Transport mechanism for calcium and phosphate in ram spermatozoa

Helium-neon laser irradiation of cryopreserved ram sperm enhances cytochrome c oxidase activity and ATP levels improving semen quality

This study examines whether and how helium-neon laser irradiation (at fluences of 3.96-9 J/cm(2)) of cryopreserved ram sperm helps improve semen quality. Pools (n = 7) of cryopreserved ram sperm were divided into four aliquots and subjected to the treatments: no irradiation (control) or irradiation with three different energy doses. After treatment, the thawed sperm samples were compared in terms of viability, mass and progressive sperm motility, osmotic resistance, as well as DNA and acrosome integrity. In response to irradiation at 6.12 J/cm(2), mass sperm motility, progressive motility and viability increased (P < 0.05), with no significant changes observed in the other investigated properties. In parallel, an increase (P < 0.05) in ATP content was detected in the 6.12 J/cm(2)-irradiated semen samples. Because mitochondria are the main cell photoreceptors with a major role played by cytochrome c oxidase (COX), the COX reaction was monitored using cytochrome c as a substrate in both control and irradiated samples. Laser treatment resulted in a general increase in COX affinity for its substrate as well as an increase in COX activity (Vmax values), the highest activity obtained for sperm samples irradiated at 6.12 J/cm(2) (P < 0.05). Interestingly, in these irradiated sperm samples, COX activity and ATP contents were positively correlated, and, more importantly, they also showed positive correlation with motility, suggesting that the improved sperm quality observed was related to mitochondria-laser light interactions.

Phosphate induced developmental arrest of hamster two-cell embryos is associated with disrupted ionic homeostasis

Culture of hamster embryos with 0.35 mM inorganic phosphate results in developmental arrest at the 2-cell stage. These arrested 2-cell embryos were found to have significantly elevated levels of both intracellular pH and intracellular free calcium. Culture of 2-cell embryos with both glucose and phosphate did not further alter intracellular ionic homeostasis. Developmental arrest of 2-cell embryos was dependent on the concentration of phosphate used. Culture with 1.25 microM phosphate did not alter development, while concentrations of 2.5 microM and 5.0 microM resulted in a percentage of embryos arresting development at the 2-cell stage. Analysis of intracellular levels of pH and calcium after culture with different phosphate concentrations revealed a significant negative correlation between intracellular calcium levels and development beyond the 2-cell stage. There was no correlation between the increase in intracellular pH and embryo development in the presence of phosphate. The increase in intracellular calcium levels after culture with phosphate appears to be derived from intracellular pools, as preventing the influx of extracellular calcium did not alter development beyond the 2-cell stage. Therefore, it is apparent that a disruption in ionic homeostasis is associated with developmental arrest of hamster embryos cultured with phosphate.

Glucose and phosphate toxicity in hamster preimplantation embryos involves disruption of cellular organization, including distribution of active mitochondria

While perinuclear clustering of active mitochondria, as revealed by Rhodamine 123 staining and confocal microscopy, is part of normal hamster embryo development, it is not known whether this reorganization is necessary for development. To determine if disruption of mitochondrial organization occurs in developmentally compromised embryos, the intensity of Rhodamine 123 staining was quantitated using NIH Image Software in different regions of cultured hamster 2-cell embryos exposed to either blocking (contains glucose and phosphate) or non-blocking culture conditions. Three regions within each blastomere were defined based on the organization of freshly collected embryos: cortical (ring beneath plasma membrane), perinuclear, and intermediate regions. While there was no treatment effect on the total staining intensity, glucose and phosphate treated embryos had significantly higher Rhodamine 123 staining in the intermediate region, with corresponding reduced intensity in the perinuclear region, implicating glucose and phosphate in the redistribution of mitochondria. Glucose and phosphate treatment also selectively reduced the FITC Phalloidin staining of actin microfilaments in the interior of the embryo. Neither cytochalasin D nor colchicine, at doses that blocked the second cleavage, caused redistribution of mitochondria like that seen with glucose and phosphate treatment. Additionally, cytochalasin D was unable to disrupt actin microfilaments in the perinuclear region, although it induced a "clumpy" appearance in both mitochondria and microfilaments. This report not only offers a more mechanistic explanation of the embryo 2-cell block (translocation of mitochondria involved in glucose and phosphate inhibition) but suggests that appropriate cellular organization, including the spatial positioning of the mitochondria, may be a prerequisite for normal development and that the physical organization of the embryo is susceptible to damage by exposure to culture conditions.

