Tetrandrine blocks voltage-dependent calcium entry and inhibits the bradykinin-induced elevation of intracellular calcium in NG108-15 cells.

Tetrandrine, a plant alkaloid used in Chinese traditional medicine blocks voltage-dependent Ca2+ entry in NG108-15 cells as assessed using fura-2 microfluorimetry. Cells were depolarized with 50 mM KCI for one min resulting in a transient increase in the 340/380 nm ratio of fura 2 fluorescence, indicative of an increase in [Ca2+]i. Treatment of the same cell with 100 microM tetrandrine for seven min followed by an identical K+ depolarization blocked the increase in 340/380 nm fluorescence ratio. Washing with tetrandrine-free solutions for 20 min partially reversed this effect. Bradykinin (Bk) induces transient and repetitive increases in [Ca2+] due to release of Ca2+ from intracellular stores via activation of the inositol trisphosphate (IP3) second messenger system. After pre-treatment with 100 microM tetrandrine for seven min, the Bk (1 microM, 1 min) response was significantly reduced. Likewise, the effect of angiotensin II (AT-II), which also causes an IP3 dependent release of Ca2+ from intracellular stores, was ablated by tetrandrine. Thus, in addition to block of voltage-dependent Ca2+ channels, tetrandrine also caused disturbances in intracellular Ca2+ signalling.

The regional distribution of cadmium in the brains of orally exposed adult rats.

Cadmium (Cd) levels were measured in 13 dissected brain regions of adult male rats from 3 treatment groups. Rats (approximately 200 g each) were each fed 10 g/day of diets containing either 20 or 100 micrograms/g (ppm) Cd or control diet to which no Cd was added but contained approximately 0.35 ppm Cd. After 67 days of treatment, the brain of each rat was removed and each was dissected into 13 anatomical regions including olfactory bulbs, frontal cortex, rest of cortex, corpus callosum, hippocampus, amygdalae, corpus striatum, colliculum, tegmentum, thalamus, hypothalamus, pons-medulla, and cerebellum. Cd residues (dry weight) in each sample were determined by flameless atomic absorption spectrophotometry. With exception of the thalamus and olfactory bulbs, each of the brain regions of the 100 ppm Cd rats had more Cd than did those from either the 20 ppm Cd rats or controls which did not differ. There was evidence of selective accumulation of Cd within the olfactory bulbs of control and treated animals. This selective accumulation may be related to anosmia reported in workers with industrial exposure to Cd.

Dietary administration of nickel: effects on behavior and metallothionein levels.

Adult male rats were fed either 0, 10, or 20 mg Ni/kg body weight (as NiCl2) via a 10 g daily food ration. Following 14 days of exposure, animals were trained over a period of 61 days to lever press for food on a VI-2 operant training schedule while continuing to experience the indicated daily doses. Those rats treated with 20 mg/kg Ni lever pressed at a significantly lower rate than controls. Group 10 mg/kg subjects were not significantly different on this behavioral measure than control subjects. Atomic absorption spectrophotometric analysis revealed a dose/response accumulation of Ni in the kidney, but analyses of blood, bone, brain, hair, small intestine, liver, and testes did not show differential agent accumulations. Neither hepatic nor renal metallothionein levels were increased above control levels. These findings were discussed within the framework of other recent behavioral and biochemical studies of heavy metal toxicity.

The effects of oral cadmium exposure on passive avoidance performance in the adult rat.

Step-down passive avoidance acquisition and 24 h retention performance were examined in adult rats given daily doses of either 0, 1, or 5 mg/kg cadmium (Cd) (as CdCl2) via the diet. Results indicated that subjects exposed to the 5 mg/kg Cd diet were less likely to step off a safe platform onto an electrified grid floor than controls. The 1 mg/kg subjects did not differ from controls on this acquisition task. None of the groups showed differential performances on a retention test administered 24 h after acquisition training. These results are discussed in terms of recent claims that Cd exposure enhances emotional reactivity in animals.

Search for Lorentz and CPT violation effects in Muon spin precession.

