Discrete regional distributions suggest diverse functional roles of calcium channel a, subunits in sperm

The Ca channels of male germ-line cells are partially characterized, but th e molecular properties and subcellular localization of the Ca channels of m ature sperm are unknown. Here, we probe rodent sperm with anti-peptide anti bodies directed to cytosolic domains of cloned rat brain alpha(1A), alpha(1 C), and alpha(1E) Ca channel subunits. Each recognizes a 200- to 245-kDa ba nd on immunoblots of whole rat sperm extracts. A smaller (similar to 110-kD a) alpha(1C) band also is detected. Confocal fluorescence images of mouse s perm show characteristic patterns of punctate alpha(1A)-, alpha(1C)-, and a lpha(1E)-immunoreactivity. For alpha(1A) the puncta are larger, less numero us, and more variable in distribution than for alpha(1C) and alpha(1E). The y are absent from the acrosomal crescent, but are present elsewhere over th e sperm head, often at the apical tip and equatorial segment. They also are found at irregular intervals along both the midpiece and the principal pie ce of the flagellum. For alpha(1C) and alpha(1E), puncta are dense along do rsal and ventral aspects of the acrosomal cap. For alpha(1E) but not alpha( 1C), the remainder of the acrosomal region also is labeled. Neither is foun d in the postacrosomal region or on the midpiece. Puncta of alpha(1C) and a lpha(1E) occur at regular intervals each in two parallel rows, at the dorsa l and ventral aspects of the proximal segment of the flagellar principal pi ece. The puncta in these arrays become less abundant and intense in the dis tal flagellum. These results demonstrate that multiple Ca channel proteins are present in mature sperm and are regionally localized in ways that may g ive them different regulatory roles. (C) 1999 Academic Press.