Immunocytochemical localization of calmodulin in intact and acrosome-reacted boar sperm

Localization of calmodulin on intact and acrosome-reacted ionophore A23187 induced boar sperm has been performed with indirect immunofluorescence and immunoelectron microscopy. The results obtained with immunofluorescence are in agreement with previous reports. Immunoelectron microscopy was performed with the methods of preembedding immunostaining and on-grid post-embedding immunostaining of Lowicryl K4M sections with the protein A-colloidal gold. The presence of calmodulin is demonstrated in the acrosomal content and in the equatorial and postacrosomal regions of intact sperm. Apparently, calmodulin is released in association with the plasma membrane and the outer acrosomal membrane in acrosome-reacted sperm and it is maintained in the equatorial and postacrosomal regions. These results provide further evidence that also in mammalian sperm multiple classes of calmodulin-binding proteins may be present.