The spin precession frequency of muons stored in the (g-2) storage ring has been analyzed for evidence of Lorentz and CPT violation. Two Lorentz and CPT violation signatures were searched for a nonzero delta omega a(=omega a mu+ - omega a mu-) and a sidereal variation of omega a mu+/-). No significant effect is found, and the following limits on the standard-model extension parameters are obtained: bZ = -(1.0+/-1.1) x 10(-23) GeV; (m mu dZ0 + HXY)=(1.8+/-6.0) x 10(-23) GeV; and the 95% confidence level limits b perpendicular mu+ <1.4 x 10(-24) GeV and b perpendicular mu- <2.6 x 10(-24) GeV.

Improved measurement of the positive-muon lifetime and determination of the Fermi constant.

The mean life of the positive muon has been measured to a precision of 11 ppm using a low-energy, pulsed muon beam stopped in a ferromagnetic target, which was surrounded by a scintillator detector array. The result, tau(micro)=2.197 013(24) micros, is in excellent agreement with the previous world average. The new world average tau(micro)=2.197 019(21) micros determines the Fermi constant G(F)=1.166 371(6)x10(-5) GeV-2 (5 ppm). Additionally, the precision measurement of the positive-muon lifetime is needed to determine the nucleon pseudoscalar coupling g(P).

Mechanisms of methylmercury-induced neurotoxicity.

Mercury in both organic and inorganic forms is neurotoxic. Methylmercury (MeHg) is a commonly encountered form of mercury in the environment. Early electrophysiological experiments revealed that MeHg potently affects the release of neurotransmitter from presynaptic nerve terminals. Recently, the hypothesis that these alterations may be mediated by changes in the intracellular concentration of Ca2+ ([Ca2+]i) has been supported. MeHg alters [Ca2+]i by at least two mechanisms. First, it disrupts regulation of Ca2+ from an intracellular Ca2+ pool and second, it increases the permeability of the plasma membrane to Ca2+. MeHg also blocks plasma membrane voltage-dependent Ca2+ and Na+ channels in addition to activating a nonspecific transmembrane cation conductance. Chronic MeHg exposure results in ultrastructural changes and accumulation of MeHg within mitochondria. In vitro, MeHg inhibits several mitochondrial enzymes and depolarizes the mitochondria membrane subsequently reducing ATP production and Ca2+ buffering capacity. Inhibition of protein synthesis is observed after in vivo or in vitro exposures of MeHg and may be an early effect of MeHg. Thus, the early cellular effects of exposure to MeHg are diverse and cell damage likely occurs by more than one mechanism, the effects of which may be additive or synergistic.

Differentiation between alterations in plasma and mitochondrial membrane potentials in synaptosomes using a carbocyanine dye.

The cationic potentiometric fluorescent probe 3,3'-diethylthiadicarbocyanine iodide [DiS-C2(5)] was used in synaptosomes to assess the relative contributions of plasma and mitochondrial membrane potentials (psi p and psi m, respectively) to overall fluorescence. Addition of synaptosomes to media containing 0.5 microM dye caused a decrease in fluorescence intensity due to dye accumulation, which equilibrated usually within 5 min. Depolarization of mitochondria by combined treatment with cyanide and oligomycin increased fluorescence by 42%, indicating significant prior accumulation of dye into intrasynaptosomal mitochondria. psi p was calculated to be -54 mV and was not altered significantly by prior depolarization of psi m with cyanide and oligomycin (hereafter referred to as "poisoned" synaptosomes). Similarly, the linear relationship between dye fluorescence and psi p was not altered by depolarization of psi m. Valinomycin, a K+ ionophore, caused a psi p-dependent increase in fluorescence in control (nonpoisoned) synaptosomes, but did not alter fluorescence of poisoned synaptosomes except when the extracellular concentration of K+ ([K+]e) was 2 mM, in which case valinomycin hyperpolarized psi p by about 5 mV. The pore-forming antibiotic gramicidin depolarized both psi p and psi m maximally. Under these conditions, Triton X-100 further increased fluorescence by 40%, indicating significant dye binding to synaptosomal components. In poisoned synaptosomes depolarized by 75 mM K+, gramicidin caused a decrease in fluorescence intensity (hyperpolarization of psi p). The organic solvent dimethyl sulfoxide, used as a vehicle for the hydrophobic ionophores, had voltage-dependent effects on psi p and psi m.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative action of methylmercury and divalent inorganic mercury on nerve terminal and intraterminal mitochondrial membrane potentials.

