Modification of Ram Sperm Membranes During Epididymal Transit1

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Abstract
Previous research established that membrane physical properties of testicular and cauda epididymal sperm differ in many respects. The data presented herein establish the region of the epididymis where these and other changes occur. Isoelectric focusing experiments were used to detect a change in the net charge of the glycocalyx. Evaluations of mixtures of sperm from proximal caput vs. distal cauda revealed bimodal distributions with a pH 5.0 band and a band at pH 5.2-5.4. In contrast, evaluation of mixtures of central caput and distal cauda sperm gave a single population focusing at pH 5.0. The charge of the glycocalyx is altered before sperm enter the central caput. Changes in the lipid bilayer occur in the lower epididymis. Sperm from the caput and corpus resisted cold shock, sperm from proximal cauda were altered, or inconsistently damaged, and membranes of sperm from distal cauda were invariably damaged by cold shock. Changes in the plasma membrane were evaluated by lectin-induced agglutination of sperm. Ricinius communis agglutinin-120 (RCA) and Ulex europaea agglutinin Type I (UEA) induced a high degree of agglutination with caput sperm, but this capacity was lost as sperm progressed through the epididymis. Concanavalin A (ConA) induced high agglutination with caput and cauda sperm, but a lower extent of agglutination with corpus sperm. In sharp contrast, wheat germ agglutinin (WGA) did not induce agglutination of sperm from the caput or corpus but did induce agglutination of sperm from the proximal and distal cauda epididymidis. Diluted sheep serum also induced head-to-head agglutination and the extent of this agglutination also changed as sperm passed through the epididymis. Continual modification of the sperm surface occurs throughout epididymal passage with specific changes at discrete locations of the duct between the proximal caput and the central cauda epididymidis.