Calcium requirement and time course of capacitation of goat spermatozoa assessed by chlortetracycline assay

We standardized chlortetracycline fluorescent assay for studies of calcium requirement and time course of capacitation of goat spermatozoa. Three distinct fluorescent patterns were easily detected in goat spermatozoa incubated under capacitating conditions. Categorised according to nomenclature reported earlier, these are: 'F' with bright fluorescence in the postacrosomal region, characteristic of uncapacitated acrosomal-intact cells; 'B' with bright fluorescence on the anterior portion of the head and dark band in the postacrosomal region, characteristic of capacitated, acrosome-intact cells; 'AR' with lack of fluorescence on the head characteristic of acrosome-reacted cells. A close correspondence was observed when the results of CTC assay were compared with those obtained by transmission electron microscopy. Goat spermatozoa were not capacitated when calcium was omitted from the medium and 80% had CTC fluorescence of 'F' type. The size of 'B' cell population increased with increase in calcium concentration; at 1.0 mmol l-1 a peak representing 65-70% capacitated cells accumulated in 4 h. At higher concentrations, 'AR' cells were found along with 'B' cells and the two cell types were in equal proportions at 1.71 mmol l-1. Time course studies revealed a 2 h incubation period at 1.0 mmol l-1 and 1 h at 2 mmol l-1 calcium concentration before transformation of 'F' cells to 'B' cells was noticed. However, at no time were 'AR' cells found exclusively pointing to an equilibrium between the two sperm populations. Goat spermatozoa were also not capacitated when phosphate was omitted from the medium. Permeant anions (NO3-, SCN-), permeant weak acid (HCO3-) and organic phosphates (beta-glycerophosphate, glucose-6-phosphate) were unable to replace phosphate. The reason for their failure for the incidence of capacitation was traced to low uptake of calcium by goat spermatozoa. In the presence of phosphate, a 6-8-fold increase was measured over the calcium uptake when phosphate was omitted (2-4 nmol l-1 10(8) cells-1). Mersalyl inhibited the calcium uptake by goat spermatozoa as well as its capacitation most likely by inhibiting the calcium phosphate transporter located in the sperm plasma membrane.

Calcium efflux mechanism in sperm mitochondria

This paper reports an investigation on calcium efflux mechanism in ram sperm mitochondria. Energized sperm mitochondria take up Ca2+ via the ruthenium-red sensitive uniporter, and possess a ruthenium-red insensitive efflux mechanism. Extramitochondrial Na+ did not affect the rate of Ca2+ efflux indicating that Na+/Ca2+ exchange mechanism is not involved. Depolarization of inner mitochondrial membrane induced by the uncoupler carbonylcyanide-p-trifluoromethoxyphenyl hydrazone (FCCP) or by the organomercurial SH-reagent mersalyl, causes high stimulation in Ca2+ efflux. This stimulated Ca2+ efflux determined in the presence of ruthenium-red and phosphate, is not inhibited by cyclosporin A (CSA), indicating that mitochondrial permeability transition pore (MTP) is not involved in this Ca2+ efflux mechanism. The stimulated Ca2+ efflux is inhibited by ADP or atractyloside suggesting that the Ca2+ transport mechanism might be intrinsic to the ADP/ATP carrier (AAC). Thus, the data indicate that sperm mitochondria contain a Ca2+ efflux mechanism operated via AAC and regulated by mitochondrial membrane potential and by ADP concentration.

Relationship between intracellular calcium, energy metabolism, and motility of ram sperm

Collective sperm motility is characterized in terms of periodic aggregation or cooperation among cells, which are seen under a microscope as a continuous wave motion. In this study, sperm motility that was made dependent on mitochondrial activity (glycolysis inhibited) was significantly inhibited by mM exogenous calcium while glycolytic-dependent (mitochondrial respiration inhibited) motility was not inhibited under these conditions. At intracellular Ca2+ above 400 nM, sperm motility was inhibited independently of the source of ATP. At [Ca2+]i of approximately 110 nM, mitochondrial- or glycomitochondrial-dependent motility showed 75 or 0% inhibition, respectively, indicating higher sensitivity of mitochondrial-dependent motility to [Ca2+]i in comparison to glycolytic-dependent motility. Under the latter conditions, intracellular level of ATP was reduced by 16% only, indicating that the 75% inhibition of mitochondrial-dependent motility was not due to reduction in ATP. The inhibition of mitochondrial-dependent motility by mM extracellular Ca2+ can be prevented by incubating the cells at pH 6.5 instead of 7.6. At pH 7.6, calcium probably interacts with negative sites on the cell surface and interferes in cell-to-cell interactions, which are important to achieve collective motility. At more acidic pH (6.5) these negative sites are probably protonated; thus Ca2+ cannot interact with them and no inhibition of motility could be seen. Glycolytic-dependent motility was not inhibited by extracellular Ca2+, since the pH of the medium becomes acidic under these conditions. Like Ca2+, mersalyl, which interacts with Ca2+ binding sites on the cell surface, showed significant inhibition of mitochondrial-dependent motility without any effect on glycolytic-dependent motility. Collective motility was directly correlated with fertility. These data are significant for establishing better conditions for spermatozoa treatment when artificial insemination or in vitro fertilization is concerned.

