Calcium pools in sea urchin eggs: roles of endoplasmic reticulum and mitochondria in relation to fertilization.
A preparation of sea urchin eggs permeabilized with digitonin (40 microM for 2.5 min) was used to study the kinetic characteristics of the two cellular compartments suspected to play a key role in cellular calcium transfer during fertilization: an ATP-dependent Ca2+ pool (Km = 0.47 microM; Vm = 0.48 nmol/min.mg protein) probably located in the endoplasmic reticulum and a mitochondrial Ca2+ pool (Km = 1.50 microM; Vm = 0.12 nmol/min.mg protein). Fertilization triggered a decrease in the rate of ATP dependent uptake by the non-mitochondrial pool (Km = 0.59 microM; Vm = 0.15 nmol/min.mg protein) while it transiently increased the Ca2+ uptake into mitochondria (2 min post-fertilization: Km = 2.20 microM; Vm = 0.40 nmol/min.mg protein). Microanalysis studies performed on quickly frozen, freeze substituted and embedded eggs showed a transient Ca2+ enrichment of mitochondria soon after fertilization thus suggesting that mitochondria behave as a Ca2+ sink at fertilization. Results are discussed in relation to the role of endoplasmic reticulum and mitochondria in handling free calcium during the early period following sea urchin egg fertilization.
Girard
J P
JP
Laboratoire de Physiologie Cellulaire et Comparée, URA 651 CNRS, Faculté des Sciences, Nice, France.
Gillot
I
I
De Renzis
G
G
Payan
P
P
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004577:Electron Probe Microanalysis; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005306:Fertilization / Q000502:physiology*; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism*; D010063:Ovum / Q000378:metabolism*; D010101:Oxygen Consumption; D012617:Sea Urchins
D000255:Adenosine Triphosphate; D002118:Calcium