Lead reduces depolarization-induced calcium entry in cultured DRG neurons without crossing the cell membrane: fura-2 measurements

Toxic effects of Pb2+ entering sperm through Ca2+ channels in the freshwater crab Sinopotamon henanense

Lead (Pb) is a heavy metal that can damage animal sperm. To study the effects of Pb on calcium homeostasis and calcium channel in the sperm of freshwater crab Sinopotamon henanense, the induction of acrosome reaction (AR) and acrosin activity were investigated when crabs were exposed to different Pb concentrations (0, 3.675, 7.35, 14.7, 29.4 and 58.8mg/L) for 3, 5 and 7 d separately. Fluorescent probe Fluo-3/AM was loaded into the sperm, and [Ca²⁺] in the sperm was measured by fluorescence microscopy and using microplate reader. The calmodulin (CaM) concentration was measured by ELISA method. Verapamil (VRP), a calcium channel blocker, was used to evaluate whether Pb can enter the sperm through calcium channels leading to sperm damage. After sperm were exposed at 50μg/L VRP, 100μg/L Pb, 50μg/L VRP+100μg/L Pb, 1000μg/L Pb and 50μg/L VRP+1000μg/L Pb for 1h in vitro，sperm quality parameters (sperm survival and sperm DNA integrity) and levels of parameters indicating oxidative stress (protein carbonylation [PCO] and malondialdehyde [MDA]) were measured. Our data showed that Pb reduced the induction of acrosome reaction (AR), down-regulated the acrosin activity, decreased the intracellular concentration of Ca²⁺ and elevated CaM concentration. Compared to controls, Pb alone induced significant stress, as reflected by decreasing sperm survival and sperm DNA integrity, and increasing PCO and MDA contents. In the presence of VRP, 100μg/L Pb-induced stresses were reduced, all the measured parameters in the sperm exposed at 100μg/L Pb returned to control levels. Our results indicate that Pb enters the sperm of the crab S. henanense through calcium channels, the inhibition of which blocks Pb-induced stresses such as sperm quality decline and oxidative damage.

The effect of lead on calcium release activated calcium influx in primary cultures of human osteoblast-like cells

To further understand the significance of bone as a target tissues of lead toxicity, as well as a reservoir of systemic lead, it is necessary to define the effect of lead on the calcium release activated calcium influx (CRACI) in primary cultures of human osteoblast-like cells (OLC). Pb2+ inhibited the immediate CRACI dose-dependent manner. Influx of Pb2+ into human OLC was increased dose-dependent manner. The present study demonstrates that the interference of Pb2+ with CRACI of human OLC is at least twofold: (1) the initiation of CRACI, i.e., the measurable influx of Ca2+ upon Ca2+ readdition, is partially inhibited by Pb2+ and (2) the influx of Pb2+ was enhanced after CRACI had been induced.

Elevated Ca2+i transients induced by trimethyltin chloride in HeLa cells: types and levels of response

Humans are exposed to organotins, like trimethyltin (TMT) chloride via air, water and food, and intoxication might result in severe health complications. Toxic effects of organotin compounds are well documented, but possible mechanisms remain unclear and only little information is available how organometallic species interact with calcium controlling mechanisms. Therefore, the aim of this work was to investigate the effects of TMT on calcium homeostasis in HeLa S3 cells. Dynamic changes of cytosolic calcium (Ca2+(i)) were monitored using laser-scanning microscopy and fluo-4 loaded cells. Application of TMT resulted in sustained as well as in transient elevations of Ca2+(i). The number of reacting cells was directly correlated to the concentration of TMT used: with 500 microM TMT all cells reacted, with 50 microM TMT 80% and with 5 microM 74%. The fast Ca2+(i)-transients (spikes), measured in single cells, occurred even with 0.25 microM TMT and varied in size and duration. The sustained increase of Ca2+(i), measured as the average over all cells, was dose dependent with an approximately 8% increase for 5 microM TMT, approximately 12.3% for 50 microM and approximately 145% for 500 microM TMT. Moreover, this effect was partly reversible. A second application resulted in a similar sustained rise of Ca2+(i) compared to the first application of TMT, there was also no difference when no calcium was added to the external solution (151+/-10% compared to 145+/-15%; 500 microM TMT). This rise of Ca2+(i) was highly reduced (<10% increase) when the internal calcium stores were depleted before TMT (500 microM) was applied. Our data suggest that TMT influences Ca2+(i)-homeostasis of HeLa S3 cells, which might be related to its toxicity in this cell line.

Effects of Pb2+ ions on Na+ transport in the isolated skin of the toad Pleurodema thaul

The effects induced by lead ions on the short-circuit current (SCC) and on the potential difference (V) of the toad Pleurodema thaul skin were investigated. Pb2+ applied to the outer (mucosal) surface increased SCC and V and when applied to the inner (serosal) surface decreased both parameters. The stimulatory effect, but not the inhibitory action, was reversible after washout of the metal ion. The amiloride test showed that the increase was due principally to stimulation of the driving potential for Na+ (V-E(Na+)) and that inhibition was accompanied by a reduction in the V-E(Na+) and also by a significant decrease in skin resistance indicating possible disruption of membrane and/or cell integrity. The effect of noradrenaline was increased by outer and decreased by inner administration of Pb2+. The results suggest that mucosal Pb2+ activates toad skin ion transport by stimulating the V-E(Na+) and that serosal Pb2+, with easier access to membrane and cellular constituents, inactivates this mechanism, revealing greater toxicity when applied to the inner surface of the skin.

Prostaglandin E2 increases the expression of the neurokinin1 receptor in adult sensory neurones in culture: a novel role of prostaglandins

(1) Peripheral inflammation causes an increase in the proportion of primary afferent neurones that express neurokinin(1) (NK(1)) receptors for substance P (SP). This upregulation may contribute to the neuronal mechanisms of inflammatory pain. The aim of this study was to identify endogenous mediators that stimulate upregulation of NK(1) receptors in dorsal root ganglion (DRG) neurones. Cultured DRG neurones from the adult normal rat were exposed for 2 days to media that contained specific mediators, namely potassium in high concentration, prostaglandin E(2) (PGE(2)), somatostatin (SRIF), and compounds influencing second messenger cascades. After fixation neurones were labelled with an NK(1) receptor antibody. (2) Repetitive addition of the inflammatory mediator PGE(2) or dibutyryl-cyclic adenosine 3',5' monophophate (db-cAMP) to the culture medium enhanced the proportion of neurones with NK(1) receptor-like immunoreactivity from about 12% up to 40%. PGE(2)-induced upregulation was prevented by coadministration of PGE(2) and a protein kinase A inhibitor or SRIF to the medium. High potassium concentration, protein kinase C inhibitors and omission of nerve growth factor from the medium had no effect. (3) In calcium-imaging experiments, bath application of SP evoked increases of the intracellular calcium concentration in about 20% of the neurones. This proportion increased to about 40% after PGE(2)-pretreatment, but the increase was prevented when PGE(2) and SRIF were coadministered to the medium. (4) These data show that the expression of NK(1) receptor-like immunoreactivity in DRG neurones is regulated by the inflammatory mediator PGE(2). This upregulation depends on the intracellular adenylyl cyclase-protein kinase A pathway.