Local reactivation of Triton-extracted flagella by iontophoretic application of ATP

Abstract

IN spite of recent progress in ultrastructural and biochemical studies of cilia and flagella¹, the mechanism of their movement is still poorly understood. Much circumstantial evidence, however, supports the sliding microtubule model of ciliary and flagellar motility² which involves active sliding between axonemal microtubules to provide the motive force for bending. For example, ATP-dependent sliding of microtubules has been demonstrated in the Triton-extracted axoneme lightly digested by trypsin³. To produce a bend in the sliding microtubule model, there should be local differences in the amount of sliding along the axoneme. Morphological evidence indicates the presence of such differences in the bent region of cilia⁴. We now report experiments involving local, brief reactivation of Triton-extracted sea urchin spermatozoa by iontophoretic application of ATP. Our results support the idea of sliding within the axoneme as the basis of flagellar bending.