Both methylmercury (MeHg) and inorganic divalent mercury (Hg++) alter the flux of ions and small molecules across nerve terminal membranes by mechanisms that may involve membrane depolarization. We compared the effects of MeHg and Hg++ on plasma (psi p) and mitochondrial membrane potentials (psi m) in synaptosomes using the potentiometric carbocyanine dye 3,3'-diethylthiadicarbocyanine iodide [diS-C2(5)]. Both mercurials (1-20 microM) produced concentration-dependent increases in dye fluorescence after 5 min of exposure which were not altered by removal of Ca++ from the medium. To determine directly effects of mercurials on psi p, predepolarization of psi m using NaN3 and oligomycin was necessary. Under this condition, MeHg- and Hg(++)-induced increases in fluorescence were associated with depolarization of psi p. A second approach was used to assess changes in psi p. In synaptosomes, the magnitude of the increase in fluorescence resulting from depolarization of psi p with a stimulus of constant intensity is a function of the resting psi p. The fluorescence response to depolarization of synaptosomes previously exposed to either MeHg or Hg++ (1-20 microM each) was reduced in a concentration-dependent manner relative to mercury-free controls. The concentration-dependent depolarization of psi p calculated in this manner correlated (r = 0.958) with calculations of psi p using direct measurements of increases in fluorescence intensity. MeHg- and Hg(++)-induced depolarizations were not altered by lowering Na+e or by the addition of the Na+ and Ca++ channel blockers tetrodotoxin and Co++, respectively. Thus, the effects of these two neurotoxic mercurials on synaptosomal membrane potentials were similar with respect to their loci but differed in magnitude.(ABSTRACT TRUNCATED AT 250 WORDS)

Nifedipine and tetrodotoxin delay the onset of methylmercury-induced increase in [Ca2+]i in NG108-15 cells.

Methylmercury (MeHg) causes a multiphasic disruption of intraneuronal cation regulation. Release of Ca2+ from internal stores and entry of extracellular Ca2+ (Ca2+e) contribute to the temporally distinct early (first Ca2+ phase) and late (second Ca2+ phase) components of increased intracellular Ca2+ concentration ([Ca2+]i). The present study was designed to explore the mechanisms mediating the second Ca2+ phase. Fluorescence intensity was monitored from single NG108-15 cells loaded with fura-2 before and during acute application of 2 microM MeHg. Nifedipine (1 or 10 microM but not 0.1 microM) significantly delayed the time-to-onset of the second Ca2+ phase. Nifedipine (1 microM but not 0.1 microM) also caused a concentration-dependent delay in the onset of both the first Ca2+ phase which is independent of Ca2+e and the elevation of non-Ca2+ cation (non-Ca2+ phase). The L-type dihydropyridine (DHP) Ca2+ channel agonist Bay K-8644 (10 nM) had no effect on the time-to-onset of the second Ca2+ phase. Neither the N-type Ca2+ channel blocker omega-conotoxin GVIA (up to 1 microM) nor the nonselective Ca2+ channel blocker Ni2+ (1 mM) altered the time-to-onset of the second Ca2+ phase. Removal of Na+e or addition of the voltage-dependent Na+ channel antagonist tetrodotoxin (TTX, 1 microM) significantly delayed the onset of the second Ca2+ phase. In a manner similar to that for 1 microM nifedipine, TTX also delayed the onset of the other phases. Thus, we hypothesize that MeHg depolarizes the plasma membrane leading to an increase in the activation of voltage-dependent Na+ and Ca2+ channels which promotes, directly or indirectly, the influx of Ca2+ during the second Ca2+ phase.

Methylmercury mobilizes Ca++ from intracellular stores sensitive to inositol 1,4,5-trisphosphate in NG108-15 cells.

