Changes in internal pH associated with initiation of motility and acrosome reaction of sea urchin sperm

What does a common channel for electrolytes and non-electrolytes in the sperm mean?

Cell volume is central to osmoregulation in intact cells. Bovine spermatozoa, as also other mammalian spermatozoa, exhibit a very rapid regulatory volume decrease (RVD) when exposed to hypotonic saline media. This response, fastest known in animal cells, is mediated by a putative potassium channel which the pharmacological properties of a conventional channel and yet admits both electrolytes and non-electrolytes. The evolutionary basis and functional role of this conserved quinine-sensitive channel in mammalian sperm could offer hitherto unexplored facets of the link(s) between ecology and reproduction.

Hydrogen ion gradients across the mitochondrial, endosomal and plasma membranes in bloodstream forms of trypanosoma brucei solving the three-compartment problem

Conditions for the use of both [14C]methylamine and 5, 5-dimethyl[14C]oxa-azolidine-2,4-dione (DMO) to measure the H+ concentration of intracellular compartments of monomorphic long thin bloodstream forms of Trypanosoma brucei were established. Neither probe was actively transported or bound to internal components of the cell and both probes equilibrated passively with a t1/2 close to 8 min. DMO was excluded from cells, while methylamine was accumulated but not metabolized. Solution of the three-compartment problem revealed that, when cells were respiring aerobically on glucose at an external pH of 7.5, the cytoplasmic pH was in the range 6.99-7.03, the pH of the mitochondrial matrix was 7.71-7.73, and the algebraic average pH of the various endosomal compartments was 5.19-5.50. Similar values were found when cells were respiring aerobically on glycerol. However, bloodstream forms of T. brucei could not maintain a constant internal H+ concentration outside the external pH range 7.0-7.5, and no evidence for the presence of an H+/Na+ exchanger was found. Full motility and levels of pyruvate production were maintained as the external pH was raised as high as 9.5, suggesting that these cells tolerate significant internal alkalinisation. However, both motility and pyruvate production were severely inhibited under acidic conditions, and the cells deteriorated rapidly below an external pH of 6.5. Physiologically, the plasma membrane of T. brucei had low permeability to H+ and the internal pH was unaffected by changes in Deltapsip, which is dominated by the potassium diffusion potential. However, in the presence of FCCP, the internal pH fell rapidly about 0.5 pH unit and came into equilibrium with Deltapsip. Oligomycin abolished the mitochondrial pH gradient (DeltapHm) selectively, whereas chloroquine abolished only the endosomal pH gradient (DeltapHe). The pH gradient across the plasma membrane (DeltapHp) alone could be abolished by careful osmotic swelling of cells. The plasma membrane had an inwardly directed proton-motive force (DeltaPp) of -52 mV and an inwardly directed sodium-motive force (DeltaNp) of -149 mV, whereas the mitochondrial inner membrane had only an inwardly directed DeltaPm of -195 mV. The pH gradient across the endosomal membranes was not accompanied by an electrical gradient. Consequently, endosomal membranes had an algebraically average outwardly directed DeltaPl within the range + 89 to +110 mV, depending on the measurement method.

Ion channels in sperm physiology

Fertilization is a matter of life or death. In animals of sexual reproduction, the appropriate communication between mature and competent male and female gametes determines the generation of a new individual. Ion channels are key elements in the dialogue between sperm, its environment, and the egg. Components from the outer layer of the egg induce ion permeability changes in sperm that regulate sperm motility, chemotaxis, and the acrosome reaction. Sperm are tiny differentiated terminal cells unable to synthesize protein and difficult to study electrophysiologically. Thus understanding how sperm ion channels participate in fertilization requires combining planar bilayer techniques, in vivo measurements of membrane potential, intracellular Ca2+ and intracellular pH using fluorescent probes, patch-clamp recordings, and molecular cloning and heterologous expression. Spermatogenic cells are larger than sperm and synthesize the ion channels that will end up in mature sperm. Correlating the presence and cellular distribution of various ion channels with their functional status at different stages of spermatogenesis is contributing to understand their participation in differentiation and in sperm physiology. The multi-faceted approach being used to unravel sperm ion channel function and regulation is yielding valuable information about the finely orchestrated events that lead to sperm activation, induction of the acrosome reaction, and in the end to the miracle of life.

Acrosome reaction inactivation in sea urchin sperm

Acrosome reaction inactivation (ARI) is a process that renders sperm irreversibly refractory to the egg jelly (the natural inducer of the acrosome reaction, AR). This process triggered by the egg jelly, is associated with an increase in [Ca2+]i. However, we show here that a rise in [Ca2+]i alone is not sufficient to induce ARI, since artificially increasing [Ca2+]i with either an ionophore or rising external pH, does not trigger ARI. Contrary to the AR which strictly requires Ca2+, ARI can be triggered almost equally well by Sr2+. On the other hand, Mn2+ inhibits ARI and, as we showed earlier, does not affect AR. These observations indicate that the mechanisms involved in ARI differ from those leading to AR. In addition, we report here that high external pH (a non-physiological inducer of AR) triggers the AR in previously inactivated sperm by opening the same Ca2+ channels activated by the egg jelly. Considering that the opening of Ca2+ channels is one of the earliest responses triggered by the egg jelly and that ARI requires the egg jelly receptor to be activated, we have concluded that ARI involves the uncoupling between the egg jelly receptor and Ca2+ channels. Furthermore, intracellular pH (pHi) determinations, in the presence or absence of ionomycin to substitute for the uncoupled Ca2+ channels, indicate that pHi regulation is also impaired in inactivated sperm. In conclusion, ARI is a manifestation of the uncoupling of the egg jelly receptor from the different ion transport systems required for the acrosome reaction.

