Measurement of the Effect of ADP on the Force Generated in Bull Sperm Flagella.

Kathleen A. Schmitz, Robin M. Blalock, and Charles B. Lindemann

The objective of this study was to examine the effect of adenosine diphosphate (ADP) on the force produced by a beating bull sperm flagellum. To accomplish this we used force-calibrated glass microprobes to measure the force exerted by the flagella of Triton X-100 extracted sperm models. The sperm models were reactivated with either 0.1mM ATP or 0.1mM ATP and 1mM ADP in the presence of 1mM Mg+2. Sperm were selected that had their head stuck to the microscope slide, the calibrated probe was then positioned so that the flagellum arrested while pushing against the probe. To be certain that ADP was producing an effect on motility we determined that the ADP significantly reduced the beat frequency of the sperm (1.07 .2 Hz in the ADP samples vs. 2.1 .4 Hz in the ATP only control samples, p< .05). It also increased the maximal curvature of the beat in the proximal 15 microns of the flagellum (average 1200 rad./cm in the ADP samples, n = 10, vs. 940 rad./cm in the ATP-only control samples, n = 6). In spite of these effects on beat frequency and waveform, we measured no significant difference in the force generated by the stalled flagella (2.08 0.8e-5 dyne for the controls, n = 16 ; and 1.94 0.4e-5 dyne for the ADP samples, n = 14). The invariance of the measured force suggests that ADP does not effect the number of dyneins or the force per dynein contributing to the flagellar stalling force. Supported by grant No. MCB-9722822 from the National Science Foundation.