Surface Changes in Rat Spermatozoa During Epididymal Transit1

Abstract

Several different approaches were employed to evaluate differences in the plasma membrane of spermatozoa from the caput and cauda epididymis of the rat. The two sperm populations showed significant differences in agglutinability by the lectin concanavalin A but not by wheat germ agglutinin or Ricinus communis 120. The surface distribution of concanavalin A receptors between caput and cauda spermatozoa is strikingly different, with caput spermatozoa showing an even distribution of Con A binding sites, whereas cauda sperm showed restricted areas of Con A binding to the head and flagellum. Direct measurement of available Con A binding sites indicated between 15%-25% more accessible sites on caput than on cauda spermatozoa. Caput spermatozoa and cauda spermatozoa also differ in the array and/or abundance of Con A receptors present; one of the major differences is a substantial increase in a component of 37k. Further surface differences were established by comparison of externally oriented surface proteins accessible to lacto-peroxidase-catalyzed iodination; a decreased labeling of specific high molecular weight components and a major increase in labeling of low molecular weight components of 26k and 28k were noted during epididymal maturation. The possible significance of these changes as well as the possible mechanisms responsible for generating these differences are discussed.