title: Bicarbonate induces membrane reorganization and CBR1 and TRPV1 endocannabinoid receptor migration in lipid microdomains in capacitating boar spermatozoa.
abstract: Mammalian spermatozoa acquire full fertilizing ability only after a morphofunctional maturation called "capacitation." During this process the high level of bicarbonate present within the upper female genital tract or in culture medium induces a marked reorganization of sperm membranes characterized by a biphasic behavior: In a few minutes, it promotes membrane phospholipid scrambling preliminary to the apical translocation of sterol that, 2-4 h later, enables spermatozoa to recognize zona pellucida after albumin-mediated cholesterol extraction. In the present research it was demonstrated that spermatozoa incubated with bicarbonate in protein-free media underwent a marked reorganization of lipid microdomains present in a detergent-resistant membrane fraction (DRM) isolated by ultracentrifugation on sucrose density gradient. In fact, bicarbonate exposed sperm (ES) cells, compared with ejaculated spermatozoa (nonexposed sperm [nES] cells), displayed an increase in protein DRM content and, in particular, in Cav-1 and CD55, markers of caveolae and lipid rafts, as well in acrosin-2, a marker of the outer acrosomal membrane (OAM). Moreover, the amount of certain proteins involved in capacitation, such as the endocannabinoid system receptors cannabinoid receptor type 1 (CBR1) and transient receptor potential cation channel 1 (TRPV1), increased in DRM obtained from ES. These data allow us to hypothesize that sperm membrane reorganization takes place even in the absence of extracellular proteins; that not only the plasma membrane but also the OAM participate in this process; and that important molecules playing a key role in inside-out signaling, such as the endocannbinoid receptors TRPV1 and CBR1, are involved in this event, with potentially important consequences on sperm function.
authors.affiliation: Department of Experimental Medicine (DIMS), University of Milano-Bicocca, Via Cadore 48, 20052, Monza, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Botto
authors.forename: Nicola
authors.initials: N
authors.lastname: Bernabò
authors.forename: Paola
authors.initials: P
authors.lastname: Palestini
authors.forename: Barbara
authors.initials: B
authors.lastname: Barboni
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D002855:Chromatography, Thin Layer; D004591:Electrophoresis, Polyacrylamide Gel; D008297:Male; D021962:Membrane Microdomains / Q000187:drug effects* / Q000378:metabolism*; D043882:Receptors, Cannabinoid / Q000378:metabolism*; D013075:Sperm Capacitation / Q000502:physiology*; D013094:Spermatozoa / Q000187:drug effects*; D013552:Swine; D050916:TRPV Cation Channels / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D043882:Receptors, Cannabinoid; D050916:TRPV Cation Channels