318
LIONEL F. JAFFE
irregular fluctuations of the order of 10% in the order of minutes. No
mechanism is apparent to coordinate current changes among all of the
hundred or so eggs in each tube. It seems likely, then, that the observed
fluctuations of the tube potential resulted from independent
fluctuations
of each cell's current. If this is true, then the fluctuations in the individual egg cell must have been y/n times those in the population of n
cells, hence about 10 times greater or the order of 100%. This means that
if measurements of single cell currents were possible, one should observe
periods of little or no current flow alternating with ones of relatively
large flow. So the membrane in the expansion region is inferred to undergo
episodes of
depolarization.
Third, in other cases of transient depolarization, the membrane's state
is known to switch from one whose potential is dominated by its potassium conductance to one dominated by that of some other ion; this is
true whether the other ion be sodium as in the squid axon (Hodgkin,
1958), calcium as in the barnacle muscle (Hagiwara et al., 1964), or
chloride as in characeous internodal cells (Mullins, 1962; Findlay and
Hope, 1964).
Plainly, all this suggests that the membrane of the expanding region
switches repeatedly between a state whose potential is dominated by
potassium and one dominated by some other ion, and that these episodes
of local nonpotassium conductance drive the current.
Whatever drives them, these currents are plainly an effect of localization. Are they also a cause? Do they act back on the egg to amplify the
differences between its ends?
Two considerations suggest that the current feeds back to help fix
polarity: First, the available data suggest that the current begins to flow
while the axes are being fixed. The measurements of Pelvetia egg currents shown in Fig. 17 and those of the course of these eggs' determination
shown in Fig. 7 were necessarily done under rather different conditions.
Nevertheless, it is notable that the rise of current and the decline of
photoreversibility in these populations occur at similar times before
germination.
Second, the polarity of Fucus eggs can be determined by imposed
voltage and potassium ion gradients of as little as 10-20 mV and 15 ml
per egg diameter, respectively (Lund, 1923; Bentrup et al, 1967; Bentrup,
1968). The current densities thus driven through the egg depend upon
the membrane's electrical resistance and potassium ion permeability,
respectively. These are not known for this cell but values of 10
3 to 10
4
ohm/cm
2 and 10~
6 to 10~
5 cm/second are found for these parameters in
LIONEL F. JAFFE
irregular fluctuations of the order of 10% in the order of minutes. No
mechanism is apparent to coordinate current changes among all of the
hundred or so eggs in each tube. It seems likely, then, that the observed
fluctuations of the tube potential resulted from independent
fluctuations
of each cell's current. If this is true, then the fluctuations in the individual egg cell must have been y/n times those in the population of n
cells, hence about 10 times greater or the order of 100%. This means that
if measurements of single cell currents were possible, one should observe
periods of little or no current flow alternating with ones of relatively
large flow. So the membrane in the expansion region is inferred to undergo
episodes of
depolarization.
Third, in other cases of transient depolarization, the membrane's state
is known to switch from one whose potential is dominated by its potassium conductance to one dominated by that of some other ion; this is
true whether the other ion be sodium as in the squid axon (Hodgkin,
1958), calcium as in the barnacle muscle (Hagiwara et al., 1964), or
chloride as in characeous internodal cells (Mullins, 1962; Findlay and
Hope, 1964).
Plainly, all this suggests that the membrane of the expanding region
switches repeatedly between a state whose potential is dominated by
potassium and one dominated by some other ion, and that these episodes
of local nonpotassium conductance drive the current.
Whatever drives them, these currents are plainly an effect of localization. Are they also a cause? Do they act back on the egg to amplify the
differences between its ends?
Two considerations suggest that the current feeds back to help fix
polarity: First, the available data suggest that the current begins to flow
while the axes are being fixed. The measurements of Pelvetia egg currents shown in Fig. 17 and those of the course of these eggs' determination
shown in Fig. 7 were necessarily done under rather different conditions.
Nevertheless, it is notable that the rise of current and the decline of
photoreversibility in these populations occur at similar times before
germination.
Second, the polarity of Fucus eggs can be determined by imposed
voltage and potassium ion gradients of as little as 10-20 mV and 15 ml
per egg diameter, respectively (Lund, 1923; Bentrup et al, 1967; Bentrup,
1968). The current densities thus driven through the egg depend upon
the membrane's electrical resistance and potassium ion permeability,
respectively. These are not known for this cell but values of 10
3 to 10
4
ohm/cm
2 and 10~
6 to 10~
5 cm/second are found for these parameters in