Flagellar movement of intact and demembranated, reactivated ram spermatozoa

Update on mammalian sperm capacitation: how much does the horse differ from other species?

In contrast to various other mammalian species, conventional in vitro fertilization (IVF) with horse gametes is not reliably successful. In particular, stallion spermatozoa fails to penetrate the zona pellucida, most likely due to incomplete activation of stallion spermatozoa (capacitation) under in vitro conditions. In other mammalian species, specific capacitation triggers have been described; unfortunately, none of these is able to induce full capacitation in stallion spermatozoa. Nevertheless, knowledge of capacitation pathways and their molecular triggers might improve our understanding of capacitation-related events observed in stallion sperm. When sperm cells are exposed to appropriate capacitation triggers, several molecular and biochemical changes should be induced in the sperm plasma membrane and cytoplasm. At the level of the sperm plasma membrane, (1) an increase in membrane fluidity, (2) cholesterol depletion and (3) lipid raft aggregation should occur consecutively; the cytoplasmic changes consist of protein tyrosine phosphorylation and elevated pH, cAMP and Ca2+ concentrations. These capacitation-related events enable the switch from progressive to hyperactivated motility of the sperm cells, and the induction of the acrosome reaction. These final capacitation triggers are indispensable for sperm cells to migrate through the viscous oviductal environment, penetrate the cumulus cells and zona pellucida and, finally, fuse with the oolemma. This review will focus on molecular aspects of sperm capacitation and known triggers in various mammalian species. Similarities and differences with the horse will be highlighted to improve our understanding of equine sperm capacitation/fertilizing events.

Regulation of axonemal motility in demembranated equine sperm

Equine in vitro fertilization is not yet successful because equine sperm do not effectively capacitate in vitro. Results of previous studies suggest that this may be due to failure of induction of hyperactivated motility in equine sperm under standard capacitating conditions. To evaluate factors directly affecting axonemal motility in equine sperm, we developed a demembranated sperm model and analyzed motility parameters in this model under different conditions using computer-assisted sperm analysis. Treatment of ejaculated equine sperm with 0.02% Triton X-100 for 30 sec maximized both permeabilization and total motility after reactivation. The presence of ATP was required for motility of demembranated sperm after reactivation, but cAMP was not. The calculated intracellular pH of intact equine sperm was 7.14 ± 0.07. Demembranated sperm showed maximal total motility at pH 7. Neither increasing pH nor increasing calcium levels, nor any interaction of the two, induced hyperactivated motility in demembranated equine sperm. Motility of demembranated sperm was maintained at free calcium concentrations as low as 27 pM, and calcium arrested sperm motility at much lower concentrations than those reported in other species. Calcium arrest of sperm motility was not accompanied by flagellar curvature, suggesting a failure of calcium to induce the tonic bend seen in other species and thought to support hyperactivated motility. This indicated an absence, or difference in calcium sensitivity, of the related asymmetric doublet-sliding proteins. These studies show a difference in response to calcium of the equine sperm axoneme to that reported in other species that may be related to the failure of equine sperm to penetrate oocytes in vitro under standard capacitating conditions. Further work is needed to determine the factors that stimulate hyperactivated motility at the axonemal level in equine sperm.

Regulations of microtubule sliding by Ca2+ and cAMP and their roles in forming flagellar waveforms

The function of Ca(2+) and cAMP in extruding doublet microtubules from sea urchin sperm axoneme and generating flagellar waves was investigated in order to clarify the regulatory mechanism of microtubule sliding and the formation mechanism of beating patterns of cilia and flagella. Almost all potentially asymmetric spermatozoa that were demembranated with Triton in the absence of Ca(2+) and reactivated with MgATP(2-) (Gibbons, B.H. and Gibbons, I.R. (1980). J. Cell Biol., 84: 13-27), beat with planar waves closely resembling those of the intact spermatozoa, whereas potentially symmetric spermatozoa, in which axonemal calmodulin was removed by detergent extraction in the presence of millimolar Ca(2+) (Brokaw, C.J. and Nagayama, S.M. (1985). J. Cell Biol., 100: 1875-1883), beat with three-dimensional waves if they were reactivated with low MgATP(2-). At a high MgATP(2-), almost all demembranated spermatozoa beat with planar waves. cAMP enhanced the three-dimensionality of the flagellar waves at a low Ca(2+). These changes in the flagellar waves were caused by different regulations of the microtubule sliding by calcium, cAMP, and MgATP(2-).

