DETERMINATION OF WATER PERMEABILITY COEFFICIENT FOR HUMAN SPERMATOZOA AND ITS ACTIVATION-ENERGY

Four experiments were conducted to determine the permeability coefficient of human sperm to water (L(p)) and its activation energy (E(a)). Critical tonicity (tonicity at which 50% of the cells swell and lyse) was determined by equilibrating sperm to 22-degrees-C (experiments 1a and 1b), 30, 22, 8, or 0-degrees-C (experiment 2a), and 0, -1, -3, -5, or -7-degrees-C (experiment 2b) and then exposing them to various hypotonic media (215-3 mOsm). For L(p) determination, sperm were equilibrated to 30, 22, 8, or 0-degrees-C (experiment 3a), 8, 0, or -3-degrees-C (experiment 3b), and -1, -3, -5, or -7-degrees-C (experiment 3c), and then were exposed for increasing times to hypotonic (40 mosm) media. Activation energies were calculated from the results of the latter experiments (experiment 4). Results indicate a temperature-dependent (p < 0.05) critical tonicity, with sperm exhibiting an increased membrane fragility at 8, 0, and -7-degrees-C, relative to 30, 22, -1, -3, or -5-degrees-C (67.5 +/- 2.4, [mean +/- SEM], 62.7 +/- 2.3, and 61.9 +/- 3.7 mOsm vs. 57.4 +/- 3.4, 57 +/- 1.2, 54.8 +/- 3.4, 60.1 +/- 5.3, and 59.8 +/- 5.2 mOsm, respectively). Human sperm have an L(p) of 2.40 +/- 0.20 mum/min/atm at 22-degrees-C and an E(a) of 3.92 +/- 0.59 kcal/mol between 30 and -7-degrees-C. The E(a) for cells incubated at temperatures above 0-degrees-C (3.92 kcal/mol) show an apparent discontinuity (p < 0.004) in water permeability in supercooled conditions (7.48 kcal/mol). These data suggest that 1) human sperm have a high L(p) and low E(a), relative to other cell types, above 0-degrees-C; and 2) this high L(p) and its low E(a) change significantly below 0-degrees-C.