Inositol triphosphate receptors in sea urchin sperm

Inositol 1,4,5-triphosphate (Ins(1,4,5)P3) is a second messenger that regulates Ca2+ channels in many important cell signalling pathways. In sea urchin sperm the outer investment of the egg triggers the acrosome reaction (AR) that involves Ins(1,4,5)P3 production and the opening of two Ca2+ channels. Here we have sought to identify a high-affinity Ins(1,4,5)P3 receptor in Strongylocentrotus purpuratus sperm. An Ins(1,4,5)P3 binding component was affinity-purified 12-fold from sperm extracts. It displayed similar characteristics to the Ins(1,4,5)P3 receptor from other sources: pH-dependent high affinity for Ins(1,4,5)P3 (KD = 261 nM), a tau1/2 of association and dissociation of 50 and 40 s, respectively, specificity (IC50 > 5 microM for Ins(1)P1, Ins(1,4)P2 and Ins(1,3,4,5)P4), and pharmacological sensitivity (10 and 100 microg heparin/ml inhibited 75% and 100% binding respectively). An antibody against the carboxy-terminal of the type I Ins(1,4,5)P3 receptor of somatic cells recognised a plasma membrane component in the sperm head and less intensely in the flagella. This antibody also recognised a 240 kDa band from isolated head plasma membranes, and weakly in flagellar membrane. This IP3 receptor-like protein may mediate the sustained uptake of Ca2+ through the second Ca2+ channel opened during the AR.

A method for preparation, storage, and activation of large populations of immotile sea urchin sperm

Reversible protein phosphorylation is associated with initiation and modulation of sperm flagellar motility. Many studies aimed at examining the signal transduction mechanisms underlying the expression of motility have relied on detergent-permeabilized sperm reactivated with exogenous 32P-ATP. However, the reactivation conditions allow variable levels of motility to be expressed and phosphorylation of many proteins that appear to be unrelated to sperm motility. Thus, identification of the few relevant proteins is difficult. We have developed a method to collect and keep sperm immotile until reactivated for analysis to normal motility levels. Artificial sea water (ASW) buffered with 5 mM 2-[N-morpholino]ethanesulfonic acid at pH 6.0 and containing 50 mM KCl allows collection and storage of immotile sea urchin sperm for up to 96 h at 4-5 degrees C. Motility under these conditions is essentially zero, but sperm is rapidly reactivated to normal motility by diluting with ASW to standard pH (8.0) and KCl concentration (10 mM).

Volume regulation of spermatozoa by quinine-sensitive channels

Bovine spermatozoa were shown to exhibit rapid regulatory volume decrease (RVD) when exposed to hypotonic saline media. This quinine- and quinidine-sensitive regulatory volume decrease was coincident with K+ release due to stretch-activation of inhibitor-specific presumptive K+ channels. The regulatory volume decrease response was much faster than a similar phenomenon observed in human peripheral blood lymphocytes. Studies on volume changes in different electrolyte and nonelectrolyte media suggested that: (1) this inhibitor-specific channel could also be a nonspecific pore in the spermatozoal membrane for nonelectrolytes below 150 daltons; (2) subpopulations (of nearly equal size) of the spermatozoa differ in the expression of the pore; (3) capacitation abolishes this distinction between subpopulations of spermatozoa; and (4) the general case of RVD for other mammalian spermatozoa was also established.

A model for flagellar motility

Experimental investigation has provided a wealth of structural, biochemical, and physiological information regarding the motile mechanism of eukaryotic flagella/cilia. This chapter surveys the available literature, selectively focusing on three major objectives. First, it attempts to identify those conserved structural components essential to providing motile function in eukaryotic axonemes. Second, it examines the relationship between these structural elements to determine the interactions that are vital to the mechanism of flagellar/ciliary beating. Third, the vital principles of these interactions are incorporated into a tractable theoretical model, referred to as the Geometric Clutch, and this hypothetical scheme is examined to assess its compatibility with experimental observations.

The role of potassium ion and extracellular alkalization in reinitiation of human spermatozoa preserved in electrolyte-free solution at 4 degrees C

OBJECTIVE

To elucidate reinitiation factors in human spermatozoa preserved in the electrolyte-free solution at 4 degrees C.

SETTING

Andrology laboratory of our hospital.

PATIENTS

Semen samples were obtained from patients attending our infertility clinic.

