The BSA-induced Ca2+ influx during sperm capacitation is CATSPER channel-dependent.
BACKGROUND
Serum albumin is a key component in mammalian sperm capacitation, a functional maturation process by which sperm become competent to fertilize oocytes. Capacitation is accompanied by several cellular and molecular changes including an increased tyrosine phosphorylation of sperm proteins and a development of hyperactivated sperm motility. Both of these processes require extracellular calcium, but how calcium enters sperm during capacitation is not well understood.


METHODS
BSA-induced changes in intracellular calcium concentration were studied using Fluo-4 and Fura-2 calcium imaging with wild-type and Catsper1 knockout mouse sperm.


RESULTS
We found that the fast phase of the BSA-induced rises in intracellular calcium concentration was absent in the Catsper1 knockout sperm and could be restored by an EGFP-CATSPER1 fusion protein. The calcium concentration increases were independent of G-proteins and phospholipase C but could be partially inhibited when intracellular pH was clamped. The changes started in the principal piece and propagated toward the sperm head.


CONCLUSIONS
We conclude that the initial phase of the increases in intracellular calcium concentration induced by BSA requires the CATSPER channel, but not the voltage-gated calcium channel. Our findings identify the molecular conduit responsible for the calcium entry required for the sperm motility changes that occur during capacitation.
Xia
Jingsheng
J
Department of Biology, University of Pennsylvania, 415 S University Ave, Philadelphia, Pennsylvania 19104, USA.
Ren
Dejian
D
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D012710:Serum Albumin, Bovine / Q000494:pharmacology*; D013075:Sperm Capacitation / Q000187:drug effects* / Q000235:genetics*; D013081:Sperm Motility / Q000187:drug effects / Q000235:genetics; D013094:Spermatozoa / Q000187:drug effects / Q000378:metabolism; D014018:Tissue Distribution / Q000187:drug effects
D015220:Calcium Channels; C488642:Catsper1 protein, mouse; D012710:Serum Albumin, Bovine; D000255:Adenosine Triphosphate; D002118:Calcium