Effect of light on calcium transport in bull sperm cells

The effect of light on calcium transport was studied. Bull sperm cells were irradiated with an He-Ne (630 mm) laser and a 780 nm diode laser at various energy doses, and 45Ca2+ uptake was measured by the filtration technique. It was found that there is an accelerated Ca2+ transport in the irradiated cells, which means that laser light can stimulate Ca2+ exchange through the cell membrane. This may cause transient changes in the cytoplasmic Ca2+ concentration which, in spermatozoa, has a regulatory role in control of motility and acrosome reaction, and in other cells can trigger mitosis.

Stimulation of Ca2+ uptake into epididymal bull spermatozoa by analogues of amiloride

Certain amiloride analogues 3',4'-dichlorobenzamil 2',4'-dimethylbenzamil and alpha',2'-benzobenzamil hydrochloride (ATBB) stimulate calcium accumulation and motility by epididymal bovine spermatozoa. This stimulation can be seen at a range of 0.1-0.4 mM, while at higher concentration there is inhibition of calcium uptake by these amiloride analogues. The amiloride derivative 5-(4-chlorobenzyl)-2',4'-dimethylbenzamil (CBDMB), which bears a 4-chlorobenzyl substituent on the 5-amino nitrogen atom, did not stimulate calcium uptake. The amiloride analogue 3',4'-dichlorobenzamil inhibits the Na+/Ca2(+)-exchange activity in isolated plasma membrane vesicles, and the stimulatory effect of 3',4'-dichlorobenzamil on calcium uptake into epididymal sperm could be seen in Na(+)-free medium. Thus, the stimulation of Ca2+ accumulation in the cells caused by 3',4'-dichlorobenzamil is not a result of inhibiting the Na(+)-dependent Ca2+ clearance. There is no stimulation of Ca2+ uptake into ejaculated cells by adding 3',4'-dichlorobenzamil, which is not due to the presence of the calcium-transport inhibitor (caltrin) in these cells [Rufo, G.A., Schoff, P.K. & Lardy, H.A. (1984) J. Biol. Chem. 259, 2547-2552]. The stimulatory effect of 3',4'-dichlorobenzamil on Ca2+ uptake is inhibited by the voltage-dependent Ca2(+)-channel blockers nifedipin and diltiazem. This indicates that the stimulation of Ca2+ uptake by the amiloride analogues is due to the activation of a voltage-dependent Ca2+ channel of the plasma membrane.

Regulation of calcium transport in bovine spermatozoa

Calcium uptake into bovine epididymal spermatozoa is enhanced by introducing phosphate in the suspending medium (Babcock et al. (1975) J. Biol. Chem. 250, 6488-6495). This effect of phosphate is found even at a low extracellular Ca2+ concentrations (i.e., 5 microM) suggesting that phosphate is involved in calcium transport via the plasma membrane. Bicarbonate (2 mM) cannot substitute for phosphate, and a relatively high bicarbonate concentration (20 mM) causes partial inhibition of calcium uptake in absence of Pi. In the presence of 1-2 mM phosphate, 20 mM bicarbonate enhances Ca2+ uptake. The data indicate that the plasma membrane of bovine spermatozoa contains two carriers for Ca2+ transport: a phosphate-independent Ca2+ carrier that is stimulated by bicarbonate and a phosphate-dependent Ca2+ carrier that is inhibited by bicarbonate. Higher phosphate concentrations (i.e., 10 mM) inhibit Ca2+ uptake into intact cells (compared to 1.0 mM phosphate) and this inhibition can be relieved partially by 20 mM bicarbonate. This effect of bicarbonate is inhibited by mersalyl. Calcium uptake into the cells is enhanced by adding exogenous substrates to the medium. There is no correlation between ATP levels in the cells and Ca2+ transport into the cell. ATP levels are high even without added exogenous substrate and this ATP level is almost completely reduced by oligomycin, suggesting that ATP can be synthesized in the mitochondria in the absence of exogenous substrate. Calcium transport into the sperm mitochondria (washed filipin-treated cells) is absolutely dependent upon the presence of phosphate and mitochondrial substrate. Bicarbonate cannot support Ca2+ transport into sperm mitochondria. There is good correlation between Ca2+ uptake into intact epididymal sperm and into sperm mitochondria with the various substrates used. This indicates that the rate of calcium transport into the cells is determined by the rate of mitochondrial Ca2+ uptake and respiration with the various substrates.

Molecular mechanisms of gossypol action on sperm motility

1. Gossypol acetic acid inhibits collective motility of ejaculated ram spermatozoa. 2. Oxygen consumption was stimulated at low gossypol concentrations and inhibited as the concentrations are increased. 3. Gossypol inhibits respiration of permeabilized spermatozoa supported by durohydroquinome, which indicates a direct inhibition of mitochondrial electron transport chain. 4. The rapid reduction of mitochondrial dependent motility, high uncoupling effect and almost complete inhibition of mitochondrial calcium accumulation, indicate that gossypol inhibits motility in a mechanism by which mitochondrial uncoupling is involved.