High-speed digital imaging of ependymal cilia in the murine brain

The development and health of mammals requires proper ciliary motility. Ciliated epithelia are found in the airways, the uterus and Fallopian tubes, the efferent ducts of the testes, and the ventricular system of the brain. A technique is described for the motion analysis of ependymal cilia in the murine brain. Vibratome sections of the brain are imaged by differential interference contrast microscopy and recorded by high-speed digital imaging. Side views of individual cilia are traced to establish their bending pattern. Tracking of individual cilia recorded in top view allows determination of bend planarity and beat direction. Ciliary beat frequency is determined from line scans of image sequences. The capacity of the epithelium to move fluid and objects is revealed by analyzing the velocity of polystyrene beads added to brain sections. The technique is useful for detailed assessment of how various conditions or mutations affect the fidelity of ciliary motility at the ependyma. The methods are also applicable to other ciliated epithelia, for example, in airways.

Testicular descent, sperm maturation and capacitation. Lessons from our most distant relatives, the monotremes

The present review examines whether monotremes may help to resolve three questions relating to sperm production in mammals: why the testes descend into a scrotum in most mammals, why spermatozoa are infertile when they leave the testes and require a period of maturation in the specific milieu provided by the epididymides, and why ejaculated spermatozoa cannot immediately fertilise an ovum until they undergo capacitation within the female reproductive tract. Comparisons of monotremes with other mammals indicate that there is a need for considerable work on monotremes. It is hypothesised that testicular descent should be related to epididymal differentiation. Spermatozoa and ova from both groups share many of the proteins that are thought to be involved in gamete interaction, and although epididymal sperm maturation is significant it is probably less complex in monotremes than in other mammals. However, the monotreme epididymis is unique in forming spermatozoa into bundles of 100 with greatly enhanced motility compared with individual spermatozoa. Bundle formation involves a highly organised interaction with epididymal proteins, and the bundles persist during incubation in vitro, except in specialised medium, in which spermatozoa separate after 2–3 h incubation. It is suggested that this represents an early form of capacitation.

Hyperactivation of monkey spermatozoa is triggered by Ca2+ and completed by cAMP

Digital image analysis of the flagellar movements of cynomolgus macaque spermatozoa hyperactivated by caffeine and cAMP was carried out to understand the change in flagellar movements during hyperactivation. The degree of flagellar bending increased remarkably after hyperactivation, especially at the base of the midpiece. Mainly two beating patterns were seen in the hyperactivated monkey sperm flagella: remarkably asymmetrical flagellar bends of large amplitude and relatively symmetrical flagellar bends of large amplitude. The asymmetrical bends were often seen in the early stage of hyperactivation, whereas the symmetrical bends executed nonprogressive, figure-of-eight movement. Beat frequency of the hyperactivated spermatozoa significantly decreased while wavelength of flagellar waves roughly doubled. To determine the conditions under which the axonemes of hyperactivated sperm flagella have asymmetrical or symmetrical bends, the plasma membranes of monkey spermatozoa were extracted with Triton X-100 and motility was reactivated with MgATP(2-) under various conditions. The asymmetrical flagellar bends were brought about by Ca(2+), whereas the symmetrical flagellar bends resulted from low levels of Ca(2+) and high levels of cAMP. Under these conditions, beat frequency and wavelength of flagellar waves of demembranated, reactivated spermatozoa were similar to those of the hyperactivated spermatozoa. These results suggest that during hyperactivation of monkey spermatozoa intracellular Ca(2+) concentrations first rise, and then decrease while cAMP concentrations increase simultaneously.

Hyperactivation is the mode conversion from constant-curvature beating to constant-frequency beating under a constant rate of microtubule sliding

Flagellar beating of hyperactivated golden hamster spermatozoa was analyzed in detail using digital image analysis and was compared to that of nonhyperactivated (activated) spermatozoa in order to understand the change in flagellar beating during hyperactivation and the active microtubule sliding that brought about the change in flagellar beating. Hyperactivated flagellar beating, which was characterized by a sharp bend in the proximal midpiece and low beat frequency, was able to alter the waveform with little change in beat frequency (constant-frequency beating), whereas activated flagellar beating, which was characterized by a slight bend in the proximal midpiece and high beat frequency, was able to alter beat frequency with little change in the waveform (constant-curvature beating). These results demonstrate that flagellar beating of hyperactivated and activated spermatozoa were essentially different modes and that hyperactivation was the mode conversion from constant-curvature beating to constant-frequency beating. Detailed analysis of flagellar bends revealed that the increase in curvature in the proximal midpiece during hyperactivation was due to the increase in total length of microtubule sliding in a nearly straight region between bends, while the rate of microtubule sliding remained almost constant.

