J. Biomedical Science and Engineering, 2010, 3, 884-891
doi:10.4236/jbise.2010.39118 Published Online September 2010 (http://www.SciRP.org/journal/jbise/
JBiSE
).
Published Online September 2010 in SciRes. http://www.scirp.org/journal/jbise
Cell cycle dependent regulation of gap junction coupling and
apoptosis in GFSHR-17 granulosa cells
Sabrina Schlie1,2, Karolina Mazur1, Willem Bintig1, Anaclet Ngezahayo1
1Institute of Biophysics, University Hannover, Herrenhäuserstr, Hannover, Germany;
2Laser Zentrum Hannover e.V., Hollerithallee, Hannover, Germany.
Received 26 November 2009; revised 10 March 2010; accepted 12 March 2010.
ABSTRACT
Recent results have shown that the level of gap junc-
tion coupling could modulate the induction of apopt-
otic reactions. We previously observed that 1H-[1,2,
4]Oxadiazole[4,3-a]quinoxalin-1-one (ODQ), a block-
er of guanylyl cyclase, inhibited gap junction coup-
ling and thereby promoted activation of characteris-
tic apoptotic reactions such as chromatin condensa-
tion, DNA strand breaking, and formation of blebs in
GFSHR-17 granulosa cells, the in vitro mod e l for gra-
nulosa cells of the maturing ovular follicle. In the pr-
esent report, we focus on the effects of ODQ with re-
spect to the cell cycle in GFSHR-17 granulosa cells.
In synchronised GFSHR-17 granulosa cells, the doub-
le whole-cell patch-clamp technique revealed that gap
junction conductance in mitotic cells was reduced in
comparison to cells in interphase. This reduction of
gap junction conductance correlated with a reduction
of non-phosphory l ated Cx43 in mitotic cells. We com-
pared the stimulation of apoptotic reactions by ODQ
between cells in mitosis and in interphase. We ob-
served that the induction of both chromatin conden-
sation and DNA strand breaking by ODQ was incr-
eased in mitotic cells, as compared to cells in inter-
phase. The effects of ODQ were not observed in He-
La cells that do not express connexins. The results in-
dicate that reduction of gap junction coupling in mit-
otic GFSHR-17 granulosa cells depends on phosphor-
rylation of Cx43 and raises the sensitivity to stimula-
tion of apoptosis. We propose that gap junction cou-
pling is involved in regulation of apoptosis of granu-
losa cells in maturing ovular follicle.
Keywords: Granulosa Cells; Cell Cycle; Gap Junction;
Apoptosis
1. INTRODUCTION
Gap junctions are adhesion structures containing cell-
to-cell channels that enable neighbouring cells to excha-
nge small molecules (≤ 1 kDa) like Ca2+, cAMP, IP3, and
to synchronise electrical as well as physiological activi-
ties [1,2]. Gap junction channels are composed of con-
nexins (Cx), which are the products of 19 and 20 genes
in mouse and human, respectively. The expression and
posttranslational modification of the connexins are spe-
cifically regulated in the different tissues and correlate
with cellular metabolic state [3].
Gap junction assembly involves oligomerisation of six
connexins in order to form a connexon that is inserted
into the cellular membrane. Two connexons of adjacent
cells associate and form a cell-to-cell channel. Since gap
junction channels allow a direct intercellular exchange
of metabolites and second messengers, specific roles in
diseases and regulation of cellular activities including
proliferation, transformation, differentiation and apopto-
sis have been hypothesised [2,4].
Gap junction coupling-dependent regulation of DNA
synthesis was shown in cardiomyocytes [5]. It was also
observed that gap junction coupling was involved in reg-
ulation of expression of cyclin dependent kinase inhibi-
tors (CDK-inhibitors) such as p21waf1/Cip1 and p27kip1 in
myoblasts [6-9]. Since such CDK-inhibitors block the
cell cycle and are invovled in stimulating apoptosis, the
previous findings established a link between gap junc-
tion coupling and regulation of cell cycle and apoptosis
as it was recently proposed [10]. Similarly, a
PKC-dependent phosphorylation of Cx43 that correlates
with a reduction of gap junction coupling was found
during G2/M phase of the cell cycle [11]
GFSHR-17 granulosa cells, the in vitro model for gra-
nulosa cells of the maturing ovular follicle, are a suitable
cell system for the analysis of gap junction coupling and
apoptosis [12]. They form gap junction channels mainly
formed by Cx43 and Cx45 [13], which regulate follicu-
lar development and atresia [14-16]. Moreover, granul-
osa cells in the ovular follicles are eliminated by apopt-
osis during atresia or the deterioration of the corpus lu-

S. Schlie et al. / J. Biomedical Science and Engineering 3 (2010) 884-891
885
teum [17,18]. During atresia, excess follicles are remo-
ved, and dominant follicles, which undergo maturation,
are selected. With the deterioration of corpus luteum, the
ovary expels superfluous cells that otherwise represent a
risk of tumour formation.
