Changes in expression and activity levels of ecto-5'-nucleotidase/CD73 along the mouse female estrous cycle

AIM

Extracellular ATP and its hydrolysis product adenosine modulate various reproductive functions such as those requiring contraction, hormone synthesis and maintenance of fluid composition. Moreover, adenosine is a key molecule for sperm capacitation. Extracellular nucleotide and nucleoside levels are affected by cell surface ectonucleotidases, amongst which the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family is the most abundant and effective to hydrolyse ATP and ADP to AMP. In the female reproductive tract three members of this family have been recently identified: NTPDase1, NTPDase2 and NTPDase3 (Histochem. Cell Biol.131, 2009, 615). The purpose of the present study was to characterize in this system the expression profile of ecto-5'-nucleotidase (CD73), the enzyme generating adenosine from AMP.

METHODS

Immunological techniques and in situ enzymatic assays were used to characterize the ecto-5'-nucleotidase expression in the mouse female reproductive tract along the four stages of the estrous cycle, that were determined by vaginal smear examination.

RESULTS

Ecto-5'-nucleotidase was abundantly detected in the corpora lutea of the ovaries, as well as in several epithelia, such as that of oviducts, uterus and endometrial glands. Marked changes in endometrial ecto-5'-nucleotidase expression and activity along the estrous cycle are described, these being maximum at estrus phase, coinciding with optimal female sexual receptivity.

CONCLUSION

The adenosine generated thereby, besides other functions, might contribute to sperm capacitation, thus significantly influencing fertility.

Haplotype frequencies of 16 Y-chromosome STR loci in the Barcelona metropolitan area population using Y-Filer™ kit

Haplotype frequencies for 16 Y-chromosomal short tandem repeat (STR) loci, included in the Y-Filer kit, were determined in 247 unrelated healthy individuals from the Barcelona metropolitan area (Catalonia, NE Spain). After PCR amplification and denaturing PAGE electrophoresis, DYS456, DYS389I, DYS390, DYS389II, DYS458, DYS19, DYS385a/b, DYS393, DYS391, DYS439, DYS635, DYS392, Y GATA H4.1, DYS437, DYS438 and DYS448 loci were typed. The aim of this study is to evaluate the performance in our population of the 16 loci of the Y-chromosome present in the new Y-Filer commercial identification kit, and acquire haplotype frequencies for mathematic processing of the forensic diagnosis in our geographical working area. In this sample, all haplotypes were unique. From the forensic point of view, the combined polymorphisms of the Y-Filer kit provide a high diagnostic efficiency.

Ionic dependence of the velocity of release of ATP from permeabilized cholinergic synaptic vesicles

Evidence is provided to show that synaptic vesicles have an internal matrix. Suspensions of cholinergic synaptic vesicles isolated from the electric organ of Torpedo marmorata fish were permeabilized in solutions containing low concentrations of Na(+) or Ca(2+). The release of ATP from the vesicular matrix was 10 times more effective with Ca(2+) than with Na(+). We ascertained whether these two cations induced a different velocity of release of ATP from the matrix. The release of ATP was monitored with the chemiluminescent reaction of luciferin-luciferase. The light signal generated was the result of the kinetics of ATP release of the enzymatic reaction. To overcome the kinetics of the enzymatic reaction, the light records were deconvoluted. The actual kinetics of ATP release of vesicles containing Na(+) or Ca(2+) were coincident. To validate this result, comparison was made with ATP release from intact nerve terminals which were already deconvoluted. The results show that the real time course of release is longer than that obtained from synaptic vesicles. This was as expected given that the release of neurotransmitters is due to successive molecular steps of synaptic vesicle exocytosis.

