Movement of Spermatozoa in Viscous Environments

Observations of the effects of increased viscosity have been important in attempting to understand the mechanical forces and molecular mechanisms involved in cell motility. Berg & Turner (1979) have recently demonstrated that the movement of bacteria at increased viscosities depends on the nature of the macromolecules used to obtain increased viscosities. With methyl cellulose, an unbranched, long-chain polymer, decreases in rotation rates of tethered E. coli were much less than with Ficoll, a highly branched polymer, even though the viscosities measured at the macroscopic level were similar. At the microscopic level, methyl cellulose apparently forms a loose, quasi-rigid network in solution, which is easily penetrated by particles on the scale of bacteria and their flagella, but makes a substantial contribution to the macroscopic viscosity of the solution even at concentrations where 'non-Newtonian' behavior is minimal. This observation has led us to re-examine earlier measurements on the effects of viscosity on the movement of sperm flagella, which were made using methyl cellulose to increase the viscosity (Brokaw, 1966; Brokaw & Simonick, 1977).