Aging-related changes in calcium oscillations in fertilized mouse oocytes.
Aging of oocytes, being not fertilized after ovulation for a prolonged time, considerably affects normal development of the fertilized oocyte. We examined effects of the aging on a series of highly repetitive Ca2+ transients commonly seen in fertilized mouse oocytes (Ca2+ oscillations). Frequency of Ca2+ oscillations in the aged oocyte [20 hrs after induction of superovulation by i.p. human chorionic gonadotropin (hCG)] was significantly higher (34.1 +/- 5.8 l/hr) than the fresh oocyte (14 hr post-hCG, 21.8 +/- 7.9 l/hr). Rates of rise and fall of individual Ca2+ transient in the aged oocyte were significantly slower than the fresh oocyte, whereas durations of individual Ca2+ transients were similar. When extracellular Ca2+ was raised from 2.04 mM to 5.00 mM, aged oocytes showed significant prolongation of the duration of individual Ca2+ transient, that resulted in a sustained elevation of intracellular Ca2+ ([Ca2+]i) in 33% of the aged oocyte. Transient increase in [Ca2+]i by photolysis of a caged Ca2+, Nitr-5, injected into cytoplasm was completely restored in the fresh oocyte [fluorescence intensity of [Ca2+]i indicator dye Fluo-3 (F480) returned to 97 +/- 2% of the control level, time constant = 37 +/- 9 sec]. In contrast, in the aged oocyte, restoration of F480 following Nitr-5 photolysis was incomplete (115 +/- 12% of the control) and slow (time constant = 64 +/- 23 sec). Because inhibition of the Ca2+ pump of the endoplasmic reticulum (ER) by 5 microM thapsigargin almost completely inhibited restoration of F480 following Nitr-5 photolysis in the fresh oocyte, we conclude that the aging-related changes in Ca2+ oscillations may be accounted for by dysfunction of intracellular Ca2+ regulation, presumably of the Ca2+ pump of the ER.
Igarashi
H
H
Department of Obstetrics and Gynecology, Yamagata University School of Medicine, Japan.
Takahashi
E
E
Hiroi
M
M
Doi
K
K
D000375:Aging / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000502:physiology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005260:Female; D005307:Fertilization in Vitro; D005470:Fluorometry; D008297:Male; D051379:Mice; D009865:Oocytes / Q000378:metabolism*; D013075:Sperm Capacitation; D015053:Zygote / Q000378:metabolism*
D000252:Calcium-Transporting ATPases; D002118:Calcium