The Interdoublet Elastic Component of the Sea Urchin Sperm Flagella.
Dominic W. Pelle, Kathleen A. Lesich and Charles B. Lindemann
Recently our lab reported that passive, vanadate-inhibited, rat sperm flagella exhibit a phenomenon described as counter-bend formation (Lindemann et al., 2005 Biophys. J. 89:1165-1174). When the basal portion of the flagellum is bent with a glass microprobe, the portion of the flagellum distal to the probe contact point develops a counter-bend in the opposite direction to the imposed bend. Rat sperm are 170 µm long and have reinforcing structures, namely the outer dense fibers and fibrous sheath; simple cilia and flagella are typically 6 to 30 µm in length and lack these structures. In this study we use sea urchin sperm to determine whether or not the counter-bend phenomenon is a property of the basic 9+2 axoneme. Sea urchin sperm extracted with 0.1% Triton X-100 and reactivated with 0.1 mM ATP were inhibited with 50 µM sodium metavanadate and manipulated to introduce a bend in the proximal flagellum. We found that the sperm respond by developing a counter-bend in the distal flagellum. We also measured the stiffness of passive sea urchin flagella under the counter-bend experimental conditions and found it to be ~ 6.0 × 10-22 Nm2. From the counter-bend curvature and the flagellar stiffness we determined the inter-doublet elasticity. Assuming the nexin links are the source, the elasticity was about 3.0 × 10-5 N/m per nexin link at 43 nm of interdoublet shear displacement. We also found that the elasticity decreased with increasing shear displacement. Our results with sea urchin sperm resemble our earlier results on rat sperm. This suggests that the counter-bend is best explained if the elasticity that produces the counter-bend is derived from structures common to both axonemes, namely the nexin links and/or radial spokes. Supported by N.S.F. grant #MCB- 0516181.