THE BUOYANT DENSITY OF BOVINE AND RABBIT SPERMATOZOA

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Abstract
Zonal isopycnic gradient centrifugation has been employed as a method for the separation of intact spermatozoa on the basis of the differing buoyant densities of the cells. Spermatozoa from rabbits and cattle were studied, and materials used for the gradient solutions have included sodium chloride, sodium nitrate, potassium tartrate, potassium iodide, caesium chloride, glycerol, sucrose, Ficoll, bovine serum albumin, a colloidal silica solution and the methyl glucamine salt (MGU) of 3,5-di''-iodo-4-pyridone-N-acetic acid (umbradilic acid). Linear density gradients were preformed with a gradient machine, and the diluted washed cells were layered as a lamella on the gradient. A normal population of spermatozoa was separated by the zonal isopycnic centrifugation into two density classes a low-density class and a high-density class.'' The relative amounts of cells in each class varied with the type and maturity of cells, the pretreatment and the conditions of the centrifugation. The low-density class of cells had a buoyant density of 1.16 to 1.19 g/ml in all solutions employed; the high-density class has buoyant density values depending upon the solute employed for the gradient solutions and varying from 1.25 to 1.32 g/ml. The separation of the cells into two classes appears to be on the basis of the premeability of the cells, as ageing, physical treatment or chemical treatment lead to an increased amount of cells in the high-density class. The cells in the high-density fraction show no apparent differences in their size or structure, but show a lower motility and fertility and a greater eosinophilia than the cells in the low-density fractions. The high-density class divides further into two sub-classes over a narrow range of densities. This subdivision may be on the differing dry weight compositions of the cells which is made evident by the replacement of internal water with external solvent.