Mechanism of human sperm activation by extracellular ATP.
We have identified the mechanism whereby extracellular ATP (ATPe) triggers the acrosome reaction in human spermatozoa. This nucleotide opens a ligand-gated ion channel expressed on the sperm plasma membrane. ATPe threshold and 50% effective concentration calculated on the total added ATPe are 0.1 and 2 mM, respectively, corresponding to a free ATP concentration (ATP4-) of 3 and 200 microM, respectively. The ATPe-gated channel is selective for monovalent cations (Na+, choline, and methylglucamine), whereas on the contrary, permeability to Ca2+ is negligible. Isosmolar replacement of extracellular Na+ with sucrose fully blocked ATPe-dependent sperm activation, thus suggesting a mandatory role for Na+ influx. These results show that human sperm express an ATPe-gated Na+ channel that might have an important role in sperm activation before egg fertilization.
Foresta
C
C
Università di Padova, III Cattedra di Patologia Medica, Italy.
Rossato
M
M
Chiozzi
P
P
Di Virgilio
F
F
D000177:Acrosome / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000502:physiology*; D000328:Adult; D002118:Calcium / Q000378:metabolism; D002414:Cations, Monovalent / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism*; D005260:Female; D006801:Humans; D015640:Ion Channel Gating; D008024:Ligands; D008297:Male; D009994:Osmolar Concentration; D015222:Sodium Channels / Q000378:metabolism; D013084:Sperm-Ovum Interactions / Q000502:physiology
D002414:Cations, Monovalent; D008024:Ligands; D015222:Sodium Channels; D000255:Adenosine Triphosphate; D002118:Calcium