Fluorescence intensity was monitored from individual NG108-15 cells loaded with the Ca(++)-selective probe fura-2, and exposed to 2 microM methylmercury (MeHg). The initial effect of 2 microM MeHg was an elevation in intracellular Ca++ concentration ([Ca++]i), which was not blocked by lowering extracellular Ca++ (Ca++e), nifedipine (0.1 microM) or by Ni++ (1 mM). Addition of 100 microM Mn++ to Ca(++)-containing medium did not alter fluorescence intensity at either the Ca(++)-insensitive excitation wavelength of 360 nm or the Ca(++)-sensitive wavelength of 380 nm. Depolarization with K+ decreased the intensity at both wavelengths, indicating Mn++ entry. In the presence of Mn++, MeHg decreased the 380 nm, but not the 360 nm signal. Bradykinin (Bk) caused a transient increase in the fluorescence ratio, which was blocked by the endoplasmic reticulum Ca(++)-adenosine triphosphatase inhibitor thapsigargin. Pretreatment with Bk and thapsigargin reduced significantly the increase in ratio induced by MeHg from 21.9 +/- 3.4 to 6.9 +/- 1.8% of base line. Bk had no effect when applied after MeHg. Caffeine reduced the Bk-induced increase in [Ca++]i and the MeHg-induced increase in ratio from 21.9 +/- 3.4 to 9.0 +/- 2.1%. Thus, Bk, caffeine and MeHg all appear to release a common pool of intracellular calcium (Ca2+i). When applied after MeHg, Bk increased inositol 1,4,5-trisphosphate (IP3) by 305 +/- 27% compared to 270 +/- 29% in controls. Thus, MeHg did not induce Ca++ release by IP3 generation, nor did it block the effects of Bk by interfering with IP3 synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Methylmercury increases intracellular concentrations of Ca++ and heavy metals in NG108-15 cells.

To determine if methylmercury (MeHg) increased [Ca++]i in intact neuron-like cells, we initiated studies using fluorescence microscopy of single NG108-15 cells preloaded with fura-2. Whereas at 0.5 microM, MeHg had no effect on the ratio of fura-2 fluorescence at 340/380 nm, at 2 and 5 microM it produced a biphasic increase in this ratio. The initial phase increase was sustained; its time to onset was concentration-dependent whereas its maximum increase was not. This phase likely consists of both intra- and extracellular components inasmuch as removal of extracellular Ca++ reduced but did not eliminate the increase. Continued exposure to MeHg resulted in a further pronounced increase in fluorescence ratio, but only in the presence of extracellular Ca++. The time to onset of this second phase was also concentration-dependent. In Ca(++)-containing, but not Ca(++)-deficient medium, the second phase increase in fluorescence ratio was followed by loss of fura-2 from the cells. Both 2 and 5 microM, but not 0.5 microM MeHg, depolarized the mitochondrial membrane potential (psi m) as measured by loss of preloaded rhodamine 123 from the mitochondria. The latency of this effect was concentration-dependent, but the maximum amplitude was not. Removal of extracellular Ca++ had no effect on the initial changes in rhodamine 123 fluorescence produced by MeHg, but did retard subsequent loss of dye from the cells. The onset as well as peak amplitude of the initial MeHg-induced increase in fura-2 fluorescence ratio occurred before changes in psi m. In the absence of MeHg, depolarization of psi m by the combination of sodium azide and oligomycin failed to elicit a significant increase in [Ca++]i, but did reduce the initial increase in fura-2 fluorescence ratio produced by 2 microM MeHg independent of extracellular Ca++. MeHg increased fura-2 fluorescence measured at the Ca(++)-insensitive excitation wavelength of 360 nm. This effect did not coincide with alterations in rhodamine 123 fluorescence and was inhibited by the cell-permeant heavy metal chelator N,N,N',N'-tetrakis-(2-pyridylmethyl)ethylenediamine, but not the cell-impermeant chelator diethylenetriaminepentaacetic acid. This suggests that the initial phase, extracellular Ca(++)-independent changes in fura-2 fluorescence were due to increases in the intracellular concentration of endogenous cations other than Ca++. Thus, MeHg altered fura-2 fluorescence in these cells in a concentration- and time-dependent fashion. The initial effect involved alterations in intracellular cation buffering as well as increased permeability of the plasma membrane to Ca++.(ABSTRACT TRUNCATED AT 400 WORDS)

Methylmercury alters intrasynaptosomal concentrations of endogenous polyvalent cations.

