Measurement and manipulation of cytoplasmic free calcium of ram and boar spermatozoa using quin 2

Release of Ca(2+) from intracellular stores and entry of extracellular Ca(2+) are involved in sea squirt sperm activation

A rise in intracellular free Ca(2+) concentration ([Ca(2+)](i)) is required to activate sperm of all organisms studied. Such elevation of [Ca(2+)](i) can occur either by influx of extracellular Ca(2+) or by release of Ca(2+) from intracellular stores. We have examined these sources of Ca(2+) in sperm from the sea squirt Ascidia ceratodes using mitochondrial translocation to evaluate activation and the Ca(2+)-sensitive dye fura-2 to monitor [Ca(2+)](i) by bulk spectrofluorometry. Sperm activation artificially evoked by incubation in high-pH seawater was inhibited by reducing seawater [Ca(2+)], as well as by the presence of high [K(+)](o) or the Ca channel blockers pimozide, penfluridol, or Ni(2+), but not nifedipine or Co(2+). The accompanying rise in [Ca(2+)](i) was also blocked by pimozide or penfluridol. These results indicate that activation produced by alkaline incubation involves opening of plasmalemmal voltage-dependent Ca channels and Ca(2+) entry to initiate mitochondrial translocation. Incubation in thimerosal or thapsigargin, but not ryanodine (even if combined with caffeine pretreatment), evoked sperm activation. Activation by thimerosal was insensitive to reduced external calcium and to Ca channel blockers. Sperm [Ca(2+)](i) increased upon incubation in high-pH or thimerosal-containing seawater, but only the high-pH-dependent elevation in [Ca(2+)](i) could be inhibited by pimozide or penfluridol. Treatment with the protonophore CCCP indicated that only a small percentage of sperm could release enough Ca(2+) from mitochondria to cause activation. Inositol 1,4,5-trisphosphate (IP(3)) delivered by liposomes or by permeabilization increased sperm activation. Both of these effects were blocked by heparin. We conclude that high external pH induces intracellular alkalization that directly or indirectly activates plasma membrane voltage-dependent Ca channels allowing entry of external Ca(2+) and that thimerosal stimulates release of Ca(2+) from IP(3)-sensitive intracellular stores.

Measurement of intracellular calcium levels of human spermatozoa acrosome reacted by electropermeabilization

Human spermatozoa readily undergo in vitro capacitation and the acrosome reaction when exposed to a single, brief, high-voltage electric pulse in a medium containing calcium. Using the fluorescent calcium indicator, Fura-2, the changes in the intracellular calcium concentration of human sperm following exposure to voltages in the range of 200-2000 V cm-1 were measured. The induction of the acrosome reaction by the electropermeabilization pulse was also monitored. In comparison, changes in calcium uptake during a standard capacitation procedure in which sperm samples were incubated for 7 h were analyzed. At hourly intervals, acrosome reaction induction and intracellular calcium uptake were measured. The results indicate that electropermeabilization rapidly and efficiently produces high populations of acrosome-reacted sperm and a corresponding and associated increase in the intracellular calcium concentration.

Calcium ion regulation of chirality of beating flagellum of reactivated sea urchin spermatozoa

Near an interface, sea urchin spermatozoa swim almost in circles. The direction is usually clockwise at the lower surface of a coverslip and counterclockwise at the upper surface of a glass slide, when viewed from above. Examination of demembranated spermatozoa has shown that Ca2+ regulates the direction of the circular motion of spermatozoa reactivated with adenosine triphosphate (ATP). This finding suggests that Ca2+ changes the chirality of the three-dimensional bending waves of sperm flagella.

Antisera to calreticulin inhibits sperm motility in mice

Mouse sperm were rapidly immobilized when exposed to rabbit antisera against rat calreticulin. The inhibition of sperm motility was concentration dependent at dilutions 1:50-350. The velocity of sperm did not change significantly as long as they were motile. Neither motility nor velocity of sperm was affected by adding sheep antisera to bovine calmodulin. The antisera to calreticulin also inhibited in vitro fertilization of mouse eggs. Using the avidin-biotin-peroxidase complex method, the antigen was found to be localized in the acrosome of sperm. The results indicate that calreticulin is present in the acrosome of mouse sperm and may play an important role in sperm motility.

Decrease of internal free calcium and human sperm movement

In order to elucidate the effects of calcium on the movement of human spermatozoa, studies were conducted using motile cells selected by swim-up migration at 37 degrees C in 5% CO2 in air in a synthetic BWW medium containing 1.7 x 10(-3) M CaCl2 or BWW without added calcium (BWW-Ca). Preliminary experiments have confirmed that the addition of EGTA (5 x 10(-3); 10(-2) M) to BWW medium decreased the intracellular calcium concentration ((Ca++)i) of spermatozoa, as measured in cells loaded with a fluorescent Ca++ indicator, Quin-2. Concomitant measurements of (Ca++)i and sperm movement (analysed by videomicrography at 200 f/s at room temperature) were carried out on Quin-2 loaded cells incubated in BWW-Ca medium plus EGTA (10(-5) M; 10(-4) M; 10(-3) M). Under these conditions a decrease in (Ca++)i was observed and associated with a decrease in mean amplitude of lateral head displacement (ALH). Analysis using an automatic analyser (Hamilton Thorn at 37 degrees C) confirmed these results: the percentage of spermatozoa swimming with ALH greater than or equal to 6 microns is decreased when the external free calcium in BWW-Ca is decreased by the addition of 10(-5) M, 10(-4) M, or 10(-3) M EGTA. Flagellar analysis of the sperm population characterized by ALH greater than or equal to 6 microns showed a large proximal curvature of the tail associated with a low propagation wave velocity and a low beat frequency as compared to the spermatozoa with ALH less than 6 microns with similar progressive velocities. These characteristics result in a high flagellar beat efficiency (in terms of head displacement per beat). The disappearance of this pattern of movement when intracellular calcium is lowered indicates that calcium plays a complex role in the relationship between curvature and wave propagation. The ability of spermatozoa to modulate their movement in response to an alteration in the intracellular calcium level confirms the role of calcium in controlling flagellar movement in intact cells.

Changes in intracellular calcium of porcine sperm during in vitro incubation with seminal plasma and a capacitating medium

The intracellular free Ca2+ concentration in ejaculated, porcine sperm was determined with a fluorescent, Ca2(+)-specific probe, Fura 2. Following suspension of sperm in a medium capable of sustaining capacitation and the acrosome reaction, the intracellular [Ca2+] increased from an initial value of about 75 nM to a peak value of 130 nM, after about 4 to 5 h of incubation. Within this period of time, a peak value of 246 nM was attained when sperm was incubated in seminal plasma. Ca2+ uptake is presumably not associated with membrane potential-dependent channels. The results indicate that a pronounced increase in intracellular free Ca2+ occurs towards the end of the incubation period when rather synchronous acrosome reactions take place in the sperm population, either in capacitating medium or in seminal plasma.