FORSKOLIN DOES NOT ACTIVATE SPERM ADENYLATE-CYCLASE

  • 1 January 1983
    • journal article
    • research article
    • Vol. 24  (1) , 42-47
Abstract
Forskolin, a potent activator of adenylate cyclase, was proposed to activate this enzyme by a direct interaction with the catalytic subunit. To test this hypothesis, the effects of forskolin were examined on sperm cAMP content and sperm adenylate cyclase activity. Forskolin or cholera toxin did not increase cAMP content in either bull or boar sperm, whereas the inhibitors of phosphodiesterase, caffeine and methylisobutylxanthine, significantly increased sperm cAMP content. Forskolin, NaF and guanylimidodiphosphate did not activate the adenylate cyclase of either sperm membranes or cytosol. When homogenates of rat, guinea pig or bull testes were centrifuged at 100,000 .times. g, the supernatant contained a forskolin-stimulated adenylate cyclase. Further centrifugation of this 100,000 .times. g supernatant fraction at 250,000 .times. g for 3 h quantitatively sedimented the forskolin-sensitive enzyme activity. Forskolin evidently does not activate either the cytosolic or membrane-bound adenylate cyclase of mammalian sperm.