Zn(II) transport and distribution in rat spermatids

Zinc Transport Differs in Rat Spermatogenic Cell Types and Is Affected by Treatment with Cyclophosphamide

Adequate zinc levels are required for proper cellular functions and for male germ cell development. Zinc transport is accomplished by two families of zinc transporters, the ZIPs and the ZnTs, that increase and decrease cytosolic zinc levels, respectively. However, very little is known about zinc transport in the testis. Furthermore, whether cytotoxic agents such as cyclophosphamide (CPA), a known male germ cell toxicant, can affect zinc transport and homeostasis is unknown. We examined zinc transporter expression and zinc transport in pachytene spermatocytes (PS) and round spermatids (RS) in a normal state and after exposure to CPA. We observed differences in the expression of members of the ZnT and ZIP families in purified populations of PS and RS. We also observed that RS accumulate more zinc over time than PS. The expression of many zinc binding genes was altered after CPA treatment. Interestingly, we found that the expression levels of ZIP5 and ZIP14 were increased in PS from animals treated daily with 6 mg/kg CPA for 4 wk but not in RS. This up-regulation led to an increase in zinc uptake in PS but not in RS from treated animals compared to controls. These data suggest that CPA treatment may alter zinc homeostasis in male germ cells leading to an increased need for zinc. Altered zinc homeostasis may disrupt proper germ cell development and contribute to infertility and effects on progeny.

Exposure of rainbow trout milt to mercury and cadmium alters sperm motility parameters and reproductive success

In the current work, seminal plasma was used for the first time as an incubation medium for monitoring short-time exposure effects of sublethal concentrations of mercury and cadmium ions on rainbow trout sperm. Sperm motility parameters (CASA) and hatching rates were used as gamete quality markers. Additionally live/dead sperm viability test and comet assay of DNA fragmentation were performed. We demonstrated that computer-assisted sperm motility analysis (CASA) may serve as a predictor of reproductive success, when milt contaminated with heavy metals is used. Results presented in this study demonstrate that mercury ions altered sperm motility characteristics at 1-10 mg Hg2+/l and 10 mg Cd2+/l and hatching rates at 10 mg Hg2+/l and 10 mg Cd2+/l after 4h of exposure. Although mercury ions affected sperm motility parameters immediately after dilution with milt as well as at 4h of exposure, no differences in sperm motility parameters were found between intact and mercury-treated milt after 24h of exposure. Our results suggest that rainbow trout seminal plasma has a protective role against the toxic effects of mercury ions of rainbow trout sperm motility.

Presynaptic α1 Adrenergic Receptors Differentially Regulate Synaptic Glutamate and GABA Release to Hypothalamic Presympathetic Neurons

The hypothalamic paraventricular nucleus (PVN) neurons that project to the spinal intermediolateral cell column and brainstem are important for the control of sympathetic outflow. Stimulation of alpha(1) adrenergic receptors in the PVN increases sympathetic outflow, but the cellular mechanisms remain unclear. In this study, we determined the role of alpha(1) adrenergic receptors in the regulation of glutamatergic and GABAergic synaptic inputs to spinally projecting PVN neurons. Whole-cell and cell-attached patch-clamp recordings were performed on retrogradely labeled PVN-spinal neurons in rat brain slices. Bath application of 10 to 100 microM phenylephrine, an alpha(1) adrenergic receptor agonist, significantly increased the frequency of spontaneous excitatory postsynaptic currents in a concentration-dependent manner. This effect was blocked by the alpha (1)adrenergic receptor antagonists prazosin or corynanthine. Phenylephrine also significantly increased the frequency of miniature excitatory postsynaptic currents (mEPSCs) but not the amplitude and decay constant of mEPSCs. Furthermore, activation of alpha(1) adrenergic receptors with phenylephrine or cirazoline significantly decreased the frequency of spontaneous inhibitory postsynaptic currents and miniature inhibitory postsynaptic currents, and this effect also was blocked by corynanthine. In addition, 50 microM phenylephrine significantly increased the firing rate of 13 labeled PVN neurons from 3.16 +/- 0.42 to 5.83 +/- 0.65 Hz. However, phenylephrine failed to increase the firing of most labeled PVN neurons in the presence of GABA(A) and ionotropic glutamate receptor antagonists. Thus, these data suggest that activation of alpha (1)adrenergic receptors increases the excitability of PVN presympathetic neurons primarily through augmentation of glutamatergic tone and attenuation of GABAergic inputs.