INTERVENTIONS

Ejaculated sperm were centrifuged and washed using the electrolyte-free Percoll gradient and then were preserved for 1 week at 4 degrees C.

MAIN OUTCOME MEASURES

The motility of preserved sperm was incubated and analyzed after the addition of electrolyte solutions.

RESULTS

The motility rate was 9.6% when the preserved sperm were incubated directly. The motility increased to 35.1% after alkalization (pH 7.8) and further increased to 40.7% when 0.1 mM KCl was added. The motility decreased to 1.4% in a weak acidic solution (pH 6.8), however, the addition of a > or = 10 mM concentration of NaCl or > or = 0.1 mM concentration of KCl increased in motility. The motility rate in 40 mM NaCl and 40 mM KCl (pH 6.8) was 19.8% and 31.5%, respectively. The restoration of motility by NaCl was inhibited by 1 mM amiloride. The motility also rose to 54.1% and 32.3% in 0.04% NH3 and 80 mM NH4Cl solution, respectively.

CONCLUSIONS

The reinitiation of preserved spermatozoa was induced by potassium ion and extracellular alkalization.

Intracellular pH of bovine sperm increases during capacitation

The effect of heparin-induced capacitation on the intracellular pH (pHi) of individual bovine sperm was determined with image analysis. Sperm were loaded with the acetoxymethyl ester of the pH sensitive fluorescent indicator, 2',7'-bis(carboxyethyl)-5(6)-carboxy-fluorescein (BCECF). The pHi of 5303 sperm was evaluated from a total of five bulls at .5, 2, 3, 4, and 5 h of incubation. The pHi did not differ between the sperm head and mid-piece (P > 0.05). An increase in sperm head pHi was seen in heparin-treated sperm at 3, 4, and 5 h of incubation relative to sperm incubated without heparin (control, P < 0.05). At 5 h of incubation, the pHi in heparin-treated sperm was 6.92 +/- 0.07, while control-treated sperm pHi was 6.70 +/- 0.03. Initially a normal frequency distribution was seen for sperm pHi in both heparin- and control-treated sperm. As the incubation progressed, the frequency distribution began to skew towards higher pHi in both samples but was more dispersed for the heparin-treated sperm. Following an NH4Cl-induced alkaline load, the pHi of both control- and heparin-treated sperm recovered toward the resting pHi with a half-time of recovery of 1.5-1.7 min. The recovery of sperm pHi was not due to leakage of NH4+ into sperm because recovery also occurred with trimethylamine. The instantaneous velocity of the pHi recovery (v(i)) was dependent on pHi and decreased as pHi decreased. Capacitation by heparin was associated with an 81% decrease in v(i) at a pHi of 7.00, but there was no effect of capacitation on the proton buffering power of the sperm, which was 87 +/- 8 mM/pH unit. Results demonstrate that both the regulation of pHi and resting pHi were altered during capacitation of bovine sperm by heparin.

Change in intracellular K+ concentration caused by external osmolality change regulates sperm motility of marine and freshwater teleosts

We previously demonstrated that osmolality isotonic to the seminal plasma suppresses sperm motility in marine and freshwater teleosts, and exposure of sperm to hypertonicity of sea water or hypotonicity of fresh water, respectively, induces the initiation of sperm motility at spawning. The motile sperm became immotile by return of osmolality to the isotonic osmolality both in a marine teleost, the puffer fish, and a freshwater teleost, the zebrafish. The initiation and termination of sperm motility could be repeated several times by changing surrounding osmolality in both species. In demembranated sperm, motility was suppressed by a K+ concentration equivalent to the seminal salt concentration in both puffer and zebrafish. Demembranated puffer sperm were reactivated when K+ concentration of the reactivating solution increased. Conversely, initiation of motility in the demembranated zebrafish sperm was induced by decreasing K+ concentration. The initiation and termination of the demembranated sperm were alternately repeated by changing K+ concentration of the reactivation solution in both species. Furthermore, intracellular K+ concentration rose when sperm motility of the puffer was initiated in hypertonic solutions. These results suggest that change in external osmolality is converted into change in intracellular K+ concentration, and that the change affects the flagellar axoneme as a signal to initiate or terminate sperm motility. The initiation and termination of motility in the demembranated puffer sperm were caused at a high pH and a low pH of the reactivating solution, respectively, suggesting the contribution of intracellular pH in the regulation of flagellar motility.

Measurement of intracellular pH in mammalian sperm cells under physiological conditions

The goal of this study was to develop a technique for the measurement of intracellular pH (pHi) in living mammalian (bovine) sperm cells under physiological conditions. Like many other biochemical measurements, pHi measurements have typically been made under non-physiological conditions on cells whose immediate functional status is not readily assessed and may even be non-viable. Additionally, many pHi measurement techniques may themselves alter the pHi of the cells being measured. Such measurements could yield misinformation. The sperm cell is unique in that its functional status can be easily and continuously monitored by means of its motility, which is directly affected by pHi. In this respect, the sperm cell provides an ideal model system for evaluating pHi measurement techniques. In this article we summarize the validation of a ratiometric absorbance technique for the measurement of pHi of mammalian (bovine) sperm cells under physiological conditions which does not affect their functional status. The pHi of ejaculated bovine sperm cells was calculated to be 6.9 +/- 0.05 (11 replicates). This approach may also be suitable for pHi measurements in other cell types.