Post-testicular sperm environment and fertility

When mammalian spermatozoa exit the testis, they show a highly specialized morphology; however, they are not yet able to carry out their task: to fertilize an oocyte. This property, that includes the acquisition of motility and the ability to recognize and to fuse with the oocyte investments, is gained only after a transit through the epididymis during which the spermatozoa from the testis travel to the vas deferens. The exact molecular mechanisms that turn these cells into fertile gametes still remain mysterious, but surface-modifying events occurring in response to the external media are key steps in this process. Our laboratory has established cartographies of secreted (secretomes) and present proteins (proteomes) in the epididymal fluid of different mammals and have shown the regionalized variations in these fluid proteins along the epididymis. We have found that the main secreted proteins are common in different species and that enzymatic activities, capable of controlling the sperm surface changes, are present in the fluid. Our studies also indicate that the epididymal fluid is more complex than previously thought; it contains both soluble and particulate compartments such as exosome-like vesicles (epididymosomes) and certainly specific glycolipid-protein micelles. Understanding how these different compartments interplay to modify sperm components during their transit will be a necessary step if one wants to control and to ameliorate sperm quality and to obtain valuable fertility markers helpful to establish a male fertility based genetic selection.

Motor apparatus in human spermatozoa that lack central pair microtubules

Electron microscopic examination of the spermatozoa from a man suffering from asthenozoospermia (poor or low sperm motility) showed that approximately 92% of the sperm flagella lacked central pair microtubules but possessed dynein arms and radial spokes while a small percentage of the spermatozoa had complete flagella. The characteristics of the motor apparatus of the spermatozoa and the effects of caffeine on the sperm motility were examined, as were the reactivation of demembranated spermatozoa and the sliding of doublet microtubules. Almost all spermatozoa were immotile in a Tyrode solution while only a small percentage of spermatozoa showed slow forward movement or feeble flagellar vibration, whereas addition of caffeine to the sperm suspension induced forward swimming of approximately half of the spermatozoa. The reactivation of demembranated spermatozoa with MgATP(2-) could not succeed because of disintegration of the demembranated flagella. However, when the demembranated spermatozoa were exposed to MgATP(2-) and then treated with elastase, the microtubular doublets of approximately half the number of the flagella slid from the end or middle of the flagella. These results suggest that the motor apparatus in the sperm flagella that lack the central pair microtubules is functionally assembled and intrinsically capable of undergoing flagellar movement but not strong enough to beat normally.

Hyperactivated motility of bull sperm is triggered at the axoneme by Ca2+ and not cAMP

Hyperactivated motility, a swimming pattern of mammalian sperm in the oviduct, is essential for fertilization in vivo. It is characterized by high-amplitude flagellar waves and, usually, highly asymmetrical flagellar beating. It had been suggested, but not tested, that Ca2+ and cAMP switch on hyperactivation by directly affecting the flagellar axoneme. In this study, the direct affects of these agents on the axoneme were tested by using detergent-demembranated bull sperm. As confirmed by TEM, treatment of sperm with 0.2% Triton X-100 disrupted the plasma, acrosomal, and inner mitochondrial membranes, leaving axonemes intact. In the presence of 2 mM ATP, the percentage of reactivated sperm that were hyperactivated increased to 80% when free Ca2+ was increased from 50 to 400 nM. The effect of the Ca2+ in this range was to increase beat asymmetry by increasing the curvature of the principal bend. No additional increases were observed above 400 nM free Ca2+, but motility was suppressed at 1 mM. The ability of Ca2+ to produce hyperactivation depended on ATP availability, such that more ATP was required to produce the high amplitude flagellar bends characteristic of hyperactivated motility than to produce activated motility. Cyclic AMP was not required for reactivation, nor for hyperactivation. Production of hyperactivated motility also required an alkaline environment (pH 7.9-8.5). These results suggest that, provided sufficient ATP is present and pH is sufficiently alkaline, Ca2+ switches on hyperactivation by enabling curvature of the principal bends to increase.