The effects of the neurotoxic organomercurial methylmercury (MeHg) on intrasynaptosomal polyvalent cation concentrations were examined using fura-2. In the presence of extracellular Ca2+ (Ca2+e), MeHg caused a concentration-dependent, biphasic elevation in the ratio of fluorescence intensity at the emission wavelength of 505 nm following excitation at 340 and 380 nm (340/380 nm ratio). The first phase was independent of Ca2+e and complete within 5 sec. The second phase was dependent upon Ca2+e and was not complete within 6 min. MeHg increased the synaptosomal membrane permeability to Mn2+, suggesting that the second phase was due to influx of Ca2+e. Ruthenium red (20 microM), mitochondrial depolarization (10 mM NaN3 plus 4 micrograms/ml oligomycin), thapsigargin (1 microM), or caffeine (40 mM) did not elevate [Ca2+]i or alter the response of the synaptosomes to MeHg. Upon closer inspection, we noticed that MeHg simultaneously increased the fluorescence intensity at the excitation wavelengths of 340 and 380 nm and at the Ca(2+)-insensitive excitation wavelength of 360 nm. Pretreatment of synaptosomes with the cell-permeant heavy metal chelator TPEN (50 microM) blocked the MeHg-induced elevations in the 360-nm intensity and the 340/380 nm ratio. TPEN given after MeHg reversed the elevations in the 360-nm intensity. The cell-impermeant heavy metal chelator DTPA (150 microM) had no effect. We conclude that MeHg disrupts polyvalent cation homeostasis by at least two mechanisms. The first involves release of endogenous non-Ca2+ polyvalent cations, while the second is due to increased Ca2+ permeability of the plasma membrane.

Inhibition of mitochondrial Ca2+ release diminishes the effectiveness of methyl mercury to release acetylcholine from synaptosomes.

The interaction of methyl mercury (MeHg) with nerve-terminal mitochondria as a potential mechanism for its effects on the release of acetylcholine (ACh) was studied using rat brain synaptosomes. The primary goal was to assess the relative contribution of extracellular Ca2+ and Ca2+ released from nerve-terminal mitochondria to the previously described stimulatory effects of MeHg on spontaneous release of ACh. A secondary goal was to address possible mechanisms by which MeHg might interact with nerve-terminal mitochondria to elicit Ca2+ discharge and subsequent release of ACh. MeHg depressed the high-affinity uptake of [3H]choline into synaptosomes by approximately 25 and 45% when synaptosomes were incubated with [3H]choline in the presence of 10 and 100 microM MeHg, respectively. In Ca(2+)-containing solutions, 10 and 100 microM MeHg increased the release of [3H]ACh from [3H]choline-loaded synaptosomes by 10 and 30%, respectively; this effect was maximal at 10 sec. Excluding Ca2+ from the reaction medium diminished the effectiveness of both 10 and 100 microM MeHg for inducing [3H]ACh release by about 30 and 25%, respectively, from that of Ca(2+)-containing solutions; however, significant increases still occurred in nominally Ca(2+)-free solutions. Ruthenium red (RR), an inhibitor of mitochondrial Ca2+ transport, was tested for its ability to disrupt MeHg-induced release. RR alone increased [3H]ACh release by 8-10 and 10-13% at 20 and 60 microM, respectively. RR-induced release was attenuated only slightly in Ca(2+)-free solutions. Preincubation of [3H]choline-loaded synaptosomes with RR reduced the stimulatory effect of MeHg on release of [3H]ACh both in the presence and in the absence of Ca2+. The fluorescent potentiometric carbocyanine dye diS-C2(5) was used to assess the ability of RR to prevent MeHg-induced depolarization of intrasynaptosomal mitochondria. RR (20 microM) itself did not depolarize the mitochondrial membrane potential, nor did it prevent MeHg from depolarizing the mitochondria. The results indicate that extracellular Ca2+ contributes only partially to MeHg-induced spontaneous release of ACh. The results with RR suggest that MeHg interacts with mitochondria to induce release of bound intraterminal Ca2+ stores, resulting ultimately in stimulated release of ACh. The ability of RR to prevent release of mitochondrial Ca2+ and, subsequently, ACh is not due to prevention of access of MeHg to the mitochondria, nor to stabilization of the mitochondrial membrane. Finally, MeHg reduces choline uptake into nerve terminals. Thus, MeHg could interfere with cholinergic neurotransmission by affecting the regulatory step in ACh synthesis and by increasing the spontaneous release of transmitter.(ABSTRACT TRUNCATED AT 400 WORDS)

Tolerance and effect of chronic dietary cobalt on sheep.

