title: Type-1 cannabinoid receptors reduce membrane fluidity of capacitated boar sperm by impairing their activation by bicarbonate.
abstract: BACKGROUND
  Mammalian spermatozoa acquire their full fertilizing ability (so called capacitation) within the female genital tract, where they are progressively exposed to inverse gradients of inhibiting and stimulating molecules.
  
  
  RESULTS
  In the present research, the effect on this process of anandamide, an endocannabinoid that can either activate or inhibit cannabinoid receptors depending on its concentration, and bicarbonate, an oviductal activatory molecule, was assessed, in order to study the role exerted by the type 1 cannabinoid receptor (CB1R) in the process of lipid membrane remodeling crucial to complete capacitation. To this aim, boar sperm were incubated in vitro under capacitating conditions (stimulated by bicarbonate) in the presence or in the absence of methanandamide (Met-AEA), a non-hydrolysable analogue of anandamide. The CB1R involvement was studied by using the specific inhibitor (SR141716) or mimicking its activation by adding a permeable cAMP analogue (8Br-cAMP). By an immunocytochemistry approach it was shown that the Met-AEA inhibits the bicarbonate-dependent translocation of CB1R from the post-equatorial to equatorial region of sperm head. In addition it was found that Met-AEA is able to prevent the bicarbonate-induced increase in membrane disorder and the cholesterol extraction, both preliminary to capacitation, acting through a CB1R-cAMP mediated pathway, as indicated by MC540 and filipin staining, EPR spectroscopy and biochemical analysis on whole membranes (CB1R activity) and on membrane enriched fraction (C/P content and anisotropy).
  
  
  CONCLUSIONS
  Altogether, these data demonstrate that the endocannabinoid system strongly inhibits the process of sperm capacitation, acting as membrane stabilizing agent, thus increasing the basic knowledge on capacitation-related signaling and potentially opening new perspectives in diagnostics and therapeutics of male infertility.
authors.affiliation: Department of Biomedical Comparative Sciences, University of Teramo, Teramo, Italy. nbernabo@unite.it
authors.forename: Barbara
authors.initials: B
authors.lastname: Barboni
authors.forename: Nicola
authors.initials: N
authors.lastname: Bernabò
authors.forename: Paola
authors.initials: P
authors.lastname: Palestini
authors.forename: Laura
authors.initials: L
authors.lastname: Botto
authors.forename: Maria Gabriella
authors.initials: MG
authors.lastname: Pistilli
authors.forename: Marco
authors.initials: M
authors.lastname: Charini
authors.forename: Enzo
authors.initials: E
authors.lastname: Tettamanti
authors.forename: Natalia
authors.initials: N
authors.lastname: Battista
authors.forename: Mauro
authors.initials: M
authors.lastname: Maccarrone
authors.forename: Mauro
authors.initials: M
authors.lastname: Mattioli
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D007150:Immunohistochemistry; D008297:Male; D008560:Membrane Fluidity / Q000502:physiology*; D043884:Receptor, Cannabinoid, CB1 / Q000502:physiology*; D013094:Spermatozoa / Q000187:drug effects* / Q000502:physiology; D013552:Swine
chemical_list: D001639:Bicarbonates; C543264:Cnr1 protein, rat; D043884:Receptor, Cannabinoid, CB1