The Journal of Cell Biology, Vol 100, 947-954, Copyright © 1985 by The Rockefeller University Press
Cytosolic free calcium-ion concentration in cleaving embryonic cells of Oryzias latipes measured with calcium-selective microelectrodes
AR Schantz
Calcium-selective microelectrodes were used to measure the free calcium-
ion concentration ([Ca2+]i) in early-cleaving embryonic cells of the golden
medaka, Oryzias latipes, a fresh water teleost fish. Embryos could be
dechorionated as early as the four-cell stage using a three- step technique
consisting of removal of some yolk to enlarge the perivitelline space,
partial digestion of the chorion with pancreatin, and removal of the
weakened chorion with forceps. Dechorionated embryos underwent cleavage at
a normal rate. Intracellular cytosolic [Ca2+]i was monitored by impaling
blastomeres first with a microelectrode filled with 5 M potassium acetate
to measure membrane potential, and a few minutes later with a
calcium-selective microelectrode. During nine rounds of cytokinesis from a
total of six different embryos, cytosolic [Ca2+]i remained constant (with
apparently random fluctuations of less than +/- 0.1 microM). During two
successive cleavages in one embryo, however, [Ca2+]i rose transiently
fourfold above the original resting level to 1.32 and 1.20 microM in
synchrony with each period of cytokinesis and returned after each rise to
submicromolar levels. Because a calcium-selective microelectrode can detect
[Ca2+]i changes only in the immediate vicinity of its 2-microns tip, we
interpreted these data to suggest that, although [Ca2+]i in most areas of
the cytosol remains between 0.01 and 0.40 microM (mean of 0.14 microM),
there may be small regions of the cell in which [Ca2+]i undergoes a
substantial increase at the time of cleavage. Evidence also is presented to
suggest that the membrane potential in these blastomeres undergoes a slow
net hyperpolarization during early cleavage stages.
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