Physical evidence for the existence of interdoublet elastic linkages in rat sperm flagella.

 

C.B. Lindemann, L.J. Macauley, K.A. Lesich

 

Triton X-100 extracted rat sperm flagella were treated with 50 mM NaVO3 in the presence of 0.1 mM ATP to disable the dyneins and relax the flagellum. When these passive flagella were bent with a glass microprobe, the portion of the flagellum distal to the microprobe contact point reacted to the imposed bend by developing a counter-bend in the opposite bending direction. When the flagellum was released from the microprobe, the counter-bend relaxed and the flagellum straightened. Interdoublet sliding was calculated by multiplying the shear angles along the flagellar length by either the spacing of the doublets or the spacing of the outer dense fibers. The observed counter-bend can be accounted for by the mechanically imposed shear, if there are extensible elements between the doublets that tend to restore the axoneme to the zero-shear configuration. The components of the axoneme most ideally positioned to provide such a function are the nexin links. Furthermore, counter-bend formation was abolished with elastase which is known to disrupt the nexin links. Based on the curvature of the counter-bends and the measured stiffness of the passive flagella, we were able to determine a value for the interdoublet elasticity. Assuming nexin links are the source, it amounts to ~3.0 10-5 N/m per nexin link. An interesting finding is that the amount of interdoublet shear that develops in the counter-bend was consistent with the amount of interdoublet sliding calculated using the outer dense fiber spacing. It was not consistent with the amount of interdoublet sliding calculated using the interdoublet spacing. This supports the hypothesis that in mammalian sperm tension generated at the doublets is transmitted through the outer dense fibers to the connecting piece at the flagellar base. Supported by N.S.F. grant MCB-0110024.