Relationship between sperm ATP content and motility of carp spermatozoa

Carp spermatozoa are immotile in seminal plasma or in saline solution of high osmolality (&gt; 400 mosmol kg-1). These ‘quiescent’ spermatozoa initiate a progressive forward motility when transferred in freshwater or in saline solution with low osmolality (&lt; 160 mosmol kg-1). In this study we investigated ‘in vitro’ the relationship between sperm ATP content (measured by bioluminescence) and sperm motility (analysed by videomicroscopy). Sperm ATP content remained high in the immobilizing medium (200 mM KCl, Tris 30 mM, pH 8.0) where no flagellar movement occurs. Dilution of these spermatozoa in the activating medium (45 mM NaCl, 5 mM KCl, Tris 30 mM, pH 8.0) triggered forward motility which varied with temperature. At 20 degrees C, sperm ATP content decreased rapidly during the progressive forward motility phase from 12 to 4 nmol/10(8) spermatozoa, concomitantly with decreases in velocity (130 to 10 microns s-1) and the beat frequency (50 to 7 Hz). An inhibitor of mitochondrial respiration (KCN 10 mM) produced a drop in sperm ATP content irrespective of the incubation medium (activating or immobilizing). A second phase of sperm motility in the activating medium was induced following a previous transfer of spermatozoa into a medium of high osmolality for a few minutes prior to the second phase. Within 10 minutes, spermatozoa recover 90% of the initial ATP level as well as forward motility. These results suggest that motility of carp spermatozoa depends on sperm ATP synthesized by mitochondrial respiration mainly stored before activation. In low osmolality conditions, the mitochondrial oxidative phosphorylation is unable to compensate for the ATP hydrolysis required to sustain motility.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Anion channels in the sea urchin sperm plasma membrane

Ionic fluxes in sea urchin sperm plasma membrane regulate cell motility and the acrosome reaction (AR). Although cationic channels mediate some of the ionic movements, little is known about anion channels in these cells. The fusion of sperm plasma membranes into lipid bilayers allowed identification of a 150 pS anion channel. This anion channel was enriched from detergent-solubilized sperm plasma membranes using a wheat germ agglutinin Sepharose column. Vesicles formed from this preparation were fused into black lipid membranes (BLM), yielding single channel anion-selective activity with the properties of those found in the sperm membranes. The following anion selectivity sequence was found: NO3- > CNS- > Br- > Cl-. This anion channel has a high open probability at the holding potentials tested, it is partially blocked by 4,4'-diisothiocyano-2,2'-stilbendisulfonic acid (DIDS), and it often displays substates. The sperm AR was also inhibited by DIDS.

Rises of intracellular Ca2+ and pH mediate the initiation of sperm motility by hyperosmolality in marine teleosts

Spermatozoa of marine teleosts, puffers and flounder, were completely quiescent when they were washed to remove electrolytic components of the seminal plasma and then diluted in nonelectrolyte solutions isotonic to the seminal plasma. Sperm motility was initiated upon dilution in hypertonic nonelectrolyte solutions. These observations suggest that sperm motility is suppressed by seminal osmolality and motility is triggered solely by the increase in external osmolality which occurs at natural spawning in hypertonic seawater. Extracellular Ca2+ had no influence on the osmolality-dependent initiation of sperm motility. However, sperm motility was initiated even in isotonic solution when Ca2+ was introduced into the sperm cells by Ca2+ ionophore. Intracellular Ca2+ increased at the osmolality-dependent initiation of sperm motility under Ca(2+)-free conditions. These results suggest that the release of Ca2+ from intracellular storage in response to the increase in external osmolality has a key role in the initiation of sperm motility. A transient increase in intracellular pH was also observed at the hyperosmolality-dependent initiation of sperm motility. Furthermore, initiation of sperm motility was induced even in isotonic solutions when intracellular pH increased by the treatment with ammonium salts. These results suggest that an increase in intracellular pH, as well as the rise in intracellular Ca2+, has an important role in the initiation of sperm motility in marine teleosts.

The control of oxidant stress at fertilization

Metazoan eggs alter their coats after fertilization to protect the early embryo. In sea urchins, this modification consists of a rapid, coordinated set of noncovalent macromolecular assembly steps that are stabilized by protein cross-linking. The sea urchin egg uses an oxidative cross-linking reaction that requires hydrogen peroxide and a secreted peroxidase and thus faces the challenge of oxidant stress at the beginning of its development. Protection from the deleterious effects of this oxidative mechanism is afforded by regulation of the production and utilization of oxidizing species. This regulation requires a specific protein kinase C-activated oxidase and ovothiol, an intracellular antioxidant.