Degeneration and necrosis of the testes and reduced spermatogenesis were recently observed in rats after prolonged intake of dietary cobalt (Co). The objective of the present study was to evaluate the effect of chronic Co intake on testicular and other tissues in sheep. Adult cross-bred rams were dosed daily for 70 days with gelatin capsules containing either 0, 3.0, or 4.5 mg Co/kg body weight. The Co dosages were increased on days 71 to 109 to 0, 10.0 and 15.0 mg Co/kg. Blood and serum samples were collected weekly and the rams were submitted to necropsy on day 109. Tissues were evaluated for histopathological changes and tissue Co residues and testicular spermatid reserves were determined. Highly significant (P less than 0.005) increases in Co levels were present in the blood, liver, kidney and testes of the treated rams. Neither gross nor microscopic lesions were observed in the testes or other tissues. Spermatid reserves remained unchanged. The absence of lesions and nonsignificant alterations in hematological and biochemical determinations indicated that prolonged exposure to Co at the dosages administered did not induce testicular degeneration in sheep and was tolerated without apparent pathological manifestations.

Effects of mercuric chloride on [3H]dopamine release from rat brain striatal synaptosomes.

Electrophysiological studies employing amphibian neuromuscular preparations have shown that mercuric chloride (HgCl2) in vitro increases both spontaneous and evoked neurotransmitter release. The present study examines the effect of HgCl2 on the release of [3H]dopamine from synaptosomes prepared from mammalian brain tissue. Mercuric chloride (3-10 microM) produces a concentration-dependent increase in spontaneous [3H]dopamine release from "purified" rat striatal synaptosomes, in both the presence and absence of extra-synaptosomal calcium. The effects of HgCl2 on transmitter release from amphibian neuromuscular junction preparations resemble those produced by the Na+, K+-ATPase inhibitor ouabain. Experiments were performed to determine whether the HgCl2 effects on mammalian synaptosomal dopamine release are a consequence of Na+, K+-ATPase inhibition. Na+, K+-ATPase activity in lysed synaptosomal membranes is inhibited by HgCl2 (IC50 = 160 nM). However, mercuric chloride in the presence of 1 mM ouabain still increased [3H]dopamine release. The specific inhibitor of Na+-dependent, high-affinity dopamine transport, RMI81,182 inhibited ouabain-induced [3H]dopamine release whereas it had no effect on HgCl2-induced [3H]dopamine release. These data suggest that augmentation of spontaneous [3H]dopamine release by HgCl2 probably is not mediated by an inhibition of Na+, K+-ATPase and HgCl2 does not act directly on the dopamine transporter.

The effects of chronic cobalt exposure on behavior and metallothionein levels in the adult rat.

Adult rats fed daily rations of laboratory chow laced with cobalt chloride were tested for operant (schedule-controlled) responding and conditioned suppression (CER). Animals exposed to 20 mg/kg Co, but not animals exposed to 5 mg/kg Co, lever pressed at a significantly slower rate than nontreated control subjects over the last 8 sessions of a 35 session operant training phase (1 session/day). Control and treatment subjects did not show significantly different CER performances. Nor were significant differences found on a test of mixed VI-2, DRO responding where subjects were required to lever press for reward during the first 15 min component and not lever press during the last 15 min component of the schedule. Testicular atrophy was evident among subjects exposed to 20 mg/kg Co. Atomic absorption spectrophotometric analyses revealed a dose-response effect regarding tissue accumulations of Co in blood, bone, brain, hair, small intestine, kidney, liver, and testes. Contrary to the biochemical pattern shown by some other heavy metals, prolonged Co exposure did not induce significant increases in metallothionein concentrations in the liver, kidney, or small intestine.

