Determination of water permeability coefficient for human spermatozoa and its activation energy

Abstract

Four experiments were conducted to determine the permeability coefficient of human sperm to water (I(p)) and its activation energy (E2). Critical tonicity (tonicity at which 50% of the cells swell and lyse) was determined by equilibrating sperm to 22°C (experiments 1a and 1b), 30, 22, 8, or 0°C (experiment 2a), and 0, -1, -3, -5, or -7°C (experiment 2b) and then exposing them to various hypotonic media (215-3 mOsm). For 1(p) determination, sperm were equilibrated to 30, 22, 8, or 0°C (experiment 3a), 8, 0, or -3°C (experiment 3b), and -1, -3, -5, or -7°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°C, relative to 30, 22, -1, -3, or -5°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 μm/min/atm at 22°C and an E(a) of 3.92 ± 0.59 kcal/mol between 30 and -7°C. The E(a) for cells incubated at temperatures above 0°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°C; and 2) this high L(p) and its low E(a) change significantly below 0°C.