Localization of wheat germ agglutinin and antibody binding sites on the plasma membranes of sea urchin sperm heads as revealed by label-fracture and fracture-flip

Freeze-fracture electron microscopy reveals that intramembrane particles are concentrated in a band encircling the posterior portion of the acrosome of Strongylocentrotus purpuratus sperm. Two colloidal gold labeling methods, label-fracture and replica-staining fracture-flip, were employed to show that the plant lectin wheat germ agglutinin, which recognizes a 210 kDa sperm surface glycoprotein, binds to this localized band of intramembrane particles. Monoclonal antibody J18/2, which also recognizes the 210 kDa surface glycoprotein, shows this localized binding in approximately 20% of the sperm observed in this study. The majority of sperm displayed a uniform distribution of receptor sites for monoclonal antibody J18/2. Since wheat germ agglutinin and monoclonal antibody J18/2 are known to agglutinate Strongylocentrotus purpuratus sperm but not sperm of another sea urchin, Lytechinus pictus, similar determinations were made for the latter species. Lytechinus pictus sperm are not labeled with wheat germ agglutinin and are only sparsely labeled with monoclonal antibody J18/2. The acrosomal localizations of wheat germ agglutinin and monoclonal antibody J18/2 receptors in Strongylocentrotus purpuratus sperm are consistent with the involvement of the 210 kDa surface glycoprotein in an egg jelly-induced sperm acrosome reaction. Low-temperature post-embed labeling of thin sections with wheat germ agglutinin and monoclonal antibody J18/2 show concentrations of label within the acrosomal vesicle of Strongylocentrotus purpuratus sperm, suggesting the presence of an intracellular storage site for the 210 kDa glycoprotein.

Energy metabolism of spermatozoa of the sea urchin Glyptocidaris crenularis

Energy metabolism in spermatozoa of the sea urchin Glyptocidaris crenularis was examined. The spermatozoa contained not only several kinds of phospholipids and cholesterol but also triacylglycerides (TG). Following dilution of the dry sperm in sea water, the TG content decreased rapidly. Other lipids, however, remained at constant levels, except for an increase in the level of free fatty acid. Oil red-O staining of spermatozoa showed that TG was principally located in part of the sperm midpiece. Also, high lipase activity was demonstrated in the spermatozoa. In both intact cells and a cell-free system, 14C-labeled fatty acids were oxidized to 14CO2. It is thus concluded that G. crenularis spermatozoa use TG as a substrate for energy metabolism.

The influence of an egg-associated peptide on energy metabolism in sea-urchin spermatozoa: the peptide stimulates preferential hydrolysis of phosphatidylcholine and oxidation of fatty acid

A study was made of the effects of a sperm-activating peptide (SAP-I: Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly) on energy metabolism in spermatozoa of the sea urchin, Hemicentrotus pulcherrimus. The swimming activity and respiratory rate in slightly acidic seawater (pH 6.6) have been shown to be somewhat less than in normal seawater (pH 8.2). Little change occurred in sperm lipid levels during incubation in seawater at pH 6.6. The addition of SAP-I to seawater at pH 6.6 enhanced the consumption of endogenous phosphatidylcholine (PC), with no change in the levels of other lipids. SAP-I also caused increase in 14CO2 production from exogenous [1-14C]oleic acid following incubation of spermatozoa at pH 6.6. However, the stimulated levels of PC consumption and fatty acid oxidation with SAP-I at pH 6.6 did not exceed those at pH 8.2. At pH 8.2, SAP-I had no effect on PC metabolism. Activities of phospholipase A2 and fatty acid oxidation were markedly influenced by pH and increased at pH exceeding 7. SAP-I is thus concluded to stimulate sea-urchin sperm energy metabolism which depends on the oxidation of endogenous PC. It follows from these results that PC metabolism is activated following increase in the intracellular pH of spermatozoa.

Ionic regulation of the plasma membrane potential of rainbow trout (Salmo gairdneri) spermatozoa: role in the initiation of sperm motility

The ionic dependence of the trout sperm plasma membrane potential was analysed by measuring the accumulation of the lipophilic ions 3H-tetraphenylphosphonium (TPP) and 14C-thiocyanate (SCN) following dilution in artificial media isotonic to the seminal fluid. Our data showed that the trout sperm plasma membrane has a mixed conductance: the plasma membrane potential is sensitive upon the transmembrane gradients of K+, Na+, and H+. This potential is negative (less than -40 mV) in a 125 mM choline chloride media (ChM) at pH 8.5. Replacement of choline by sodium has a small depolarizing effect. The membrane potential is about -15 mV in a 125 mM potassium chloride and falls near zero mV only if valinomycin is added. In ChM changing the external pH (pHe) greatly affects the membrane potential: its value rises from less than -40 mV at pHe 9.0 to -17 mV at pHe 5.0. This pH effect is observed also in presence of sodium or potassium. A decrease in the transmembrane proton gradient produced by increasing internal pH without changing pHe induces also a depolarisation of the plasma membrane. In the different media in which trout sperm remain immotile after dilution (media with [K+] greater than 20-40 mM or a pH less than 7.5) the plasma membrane is more depolarized than in media allowing motility, suggesting a relationship between the state of membrane polarization and the intracellular effectors of the axonemal movement.

