Effect of Ca2+ channel antagonists on the acrosome reaction of guinea pig and golden hamster spermatozoa

Understanding sperm physiology: Proximate and evolutionary explanations of sperm diversity

Much can be gained from the comprehensive study of a biological system. Based on what is known as Mayr's proximate-ultimate causation and the subsequent expansion to Tinbergen's four questions, biological traits can be understood by taking into account different approximations that try to explain mechanisms, development, adaptive significance or phylogeny. These, in principle, separate areas, can be integrated crossing boundaries, but bearing in mind that answers to one question would not explain a different query. Studies of sperm biology have, until now, not benefited much from this framework and potential integration. Proximate causes (particularly mechanisms) have been the subject of interest for reproductive biologists, and evolutionary explanations have been the domain of behavioural ecologists with interest in adaptive significance of traits in the context of post-copulatory sexual selection. This review will summarize opportunities for research in the different areas, focusing on sperm preparation for fertilization and suggesting possible integration within and between proximate and evolutionary studies.

Seminal Plasma Calcium in Normal and Infertile Patients

Introduction

In this study an attempt is made to find out the level of calcium in seminal plasma of normal and infertile patients.

Materials and Methods

Semen samples are collected from 34 normal men and 112 infertile patients. After semen evaluation seminal plasma was separated and calcium level was measured in it.

Results

Calcium level in mg% is recorded in each group as follows; in normozospermia (n34) 20.14 ± 1.25 (±SE), oligozoospermia (n26) 9.76 ± 1.17, azoospermia (n33) 14.65 ± 2.63, oligoasthenozoosperma (n28) 20.91 ± 1.94 and in asthenozoospermia (n25) 11.56 ± 1.68. Statistically highly significant reduction in calcium is seen in Oligozoospermia and asthenozoospermia.

Conclusions

The probable reasons for these two conditions are discussed.

Pregnancies established from water buffalo () blastocysts derived from in vitro matured, in vitro fertilized oocytes and co-cultured with cumulus and oviductal cells

Buffalo ovaries were collected immediately after slaughter and were transported to laboratory in sterile saline at 37 degrees C. Follicular oocytes with the cumulus mass aspirated from 2 to 6 mm in diameter follicles were cultured in TCM-199 medium supplemented with 10% buffalo estrus serum (BES) in 5% CO(2) at 38.5 degrees C. After 20 to 24 h of incubation, the oocytes were inseminated with precapacitated frozen thawed spermatozoa for 6 h. The fertilization rate was 78.15% of the matured oocytes. Over an in vitro culture period of 3 to 9 d, 4.02% of the inseminated oocytes developed to the morula stage when cultured with cumulus cells alone and 17.83% when cumulus cells plus oviductal epithelial cells were used. The percentage of developed blastocysts was very low (0.57%) when the oocytes were co-cultured with cumulus cells from the original oocytes. However, 8% of the inseminated oocytes that were denuded 3 d after insemination developed to the blastocyst stage when they were co-cultured with cumulus and oviductal epithelial cells. Sixteen early/expanded blastocysts were transferred non-surgically to 16 recipients. Four of the 16 recipients became pregnant, of which 2 delivered normal buffalo male calves.

Activation of voltage-dependent calcium channels of mammalian sperm is required for zona pellucida-induced acrosomal exocytosis

