta1, beta2, and beta3) subunits that constitute the enzyme. The various isozymes are characterized by unique enzymatic properties and a highly regulated pattern of expression that depends on cell type, developmental stage, and hormonal stimulation. The molecular complexity of the Na,K-ATPase goes beyond its alpha and beta isoforms and, in certain tissues, other accessory proteins associate with the enzyme. These small membrane-bound polypeptides, known as the FXYD proteins, modulate the kinetic characteristics of the Na,K-ATPase. The experimental evidence available suggests that the molecular and functional heterogeneity of the Na,K-ATPase is a physiologically relevant event that serves the specialized functions of cells. This article focuses on the functional properties, regulation, and the biological relevance of the Na,K-ATPase isozymes as a mechanism for the tissue-specific control of Na+ and K+ homeostasis.

Influence of cigarette smoking on spermatozoa via seminal plasma

Numerous investigations have been conducted on the relationship between cigarette smoking and male infertility, however, the exact molecular mechanisms are not well understood in most of the cases. Few studies have indicated the direct effect of seminal plasma (SP) [in different dilutions with phosphate buffer solution (PBS)] from smokers (SM) on the sperm functional parameters from nonsmokers (non-SM). The aim of this study was to provide evidence that cigarette smoking affects male fertility via altering the sperm quality. Our results indicated that exposure of spermatozoa from the non-SM to the SP from the SM yielded a significant reduction in the sperm motility and acrosome reaction and an elevation in the amount of malondialdehyde (MDA), in a certain time course. Exposure of spermatozoa from the SM to the SP from the non-SM or with PBS resulted in the nonsignificant improvement in the altered sperm functional parameters indicating removal of SM's SP and then subsequent reconstitution with physiological media could be of clinical significance in the various assisted reproductive technologies applied for SM. However, the detrimental effect of SM's SP on non-SM's spermatozoa was prominent. In addition, as spermatozoa in SM's SP are susceptible to peroxidative damages, men with such cells who wish to have children should especially benefit from quitting smoking.

Thallium-201 chloride (Tl-201) accumulation and Na+/K+-ATPase expression in tumours of the head and neck

OBJECTIVES

The purpose of this report was to evaluate the relationship between the tumour retention index of thallium-201 chloride (Tl-201) scintigraphy and the Na+/K+-ATPase expression in tumours of the head and neck.

METHODS

Tl-201 scintigraphy was performed in 146 patients (129 with malignant tumours, ten with benign tumours and seven with inflammation). The tumour retention index was obtained from the early and delayed dynamic Tl-201 scans. The Na+/K+-ATPase expression was evaluated immunohistochemically in 61 of 129 patients with malignant tumour. Furthermore, another 22 patients with benign tumour were evaluated immunohistochemically as a benign control. Comparison of the correlations between the grade of histopathological differentiation of tumour, the tumour retention index of Tl-201 scintigraphy and the Na+/K+-ATPase expression was performed.

RESULTS

The grade of histopathological differentiation of tumour, the tumour retention index of Tl-201 scintigraphy and the expression of Na+/K+-ATPase showed a good correlation indicating that Na+/K+-ATPase plays an important role in transportation for Tl-201 to go through the tumour cell membrane.

CONCLUSIONS

Na+/K+-ATPase is one of the most important factors for Tl-201 accumulation in tumour.

The human Na,K-ATPase alpha4 isoform is a ouabain-sensitive alpha isoform that is expressed in sperm

The Na,K-ATPase generates electrochemical gradients across the plasma membrane that are responsible for numerous cellular and physiological processes. The active Na,K-ATPase is minimally composed of an alpha and a beta subunit and families of isoforms for both subunits exist. Recent studies have identified a physiological role for the rat Na,K-ATPase alpha4 isoform in sperm motility. However, very little is known about the human Na,K-ATPase alpha4 isoform other than its genomic sequence and structure and its mRNA expression pattern. Here, the human alpha4 isoform of the Na,K-ATPase is cloned, expressed, and characterized. Full length cDNAs encoding the putative human alpha4 isoform of the Na,K-ATPase were identified from a number of ESTs and a protein product corresponding to this isoform was shown to be expressed from these cDNAs. The human Na,K-ATPase alpha4 isoform protein was found to be expressed in mature sperm in human testes sections and it is localized specifically to the principle piece of human sperm. In addition, the presence of the Na,K-ATPase alpha4 isoform is absent in immature testes however its expression appears coincident with sexual maturity. And finally, the human Na,K-ATPase alpha4 isoform was shown to be as sensitive to cardiac glycoside inhibition as the human Na,K-ATPase alpha1 isoform. Considering the important role of the rat Na,K-ATPase alpha4 isoform in rat sperm motility, the demonstration that the human alpha4 isoform is a sperm-specific protein localized to the flagellum suggests a role for the human Na,K-ATPase alpha4 isoform in human sperm physiology.