Biochemical parameters of initiation and regulation of sperm motility

Studies of in vitro models demonstrate that a forward motility protein (FMP) is required for the initiation of forward motility in the immature epididymal spermatozoa. FMP is a heat-stable glycoprotein derived from epididymal plasma. During the epididymal maturation of spermatozoa in vivo, there is a marked increase of intrasperm pH and level of cyclic adenosine monophosphate (cAMP). Several studies suggest that exogenous FMP in concert with elevated intrasperm pH and level of cAMP initiates flagellar motility during the epididymal transit of sperm. cAMP activates sperm cytosolic cAMP-dependent protein kinases, which in turn phosphorylate multiple intrasperm phosphoproteins that may regulate flagellar motility. Exogenous calcium ion activates intact sperm motility, although it inhibits motility of demembranated cells on reactivation. Occurrence of cAMP-dependent type I and II protein kinases, a novel cAMP-independent protein kinase, and a phosphoprotein phosphatase has been demonstrated on the external surface of spermatozoa. The sperm surface has a coupled-enzyme system: ecto-cAMP-independent protein kinase and phosphoprotein phosphatase that regulate the phosphorylation and dephosphorylation of endogenous sperm ectophosphoproteins. The specific activities of these ecto-enzymes increase markedly during forward progression, suggesting that they may have a role in regulating flagellar motility.

Activation of Ca2+ channels during the acrosome reaction of sea urchin sperm is inhibited by inhibitors of chymotrypsin-like proteases

Probable participation of sperm protease in the acrosome reaction was investigated using several inhibitors and substrates. Among those examined, L-1-tosylamide-2-phenylethyl chloromethyl ketone (TPCK) and chymostatin, chymotrypsin inhibitors, p-nitrophenyl-p'-guanidinobenzoate (NPGB), a serine protease inhibitor, and N-benzoyl-L-tyrosine ethyl ester (BTEE), a chymotrypsin substrate, inhibited the egg jelly-induced acrosome reaction of Strongylocentrotus intermedius. TPCK and BTEE, however, did not inhibit the reaction caused by ionophores, A23187, or nigericin. To know the mechanism of inhibition by chymotrypsin inhibitors and substrates of the egg jelly-induced acrosome reaction, intracellular Ca2+ concentration [( Ca2+]i) and pH (pHi) were measured with fura-2 and 2',7'-bis (carboxy-ethyl)carboxyfluorescein (BCECF), respectively. Egg jelly caused increase of [Ca2+]i, which was depressed by BTEE. Egg jelly also caused a transient rise of pHi, which was not depressed by BTEE. In the presence of verapamil, the acrosome reaction by egg jelly was significantly inhibited concomitant with depressed increase of [Ca2+]i. The rise of pHi was not depressed by verapamil. Thus, modes of action of BTEE and of verapamil are similar to each other. Bringing these findings together, the authors present a view that a chymotrypsin-like protease of sea urchin sperm activates verapamil-sensitive Ca2+ channels, which take part in the acrosome reaction.

Egg jelly induces the phosphorylation of histone H3 in spermatozoa of the sea urchin Arbacia punctulata

When spermatozoa of Arbacia punctulata are labeled with 32P and treated with soluble egg jelly, radiolabel is incorporated into histone H3. The time course of labeling correlates with the period of chromatin decondensation of sperm pronuclei in eggs. Phosphorylation is on serine and may result from increased turnover of phosphate on H3. The macromolecular fraction of egg jelly (and not the peptide fraction) is the inducer of H3 phosphorylation. The reaction is dependent on external Ca2+ and is induced by monensin and A23187. H3 phosphorylation is not induced by the phosphodiesterase inhibitor IBMX and relatively high (250 microM) concentrations of the protein kinase inhibitor H8 are needed to block the reaction, suggesting that it is cAMP independent. A surprising finding is that merely diluting the cells into Na+ free media is the most effective method to induce the radiolabeling of H3. These results are in contrast to findings on the egg jelly induced phosphorylation of histone H1 in S. purpuratus spermatozoa. These species differences must reflect the great evolutionary divergence between these two sea urchin species in the mechanism of regulation of the phosphorylation of nuclear proteins during fertilization.

Fatty chain composition of phospholipids in sea urchin spermatozoa

1. An analysis was made of lipids extracted from the spermatozoa of the sea urchins, Hemicentrotus pulcherrimus and Anthocidaris crassispina. 2. Nearly all the lipids from both species consisted of phospholipids (about 80%) and cholesterol (about 14%). Triglyceride and cholesterol ester were present in trace amounts. 3. The fatty acid composition of each phospholipid was determined by gas-liquid chromatography. In both species, the fatty acid consisting of phosphatidylethanolamine was of the unsaturated type for the most part, while cardiolipin was comprised to a considerable degree of saturated fatty acids. In phosphatidylcholine and phosphatidylserine from H. pulcherrimus sperm, unsaturated fatty acid content was somewhat higher than that in phospholipids from A. crassispina sperm.

