Mobility shift assay of calcium-binding proteins of mouse epididymal spermatozoa

The calcium-binding proteins (CBPs) of mouse epididymal spermatozoa were an alysed by mobility changes in the presence of added Ca2+ in two-dimensional sodium dodecyl sulphate-polyacrylamide cel electrophoresis (SDS-PAGE). The expression patterns of relatively high molecular weight CBPs (Mr > 20 kDa) were different between caput and cauda epididymal spermatozoa. There was a constitutive expression of low molecular weight CBPs (M-r < 20 kDa) regard less of the epididymal region. Most of the CBPs disappeared after the acros ome reaction (AR) induced by Ca2+ ionophore A23187, suggesting that they or iginated from the acrosome and/or the plasma membrane overlaying the acroso me. Taken together, it can be suggested that changes in CBPs of spermatozoa are important features of sperm maturation during epididymal transit, and that they may be related to the fertilizing ability of mouse epididymal spe rmatozoa.