Measurement Of The Passive Stiffness Of Bull Sperm Flagella Using Force-calibrated Glass Microprobes

Dana L. Holcomb-Wygle, Kathleen A. Schmitz, and Charles B. Lindemann

Modeling a biological structure such as a flagellum requires knowledge of the mechanical properties of the structure. An important property of flagella, for the purpose of physical analysis of flagellar mechanics, is the passive stiffness of the structure without the influence of active dynein. Sodium vanadate has been shown to disable the dynein arms (Okuno, J. Cell Biol., V85:712, 1980). Triton X-100-extracted bull sperm treated with 50 µM sodium metavanadate at pH 8.0 and 0.1 mM ATP relaxes bull sperm flagella to their lowest stiffness, as judged by the speed of recoil after repositioning with a microprobe. Flagella in this condition were bent with a force-calibrated microprobe. The stage was then repositioned causing the flagellum to release from the probe. The deflection of the probe from equilibrium and curvature of the bent flagellum yielded measurements of stiffness. The stiffness of the midpiece region was found to be 1.6 ± 0.6 x 10-11 dyne ´ cm2 (n=20). The stiffness of the basal end of the principal piece (at ~20µm) was considerably less at 9.3 ± 5.0 x 10-12 dyne ´ cm2 (n=8). Supported by NSF grant MCB-9722822.