[Mechanism and significance of arteriolar media hypertrophy/ hyperplasia in arterial hypertension. Role of the Na+/H+ antiport]

The most common haemodynamic abnormality in human essential hypertension is an increase in systemic vascular resistance. Morphologic substrate for increased flow resistance is a narrowing of the lumen of arteriolar resistance vessels. During the course of essential hypertension, this is associated with an increase in wall (mainly media) thickness due to hypertrophy and hyperplasia of vascular smooth muscle cells. In contrast to concepts interpreting media thickening strictly as structural adaptation to increased perfusion pressure, various lines of evidence also point to pressure independent factors. In this context, extracellular factors such as "growth factors" as well as alterations in the activity of intracellular messenger systems must be considered. Recent studies suggest that substances generally known to act as vasoconstrictors such as angiotensin II, noradrenaline and arginine-vasopressin may also stimulate vascular smooth muscle cell growth and proliferation. Intracellular messenger systems with possible significance in the response to trophins and/or mitogens of vascular smooth muscle cells are phospholipase C, protein kinase C and the Na+/H+-antiport. These systems have been demonstrated to be altered in hypertension supporting the concept that one endogenous factor in human essential hypertension with pathophysiological significance, at least in a subgroup of patients, may be an enhanced reactivity of vascular smooth muscle cells to trophic and mitogenic stimuli. In this context, intracellular messenger systems such as phospholipase C, protein kinase C and/or the Na+/H+-antiport may play an important pathophysiological role.

Monoclonal antibodies to a membrane glycoprotein induce the phosphorylation of histone H1 in sea urchin spermatozoa

Two groups of mAbs reacting with external domains of a major sea urchin sperm membrane glycoprotein of 210 kD were isolated. Previous studies have shown that group I mAbs inhibit the acrosome reaction induced by egg jelly and also cause large increases in intracellular Ca2+ [( Ca2+]i). Group II mAbs, at comparable levels of cell surface binding, neither inhibit the egg jelly-induced acrosome reaction nor cause increases in [Ca2+]i. In this paper, we investigate the ability of these mAbs to induce the cAMP-dependent phosphorylation of sperm histone H1. Group I mAbs induce H1 phosphorylation to the same level and on the same peptide, as occurs upon treatment of sperm with egg jelly. These mAbs also activate adenylate cyclase to the same extent as egg jelly. Group II mAbs do not induce H1 phosphorylation and are only poor activators of adenylate cyclase. Group I mAbs compete with each other, but not with group II mAbs, for binding to the cell surface. These data indicate that the activation of adenylate cyclase is an initial event in the pathway leading from the binding of mAbs to a specific domain of the 210-kD protein at the cell surface, to the discrete phosphorylation of histone H1 in highly condensed sperm chromatin. The domain on the 210-kD protein recognized by group I mAbs plays a critical role in signal transduction during the early events of fertilization.

Sea urchin sperm head plasma membranes: characteristics and egg jelly induced Ca2+ and Na+ uptake

Sea urchin sperm respond to egg factors with changes in the ionic permeability of their plasma membrane. It has been previously shown that plasma membranes isolated preferentially from sea urchin sperm flagella respond to egg jelly increasing their Ca2+ and Na+ uptake (Darszon et al. (1984) Eur. J. Biochem. 144, 515-522). However, the egg jelly induced acrosome reaction occurs in the sperm head, and there is evidence for an heterogeneous distribution of plasma membrane components within the various regions of this cell. We here report a method for purifying sperm head membranes using positively charged beads according to Jacobson (1977) Biochim. Biophys. Acta 471, 331-335). Under the transmission electron microscope these membranes appeared homogeneous and apparently free of internal membranes. The yield of the preparation was 0.9% of the total protein in the sperm homogenate. The preparation contained less than 5% of the mitochondrial marker cytochrome oxidase, and 10% of the total DNA/mg protein. Surface labeling with 125I indicated a 2.5-3-fold enrichment in specific activity of the head membranes with respect to whole sperm. The SDS band pattern and the lipid composition of this preparation were different from those of isolated flagellar membranes. Phosphatidylcholine was higher in the head membranes, while phosphatidylserine and phosphatidylethanolamine were lower. The head membranes displayed a 1.7-2.3-fold higher Ca2+-ATPase activity and a 2.5-fold lower Na+/K+-ATPase activity, than the flagellar membranes. These results are consistent with a heterogeneous distribution of membrane components along the sea urchin sperm plasma membranes. Isolated head membranes sonicated in the presence of soybean phospholipid liposomes responded to egg jelly with a species-specific increase in Ca2+ and Na+ uptake. As in whole sperm, Ca2+ uptake was inhibited by the Ca2+ channel blocker nisoldipine. A close analog of this compound, [3H]nitrendipine, binds with high affinity to head membranes in a saturable, reversible manner, showing a Kd and Bmax of 31 nM and 5.3 pmol/mg protein, respectively.