Previous work indicates that antagonists of the L-type voltage-dependent Ca2+ channel (VDCC) prevent the Ca(i) increase in mammalian sperm that is promoted by incubation in alkaline, K(+)-based media. Here, were provide additional evidence that sperm possess VDCC and show that their activation is required for the Ca2+ entry that mediates acrosomal exocytosis in both the presence and the absence of egg agonists. Specifically, we report that: (1) Sperm membrane potential changes, Ca(i) elevation, and acrosomal exocytosis have similar K+ dose dependencies, consistent with a characteristic requirement of a large depolarization for activation of the sperm VDCC; (2) High affinity binding sites (Kd approximately 0.35 +/- 0.03 and 0.45 +/- 0.06 nM; Bmax = 16.0 +/- 1.4 and 5.8 +/- 0.8 fmole/mg protein) for the VDCC antagonist, PN200-110, respectively, are present in membrane preparations from sperm of the ram and bull; (3) PN200-110 and the other VDCC antagonists nitrendipine, nisoldipine, verapamil, diltiazem, Ni2+, or Co2+ inhibit (IC50 = 0.1, 0.4, 0.6, 0.8, 1.0, 60, and 110 microM, respectively) the acrosomal exocytosis produced by combined elevation of pH0 and membrane depolarization; (4) Exocytosis induced by the ZP3 agonist of the mammalian egg also is inhibited by VDCC antagonists with similar dose dependencies; (5) Depolarizing treatments that presumably activate the sperm VDCC bypass the blockade of ZP3-induced exocytosis imposed by pertussis toxin. These results indicate that activation of the sperm VDCC is sufficient to induce sperm acrosomal exocytosis and that VDCC activation is necessary in the ZP3 signal transduction pathway. They also indicate that the presumed G-protein targets of pertussis toxin probably produce a required but indirect activation of the putative sperm VDCC. Possible intervening events include alteration of the voltage sensitivity of the VDCC, membrane depolarization, or both. We suggest that the depolarization-induced acrosome reaction may provide a useful system to investigate subsequent events in the exocytotic process.

Preloading of micromolar intracellular Ca2+ during capacitation of Sicyonia ingentis sperm, and the role of the pHi decrease during the acrosome reaction

In studying the mechanism controlling the sperm acrosome reaction (AR) in the marine shrimp Sicyonia ingentis, intracellular Ca2+ and pH were measured using the fluorescent indicators Fura-2 and Fluo-3 for Ca2+, and SNARF-1 for pH. Capacitated sperm possessed an apparent resting Ca2+ concentration of 1-2 microM which remained constant upon induction of the AR with egg water. Uncapacitated sperm had extremely low Ca2+ levels and did not respond to egg water. These results suggest that, while in other species the Ca2+ is elevated to micromolar levels during initiation of the AR, S. ingentis sperm are preloaded with Ca2+ during capacitation and the trigger for the AR is downstream of the Ca2+ increase. The notion that Ca2+ influx is not involved at the actual time of the AR in capacitated S. ingentis sperm is supported by the inability of Ca2+ ionophore A23187 to induce the AR and the ineffectiveness of Ca2+ channel antagonists to block egg water-induced AR. Measurements of capacitated sperm pH showed a significant decrease during the first 10-15 min of the AR, which did not correlate temporally to either acrosomal exocytosis (at 5 min post-induction) or filament formation (after 45 min). Inhibition of egg protease activity required for induction of filament formation did not inhibit the pH drop, indicating that intracellular acidification is not the final trigger for filament formation, although it may be required prior to action of the protease.

Calcium transport and Ca(++)-ATPase activity in spermatozoal plasma membrane vesicles of nifedipine-administered guinea pigs

Spermatozoal plasma membrane vesicles isolated from distal portion of the epididymis and vas deferens were found to contain Ca(++)-activated ATPase and calcium transport activities. Nifedipine was administered at two different doses (1.0 and 2.5 mg/kg b.w./day) and the effect was observed for both short- (4 week) and long-term (12 week) period. The cellular ionic calcium content and Ca(++)-ATPase activity were observed to be enhanced in the drug-treated animals. The recovery studies carried out after 4 and 6 weeks of withdrawal of the drug treatment exhibited partial to complete restoration of observed changes. The stimulatory rather than inhibitory effect of Nifedipine, a specific calcium channel blocker, on calcium uptake may suggest that voltage-sensitive calcium channels may be lacking in guinea pig spermatozoa. The stimulatory effect of the drug is speculated to be either by inhibition of Na(+)-Ca++ antiporter or G-protein activated agonistic effect or probably due to altered physicochemical properties of the drug-treated sperm plasma membranes.

