THE REACTIVATION OF DEMEMBRANATED HUMAN SPERMATOZOA LACKING OUTER DYNEIN ARMS IS INDEPENDENT OF PH

The effect of pH, Mg-ATP, and free calcium on activity of the inner dy nein arm was investigated using demembranated human spermatozoa lackin g the outer dynein arms (LODA). The results were compared with those o btained for demembranated-reactivated normal spermatozoa to evaluate t he functional properties of the inner and outer dynein arms in axonema l motility. The reactivation of Triton X-100-demembranated LODA sperma tozoa was analysed at various pHs and concentrations of Mg-ATP and cal cium using video recordings. The percentage of reactivated LODA sperma tozoa as a function of Mg-ATP concentration was not dependent on pH, w hereas reactivation of normal human spermatozoa is pH dependent. This suggests that there may be a pH-dependent regulatory mechanism associa ted with the outer dynein arms. A delay in the principal bend propagat ion of normal and LODA reactivated cells was found at pH 7.1. This dis appeared at pH 7.8 in normal but not in LODA populations. This suggest s a role for outer dynein arms in the initiation of the propagation of flagellar bends at alkaline pH. The level of LODA and normal sperm re activation both depended on the calcium concentration in the medium. A t lower free calcium concentrations, the reactivation level and beat f requency of reactivated cells were higher. Our results suggest a funct ional difference between outer and inner dynein arms of human spermato zoa based on a differential pH sensitivity. Moreover, calcium seems to exert its regulatory action elsewhere than on the outer dynein arms. (C) 1998 Wiley-Liss, Inc.