The pharmacology of novel acetylcholinesterase inhibitors, (+/-)-huprines Y and X, on the Torpedo electric organ

The effects of the tacrine-huperzine A hybrid acetylcholinesterase inhibitors, (+/-)-12-amino-3-chloro-9-methyl-6,7,10,11-tetrahydro-7,11-methanocycloocta[b]quinoline hydrochloride ((+/-)-huprine Y) and (+/-)-12-amino-3-chloro-9-ethyl-6,7,10,11-tetrahydro-7,11-methanocycloocta[b]quinoline hydrochloride ((+/-)-huprine X), were tested on spontaneous synaptic activity by measuring the amplitude, the rise time, the rate of rise, the half-width and the area or the electrical charge of the miniature endplate potentials (m.e.p.ps) recorded extracellularly on Torpedo electric organ fragments. (+/-)-Huprine Y and (+/-)-huprine X at a concentration of 500 nM increased all the m.e.p.p. variables analyzed. The effect of (+/-)-huprine Y was smaller than that of (+/-)-huprine X for all the variables except for the rate of rise where there was no significant difference. The effects of these drugs were also tested on nicotinic receptors by analyzing the currents elicited by acetylcholine (100 microM) in Xenopus laevis oocytes, transplanted with membranes from Torpedo electric organ. Both drugs inhibited the currents in a reversible manner, (+/-)-huprine Y (IC(50)=452 nM) being more effective than (+/-)-huprine X (IC(50)=4865 nM). The Hill coefficient was 0.5 for both drugs. The inhibition of the nicotinic receptor was voltage-dependent and decreased at depolarizing potentials, and there was no significant difference in the effects between (+/-)-huprine Y and (+/-)-huprine X at concentrations near to their IC(50) values. At depolarizing potentials between -20 and +15 mV, these drugs did not have any detectable effect on the blockade of the nicotinic receptor. Both huprines increased the desensitization of the nicotinic receptors since the current closed quickly in the presence of the drugs, and there was no significant difference in this effect between (+/-)-huprine Y (500 nM) and (+/-)-huprine X (5 microM). We conclude that (+/-)-huprine Y and (+/-)-huprine X increase the level of acetylcholine in the synaptic cleft more effectively than tacrine. The interaction of (+/-)-huprine X with nicotinic receptors is weaker than that of (+/-)-huprine Y, suggesting that (+/-)-huprine X would be more specific to maintain the extracellular acetylcholine concentration.

Trk neurotrophin receptor family immunoreactivity in rat and human pituitary tissues

Several lines of evidence suggest that neurotrophins may be involved in pituitary function. By immunocytochemical methods we analyzed the cellular distribution of their functional receptors in the pituitary gland. In the rat pituitary gland Trks were differentially distributed. Punctate immunoreactivity for TrkA was observed within the neural lobe, whereas numerous nerve endings were immunostained for TrkB and TrkC in the intermediate lobe. Endocrine cells of the intermediate lobe exhibited intense immunoreactivity for the three Trks, whereas scattered endocrine cells of the anterior lobe displayed a robust immunostaining for TrkC. In addition, TrkA and TrkB immunoreactivity was located in normal and neoplastic endocrine cells from human pituitary adenomas. The differential distribution of Trks in the hypophysis suggests a potential role of different neurotrophins in pituitary functions.

8-Azido-nucleotides as substrates of Torpedo electric organ apyrase. effect of photoactivation on apyrase activity