Requirement of an extracellular energy substrate for the guinea pig sperm acrosome reaction induced by calcium ionophore

It is well established that calcium ionophore A 23187 induces acrosome reaction (AcR) of uncapacitated spermatozoa in the presence of extracellular Ca2+ ions. In the present study, we have investigated how extracellular energy substrates (glucose, pyruvate, and lactate) affect the ionophore-induced AcR of guinea pig spermatozoa. It was found that 0.3 microM concentration of A 23187 had the maximum effect to initiate AcR of guinea pig spermatozoa. Virtually no spermatozoa underwent their AcR when incubated in substrate-free modified Tyrode's medium containing 0.3 microM A 23187 and 2 mM Ca2+. At least one exogenous substrate is essential for the ionophore-induced AcR of spermatozoa. As for efficacy of the substrates, lactate was more effective than pyruvate and glucose. However, a better result was observed when lactate was added along with pyruvate. Malonate inhibited the ionophore-induced AcR but not the hyperactivated motility of spermatozoa. The mitochondrial electron transport chain blockers rotenone, antimycin, and oligomycin failed to inhibit AcR, although in the presence of these blockers spermatozoa were unable to show hyperactivated motility. These results suggest that the mitochondrial citric acid cycle, not the electron transport chain, is probably the energy source for ionophore-induced AcR of guinea pig spermatozoa.

Verapamil stimulates Ca(++)-uptake and Ca(++)-ATPase in plasma membrane vesicles of guinea pig spermatozoa

Verapamil, a potent calcium channel blocker, was administered orally at three different doses to guinea pigs for both short- (4 weeks) and long-term (12 weeks) effects. The drug treatment stimulated Ca(++)-transport and Ca(++)-activated ATPase in isolated plasma membrane vesicles of guinea pig spermatozoa. Ca(++)-uptake studies exhibited partial to complete restoration of stimulated Ca(++)-transport during recovery period, whereas the CA(++)-activated ATPase system remained stimulated even after 4 and 6 weeks of withdrawal of the drug treatment. The lack of inhibitory effect of verapamil on Ca(++)-uptake ruled out the involvement of calcium channels in spermatozoal calcium uptake in guinea pigs. The stimulatory effect of the drug on CA(++)-uptake, on the other hand, might indicate the possible capability of this lipophilic compound to induce favourable changes in the lipid microenvironment of the membrane, wherein the integral membrane proteins operate.

Effect of verapamil on different spermatozoal functions in guinea pigs--a preliminary study

Verapamil, a calcium channel blocker, was administered orally using three different doses to guinea pigs. Both short-term (4 weeks) and long-term (12 weeks) effects of the drug were observed. The drug administration resulted in a marked decrease in sperm density, sperm motility and cellular energy content (ATP). Zona pellucida penetration by the sperm obtained from drug-treated animals was significantly lower when compared with sperm from normal animals. Histopathological findings exhibited partial arrest of spermatogenesis. Partial to complete recovery was observed after 4 and 6 weeks of withdrawal of the drug treatment.

Cross-fertilization between Syrian and Chinese hamsters

The role of the zona pellucida in the specificity of fertilization was studied by cross-inseminations between Syrian (Golden) and Chinese hamster gametes. Cumulus-enclosed eggs from both Syrian and Chinese hamsters were placed together in one dish and inseminated with spermatozoa from either one or the other species. Fertilization always took place between gametes of homologous species. Chinese hamster spermatozoa failed to bind to the zona pellucida of Syrian hamster eggs; hence, fertilization was never observed. However, Chinese hamster spermatozoa could fertilize zona-free Syrian hamster eggs. In the reciprocal cross, a large number of Syrian hamster spermatozoa could bind to and penetrate the zonae of Chinese hamster eggs. However, fusion of Syrian hamster spermatozoa with the vitellus of zona-intact Chinese hamster eggs was never observed. After removal of the zona pellucida, only a small percentage (31%) of Syrian hamster spermatozoa could fuse with Chinese hamster vitelli. Thus, in these species, the mechanisms of interspecific gamete recognition and the prevention of interspecies fertilization seem to differ according to the direction of the cross. In Syrian hamster eggs, the block to interspecies fertilization seems to exist at the level of the zona pellucida, while in Chinese hamster eggs the block is at the level of the egg plasma membrane. The implications of these results in analyses of the genetics of spermatozoa, the molecular basis of sperm-egg recognition, and mechanisms of reproductive isolation leading to speciation, are discussed.

