Abstract: 35

EVIDENCE SUPPORTING THE PRESENCE OF INTERNAL CALCIUM STORES IN MAMMALIAN SPERM.

Ming-Wen Li^{1 *}, Da-Yuan Chen²
Division of Reproductive Biology, Department of Obstetrics and Gynecology, University of California, Davis ¹
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, China ²

To determine whether the internal Ca²⁺ stores are present in mammalian sperm, calcium distribution changes were studied systematically during spermatogenesis, epididymal maturation, capacitation and acrosome reaction using potassium antimonate in situ precipitation technique at EM level. Before capacitation, calcium in the sperm of guinea pig, mouse and rhesus monkey was mainly localized on the inner surface of the outer acrosomal membrane (OAM) and in the perinuclear space between the inner acrosomal membrane (IAM) and the nuclear membrane (mainly on the surface of IAM). The calcium deposits in the perinuclear space began to appear in the acrosomal phase and the calcium deposits on the inner surface of OAM began to appear in the maturation phase during spermatogenesis in guinea pig. The source of Ca²⁺ in these two internal stores might be the smooth endoplasmic reticulum vesicles or the calciosomes present in the Sertoli cells in which large amount of Ca²⁺ deposits were observed. During capacitation, the Ca²⁺ in the two internal stores stated above was mobilized and disappeared at the time of acrosome reaction. Ca²⁺-pump or Ca²⁺-ATPase was localized on the plasma membrane of the periacrosomal region and on the OAM of rhesus monkey sperm using capture method with lead ions at pH 9.0. It is very interesting that the nuclear membrane of the giant panda sperm possessed Ca²⁺-ATPase activity, which might regulate the Ca²⁺ concentration in the perinulear space and then regulate the Ca²⁺ concentration in the whole sperm. Thapsigargin, an inhibitor of the endoplasmic reticulum Ca²⁺-ATPase, could induce capacitated guinea pig sperm to acrosome react to 100% at 100 µM in the presence or absence of Ca²⁺. Taken together these findings support the hypothesis that mammalian sperm possess internal Ca²⁺ stores and the Ca²⁺ mobilized from internal stores play important role in acrosome reaction.

    This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.