Identification of dynein heavy chain 7 as an inner arm component of human cilia that is synthesized but not assembled in a case of primary ciliary dyskinesia

Although the basic structure of the axoneme has been highly conserved throughout evolution, the varied functions of specialized axonemes require differences in structure and regulation. Cilia lining the respiratory tract propel mucus along airway surfaces, providing a critical function to the defense mechanisms of the pulmonary system, yet little is known of their molecular structure. We have identified and cloned a dynein heavy chain that is a component of the inner dynein arm. Bronchial epithelial cells were obtained from normal donors and from a patient with primary ciliary dyskinesia (PCD) whose cilia demonstrated an absence of inner dynein arms by electron microscopy. Cilia from normal and PCD cells were compared by gel electrophoresis, and mass spectrometry was used to identify DNAH7 as a protein absent in PCD cilia. The full-length DNAH7 cDNA was cloned and shares 68% similarity with an inner arm dynein heavy chain from Drosophila. DNAH7 was induced during ciliated cell differentiation, and immunohistochemistry demonstrated the presence of DNAH7 in normal cilia. In cilia from PCD cells, DNAH7 was undetectable, whereas intracellular DNAH7 was clearly present. These studies identify DNAH7 as an inner arm component of human cilia that is synthesized but not assembled in a case of PCD.

Maintenance of motility in mouse sperm permeabilized with streptolysin O

One approach to studying the mechanisms governing sperm motility is to permeabilize sperm and examine the regulation of motility by manipulating the intracellular milieu of the cell. The most common method of sperm permeabilization, detergent treatment, has the disadvantage that the membranes and many proteins are extracted from the cell. To avoid this problem, we have developed a method that uses streptolysin O to create stable pores within the plasma membrane while leaving internal membranes intact. Sperm were permeabilized, preincubated, and then treated with 0.6 U/ml of streptolysin O. Permeabilization was assessed by fluorescent dye technologies and endogenous protein phosphorylation using exogenously added [gamma-32P]ATP. Streptolysin O-induced permeabilization rendered the sperm immotile, and the effect was Ca2+-dependent. When the cells were treated simultaneously with a medium containing ATP, streptolysin O-treated sperm maintained flagellar movement. These results demonstrate that the streptolysin O permeabilization model system is a useful experimental method for studying the mechanisms that regulate sperm motility since it allows the flagellar apparatus to be exposed to various exogenously added molecules.

Manipulation of bovine sperm metabolism and motility using anoxia and phosphodiesterase inhibitors

Bovine sperm that were subjected to extended anoxia (2.5 h) in the absence of glycolytic substrates then diluted into oxygenated medium were immotile but metabolically active, producing ATP from lactate via oxidative phosphorylation. In response to anoxia sperm ATP titers dropped from 15-20 mumoles/10(8) cells to 1-2 mumoles/10(8) cells in the first 5 min then remained extremely low until reoxygenation. Cyclic AMP titers declined slowly over the anoxic period, but did not show the same scale of depression as ATP. After dilution and re-oxygenation ATP recovered to pre-anoxia levels within 1 min, and cAMP rose to about the pre-anoxia levels. However, motility, which varied quantitatively and qualitatively between ejaculates prior to anoxic treatment, was substantially depressed after extended anoxia in all cases; progressive motility was almost non-existent in post-anoxic sperm. Addition of isobutylmethylxanthine or Cibacron Blue F3GA, both putative phosphodiesterase inhibitors, stimulated a transient peak of cAMP, which was accompanied by motility stimulation. These techniques provide a protocol to manipulate and dissect the biochemical pathways of motility initiation in mammalian sperm.

Reactivated movement of decondensed rat sperm models and a description of their ultrastructure

