Stimulation of Ca(2+)-dependent exocytosis of the sperm acrosome by cAMP acting downstream of phospholipase A2.
Spermatozoa undergo exocytosis in response to agonists that induce Ca2+ influx and, in turn, activation of phosphoinositidase C, phospholipase C, phospholipase A2, and cAMP formation. Since the role of cAMP downstream of Ca2+ influx is unknown, this study investigated whether cAMP modulates phospholipase C or phospholipase A2 using a ram sperm model stimulated with A23187 and Ca2+. Exposure to dibutyryl-cAMP, phosphodiesterase inhibitors or forskolin resulted in enhancement of exocytosis. However, the effect was not due to stimulation of phospholipase C or phospholipase A2: in spermatozoa prelabelled with [3H]palmitic acid or [14C]arachidonic acid, these reagents did not enhance [3H]diacylglycerol formation or [14C]arachidonic acid release. Spermatozoa were treated with the phospholipase A2 inhibitor aristolochic acid, and dibutyryl-cAMP to test whether cAMP acts downstream of phospholipase A2. Under these conditions, exocytosis did not occur in response to A23187 and Ca2+. However, inclusion of dibutyryl-cAMP and the phospholipase A2 metabolite lysophosphatidylcholine did result in exocytosis (at an extent similar to that seen when cells were treated with A23187/Ca2+ and without the inhibitor). Inclusion of lysophosphatidylcholine alone, without dibutyryl-cAMP, enhanced exocytosis to a lesser extent, demonstrating that cAMP requires a phospholipase A2 metabolite to stimulate the final stages of exocytosis. These results indicate that cAMP may act downstream of phospholipase A2, exerting a regulatory role in the exocytosis triggered by physiological agonists.
Garde
J
J
Departamento de Ciencia y Tecnología Agroforestal, ETSI Agrónomos, Universidad de Castilla-La Mancha, Albacete, Spain.
Roldan
E R
ER
D000177:Acrosome / Q000187:drug effects / Q000378:metabolism; D020101:Acrosome Reaction / Q000187:drug effects*; D000704:Analysis of Variance; D000818:Animals; D034341:Aristolochic Acids; D003994:Bucladesine / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D008297:Male; D010616:Phenanthrenes / Q000494:pharmacology*; D010741:Phospholipases A / Q000037:antagonists & inhibitors* / Q000378:metabolism; D054467:Phospholipases A2; D047428:Protein Kinase Inhibitors; D012756:Sheep; D013268:Stimulation, Chemical; D013449:Sulfonamides
D034341:Aristolochic Acids; D004791:Enzyme Inhibitors; D007476:Ionophores; D007546:Isoquinolines; D008244:Lysophosphatidylcholines; D010616:Phenanthrenes; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D005576:Colforsin; D000001:Calcimycin; D002110:Caffeine; D003994:Bucladesine; C000228:aristolochic acid I; D000242:Cyclic AMP; D010741:Phospholipases A; D054467:Phospholipases A2; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D002118:Calcium