Gap junction coupling is regulated by the expression
of connexins and posttranslational modifications such as
phosphorylation [19]. Since both expression of connex-
ins and posttranslational modification depend on the me-
tabolic state of the cells, it is postulated that gap junction
coupling of GFSHR-17 granulosa cells could be modif-
ied during the cell cycle. Furthermore, it was shown that
the induction of apoptosis is partly related to the degree
of gap junction coupling [10]. If the degree of gap junct-
ion coupling’s regulation is dependent upon the cell cy-
cle, the induction of apoptosis could also be modulated
relative to the cycle phase of the GFSHR-17 granulosa
cells. This hypothesis was tested by application 20 µM
ODQ, a dose that was shown to inhibit gap junction
coupling in GFSHR-17 granulosa cells [10]. In synchro-
nised GFSHR-17 granulosa cells, we observed that the
macroscopic conductance of gap junctions between cells
in mitosis was reduced compared to cells in interphase.
Correspondingly, non-phosphorylated Cx43, the main
connexin of granulosa cells [13] seemed to be reduced in
mitotic cells compared to cells in interphase. The gap
junction uncoupler ODQ induces an increase in chroma-
tin condensation as well as DNA strand breaks in cells in
the mitotic phase, compared to cells in interphase. The
results indicate an involvement of gap junction coupling
in cell cycle-dependent modulation of apoptosis.
2. METHODS
2.1. Chemicals and Cell Culture Media
If not otherwise specified, the chemicals and the cell cul-
ture media were obtained from Sigma-Aldrich (Taufkir-
chen, Germany).
2.2. Cell Culture
Granulosa cells were cultivated as described previously
[10,20] using Dulbecco’s Modified Eagle Medium (DM-
EM) supplemented with 5% foetal calf serum (FCS) and
antibiotics. The culture medium was renewed every 2-3
days, and the cells were passaged every 7 days. The dou-
bling time of the cells was evaluated by counting the cell
density 12 h, 24 h, 36 h, 48 h and 72 h after seeding.
To test the effect of the ODQ on GFSHR-17 granulo-
sa cells, a 20 mM stock solution of ODQ in DMSO was
prepared. This solution was added to the cell culture
medium to achieve a concentration of 20 µM ODQ, and
DMSO was added to achieve a working concentration of
0.5% DMSO. The control experiments were performed
in cells cultivated in the presence of 0.5% DMSO. Gap
junction coupling, activation of chromatin condensation
and DNA strand break were analysed after 6 h incuba-
tion in the presence of ODQ.
2.3. Synchronisation of the Cells
To achieve a synchronisation of the GFSHR-17 granu-
losa cells, mitotic cells were isolated from a monolayer
using the mitotic-shake-off technique [21]. This techn-
ique is based on the observation that cells in mitosis do
not adhere very well to the surface. The monolayer was
washed with PBS. After addition of fresh culture me-
dium, the cells in Petri dish were carefully shaken to
release cells in mitotic phase into the culture medium.
The culture medium with cells in mitotic phase was col-
lected and preserved at room temperature. Fresh culture
medium was added to the monolayer, and the cells were
incubated in the cell culture incubator for an additional
hour. The shaking procedure was repeated twice. The
collected cell suspsension was centrifuged at 800g for 15
min. The cells in the pellet were resuspended in cell cul-
ture medium and counted using a Rosenthal cell counter
device. A quantity of 4 × 104 cells were seeded into 2 ml
of culture medium in a culture dish with 35 mm in .
The proliferation was evaluated 1.5, 3, 4.5, 14.5, 16,
17.5, 19, 20.5, and 40 h after seeding. For a better com-
parison between experiments, the cell population at each
time point was normalised to the seeding population at
time 0 h. The results are given as average  SEM for n =
4 experiments.
2.4. Analysis of Gap Junction Coupling with
Lucifer Yellow Transfer
To analyse the effect of ODQ on gap junction coupling
of the GFSHR-17 granulosa cells, the cells were grown
on cover slips with 10 mm Ø. A cover slip with a mon-
olayer was placed in a superfusion chamber containing
0.5 ml of a bath solution containing (in mM): 140 NaCl,
10 KCl, 2 CaCl2, 1 MgCl2, 5 glucose and 10 HEPES.
After an adaptation to room temperature for at least 30
min, a whole-cell patch-clamp configuration was estab-
lished on one cell within the monolayer. Lucifer yellow
(0.5 %) was dissolved in the pipette filling solution that
contained (in mM): 100 K-gluconate, 40 KCl, 5 Na2ATP,
2.5 MgCl2, 0.25 CaCl2, 1 BAPTA, 0.2 cGMP, 1 glucose
and 10 HEPES. The pH and osmolarity of both the bath
and the pipette filling solution were adjusted to 7.4 and
295 mOsmol/l, respectively. Lucifer yellow was allowed
to directly diffuse into the cell under whole-cell con-
figuration and through the gap junction channels in the
adjacent cells. Ten minutes after establishment of the
whole cell configuration, the gap junction coupled cells
were counted using a fluorescence microscope (excita-
tion at 438 nm, emission at 510 nm). The results are

S. Schlie et al. / J. Biomedical Science and Engineering 3 (2010) 884-891
886
given as average  SEM for n = 6 experiment for each
treatment.
