Na+ /Ca2+ exchanger contributes to asterosap-induced elevation of intracellular Ca2+ concentration in starfish spermatozoa.
Asterosap, a group of equally active isoforms of sperm-activating peptides from the egg jelly of the starfish Asterias amurensis, functions as a chemotactic factor for sperm. It transiently increases the intracellular cGMP level of sperm, which in turn induces a transient elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)). Using a fluorescent Ca(2+)-sensitive dye, Fluo-4 AM, we measured the changes in sperm [Ca(2+)](i) in response to asterosap. KB-R7943 (KB), a selective inhibitor of Na(+)/Ca(2+) exchanger (NCX), significantly inhibited the asterosap-induced transient elevation of [Ca(2+)](i), suggesting that asterosap influences [Ca(2+)](i) through activation of a K+-dependent NCX (NCKX). An NCKX activity of starfish sperm also shows K(+) dependency like other NCKXs. Therefore, we cloned an NCKX from the starfish testes and predicted that it codes for a 616 amino acid protein that is a member of the NCKX family. Pharmacological evidence suggests that this exchanger participates in the asterosap-induced Ca(2+) entry into sperm.
Islam
M Sadiqul
MS
Department of Biosciences and Informatics, Keio University, 3-14-1, Hiyoshi, Kouhoku-ku, Yokohama 223-8522, Japan.
Kawase
Osamu
O
Hase
Sumitaka
S
Minakata
Hiroyuki
H
Hoshi
Motonori
M
Matsumoto
Midori
M
D000595:Amino Acid Sequence; D000818:Animals; D047271:Asterias / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D011188:Potassium / Q000502:physiology; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D013094:Spermatozoa / Q000378:metabolism*
D019831:Sodium-Calcium Exchanger; C074530:potassium-dependent sodium-calcium exchanger; D011188:Potassium; D002118:Calcium