132 C
The kinetics of the calcium current were described with a from sham operated animals n 528. The maximal con-
second order activation and a first order inactivation ductance in the native group was 213622 nS, which was
2
function m h: not significantly different from the value derived from the
sham group 182629 nS. In both groups the calcium
2
t 2 t t 2 t
currents, evoked by an activation protocol Fig. 2, had an ]]
]] IT 5 I
1 2 exp exp
2
F S DG S D
max
t t
a i
activation threshold around 240 mV and reached their maximal amplitude between 0 and 10 mV Fig. 3. The
where: I is the current amplitude and the voltage
max
mean current amplitude at 10 mV, as evaluated by a fit with dependent activation
t and inactivation t time con-
a i
Eq. 1, was 21.3 nA in the native group and 21.2 nA in stants following a voltage step at time t .
cells from the sham operated animal group. Also the The voltage dependence of steady state inactivation can
potential of half-maximal activation V and the slope
h,a
be estimated using the relation between the normalized V at the point V
were not different among both groups,
c h,a
peak amplitude of the current and the prepulse potential. with V : 2162 mV sham, 261 mV native and V :
h,a c
This relation was well described by a Boltzmann function: 27.460.3 mV in the sham group and 27.560.2 mV in the
IV 1
native group. Calcium currents in neurons n 510 from ]]
]]]]] NV 5
5 3
I V 2 V
contralateral sensory cortex of infarcted animals moderate
max h
]] 1 1 exp
S D
V infarct had a maximal current amplitude around 15 mV
c
which was by 10 larger 21.5 vs. 21.3 nA than that where: NV is the level of steady state inactivation
measured in sham operated animals Fig. 2. The current determined from the current amplitude IV normalized to
amplitude at a test potential of 10 mV was similar in both I
, V is the prepulse potential, V is the potential of half
max h
groups 1.4 vs. 1.3 nA. The increase in maximal am- maximal inactivation and V is a factor proportional to the
c
plitude was paralleled by a significant increase in maximal slope of the curve at V .
h
conductance Fig. 4 to 342654 nS P ,0.05. Moreover, Data are given as the mean6standard error of the mean
the potential of half-maximal activation was shifted by 11 S.E.M.. Statistical comparisons were made by two-way
mV Table 1 in positive direction to 1062 mV P ,0.01, ANOVA and Bonferroni test. Significance was achieved
while the slope V was not different 27.660.3 when
c
with P ,0.05. compared with the sham group Fig. 3C. Similar changes
in calcium current properties were also found in neurons n 57 from animals, which were allowed to recover from
3. Results surgery for 4 weeks, which implies that these alterations
were long-lasting. The maximal amplitude 21.5 nA and Among six animals that were allowed to recover for 1
the maximal conductance 403682 nS; P ,0.01 were still week, three animals had neocortical infarcts of moderate
larger than in sham operated animals, and the half-maxi- size, i.e. at least half of the ipsilateral cortex was still
mal potential of activation V remained almost at the
h,a
intact. The other three animals all had large cortical same positive value as in the group of animals with 1 week
infarcts, where only relatively small neocortical regions of recovery 1364 mV, P ,0.01; when compared with the
close to midline remained intact. In the long-term group sham group. Again, the slope V was not altered and had a
c
n 53, with a 4 week recovery period, all animals had by value of 27.760.3 mV.
chance cortical infarcts of moderate size. Infarction of the Calcium currents of neurons from the contralateral
striatum was evident in all experimental animals. None of hemisphere n 513 in animals with severe infarction,
the control animals sham and native group; both n 56 lacking wide parts of the ipsilateral sensory cortex, had
showed signs of ischemic damage. current characteristics which equaled much more than
Neurons were measured from both ipsi- and contralater- those from native or sham operated animals. The maximal
al sensory cortex in the native and the sham group, as well conductance was not different 220650 nS and the
as in those animals with lesions of moderate size, while potential of half-maximal activation 262 mV resembled
only neurons from the contralateral sensory cortex were the values of the native or sham group. The same held true
taken from the group with large infarcts. The groups will for the mean current amplitude measured at 10 mV 1.3
be referred to as: ipsi mod ipsilateral moderate infarct; nA and the slope V at the point of V
28.360.4 mV.
c h,a
cont mod contralateral moderate infarct; cont sev con- Alterations of calcium current characteristics in neurons
tralateral severe infarct. Neurons measured from animals from the ipsilateral sensory cortex of animals with moder-
surviving 4 weeks will be referred to as: ipsi 4wk ate infarction were only moderate, when compared to
ipsilateral 4 weeks survival and con 4wk contralateral neurons from the contralateral side, and showed no signifi-
4 weeks survival. cant difference to the sham operated animal group. The
Calcium currents from neurons of untreated native mean current amplitude at 10 mV and the maximal
animals n 528 had similar current amplitudes measured conductance in the group of neurons n 512 with moder-
at 110 mV and maximal conductances as neurons derived ate infarction and a recovery period of 1 week were quite
C . Bruehl et al. Brain Research 884 2000 129 –138
133
group, V was slightly more positive in this group 562
h,a
mV and the slope V at the point of V was in the same
c h,a
range with 27.060.2 mV. As described above, neurons from the contralateral hemisphere showed no additional,
time-related changes when the groups with 1 week or with 4 weeks recovery were compared. In contrast to this
finding neurons from the infarcted brain hemisphere, in animals with 4 week recovery, tended to show smaller
maximal conductances and smaller mean current am- plitudes, than neurons from animals with 1 week recovery.
The mean maximal conductance amounted to 156629 nS and the mean current amplitude, measured at 10 mV, was
lowered to 21.0 nA. The potential of half-maximal activation V
was similar to the sham or native group
h,a
062 mV, but the slope V was slightly steeper with a
c
value of 26.760.3 mV. The time constants of activation and inactivation were
fitted with Eq. 2 for five different voltages 220, 210, 0, 10, 20 mV. This evaluation revealed no significant
differences among all groups compared. Since time con- stants at the given voltages did not differ, they were
lumped together for each group giving values for the time constant of activation of 21.2 and 70–80 ms for inactiva-
tion for details see Table 1. Only neurons from animals with a severe infarction showed a significantly faster
activation 20.960.1 ms; P ,0.05 and inactivation 26167 ms; n.s.. The steady state inactivation of calcium
currents can be evaluated by holding the cell for 3 s at stepwise increased potentials, which are followed by a
fixed test-pulse to 10 mV.
When the amplitudes of the evoked calcium currents were normalized to the maximal current amplitude and
plotted against the pre-potentials, the resulting current voltage relationship could well be described by Eq. 3.
This Boltzmann fit delivers the half-maximal potential of inactivation V
and the slope of the Boltzmann curve V
h,i c,i
at this point. This evaluation showed a highly significant, but unique, increase in the slope of the Boltzmann curve
for all
groups with
infarction range
of V :
c,i
10.760.7 . . . 13.861.7 mV vs. 9.360.3 mV in sham; for detail see Table 1. Furthermore, there was a tendency for
the potential of half-maximal inactivation V to be more
h,i
positive even in the sham group than in native animals range V : 23063 . . . 22663 mV vs. 23362 mV in
h,i
Fig. 3. IV-curves from different animal groups and infarct characteristics.
native.
The IV-curves were computed with Eq. 1 and multiplied with the appropriate inactivation factor derived from Eq. 3 at holding potential
280 mV. A Neurons from sham operated and native no operation animals. B Neurons from the ipsilateral side at P7 and P28 moderate
4. Discussion