Ecto-apyrase is a widespread enzymatic activity that hydrolyses tri- and diphosphonucleotides and consequently controls the amount of available extracellular ATP and ADP. In the nervous system, purines have important neuromodulatory actions, acting at pre- and postsynaptic sites, and consequently, ecto-apyrase may play an indirect role in the modulation of nucleotide- and nucleoside-mediated processes. The azido-nucleotides have been largely employed to characterize the nucleotide binding sites of several proteins. In the present work the azido-nucleotides are described as putative substrates for apyrase activity in a presynaptic plasma membrane preparation (PSPM) from the Torpedo electric organ. Both 8-N3-ATP and 8-N3-ADP were hydrolyzed in a calcium-dependent manner showing Vmax of 23.8 +/- 4.8 and 14.5 +/- 3 U/mg of protein, and Km values (in microM) of 116 +/- 39 and 119 +/- 4, respectively. Vmax for calcium-dependent hydrolysis of ATP and ADP were significantly higher: 59.2 +/- 3.9 and 32.9 +/- 3.5 U/mg of protein respectively, while Km values did not show any significant differences regarding azido-nucleotides: 83.8 +/- 12 microM for Ca2+-ATP and 121 +/- 34 microM for Ca2+-ADP. The photoactivation of the PSPM in the presence of the azido-derivatives results in an irreversible inactivation of apyrase activity, showing an IC50 of 10 microM and a maximal inhibitory effect of 38 and 60% on Ca2+-ATPase and Ca2+-ADPase activities. Apyrase was protected from inactivation by nucleotides that are natural substrates for this enzymatic activity and also by AMP while adenosine did not protect from apyrase inhibition.

Action of suramin upon ecto-apyrase activity and synaptic depression of Torpedo electric organ

1. The role of ATP, which is co-released with acetylcholine in synaptic contacts of Torpedo electric organ, was investigated by use of suramin. Suramin [8-(3-benzamido-4-methylbenzamido)naphthalene-1,3,5-trisulphoni c acid], a P2 purinoceptor antagonist, potently inhibited in a non-competitive manner the ecto-apyrase activity associated with plasma membrane isolated from cholinergic nerve terminals of Torpedo electric organ. The Ki was 30 microM and 43 microM for Ca(2+)-ADPase and Ca(2+)-ATPase respectively. 2. In Torpedo electric organ, repetitive stimulation decreased the evoked synaptic current by 51%. However, when fragments of electric organ were incubated with suramin the evoked synaptic current declined by only 14%. Fragments incubated with the selective A1 purinoceptor antagonist, DPCPX, showed 5% synaptic depression. 3. The effects of suramin and DPCPX on synaptic depression were not addictive. Synaptic depression may thus be linked to endogenous adenosine formed by dephosphorylation of released ATP by an ecto-apyrase. The final effector in synaptic depression, adenosine, acts via the A1 purinoceptor. 4. ATP hydrolysis is prevented in the presence of suramin. It slightly increased (20%) the mean amplitude of spontaneous miniature endplate currents. The frequency distribution of the amplitude of spontaneous events was shifted to the right, indicating that ATP, when not degraded, may modulate the activation of nicotinic acetylcholine receptors activated by the quantal secretion of acetycholine.

Inhibition of ATP-diphosphohydrolase(apyrase) of Torpedo electric organ by 5'-p-fluorosulfonylbenzoyladenosine

It has been shown previously that ATP is released into extracellular space from pre- and postsynaptic sources in peripheral synapses. The extracellular metabolism of ATP is likely to affect nucleotide- and nucleoside-mediated regulation of neurotransmission. The enzymes responsible for ATP breakdown are nucleotidases whose active site faces the extracellular space. ATPase and ADPase Ca(2+)-dependent activities were characterized in presynaptic plasma membrane preparation from the electric organ of Torpedo. Features described were in accordance with the presence of an ATP-diphosphohydrolase (apyrase EC 3.6.1.5) in this fraction. Active site studies using the affinity label 5'-fluorosulfonylbenzoyladenosine were performed on Torpedo apyrase. ATPase and ADPase Ca(2+)-dependent activities were inhibited with 5'-fluorosulfonylbenzoyladenosine. From this study it is concluded: (1) 5'-fluorosulfonylbenzoyladenosine binds specifically to the active site of apyrase. (2) Divalent cations accelerate the apyrase inactivation rate. (3) Divalent cations are not required for the binding of either the substrate or the inhibitor to the active site. (4) The apyrase active site is more specific for highly phosphorylated nucleotides. The results presented may be extrapolated to apyrases from other sources. The importance of this enzyme and its regulation are discussed.