Biochemical and physiological aspects of volume regulation in immature and mature bovine spermatozoa

Medientyp: E-Book; Hochschulschrift

Titel: Biochemical and physiological aspects of volume regulation in immature and mature bovine spermatozoa

Beteiligte: Sahin, Basak Evrim [Sonstige Person, Familie und Körperschaft]

Erschienen: 2009

Umfang: Online-Ressource (99 S. = 1.531 Kb, text); Ill., graph. Darst

Sprache: Deutsch; Englisch

Identifikator:

Schlagwörter: Rind > Spermatozyt > Nebenhoden > Spermaplasma > Osmolarität

Entstehung:

Hochschulschrift: Zugl.: Hannover, Tierärztl. Hochsch., Reproduktionsmed. Einheit der Kliniken, Diss., 2009

Anmerkungen:

Beschreibung: Nebenhodenspermien, Volumenregulation, Fn2 Proteine. - Mammalian spermatozoa experience significant osmotic changes during their life span, both during ejaculation as well as during the transport in the female genital tract. Mature sperm possess a mechanism to maintain their volume and to regulate it after initial swelling following exposure to hypoosmotic conditions, named regulatory volume decrease (RVD). In rodents and primates RVD appears to be acquired during epididymal maturation, but in large domestic animals this aspect has not yet been examined. The aim of this study was to establish an optimal experimental system for physiological studies on cell volume of epididymal sperm and to investigate 1) whether bull epididymal spermatozoa are able to regulate their volume 2) whether this ability differs between caput and cauda epididymal spermatozoa and 3) whether bovine Fn2-module-containing proteins play a role in acquisition of volume regulation ability during sperm maturation. Sperm volumes were measured by electronic cell sizing; evaluation of plasma and acrosomal membranes integrities were performed using flow cytometry. It has been shown that the recovery and incubation in the medium isotonic with caudal epididymal plasma result in better viability and volume regulatory ability of epididymal spermatozoa than conventional system of media isotonic with seminal plasma, or seminal plasma itself. This experimental system was used for subsequent physiological studies. Two subpopulations were observed in volume distributions of caput and cauda epididymal spermatozoa, characterized by differing ability to swell in response to hypotonic conditions. Both sperm subpopulations in caput as well as in cauda were able to undergo RVD. Caput epididymal spermatozoa had a higher cell volume under isotonic conditions compared to cauda epidiymal spermatozoa. Substitution of sodium and chloride by choline and sulfate resulted in a decreased caput spermatozoa isotonic volume. Furthermore, the differences abolished between caput and cauda epididymal spermatozoa. The results of the present study indicate that uptake of Na+ and Cl- ions is less controlled in caput epididymal spermatozoa than in cauda, probably due to premature activation of transport mechanisms. Thus, although spermatozoa from the caput epididymidis are able to undergo RVD after hypotonic challenge, the mechanisms controlling ion transport under isotonic conditions are not fully developed. To clarify this mechanism, the role of sperm binding Fn2-module-containing proteins was investigated. Mainly two classes exist which differ by having either two Fn2 modules, as the major member BSP-A1/2 (small Fn2 protein), or having four Fn2 modules such as ELSPBP1 (long Fn2 protein). The first two modules have similar three-dimensional structures. Both proteins bind to the sperm through interaction with phosphorylcholine. It is shown that long Fn2 protein (ELSPBP1) is present in the caput, corpus and cauda regions of the bull epididymis whereas it binds to the spermatozoa during their transit through the epididymis; it was detected in mature (cauda) spermatozoa but not in immature (caput) epididymal spermatozoa. Small Fn2 proteins (BSP-A1/2) bind to spermatozoa upon ejaculation. Both the long and the small Fn2 proteins are essentially localized in the head and midpiece regions of mature bovine spermatozoa. These common features suggest similar functions; therefore, BSP-A1/2 was used as a model protein. Cauda epididymal spermatozoa showed progressive volume regulation both in the absence and presence of BSP-A1/2. The protein treatment caused caput epididymal spermatozoa to swell more in response to hypotonic stress after 5 min and to regulate their volume after 20 min incubation in a similar fashion to cauda epididymal spermatozoa. It is suggested that BSP-A1/2 affects the premature activation of transport mechanisms (such as ion channels, for example). The premature activation of these channels could lead to uncontrolled uptake of Na+ and Cl- ions. This uptake and coupled water transport is the likely cause of elevated isotonic volume levels in caput spermatozoa. At the same time, this premature activation accounts for the accelerated response to hypotonic challenge as the osmotically induced volume-sensitive response would be initiated faster. BSP-A1/2 possibly deactivates this premature activation. Therefore, the response to hypotonic conditions becomes slower and the relative volumes in caput epididymal spermatozoa match those in cauda epiddiymal spermatozoa. In conclusion, this study has provided further insights into the mechanism of spermatozoa volume regulation during epididymal maturation. A new superior experimental system was established for physiological volume regulation studies in bovine epididymal spermatozoa. Caput epididymal spermatozoa are able to undergo RVD after hypotonic challenge. However, the mechanisms controlling ion transport under isotonic conditions are not fully developed compared to cauda epididymal (mature) sperm. It seems highly probable that the attachment of long Fn2 protein to the maturing spermatozoa has a regulatory effect on cell volume control as they pass down the epididymis. For the first time, long Fn2 protein was detected in bovine epididymis and its contribution to volume regulation of maturating epididymal spermatozoa is discussed.

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