title: Calcium regulation of the soluble adenylyl cyclase expressed in mammalian spermatozoa.
abstract: In mammals, Ca2+ and HCO3- ions play a critical role in the regulation of sperm function, most likely by regulation of cAMP levels. Mammalian germ cells contain a soluble adenylyl cyclase (sAC) with properties distinct from the well characterized membrane-bound enzymes Here we investigated whether the cyclase expressed in mature spermatozoa has the properties of sAC and whether it is regulated by Ca2+. In addition to an HCO3--dependent activation, the cyclase endogenous to human spermatozoa is stimulated 2- to 3-fold by Ca2+ in a concentration-dependent manner (EC50 approximately 400 nM). In a similar fashion, Ca2+ activates the recombinant rat and human full-length sAC with similar EC50 values. The Ca2+ stimulation was also observed when sAC was activated with HCO3-, was independent of calmodulin, and was associated with an increase in Vmax without changes in Km for ATP-Mg2+. An increase in intracellular Ca2+ by ionophore or by a muscarinic cholinergic receptor agonist increases cAMP in cells transfected with FL-hsAC, but not in mock-transfected cells. Similarly, both Ca2+ and HCO3- stimulate cAMP accumulation in human spermatozoa. These findings provide evidence that human spermatozoa express a cyclase with the properties of sAC and that Ca2+ can substitute for HCO3- in the stimulation of this enzyme, underscoring an important role for sAC in the control of sperm functions.
authors.affiliation: Division of Reproductive Biology, Department of Obstetrics and Gynecology, Stanford University School of Medicine, Stanford, CA 94305-5317, USA.
authors.forename: Bijay S
authors.initials: BS
authors.lastname: Jaiswal
authors.forename: Marco
authors.initials: M
authors.lastname: Conti
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D017931:DNA Primers; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012995:Solubility; D013094:Spermatozoa / Q000201:enzymology*
chemical_list: D017931:DNA Primers; D011994:Recombinant Proteins; D000262:Adenylyl Cyclases; D002118:Calcium