Internal GTP stimulates the speract receptor mediated voltage changes in sea urchin spermatozoa membrane vesicles

A voltage-sensitive Na+/H+ exchanger in the flagellar membrane is responsible for regulating the intracellular pH of the sea urchin spermatozoa. A previous study has shown that the egg peptide speract can modulate this Na+/H+ exchanger through its hyperpolarizing effect on the membrane potential. The effect of GTP on this speract receptor mediated process is investigated in this study. Plasma membrane vesicles with an outwardly directed K+ gradient were prepared from the isolated flagella by osmotic lysis. Vesicular membrane potential was monitored by a cationic probe, diS-C3-(5), and an anionic probe, diS-BA-C2-(3). Results show that the presence of internal GTP greatly stimulated the speract induced membrane hyperpolarization in this vesicle system. The analog GTP gamma S was not only active but could, by itself, induce partial hyperpolarization which was further enhanced by speract addition. Internal GDP was partially active in supporting the speract effect, whereas GDP beta S, cGMP, GMP, and ATP were all inactive. The ionic selectivity of the speract effect was investigated by increasing the external concentration of various cations. K+ and Rb+ abolished the hyperpolarization while Cs+ had no effect. These results indicate that internal GTP is involved in the coupling between the speract receptor and the membrane hyperpolarization, which is most likely due to the activation of K+ selective channels.

A 31P-NMR study on the recovery of intracellular pH in LLC-PK1/Cl4 cells from intracellular alkalinization

The regulation of intracellular pH (pHi) in a renal epithelial cell line, LLC-PK1/Cl4, during re-acidification from an alkaline load was studied by 31P-NMR. Intracellular alkalinization was induced by 10 mM ammonium glucuronate or by preloading with and subsequent removal of 20% CO2; the rate of re-acidification was found to be 0.047 pH units/min and 0.053 pH units/min, respectively. This rate of re-acidification was inhibited by 83% if Cl- was removed from the extracellular medium. A similar inhibition was found in the presence of 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS) (76% inhibition) and 1 mM bumetanide (81% inhibition). No change in recovery was found after removing sodium from the extracellular medium, indicating that LLC-PK1/Cl4 cells recover from an intracellular alkaline load by a Cl-/HCO3- exchanger, which is SITS- and bumetanide-sensitive and has no requirement for sodium. In addition, the steady-state pHi in Cl4 cells was monitored by 31P-NMR. Removal of Cl- from the extracellular medium introduced an increase in pHi by 0.33 pH units, whereas 1 mM SITS and 1 mM bumetanide caused an increase in pHi by 0.14 or 0.13 pH units. In the presence of 1 mM amiloride, an inhibitor of the Na+/H+ exchanger, the steady-state pHi did not change significantly. These results indicate that at pHo 7.4 the steady-state intracellular pH of LLC-PK1/Cl4 cells strongly depends on the activity of the Cl-/HCO3- exchanger. Under the same conditions the activity of the Na+/H+ exchanger seems to be negligible.

Regulation of sperm flagellar motility by calcium and cAMP-dependent phosphorylation

There is substantial evidence that cAMP-dependent phosphorylation is involved in the activation of motility of spermatozoa as they are released from storage in the male reproductive tract. This evidence includes observations that in vivo activation of motility can be inhibited by protein kinase inhibitors, can be reversed by protein phosphatase treatment of demembranated spermatozoa, and is associated with phosphorylation of sperm proteins, and observations that spermatozoa that have not been activated in vivo can be activated in vitro by cAMP-dependent phosphorylation. Activation in vivo can often be triggered by conditions that increase intracellular pH, but the relevance of this to in vivo activation under natural conditions and the steps between pH increase and cAMP increase have not been fully established. The relationships between changes in the protein substrates for cAMP-dependent phosphorylation and changes in axonemal function are still unknown. Sperm chemotaxis to egg secretions is widespread; in the sea urchin Arbacia, the egg jelly peptide resact has been identified as a chemoattractant. Response to chemoattractants involves changes in asymmetry of flagellar bending waves, and similar changes in asymmetry can be produced in vitro by increases in [Ca++]. Temporal changes in resact receptor occupancy might lead to transient changes in intracellular [Ca++] and the asymmetry of flagellar bending, but many links in this hypothetical sequence remain to be established. Both of these signalling systems offer immediate opportunities for investigations of biochemical pathways leading to easily assayable biological responses. However, complications resulting from interactions between these two systems need to be considered.

A lithium-sensitive regulator of sperm flagellar oscillation is activated by cAMP-dependent phosphorylation

Specific effects of both in vivo activation and in vitro activation by cAMP-dependent phosphorylation on bending wave parameters of demembranated, reactivated, tunicate (Ciona intestinalis) and sea urchin (Lytechinus pictus) sperm flagella can be reversed by exposure to protein phosphatase. The effects of protein phosphatase incubation can be imitated by inclusion of LiCl in the reactivation solutions. The primary effect of cAMP-dependent phosphorylation appears to be activation of a regulatory mechanism controlling flagellar oscillation, rather than activation of the active sliding mechanism. Lithium appears to act on the same regulatory mechanism.