Cell subpopulation-related volumetric parameters: A complementary tool of the modified hypo-osmotic swelling test on model of boar spermatozoa

It is a general property of the intact animal cell to swell rapidly in resp onse to hypo-osmotic conditions. The modified hypoosmotic swelling test (HO S-test) is an indicative test to evaluate the integrity of the plasma membr ane by means of an electronic cell counter, based on the relative increase of the cell volume in response to hypo-osmotic conditions. In this study th e relationships between the: osmotically induced changes df the cell volume of boar spermatozoa as determined by cell counter and the integrity of the membrane as determined by propidium iodide staining (PI) were studied. Boa r sperm cell volume distributions were measured under iso-osmotic (300 mosm olar) conditions and after a hypo-osmotic stress (150 mosmolar). The relati ve volume shift of mean and modal volume were calculated as a proportion co efficient of modal and mean values of the cell volume distributions by tran sition from iso-osmotic to hypoosmotic conditions. The volumetric parameter s related to the different cell subpopulations were derived from the differ ent peaks of cell volume distributions. PI-staining techniques were used fo r comparison. The Values of the volume shift and of derived percentages of the osmotically inactive cells were correlated negatively and positively, r espectively (p < 0.05) with the percentage of the PI-stained cells. This co rrelation indicates that a relationship exists between membrane functions o f the different cell compartments (sperm head and tail) due to the circumst ance that the increase of the cell volume in the HOS-test is associated wit h the morphological changes in the tail and the PI-staining is associated w ith the: membrane integrity and permeability of the head region. The advant age of computer-assisted volume measurement is that a large number of cells (5000-50000 spermatozoa) can be measured and evaluated during one procedur e and in a very short time. The relative volume shift is a quantitative con tinuous parameter characterizing the osmotic reactivity and membrane functi onal competence of a cell population and of subpopulations within one ejacu late. This parameter could be useful to evaluate membrane functional compet ence rapidly and sensitively.