Cytochemical study of intracellular calcium in hamster spermatozoa during the acrosome reaction

Calcium was localized by a pyroantimonate technique in hamster spermatozoa during the acrosome reaction and pyroantimonate precipitates were observed in the anterior region of the acrosome. The calcium was also localized in the postacrosomal lamina of spermatozoa undergoing the acrosome reaction. Spermatozoa, incubated in capacitating medium containing verapamil, showed denser precipitates with an increase in concentration of this drug. Ionophore A23187 enhanced binding of calcium to the acrosomal region. The sodium channel inhibitor amiloride inhibited the acrosome reaction and the pyroantimonate precipitates were absent in these spermatozoa, whereas ionophore monensin enhanced the acrosome reaction. This suggests that the Na+/Ca++ antiporter may be responsible for intracellular Ca++ regulation during the acrosome reaction in hamster spermatozoa.

Calcium uptake in human spermatozoa: characterization and mechanisms

Basal 45Ca2+ influx was analyzed in human seminal spermatozoa using a method that allows these highly reactive cells to be easily and safely handled. The uptake was a time-dependent process, with its maximum at 400 s. The kinetics of 45Ca2+ transport was saturating as a function of extracellular Ca2+ concentration with a Km of 429 microM and a Vmax of 1.6 nmol 45Ca2+/mg protein/2.5 min. Depolarizing conditions and the calcium channel blocker verapamil did not affect the uptake; based on this, the presence of operating calcium channels in seminal spermatozoa is excluded. The independence of 45Ca2+ uptake on external concentration of both Na+ and Ca2+ suggests that Na+/Ca2+ exchange does not occur in these cells. The anticalmodulin drug trifluoperazine, the mitochondrial inhibitor antimycin A, and the SH reagents N-ethylmaleimide and mersalyl all inhibited the ion transport. A calmodulin-regulated, energy-requiring, proteinaceous Ca2+ transporter seems to be the main operating mechanism of calcium uptake in human seminal gametes.

Ethanol accelerates acrosomal loss in human spermatozoa

The effects of ethanol on the loss of the human sperm acrosome, as determined by the chlortetracycline fluorescence assay and by indirect immunofluorescence assay, were assessed over 6 hours during incubation at 37 C in BWW medium containing 0 to 250 mM ethanol. Both assays gave the same results. At the end of 6 hours, 48 +/- 6% acrosomal loss was found in samples in 250 mM ethanol compared with 4 +/- 1% in the absence of ethanol. After 0.25 hour, the first time point chosen for sampling, the spermatozoa in 250 mM ethanol showed 23 +/- 3% loss of acrosomes compared with less than 1% in the absence of ethanol. Ultrastructural studies revealed that the ethanol-treated spermatozoa showed complete acrosomal loss as well as loss of the equatorial segment. No examples of the vesiculation characteristic of the physiologic acrosome reaction were found in the 150 cells examined. Calcium is required for the ethanol-mediated acrosomal loss: omission of Ca2+, addition of 2 mM EGTA, or 0.2 mM verapamil blocked the effect. Ethanol induced a dose-dependent efflux of cholesterol from human spermatozoa, but the ethanol-induced acceleration of acrosomal loss occurred to the same extent in the presence of cholesterol microdispersions that prevented this efflux. The loss of the equatorial segment, which is necessary for egg penetration, during ethanol-induced acrosomal loss would explain the known effect of ethanol in inhibiting, rather than enhancing, the penetration of zona-free hamster eggs by human spermatozoa.