This study aimed at finding optimal conditions to decondense rat sperm nuclear chromatin with minimal damage. This was judged by the ability of the sperm-tail axoneme in the partially decondensed sperm models to be reactivated. Decondensation was assessed by phase contrast microscopy. Partial decondensation was judged to occur when the bright refractive appearance of the sperm nucleus turned black, and full decondensation when the nucleus turned pale and increased in volume. Demembranation was shown to have occurred by electron microscopy. With 0.03% Triton X-100 rat caudal epididymal sperm were partially demembranated to produce sperm models. Demembranation using a 0.1% solution of Triton X-100 was complete, but as with the solution of 0.05% Triton X-100, resulted in poorer reactivation of the partially decondensed sperm models. Reactivated movement of decondensed sperm models was used to assess the effect of the decondensing agents DTT and heparin. We were only able to achieve reactivation of sperm models that had undergone partial decondensation. Optimal reactivation was obtained after rat sperm models had decondensed in the decondensation solution containing 5 mM DTT, 6 mM EDTA, and 27.3 or 34.1 USP/ml heparin. Concentrations of heparin above or below these values resulted in a decrease in the number of sperm models reactivated. Ultrastructurally, sperm partially decondensed with 5 mM DTT, 6 mM EDTA, and 34.1 USP/ml heparin had their plasma membrane further extracted compared with sperm treated with 0.03% Triton X-100 alone. Decondensation was greatest in the peripheral regions of the nucleus with extraction of the acrosome but not of the perforatorium. The decondensed regions had a filamentous appearance. This procedure will allow access to sperm nuclear chromatin for experimental manipulation in rat sperm models.

Borrelia burgdorferi swims with a planar waveform similar to that of eukaryotic flagella

Borrelia burgdorferi is a motile spirochete with multiple internal periplasmic flagella (PFs) attached near each end of the cell cylinder; these PFs overlap in the cell center. We analyzed the shape and motion of wild type and PF-deficient mutants using both photomicrography and video microscopy. We found that swimming cells resembled the dynamic movements of eukaryotic flagella. In contrast to helically shaped spirochetes, which propagate spiral waves, translating B. burgdorferi swam with a planar waveform with occasional axial twists; waves had a peak-to-peak amplitude of 0.85 micron and a wavelength of 3.19 microns. Planar waves began full-sized at the anterior end and propagated toward the back end of the cell. Concomitantly, these waves gyrated counter-clockwise as viewed from the posterior end along the cell axis. In nontranslating cells, wave propagation ceased. Either the waveform of nontranslating cells resembled the translating form, or the cells became markedly contorted. Cells of the PF-deficient mutant isolated by Sadziene et al. [Sadziene, A., Thomas, D. D., Bundoc, V. G., Holt, S. C. & Barbour, A. G. (1991) J. Clin. Invest. 88, 82-92] were found to be relatively straight. The results suggest that the shape of B. burgdorferi is dictated by interactions between the cell body and the PFs. In addition, the PFs from opposite ends of the cell are believed to interact with one another so that during the markedly distorted nontranslational form, the PFs from opposite ends rotate in opposing directions around one another, causing the cell to bend.

Effect of lipid peroxidation on beating frequency of human sperm tail

The tail beat frequency (TBF) of sperm was measured with a sperm-head fixation method which was based on the tendency of sperm to attach its head to the surface of a glass slide. Ferrous sulphate, a promotor of lipid peroxidation, inhibited TBF within 5 min of mixing with sperm. This inhibition can be reversed dose-dependently by superoxide dismutase, catalase, glutathione, and albumin. It was concluded that TBF could be a new pharmacological model for studying the effect of lipid peroxidation and antioxidant on sperm motility. Both enzymatic and non-enzymatic antioxidants can be screened with this method.

Role of cAMP in the reactivation of demembranated ram spermatozoa

Ejaculated ram sperm were demembranated with Triton X-100, separated from the detergent-soluble matrix, and reactivated [San Agustin and Witman (1993): Cell Motil. Cytoskeleton 24:264-273]. The percent motility of models prepared from freshly washed sperm was comparable to that of the washed sample before demembranation, regardless of whether cAMP was included in the reactivation medium. However, demembranated models derived from aging or metabolically inhibited sperm exhibited a lower percent reactivation and required cAMP to attain the level of motility of freshly washed sperm. Cyclic AMP was approximately 100 times more effective than cGMP. The requirement for cAMP could be bypassed by addition of porcine heart cAMP-dependent protein kinase (PKA) catalytic subunit to the reactivation medium, demonstrating that cAMP was acting via PKA. The cAMP stimulation of reactivation was not affected by inclusion of the PKA inhibitor PKI(5-24) in the reactivation medium, but was decreased when the models were preincubated with PKI(5-24) prior to reactivation. The cytosol-free models retained > 90% of the sperm PKA activity; therefore, the PKA appears to be anchored to internal sperm structures. This PKA could not be extracted by cAMP or Triton X-100 alone, but only by cAMP and Triton X-100 in combination. We conclude that cAMP-dependent protein phosphorylation is critical for sperm motility, but that the essential protein phosphate sites turn over slowly under our reactivation conditions, so that the cAMP requirement is apparent only in models prepared from sperm having a low internal ATP or cAMP content. Interestingly, reactivation was rapidly blocked by the peptide arg-lys-arg-ala-arg-lys-glu, which has been reported to be a selective inhibitor of cGMP-dependent protein kinase.

