Pentoxifylline-stimulated capacitation and acrosome reaction in hamster spermatozoa: involvement of intracellular signalling molecules.
We investigated the role of cAMP/cGMP, protein kinases and intracellular calcium ( [Ca2+]i) in pentoxifylline-stimulated hamster sperm capacitation and the acrosome reaction (AR) in vitro. Treatment with pentoxifylline (0.45 mM) initially increased sperm cAMP values 2.8-fold, compared with untreated controls (396 +/- 9.2 versus 141 +/- 6.0 fmoles/10(6) spermatozoa; mean +/- SEM, n = 6) after 15 min, although by 3 h, cAMP values were similar (503-531 fmoles/10(6) spermatozoa). cGMP values ( approximately 27 fmoles/10(6) spermatozoa) were the same in treated and control spermatozoa. Both sperm capacitation and the AR, determined from the absence of an acrosomal cap, were stimulated by pentoxifylline; these were almost completely inhibited by a Cl-/ HCO3- antiporter inhibitor (4,4-diisothiocyanato-stilbene-2,2 disulphonic acid; 1 mM) defined from the degree of sperm motility and by a protein kinase A inhibitor (H89; 10 microM). A protein kinase C inhibitor (staurosporine, 1 nM) did not affect pentoxifylline-stimulated capacitation but inhibited the AR by 50%. A protein tyrosine kinase inhibitor (tyrphostin A-47, 0.1 mM) had no effect on either pentoxifylline-stimulated capacitation or AR. A phospholipase A2 inhibitor (aristolochic acid, 0.4 mM) markedly inhibited the pentoxifylline-stimulated AR but not capacitation. When intracellular sperm calcium [Ca2+/-]i was measured using fura-2-AM, there was an early rise (271 nM at 0.5 h) in pentoxifylline-treated spermatozoa; this appeared to be due to intracellular mobilization rather than to uptake. In the absence of extracellular Ca2+, sperm motility was maintained in the presence of pentoxifylline, but capacitation did not occur; spermatozoa exhibited a low level of hyperactivated motility and had a poor rate of AR (20.5 +/- 2.3%). These results suggest that: (i) the pentoxifylline-stimulated early onset of sperm capacitation may be mediated by an early rise in cAMP and [Ca2+/-]i and involves protein kinase A activity; and (ii) pentoxifylline-stimulated AR may require phospholipase A2 and protein kinase C activity.
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Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560012, India.
Uma Devi
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Shivaji
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Seshagiri
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PB
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D020101:Acrosome Reaction / Q000187:drug effects*; D000818:Animals; D034341:Aristolochic Acids; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008647:Mesocricetus; D008954:Models, Biological; D010431:Pentoxifylline / Q000494:pharmacology*; D010616:Phenanthrenes / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors; D054467:Phospholipases A2; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013075:Sperm Capacitation / Q000187:drug effects*; D013081:Sperm Motility / Q000187:drug effects; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology*; D019311:Staurosporine / Q000494:pharmacology; D020032:Tyrphostins / Q000494:pharmacology
D034341:Aristolochic Acids; D004791:Enzyme Inhibitors; D010616:Phenanthrenes; D047428:Protein Kinase Inhibitors; D020032:Tyrphostins; C060152:tyrphostin 47; C000228:aristolochic acid I; D000242:Cyclic AMP; D011494:Protein Kinases; D010741:Phospholipases A; D054467:Phospholipases A2; D019311:Staurosporine; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D010431:Pentoxifylline