Kinetics, molecular basis, and differentiation of L-lactate transport in spermatogenic cells

Round spermatid energy metabolism is closely dependent on the presence of L-lactate in the external medium. This L-lactate has been proposed to be supplied by Sertoli cells in the seminiferous tubules. L-Lactate, in conjunction with glucose, modulates intracellular Ca(2+) concentration in round spermatids and pachytene spermatocytes. In spite of this central role of L-lactate in spermatogenic cell physiology, the mechanism of L-lactate transport, as well as possible differentiation during spermatogenesis, has not been studied in these cells. By measuring radioactive L-lactate transport and intracellular pH (pH(i)) changes with pH(i) fluorescent probes, we show that these cells transport L-lactate using monocarboxylate-H(+) transport (MCT) systems. RT-PCR, in situ mRNA hybridization, and immunocyto- and immunohistochemistry data show that pachytene spermatocytes express mainly the MCT1 and MCT4 isoforms of the transporter (intermediate- and low-affinity transporters, respectively), while round spermatids, besides MCT1 and MCT4, also show expression of the MCT2 isoform (high-affinity transporter). These molecular data are consistent with the kinetic data of L-lactate transport in these cells demonstrating at least two transport components for L-lactate. These separate transport components reflect the ability of these cells to switch between the generation of glycolytic L-lactate in the presence of external glucose and the use of L-lactate when this substrate is available in the external environment. The supply of these substrates is regulated by the hormonal control of Sertoli cell glycolytic activity.

Metal ions and human sperm mannose receptors

Zinc and lead concentrations were measured in seminal plasma from fertile donors, infertile men with varicocoele and men undergoing work-ups for in vitro fertilization. Ejaculated spermatozoa from these subjects were incubated in vitro with various metal ions and/or dibromoethane and dibromochloropropane. Mannose receptor expression was correlated with metal and toxicant levels. Sperm distributions of potassium channels were compared with lead ions and calcium channels with zinc ions. Mannose receptor expression by capacitated spermatozoa increased linearly with seminal plasma zinc levels, and correlated inversely with lead levels. Cobalt had no effect on mannose receptor expression, but nickel had a concentration-dependent biphasic effect. Mannose receptor expression was not affected by dibromoethane and dibromochloropropane if the cholesterol content of the sperm membrane was high, but mannose receptor expression was decreased in low cholesterol spermatozoa by exposures below estimated permissive exposure limits. Potassium channels and lead ions co-localized over the entire head of human spermatozoa, while both calcium channels and zinc ions were confined to the equatorial segment of the head. Mannose receptor expression on the external surface of the human sperm plasma membrane is a biomarker for the effects of transition and heavy metals and organic toxicants on sperm fertility potential.

Central nervous system norepinephrine metabolism in hypertension

Although the pivotal role played by the brain in the maintenance of optimal physiologic and psychologic health has long been recognized, methods for the direct examination of human central nervous system processes have only recently been developed. A growing body of evidence indicates that central nervous systemmonoaminergic cell groups, in particular those utilizing norepinephrine as their neurotransmitter, participate in the excitatory regulation of the sympathetic nervous system and the development of the hypertensive state.

Neuropeptide Y prevents agonist-stimulated increases in contractility

Neuropeptide Y has been shown to inhibit contractility in the rat heart. Although the reasons for this effect are not known, it is possible that postsynaptic adrenergic mechanisms involving neuropeptide Y may be responsible. To ascertain whether this neuromodulatory effect is possible for decreasing contractility, we investigated the effect of neuropeptide Y on agonist-stimulated contractility of the isolated rat myocardium. Receptor binding studies of purified cardiac membranes showed that incubating membrane in the presence of neuropeptide Y (10(-7) mol/L) decreased the number of alpha-/beta-adrenoceptor binding sites without affecting the affinity of these receptors. Isolated hearts perfused with phenylephrine (10(-5) to 10(-10) mol/L) or isoproterenol (10(-5) to 10(-10) mol/L) in a nonrecirculating Langendorff setup demonstrated a significant increase in contractility over control values, whereas no change in contractility was observed when the hearts were perfused with neuropeptide Y (10(-7) mol/L). However, in the presence of both agonist and neuropeptide Y the increase in contractility previously seen with agonist alone was not evident. Comparisons made with hearts taken from aortic banded rats yielded similar results. Although neuropeptide Y itself was ineffective in decreasing contractility, it prevented the agonists from stimulating contractility when perfused together. We conclude that neuropeptide Y does not directly decrease contractility but prevents agonist-stimulated increases in contractility through alpha-/beta-adrenoceptor pathways. This neuromodulatory effect of neuropeptide Y is unchanged in situations of increased sympathetic activity, such as hypertension.