Dynamic aspects of microtubule sliding in sperm flagella

The force of microtubule sliding in reactivated sea urchin sperm flagella was determined under defined mechanical conditions by attaching two glass microneedles to a demembranated flagellum and measuring the small displacements of the needle caused by the sliding force. Upon reactivation with a solution containing elastase as well as ATP, oscillatory force generation was observed under an isometric condition, followed by a plateau of isometric force. The average isometric force was about 1 pN per dynein arm which did not change with the ATP concentration (4 to 500 microM).