Sperm initiate a Ca2+ wave in frog eggs that is more similar to Ca2+ waves initiated by IP3 than by Ca2+.
We have measured the initial propagation velocity of the sperm-induced Ca(2+) wave in the egg of Xenopus laevis and have compared it with the initial propagation velocities of the inositol triphosphate (IP(3))-induced and Ca(2+)-induced Ca(2+) waves. The initial mean propagation velocity of the sperm-induced wave (13 microm/s) is very similar to that of the IP(3)-induced waves (12.3 microm/s) and two times faster than the mean Ca(2+)-induced wave velocity (6.6 microm/s). We have generated realistic simulations of the fertilization wave in the frog egg using a computational technique based on the finite difference method. Modeling refinements presented here include equations for the production, degradation, and diffusion of IP(3), a description for Ca(2+) dynamics in the endoplasmic reticulum, and a highly concentrated endoplasmic reticulum in the egg cortex. We conclude that models incorporating sperm-induced IP(3) generation fit the data best and those involving the influx of either Ca(2+) or a diffusible sperm factor fit the data poorly. This independence from Ca(2+) influx is also supported by electrophysiological data indicating that Ca(2+) influx is not needed to maintain open Cl(-) channels that generate the fertilization potential.
Bugrim
Andrej
A
Institute of Theoretical Dynamics and Section of Molecular and Cellular Biology, University of California, Davis 95616, USA. andrej@genego.com
Fontanilla
Ray
R
Eutenier
Bridget B
BB
Keizer
Joel
J
Nuccitelli
Richard
R
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology*; D003198:Computer Simulation; D004058:Diffusion; D004721:Endoplasmic Reticulum / Q000473:pathology / Q000502:physiology; D005306:Fertilization / Q000502:physiology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D015640:Ion Channel Gating / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008954:Models, Biological; D010063:Ovum / Q000166:cytology / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D013094:Spermatozoa / Q000378:metabolism*; D014982:Xenopus laevis
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D002118:Calcium