A direct measurement of increased divalent cation influx in fertilised mouse oocytes.
On fertilisation of mouse oocytes, the fusing spermatozoon triggers a series of repetitive calcium (Ca2+) spikes. The Ca2+ spikes seem to be necessary for successful progression through the cell cycle and are regulated in a cell-cycle-dependent manner. The spikes appear to require the linkage of continuous Ca2+ influx to the periodic release of Ca2+ from intracellular stores by a process of Ca(2+)-induced Ca2+ release. The precise role of Ca2+ influx was explored using the manganese (Mn2+)-quench technique to monitor unidirectional cation influx into single mouse oocytes. There was a marked stimulation of cation influx associated closely with the upsweep of the first and subsequent fertilisation Ca2+ spikes. A smaller but significant increase in the rate of cation influx persisted in the interspike period in fertilised oocytes. Spike-associated entry was not as apparent in oocytes stimulated to spike repetitively by thimerosal or acetylcholine application. Instead, there was a continuous increase in cation influx underlying Ca2+ spiking which commenced with the onset of the first spike. Using the specific microsomal inhibitor thapsigargin and the Ca2+ ionophore ionomycin, we found evidence for a capacitative entry mechanism in mouse oocytes. We propose that the persistent influx of Ca2+ observed in response to all stimuli examined is controlled by a capacitative mechanism and sets the frequency of spiking by determining the time taken to refill the internal stores to a point where they are again sensitive enough to initiate the next spike.
McGuinness
O M
OM
The Babraham Institute, Laboratory of Molecular Signalling, Department of Zoology, University of Cambridge, UK.
Moreton
R B
RB
Johnson
M H
MH
Berridge
M J
MJ
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002453:Cell Cycle / Q000502:physiology; D005260:Female; D005307:Fertilization in Vitro; D005453:Fluorescence; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008345:Manganese / Q000378:metabolism; D051379:Mice; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D013084:Sperm-Ovum Interactions / Q000187:drug effects / Q000502:physiology*; D013094:Spermatozoa / Q000187:drug effects / Q000502:physiology*; D013268:Stimulation, Chemical; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013849:Thimerosal / Q000494:pharmacology
D007476:Ionophores; D013729:Terpenes; D013849:Thimerosal; D008345:Manganese; D015759:Ionomycin; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D000109:Acetylcholine; D002118:Calcium