Novel touch-induced, Ca(2+)-dependent phobic response in a flagellate green alga

The biflagellate green alga Spermatozopsis similis exhibits a remarkable avoidance reaction in addition to the photophobic or stop response characteristic of such algae. S. similis normally swims forward with its anteriorly attached flagella directed posteriorly and propagating sine-like waves base to tip. Upon contact with surfaces or other cells, S. similis responds with rapid backward swimming, covering distances of up to 50 microns in 140 to 220 msec. This reaction, which we term the mechanoshock response, also can be triggered by vigorous mechanical stimulation, but not by physiological light intensities. It consists of 3 phases: (1) a rapid acceleration phase with average duration of 31 msec; (2) a phase of about 66 msec with constant high speed (maximal velocities of > 600 microns.sec-1) or slow deceleration; and (3) a deceleration phase of approximately 83 msec, followed by a stop or short period of circling. The cells then resume forward swimming in a random direction. Prior to the mechanoshock response the flagella rapidly are brought together into a close parallel configuration extending anteriorly of the cell body. They then appear to propel the cell by undulatory beating, while the cell describes a pronounced helical path. Small decreases in the extracellular Ca2+ concentration, as well as low concentrations of Ba2+, strongly suppress the probability of this phobic reaction. We conclude that this mechanoshock response involves large Ca2+ influxes, probably mediated by mechanosensitive and/or stretch-activated ion-channel(s).

Tail beat frequency of human sperm: evaluated with sperm head fixation method and computer-assisted semen analysis

Tail beat frequency (TBF) of individual sperm in 15 semen samples was evaluated with a sperm head fixation method (SHFM). Motility parameters of the semen samples were also measured with computer-assisted semen analysis (CASA). The TBF obtained from SHFM correlated best with beat cross-frequency obtained from CASA. The TBF measured soon after sperm head fixation also correlated well with total motility and rapid motility, but not with progress motility and critical motility measured with CASA. SHFM is a simple method for the study of tail beat frequency and the TBF of individual sperm is closely related to the overall motility in a semen sample.

A motile human sperm head fixation method

In a solution containing less than 5% seminal fluid, human sperm has a tendency to attach its head on the smooth surface of an object. Based on such a phenomenon, a simple method was developed to fix sperm head on the surface of glass slide. This method was demonstrated by studying caffeine effect on the tail movement of human sperm in phosphate buffered saline. By analysing the images recorded on a videocassette, caffeine, a well known stimulator of human sperm motility, was shown to induce an immediate increase of sperm TBF (tail beat frequency) and the amplitude of TBF increase was found to be larger in sperm with lower basal TBF value. This method can provide a flock of head-fixed motile sperm for a precise sperm tail movement assessment or for other purposes.

Reactivation of demembranated, cytosol-free ram spermatozoa

A procedure for preparing cytosol-free ram sperm models was developed. Sperm are introduced to a Triton X-100-containing demembranation medium layered on top of a discontinuous Percoll gradient. After brief exposure to the demembranating solution, the sperm are separated from the detergent-soluble components by centrifugation through a 55% Percoll layer, finally collecting on top of a 90% Percoll cushion from where they are recovered. Optimum conditions consisted of Triton X-100 at 0.20% and a demembranation time of 35 sec. Cross-sections of midpieces and principal pieces of the demembranated sperm were examined by electron microscopy. With 0.20% Triton X-100 in the demembranation medium, 86% of the cross-sections showed no plasma membranes and the rest had broken plasma membranes. The remaining tail structures appeared to be morphologically intact. Assay of phosphoglucose isomerase as a marker enzyme confirmed that at least 98% of the cytosolic protein was removed. Ram sperm models obtained by this procedure could be reactivated, and the percent motility and beat parameters were similar to those of the intact sperm. Reconstitution with the detergent-soluble components was neither required for, nor enhanced, reactivation. Therefore, demembranated ram sperm do not require a detergent-soluble protein factor for reactivation.

