Modulation of adenylyl cyclase by FPP and adenosine involves stimulatory and inhibitory adenosine receptors and g proteins.
FPP and adenosine modulate the adenylyl cyclase (AC)/cAMP signal transduction pathway in mammalian spermatozoa to elicit a biphasic response, initially stimulating capacitation and then inhibiting spontaneous acrosome loss. This study addressed the hypothesis that responses to FPP involve interactions between receptors for FPP and adenosine, the biphasic responses involving stimulatory and inhibitory adenosine receptors. Gln-FPP, a competitive inhibitor of FPP, significantly inhibited binding of an adenosine analogue and responses to adenosine, especially in capacitated suspensions, consistent with interaction between FPP and adenosine receptors. CGS-21680 (1 microM), a stimulatory A2a adenosine receptor agonist, significantly stimulated capacitation and cAMP in uncapacitated cells, while cyclopentyl adenosine (1 microM), an inhibitory A1 adenosine receptor agonist only affected capacitated cells, inhibiting spontaneous acrosome loss. Responses to FPP and adenosine were inhibited in uncapacitated cells by a selective A2a antagonist and in capacitated cells by a selective A1 antagonist; subsequent investigations indicated possible involvement of G proteins. Like FPP, cholera toxin stimulated capacitation and cAMP production in uncapacitated cells, suggesting involvement of a G protein with a Galphas subunit. In contrast, pertussis toxin prevented FPP's inhibition of both spontaneous acrosome loss and cAMP production, suggesting involvement of a Galphai/o subunit. Immunoblotting evidence revealed the presence of proteins of the appropriate molecular weights for Galphas, Galphai2, Galpha i3, and Galphao subunits. This study provides the first direct evidence suggesting the involvement of two different types of adenosine receptors and both Galphas and Galphai/o subunits in the regulation of capacitation, resulting in modulation of AC activity and availability of cAMP.
Anatomy and Human Biology, King's College London, Strand, London, United Kingdom. lynn.fraser@kcl.ac.uk
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D000241:Adenosine / Q000494:pharmacology*; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D051379:Mice; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins / Q000378:metabolism; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D018047:Receptors, Purinergic P1 / Q000187:drug effects* / Q000378:metabolism*; D015398:Signal Transduction; D013075:Sperm Capacitation; D013094:Spermatozoa / Q000187:drug effects* / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology*; D044767:Ubiquitin-Protein Ligases; D056427:t-Complex Genome Region
D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D018047:Receptors, Purinergic P1; D013973:Thyrotropin-Releasing Hormone; C059697:pyroglutamyl-glutamyl-proline amide; D006160:Guanosine Triphosphate; C116196:PPP1R11 protein, human; D044767:Ubiquitin-Protein Ligases; D019204:GTP-Binding Proteins; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs; D000262:Adenylyl Cyclases; D000241:Adenosine; D011761:Pyrrolidonecarboxylic Acid