ADENYLATE-CYCLASE ACTIVITY INCREASES CONCOMITANTLY WITH THE ONSET OF CAPACITATION IN HEPARIN-TREATED BOVINE SPERMATOZOA

This study examined the effect of metal ions Ca2+, Mg2+, and Mn2+ and sonication on ejaculated frozen-thawed bovine sperm adenylate cyclase activity, and whether cAMP levels in sperm changed during capacitation with heparin. The sperm adenylate cyclase was almost insensitive to C a2+ at concentrations up to 10 mM when cold-shocked homogenized sperma tozoa were used. Adenylate cyclase activity, as observed by cAMP forma tion (pmol/mg protein/min), did not increase significantly in the pres ence of 5 mM Mg2+. However, a 40-fold stimulation (cAMP 400-800 pmol/m g protein/min) occurred in the presence of 5 mM Mn2+. Although Ca2+ pe r se had no effect, it acted synergistically with Mg2+ and Mn2+ in sti mulating sperm adenylate cyclase. Adenylate cyclase activity was highe st in cold-shocked, homogenized spermatozoa. Sonication of cold-shocke d spermatozoa resulted in loss of adenylate cyclase activity, and a lo garithmic decrease in cAMP production (1155.5 to 109.7 pmol cAMP) occu rred when sonication was increased from 2 x 5 to 2 x 25 s on ice. Cycl ic AMP levels in spermatozoa incubated under non-capacitating conditio ns, both untreated and treated with glucose or heparin plus glucose, r emained higher (P < 0.01) compared with those incubated with heparin f or the first 4 h of incubation. When spermatozoa were incubated under non-capacitating conditions, cAMP levels increased (P < 0.01), especia lly during the first hour of incubation, and then declined gradually t hroughout the incubation. In contrast, cAMP levels of heparin-treated spermatozoa declined gradually for 3 h, at which time they began to ri se, peaked at 4 h and then remained fairly stable until 6 h. Glucose a ntagonized the effect of heparin on adenylate cyclase activity but not for more than 4 h. We conclude that: i) Ca2+ stimulates adenylate cyc lase in the presence of Mg2+; ii) homogenization by sonication reduces cyclase activity in frozen-thawed, cold-shocked spermatozoa; iii) ade nylate cyclase activity is inhibited by heparin but rises concomitantl y with the onset of capacitation (after 4 h) in spermatozoa incubated under capacitating conditions; and iv) glucose, which prevents capacit ation by heparin, antagonizes heparin action on adenylate cyclase.