The motile beta/IC1 subunit of sea urchin sperm outer arm dynein does not form a rigor bond

We used in vitro translocation and cosedimentation assays to study the microtubule binding properties of sea urchin sperm outer arm dynein and its beta/IC1 subunit. Microtubules glided on glass-absorbed sea urchin dynein for a period of time directly proportional to the initial MgATP2- concentration and then detached when 70-95% of the MgATP2- was hydrolyzed. Detachment resulted from MgATP2- depletion, because (a) perfusion with fresh buffer containing MgATP2- reconstituted binding and gliding, (b) microtubules glided many minutes with an ATP-regenerating system at ATP concentrations which alone supported gliding for only 1-2 min, and (c) microtubules detached upon total hydrolysis of ATP by an ATP-removal system. The products of ATP hydrolysis antagonized binding and gliding; as little as a threefold excess of ADP/Pi over ATP resulted in complete loss of microtubule binding and translocation by the beta/IC1 subunit. In contrast to the situation with sea urchin dynein, microtubules ceased gliding but remained bound to glass-absorbed Tetrahymena outer arm dynein when MgATP2- was exhausted. Cosedimentation assays showed that Tetrahymena outer arm dynein sedimented with microtubules in an ATP-sensitive manner, as previously reported (Porter, M.E., and K. A. Johnson. J. Biol. Chem. 258: 6575-6581). However, the beta/IC1 subunit of sea urchin dynein did not cosediment with microtubules in the absence of ATP. Thus, this subunit, while capable of generating motility, lacks both structural and rigor-type microtubule binding.

Reversible intracellular ATP changes in intact rat spermatozoa and effects on flagellar sperm movement

The initiation of motility and modification of energy metabolism of rat caudal epididymal spermatozoa can be induced by dilution in a saline medium. We have investigated in these cells the relationships between the energy reserve (sperm ATP content measured by bioluminescence) and flagellar movement (high speed videomicrography, 200 frames/sec). A steady state was observed in sperm ATP content, progressive velocity (Vp) and flagellar beat frequency (F) with sperm dilution in a medium with glucose, lactate, pyruvate and acetate substrates after 30 minutes of incubation. Without these substrates, changes in metabolic pathways occurred immediately and initially disturbed the relationship between ATP levels and F, suggesting differences in motility initiation when energy is from an endogenous origin via mitochondrial oxidative phosphorylation. This "energy crisis" was reversed by the addition of substrates to the medium. The three-dimensional flagellar movement observed in the presence of substrates quickly became two-dimensional in their absence. The flagellar beat envelope became more splayed, the mean amplitude of lateral head displacement increased and F decreased. The resulting high flagellar beat efficiency can be compared to that observed during hyperactivation which is a physiological event related to a fall in intracellular ATP level. In both media, the displacement of the flagellum in relation to the wave axis varied sinusoidally. The sine period increased with time when the spermatozoa were incubated in the medium without substrates. These results suggest a gradual slowing-down of the velocity of wave formation in the proximal part of the flagellum.

Effects of pH on the reactivation of human spermatozoa demembranated with Triton X-100

The aim of this work was to study the role of different parameters involved in the motility of human spermatozoa. Human spermatozoa were totally demembranated with 0.05% Triton X-100, and the demembranation was checked using electron microscopy. We have shown that, with a concentration of ATP-Mg lower than 2 mM, a pH effect was observed with a dose-dependent motility reactivation at pH 7.1, with 14% +/- 2.0% motile cells at 1 mM ATP-Mg and a straight line velocity (VSL) of 12.0 +/- 1.4 microns/sec. However, at pH 7.8, more than 65% of the spermatozoa were reactivated with as low as 0.02 mM ATP-Mg and 77.8% +/- 2.5% of them were motile at 1 mM ATP-Mg and had a VSL of 23.4 +/- 3.9 microns/sec. The depletion of free calcium by the addition of 0.5 mM EGTA in the reactivation medium (RM) improved the percentage of motile cells and the VSL most markedly at low ATP-Mg and low pH. If no MgSO4 was added in RM, cells were not motile at pH 7.8, but 30-40% reactivated at pH 7.1. If 5 mM Ca2+ was added to the RM, up to 88% of the cells became reactivated at both pHs, but the beat frequencies were very low, suggesting different mechanisms of reactivation when Mg2+ or when Ca2+ is present in the RM.