Ca2+ dynamics in neuronal growth cones: regulation and changing patterns of Ca2+ entry.
Digital ratio imaging of Fura-2 fluorescence was used to determine spatially resolved dynamics of Ca2+ changes in neuronal growth cones from the molluscs, Helisoma and Aplysia. Time resolution was approximately 1 s and spatial resolution a few mm depending upon the thickness of the cell region examined. Isolated growth cones of Helisoma were shown to recover from large Ca2+ loads over a time course of minutes, therefore demonstrating Ca2+ regulation mechanisms not dependent on the rest of the cell. Ca2+ changes monitored during action potential discharge showed sharply defined spatial gradients within the growth cones, probably arising from clustering of voltage-gated Ca-channels in the surface membrane. The regions of peak concentration change appeared to shift from central regions to the growth cone periphery as the growth cones matured. There was a marked difference in soma Ca2+ changes produced by action potentials depending on whether or not the soma had sprouted neurites. Neurite-free somata showed large Ca2+ changes, whereas in somata that had recently sprouted neurites there were almost no changes for similar electrical stimulation. Measurements on growth cones of N1E115 neuroblastoma cells showed static distributions of Ca2+ similar to those in the molluscan neurons.
Connor
J A
JA
A.T.&T. Bell Laboratories, Murray Hill, New Jersey.
Kater
S B
SB
Cohan
C
C
Fink
L
L
D000818:Animals; D001048:Aplysia; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D008974:Mollusca; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D001572:Benzofurans; D005456:Fluorescent Dyes; D002118:Calcium; D016257:Fura-2