Interdoublet Sliding in Bovine Spermatozoa: Its Relationship to Flagellar Motility and the Action of Inhibitory Agents

Abstract

Interdoublet sliding rates were assessed in bull sperm, utilizing a freeze–thaw procedure to allow axonemal disintegration. The sliding rate at 23°C increased with increasing MgATP concentrations up to 1 mMATP, to plateau at 8 μm/sec. The analyzed interdoublet shear in both live and demembranated (Triton X-100-extracted) bull sperm reactivated with 1 mMATP established maximal microtubule sliding rates at 6 μm/sec during flagellar beating. Therefore,in vitrosliding rates were sufficient to account for the beat in intact flagella. The effect of inhibitors of flagellar motility onin vitrosliding rates was evaluated. While 8 μMvanadate minimally reduced the sliding rate (to ≈ 4 μm/sec), only 0.5 μMvanadate was sufficient to terminate reactivated bull sperm motility. Nickel ion (0.66 mM) terminated all spontaneous motility, while only reducing microtubule sliding rates to ≈ 5.0 μm/sec. Exposing intact bull sperm to theophylline (1 mM), and incubating the subsequently demembranated sperm in cAMP (3 μM), improved flagellar motility, but had little impact on microtubule sliding rates as determined by axonemal disintegration. Furthermore, deactivating live sperm with 2 mMKCN and 4 mM2-deoxy-d-glucose renders the subsequently reactivated sperm immotile (as long as exogenous cAMP is absent). Yet, this treatment only reduced the sliding rate by 38%. Paradoxically, 4 mMMgADP reduced the sliding rates most dramatically (86%), whereas demembranated sperm models retain a strong, coordinated beating pattern in the presence of MgADP. These results demonstrate that there is no direct relationship between interdoublet sliding rates and the capacity for coordinated flagellar beating.