Cholesterol Efflux	Back to Home
	The efflux of cholesterol from the sperm cell has long been considered a part of capacitation. Because the movement of sterols is relatively easy to measure in comparison with other parts of capacitation, the efflux was discovered early and purported to initiation capacitation. However, evidence from the previously reviewed pages suggests that cholesterol efflux is preceded by bicarbonate entry, sAC activation, cAMP-dependent PKA signaling, and phospholipid scramblase. In Flesch et al.’s research, cholesterol redistributes from general parts of the sperm cell membrane to the apical head site. This is evidenced by filipin molecule patterns A vs B seen below.
This image is used with permission from senior author of: Flesch FM, Brouwers JFHM, Nievelstein PFEM, Verkleij AJ, van Golde LMG, Colenbrander B, Gadella BM. 2001. Bicarbonate stimulated phospholipid scrambling induces cholesterol redistribution and enables cholesterol depletion in the sperm plasma membrane. Journal of Cell Science 114(19):3543-55.
The cholesterol efflux requires albumin (BSA), which acts as a cholesterol sink. Flesch et al. also showed that cholesterol was not extracted from the membrane without the presence of BSA. The research of Flesch et al also suggest that the cholesterol redistribution changes caused by bicarbonate and in-turn, phospholipid scramblase allow the albumin-mediated cholesterol extraction. Below, notice that no change was seen in media lacking bicarbonate but containing albumin.
This image is used with permission from senior author of: Flesch FM, Brouwers JFHM, Nievelstein PFEM, Verkleij AJ, van Golde LMG, Colenbrander B, Gadella BM. 2001. Bicarbonate stimulated phospholipid scrambling induces cholesterol redistribution and enables cholesterol depletion in the sperm plasma membrane. Journal of Cell Science 114(19):3543-55.
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This webpage was made as a part of student projects in Dr. Dorcas' Animal Physiology class at Davidson College.