Hyperpolarization/Depolarization on 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) of 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 (20 min at 37 °C). By using this differential, the value obtained was inserted in the Nernst equation and the value yielded a ψ of — 69 ± 2 mV. When the Na⁺ or K⁺ concentration is high in the medium, the accumulation of TPMP⁺ in the membrane sperm cells was increased or decreased, respectively, inducing hyperpolarization and depolarization of the membrane 20% and 85%, respectively. The presence of divalent cations Zn^{+ +} and Mg^{+ +} in the incubation medium both induced a hyperpolarization of 10% and 8.6%, respectively. The addition of specific reagents such as p-chloromercuribenzenosulfonate and ethylenediaminetetraacetic acid sodium salt both decreased the ψ 35% and 58%, respectively. The agents acting on the sperm cell membrane, such as dithiothreitol and progesterone, both induced hyperpolarization and depolarization of the membrane 16% and 40%, respectively. The presence of propranolol and L-α-lysophosphatidylcholine, which affect the ionic gradients present across the plasma membrane, both induced a depolarization from 43% and 92%, respectively. Finally the ψ was glucose-dependent. The result of these studies was that, by the use of agents causing hyperpolarization or depolarization, we obtained changes in the ψ of - 83.4 ± 2.2 mV, until — 6 ± 0.6 mV changes of —76.8 ± 2 mV translated across the sperm cell membrane.

Key Words:

• Triphenylmethylphosphonium
• Nernst equation
• Membrane potential
• Spermatozoa.