Testicular degeneration and necrosis induced by dietary cobalt.

Dietary cobalt (265 ppm Co) induced polycythemia and consistent degenerative and necrotic lesions in the seminiferous tubules of rats. Cyanosis and engorgement of testicular vasculature on day 35 and thereafter was followed on day 70 by degenerative and necrotic changes in the germinal epithelium and Sertoli cells. Spermatogonia, primary spermatocytes and round spermatids were markedly affected, while elongated spermatids, spermatozoa, and sertoli cells were more resistant. Damaged tubules, often present side by side with normal tubules, contained multinucleated giant cells composed of degenerated and necrotic spermatocytes and/or spermatids, sloughed germinal and Sertoli cells, and calcified necrotic debris. Necrotic tubules were frequently collapsed and devoid of epithelium except for occasional spermatogonia and surviving Sertoli cells. Lesions were not observed in the Leydig cells, cauda epididymis or seminal vesicles.

Effects of inorganic mercury on [3H]dopamine release and calcium homeostasis in rat striatal synaptosomes.

Inorganic mercury (Hg2+) in vitro increases spontaneous transmitter release from nerve terminals. The mechanisms of action are not well understood but may involve alterations in intraterminal Ca2+ dynamics. In this study we describe actions of Hg2+ in vitro on isolated mammalian CNS striatal nerve terminals (synaptosomes). Cobalt (2 mM) completely blocked the effect of 2 microM Hg2+ on spontaneous [3H]dopamine release. Cadmium (100 microM) was equipotent to Co2+ in blocking depolarization-dependent [3H]dopamine release, but did not alter the 2 microM Hg2(+)-induced spontaneous [3H]dopamine release. Depolarization-dependent [3H]dopamine release was not altered by 5 microM Hg2+. It appears that the site of action of Hg2+ on spontaneous [3H]dopamine release is not the Ca2+ channel. The effects of Hg2+ on intraterminal ionized Ca2+ [( Ca2+]i) were evaluated using the Ca2(+)-specific fluorescent probe, fura-2. Hg2+ (1-8 microM) had no effect on [Ca2+]i in 1.2 mM Ca2(+)-containing buffers. In nominal Ca2+ media, 4 and 8 microM Hg2+ significantly decreased [Ca2+]i. Following exposure to 4 and 8 microM Hg2+ the quenching of extrasynaptosomal fura-2 by Mn2+ was increased, suggesting that Hg2+ facilitated the leakage of fura-2. This apparent leakage was probably due to a nonspecific increase in membrane permeability since 2 microM Hg2+ produced a Co2(+)-insensitive increase in [3H]deoxyglucose phosphate efflux. Hg2+ did not increase the leakage of either lactate dehydrogenase or soluble protein from synaptosomes. Hg2+ produced a concentration-dependent (1-8 microM) increase in 45Ca2+ efflux from superfused synaptosomes which was insensitive to blockade either by 2 mM Co2+ or by 100 microM Cd2+. These data suggest that the transmitter releasing action of Hg2+ involves interactions with sites that also interact with Co2+ but not with Cd2+. Furthermore, Hg2+ may have direct transmitter releasing actions (i.e., Ca2(+)-mimetic properties), as well as nonspecific actions on plasma membrane permeability which may not necessarily be linked to [3H]dopamine release.

Effects of dietary cobalt on testicular structure.

Adult male rats were maintained on a diet containing 265 ppm cobalt for up to 98 days. Three rats were sacrificed weekly and assayed for testicular damage by light and electron microscopy. Testicular damage was first apparent after 70 days of treatment, followed by a progressive deterioration of cell architecture and decrease in testicular volume. The degenerative changes were of a very general nature; e.g., thickening of basal lamina and basement membranes, increased packing of red blood cells in veins and arteries, formation of "giant" cells, loss of sperm tail filaments, and degeneration of sperm mitochondria. No cobalt residues could be detected by energy dispersive x-ray microanalysis. These data indicate that testicular degeneration was not a primary response to cobalt and suggest that the testes become hypoxic due both to blockage of veins and arteries by red blood cells and to changes in permeability caused by thickening of basal lamina and basement membranes.