title: Acrosomal Swelling Is Triggered by cAMP Downstream of the Opening of Store-Operated Calcium Channels During Acrosomal Exocytosis in Human Sperm.
abstract: Acrosomal exocytosis in mammalian sperm is a regulated secretion with unusual characteristics. One of its most striking features is the postfusion loss of the outer acrosomal membrane and the overlying plasma membrane as hybrid vesicles. We have previously reported in human sperm that, by preventing the release of calcium from the acrosome, the exocytic process can be arrested at a stage where the acrosomes are profusely swollen, with invaginations of the outer acrosomal membrane. In this report, we show by transmission electron microcopy swelling with similar characteristics without arresting the exocytic process. Acrosomal swelling was observed when secretion was promoted by pharmacological and physiological inducers of the acrosome reaction that trigger exocytosis by different mechanisms. We show that progesterone- and thapsigargin-induced swelling depended on a calcium influx from the extracellular medium through store-operated calcium channels. However, calcium was dispensable when sperm were stimulated with cAMP analogs. KH7, an inhibitor of the soluble adenylyl cyclase, blocked progesterone-induced swelling. Our results indicate that swelling is a required process for acrosomal exocytosis triggered by activation of an adenylyl cyclase downstream of the opening of store-operated calcium channels.
authors.affiliation: Instituto de Histología y Embriología de Mendoza (IHEM/CONICET-UNCuyo), School of Medicine, National University of Cuyo, Mendoza, Argentina.
authors.forename: Claudia M
authors.initials: CM
authors.lastname: Sosa
authors.affiliation: Instituto de Histología y Embriología de Mendoza (IHEM/CONICET-UNCuyo), School of Medicine, National University of Cuyo, Mendoza, Argentina.
authors.forename: M Natalia
authors.initials: MN
authors.lastname: Zanetti
authors.affiliation: Instituto de Histología y Embriología de Mendoza (IHEM/CONICET-UNCuyo), School of Medicine, National University of Cuyo, Mendoza, Argentina.
authors.forename: Cristian A
authors.initials: CA
authors.lastname: Pocognoni
authors.affiliation: Instituto de Histología y Embriología de Mendoza (IHEM/CONICET-UNCuyo), School of Medicine, National University of Cuyo, Mendoza, Argentina lmayorga@fcm.uncu.edu.ar.
authors.forename: Luis S
authors.initials: LS
authors.lastname: Mayorga
mesh_terms: D020101:Acrosome Reaction / Q000502:physiology*; D000328:Adult; D000001:Calcimycin / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D006801:Humans; D008297:Male; D011374:Progesterone / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D000001:Calcimycin; D011374:Progesterone; D000242:Cyclic AMP
keywords: acrosomal swelling; acrosome reaction; cAMP; calcium; human sperm; regulated exocytosis; secretory granules