Thermotropic phase transitions in the plasma membrane of ram spermatozoa

Abstract

A steady-state fluorescence polarization technique, using the membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH), showed that separately detectable transitions occurred in the regions of 17, 26 and 36 degrees C in isolated preparations of ram sperm plasma membrane. An independent technique based on the temperature-related behaviour of calcium- and magnesium-activated ATPase detected a single phase transition in the region of 24 degrees C. Modulation of ATPase by neighbouring lipid composition was inferred from findings that phospholipase A2 caused significant stimulation of the enzyme. Cholesterol-rich liposomes caused an upward shift of the phase-transition temperature from 24 degrees C to 30 degrees C, but the reasons for this are unclear. It is considered that these phase transitions may have profound effects on sperm survival and physiology, both during normal fertilization processes and in response to cryostorage.

Effect of different media additives on capacitation of frozen–thawed ram spermatozoa as a potential replacement for estrous sheep serum

“…In addition, we speculated that the lack of effect observed in our study for both media supplemented with P 4 and E 2 could relate to the composition of the sperm plasma membrane, which is species specific [55,56]. These hormones act through receptors located on the surface of spermatozoa [57][58][59], which may be potentially lost or damaged during cryopreservation [60] to a different degree depending on the species [55,61].…”

Recent developments and concepts in the cryopreservation of spermatozoa and the assessment of their post-thawing function

“…Since then, differences between membranes in the sperm cell have been recognized (Parks et al 1987;Canvin and Buhr 1989;De Leeuw et al 1990;Parks and Lynch 1992), and the implications for the behaviour of sperm membranes in relation to temperature have been studied (Holt and North 1985;Holt et al 1992;DeLeeuw et al 1993). The concept of phase transition has been demonstrated in sperm membranes (Holt and North 1986;Crowe et al 1989;Wolf et al 1990;Holt and North 1991;Parks and Lynch 1992;Drobnis et al 1993) and the influence of phase events on membrane function and integrity has begun to be examined.…”

Cryopreservation alters the Ca2+ flux of bovine spermatozoa

“…Freezing and thawing may weaken the binding of such decapacitation factors so that they would be more easily removed during experimental procedures. Ultrastructural damage such as lateral phase ieparation of membrane bilayers has been attributed to freezing and thawing (Holt and North 1986;de Leeuw et al 1991),"and such disiuption of the environment of the CaZ+ regulatory proteins may inhibit their function. Before the acrosome reaction, low intracellular Ca'-concentrattons tn bovine spermatozoa are maintained by a Ca2*-ATPase (Vijayasarathy et al 1980;Breitbart and Rubenstein 1983; ilreitUart "t ui.…”