Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 34, Pages 14342-14347Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1111695108
Keywords
infertility; P2X channel; purinergic ion channel; reproduction
Categories
Funding
- National Institutes of Health [P30-HD18655]
- Bill and Melinda Gates Foundation
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Sperm cells acquire hyperactivated motility as they ascend the female reproductive tract, which enables them to overcome barriers and penetrate the cumulus and zona pellucida surrounding the egg. This enhanced motility requires Ca(2+) entry via cation channel of sperm (CatSper) Ca(2+)-selective ion channels in the sperm tail. Ca(2+) entry via CatSper is enhanced by the membrane hyperpolarization mediated by Slo3, a K(+) channel also present in the sperm tail. To date, no transmitter-mediated currents have been reported in sperm and no currents have been detected in the head or midpiece of mature spermatozoa. We screened a number of neurotransmitters and biomolecules to examine their ability to induce ion channel currents in the whole spermatozoa. Surprisingly, we find that none of the previously reported neurotransmitter receptors detected by antibodies alone are functional in mouse spermatozoa. Instead, we find that mouse spermatozoa have a cation-nonselective current in the midpiece of spermatozoa that is activated by external ATP, consistent with an ATP-mediated increase in intracellular Ca(2+) as previously reported. The ATP-dependent current is not detected in mice lacking the P2X2 receptor gene (P2rx2(-/-)). Furthermore, the slowly desensitizing and strongly outwardly rectifying ATP-gated current has the biophysical and pharmacological properties that mimic heterologously expressed mouse P2X2. We conclude that the ATP-induced current on mouse spermatozoa is mediated by the P2X2 purinergic receptor/channel. Despite the loss of ATP-gated current, P2rx2(-/-) spermatozoa have normal progressive motility, hyperactivated motility, and acrosome reactions. However, fertility of P2rx2(-/-) males declines with frequent mating over days, suggesting that P2X2 receptor adds a selection advantage under these conditions.
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