The rate at which human sperm are immobilized and killed by mild acidity

Fertil Steril. 2000 Apr;73(4):687-93. doi: 10.1016/s0015-0282(99)00640-8.


Objective: To determine the rate at which mild acidity immobilizes and kills human sperm and to evaluate an acidic microbicide, BufferGel, for sperm immobilization.

Design: Controlled in vitro study.

Setting: An academic research university and hospital andrology lab.

Patient(s): Eight volunteer male sperm donors.

Intervention(s): Semen samples were treated with hydrochloric acid (HCl) or BufferGel.

Main outcome measure(s): Sperm motility was measured by using a computerized automated semen analyzer and video microscopy. Sperm membrane permeability and intracellular pH were measured by using fluorescent techniques.

Result(s): In semen acidified with HCl to pH 4.0, sperm were rapidly immobilized (within 1 min) and were irreversibly immobilized (killed) within 10 minutes. The speed of immobilization and of killing were both linearly proportional to hydrogen ion activity over a pH range of 7.5-4.0. Across the same range, the intracellular pH of human sperm equilibrated to within 0.5 pH units of extracellular pH within 1-2 minutes. BufferGel immobilized sperm significantly faster than HCl from pH 4.0-6.0.

Conclusion(s): Exposure to mild acidity rapidly acidifies the intracellular pH of human sperm and is rapidly spermicidal. BufferGel accelerates acid immobilization of sperm.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acids
  • Cell Death
  • Cell Membrane Permeability
  • Humans
  • Hydrochloric Acid / chemistry
  • Hydrogen-Ion Concentration
  • Male
  • Propidium / pharmacokinetics
  • Sperm Motility
  • Spermatozoa / chemistry*
  • Spermatozoa / physiology*
  • Time Factors


  • Acids
  • Propidium
  • Hydrochloric Acid