Optical determination of motility forces in human spermatozoa with laser tweezers

Abstract

Laser tweezers may act as optical force transducers. We report on the determination of intrinsic motility forces of human spermatozoa by employing an 800 nm optical trap. The cellular forces were calculated from calibrated trapping forces. The determination of trapping forces based on a hydrodynamic model for ellipsoidal specimens, the measurement of the minimum laser power required to confine a single cell in the trap, and the calculation of viscous forces during the movement of optically trapped sperm heads through a laminar fluid. A mean motility force of 44±24 pN was calculated for spermatozoa of healthy donors.

Measurements of forces produced by the mitotic spindle using optical tweezers

“…To convert milliwatts of laser power to trapping force, the basic formula is F = nQP / c , where F is the force, n is the refractive index of the object being trapped divided by the refractive index of the surroundings (Ashkin, 1992; Konig et al ., 1996), P is the power in the trap, and c is the speed of light. Q is a conversion factor that, for objects that absorb some of the trap, has a range of 0–1, where 1 is equivalent to total absorption (Ashkin, 1992; Svoboda and Block, 1994a; Konig et al ., 1996; Neuman and Block, 2004).…”

“…Q is a conversion factor that, for objects that absorb some of the trap, has a range of 0–1, where 1 is equivalent to total absorption (Ashkin, 1992; Svoboda and Block, 1994a; Konig et al ., 1996; Neuman and Block, 2004). Q is the fraction of momentum transferred to a trapped object, and its value determines whether an object will be trapped (Wright et al ., 1994).…”

“…The forces determined in our experiments are comparable to those of motor molecules and of motile sperm that were measured using optical tweezers: 1.7 pN for myosin (Molloy et al ., 1995); 2.6 pN for a single motor molecule driving mitochondria (Ashkin et al ., 1990); 5–6 pN for kinesin molecules (Svoboda and Block, 1994b); 9.2 pN for the unbinding of actin and myosin (Nishizaka et al ., 1995); and 44 pN for the motion of healthy sperm (Konig et al ., 1996). Because of the large difference between our values and those reported previously, we need to consider whether our numbers could be erroneously low.…”

Determination of motility forces on isolated chromosomes with laser tweezers

“…In addition, it also requires knowledge of the viscosity of the surrounding medium. As this cannot be easily performed within the cell, the corresponding forces were estimated by assumption of a range of values for chromosomes trapping efficiency that was based on previous chromosome fragment trapping experiments 8 , and experiments to trap sperm heads after removal of their tails 11 19 .…”

Optical tweezers and non-ratiometric fluorescent-dye-based studies of respiration in sperm mitochondria

“…In addition to VCL, laser trapping has been used to measure the actual swimming force of human sperm (Tadir et al 1989) as well as sperm from other vertebrate species (Nascimento et al 2006). The ideal optical tweezer wavelengths for sperm trapping fall between 800 and 1064 nm (Konig et al 1996). Using laser tweezers, Patrizio found that the swimming force of sperm dramatically increases upon addition of pentoxifylline (Patrizio et al 2000), while Nascimento studied sperm competition based on mating type (polygamous versus monogamous) in several primate species, including human (Nascimento et al 2008a).…”