Effect of Steroid Hormones and Capacitation on Membrane Potential of Human Spermatozoa

Abstract

The accumulation of the lipophilic cation radiolabeled triphenylmethylphosphonium (TPMP ⁺) was utilized to determine the resting membrane potential across the plasma membrane (ψ) on human sperm. Washed sperm were suspended and incubated in low-K⁺ and high-K⁺ medium and allowed to take up the cation to a steady state (that is, 20 min at 37 °C). The data were transformed according to concentration using the intracellular volume and with these values inserted in the Nernst equation we obtain ψ. When the concentration of K⁺ was low in the medium, the ψ was -69 ± 2 mV, the ψ was temperature- and pH-dependent. The sperm were incubated in the same conditions in the presence of testosterone, estradiol, and progesterone. The addition of these hormones induced the decrease in ψ by about 29%, 32%, and 40%, respectively. On the other hand, capacitation of spermatozoa was induced by the addition of calcium and the ionophore A23187 and in these conditions the ψ decreased 50%. The action of the hormones on sperm membrane was accompanied by some steroid-dependent structural modification promoting the ψ decrease. This effect plays an important role in the capacitation, preparing it for sperm penetration in the ova.

Key Words:

• Triphenylmethylphosphonium
• Capacitation
• Membrane potential
• Steroids