Qualitative and quantitative changes in sperm surface, epididymal tissue and luminal fluid proteins during epididymal transit in rattus rattus

Changes in the sperm surface membrane epididymal tissue and luminal proteins of house rat were analyzed during epididymal transit. The total protein concentration in the tissue and fluid was greater in caput as compared to that in corpus and cauda indicating its highest secretory activity. A maximum number of 15 proteins were separated by SDS-PAGE in tissue, followed by 13 in sperm membrane extract (SME) and minimum (10) in fluid from three regions of epididymis. The present study demonstrated that sequential dramatic changes occur in protein composition of the sperm membrane and epididymal fluid during epididymal transit. The proteins of 97, 39 and 23 kDa were present in tissue and sperm membrane extract (SME) of three regions but absent in fluid indicating their incorporation into the spermatozoa in the caput region. A decrease in the quantity of 66, 52, 41, 33, 26 and 18 kDa proteins in luminal fluid and simultaneous increase in SME from caput to cauda showed probable incorporation of these proteins into the spermatozoa membrane during epididymal maturation process. However, the spermatozoa acquire only selective proteins from the fluid, as proteins of 20 and 14 kDa were not absorbed by spermatozoa inspite of their presence in the luminal fluid. During epididymal transit spermatozoa also lose some of their proteins, as in present studies a 10 kDa protein was detected in caput SME only, but luminal fluid of all the three regions. These results revealed that interaction of the spermatozoa with the surrounding fluid results either in removal, masking or unmasking of pre-existing membrane proteins or the absorption and incorporation of new epididymal fluid proteins.