Sperm-induced local [Ca2+]i rise separated from the Ca2+ wave in sea urchin eggs in the presence of a gamete fusion inhibitor, jaspisin .
An increase in intracellular Ca2+ concentration ([Ca2+]i) at a focal plane was recorded simultaneously with sperm-egg binding and membrane current upon insemination of sea urchin Hemicentrotus pulcherrimus eggs. No change in current and [Ca2+]i occurred in the presence of jaspisin, a novel substance that inhibits metallo-endoproteinase and sperm-egg membrane fusion (S. Ikegami, H. Kobayashi, Y. Myotoishi, S. Ohta and K. H. Kato (1994) J. Biol. Chem. 269, 23262-23267). With low doses of jaspisin, a spermatozoon first produced a step inward current (I(on)) as an indication of gamete membrane fusion and then induced a local [Ca2+]i rise at the site of sperm attachment 6-10 seconds after I(on). The sperm, however, soon detached from the egg. Increasing inward current was abruptly cut off (I(off)) within 9-15 seconds and the local [Ca2+]i rise began to decline 1-3 seconds after I(off). In most cases, no further responses or an elevation of fertilization envelope (FE) occurred. In some cases, [Ca2+]i at the sperm attachment site increased again even after the sperm detached and triggered a Ca2+ wave which caused an activation current and FE formation. This recording of a gamete membrane-fusion-induced local [Ca2+]i rise, separated from the Ca2+ wave, is a key phenomenon for elucidating the initial sperm stimulation of the egg at fertilization.
Mohri
T
T
Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Japan. tsmohri@nips.ac.jp
Miyazaki
S
S
Shirakawa
H
H
Ikegami
S
S
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D005260:Female; D008297:Male; D010063:Ovum / Q000378:metabolism* / Q000502:physiology; D018408:Patch-Clamp Techniques; D012617:Sea Urchins; D013084:Sperm-Ovum Interactions / Q000187:drug effects*; D013094:Spermatozoa / Q000502:physiology*; D013343:Styrenes / Q000494:pharmacology*
D013343:Styrenes; C089326:jaspisin; D002118:Calcium