2.5. Analysis of Gap Junction Coupling Using
the Double Whole-Cell Patch-Clamp
Technique
The double whole-cell patch-clamp configuration allows
imposition of a voltage difference (ΔVj) between two ce-
lls that are joined by gap junction channels. It is thereby
possible to evaluate the conductance of the gap junction
channels (Gj). The double whole-cell patch-clamp con-
figuration was established on pairs of synchronised
GFSHR-17 granulosa cells in different phases of the cell
cycle. The pipette filling solution and the extracellular
solution are described above. These solutions were pre-
viously shown to sustain the macroscopic conductance
of the gap junction channels [20].
2.6. Western Blot
To isolate proteins, cells were collected from the culture
dishes in ice cold phosphate buffered solution (PBS) con-
taining (in mM): 137 NaCl, 2.7 KCl, 10 Na2HPO4, 1,8
KH2PO4, pH 7.4. After centrifugation at 500 g at 4°C for
5 min, the supernatant was discarded, and the cells were
diluted in a lysis buffer containing (in mM): 10 NaCl, 25
HEPES, 2 EDTA, protease inhibitors (aprotinin and ph-
enylmethylsulphonyl fluoride), pH 7.5. The subsequent
sonication at 4°C for 10 min was followed by a centri-
fugation step at 15000 g at 4°C for 30 min. The superna-
tant was again discarded and the pellet was dissolved in
30-50 µl of a solubilisation buffer containing (in mM):
200 NaCl, 50 HEPES, protease inhibitors, pH 7.5. Equal
volume of a 2% Chaps solution was added to the solubi-
lisation buffer, and a centrifugation step was performed
at 6500 g at 4°C for 10 min. The protein concentration in
the supernatant was estimated using the Bradford tech-
nique. For each experiment, samples containing 5-10 µg
of protein were applied to an SDS polyacrylamide gel
and separated by electrophoresis. The separated proteins
were transferred to a nitrocellulose membrane using 1.2
mA/cm2 for 120 min. Staining the nitrocellulose membr-
ane was performed by overnight incubation at 4°C with
the corresponding primary rabbit-anti-Cx43 antibody
(Alomone Labs Ltd., Jerusalem, Israel) diluted to 1:1000.
The membrane was washed with TBST (145 mM NaCl,
20 mM Tris-HCl, 0.5% Tween; pH 7.5) and then incu-
bated for 1-2 h with secondary goat-anti-rabbit IgG an-
tibodies conjugated with alkaline phosphatase and dilu-
ted to 1:500. The proteins were visualised by Sigma Fast
BCIP/NBT (5-Bromo-4-chloro-3-indolyl phosphate/Nitro
blue tetrazolium) followed by a final washing step in H2O.
During all washing steps and the incubation with prim-
ary and secondary antibody, 3% milk was used to neutra-
lise the non- specific binding.
2.7. Analysing Chromatin Condensation
The chromatin structure was analysed by visualisation of
nuclear after staining with DAPI. Cells grown on cover
slips were fixed by a 10 min incubation in PBS contain-
ing 4% formaldehyde. The cells were permeabilised by
incubation in PBS containing 0.3% Triton X-100 for 10
min. The chromatin was stained by an incubation in PBS
containing 1 µM DAPI (Invitrogen, Karlsruhe, Germany)
for 10 min. The cells were washed and preserved with
PBS for further analysis.
The chromatin structure was observed using an inver-
ted fluorescence microscope (Zeiss, Oberkochen, Germ-
any) equipped with a monochomator polychrome II (Ha-
mamatsu, Herrsching, Germany). The excitation wave-
length for DAPI (348 nm) was produced by a 75 W XBO
xenon lamp. Fluorescence images were acquired using a
CCD camera (Hamamatsu, Herrsching, Germany) con-
nected to a computer. The monochromator as well as the
camera were controlled by Aquacosmos software (Ham-
amatsu, Herrsching, Germany). The quantitative evalua-
tion of the results was performed by counting the total
number of cells as well as the cells exhibiting chromatin
condensation in four different areas of each cover slip.
The percentage of cells with condensed chromatin was
calculated for each cover slip. The results are given as
mean ± SEM for 20 cover slips, for each treatment. At
least 1000 cells per treatment were evaluated.
2.8. Evaluation of DNA Strand Beaks Using
Comet Assay
Comet assay experiments were performed according to
previous description [10]. The cells were trypsinised, co-
llected and centrifuged for 10 min at 800 g. The pellets
were resuspended in PBS to 2 × 106 cells/ml. Later, 50 µl
of the cell suspension was mixed with 100 µl of low me-
lting agarose (0.6 %). One hundred microlitres of this
mixture was applied to agarose-coated glass slides and
covered with a cover slip. The slides were incubated for
10 min at 4ºC for solidification of the agarose. The cover
slip was removed, and an addtional 100 µl of agarose
was added. After solidification at 4ºC, the slides were
incubated for 90 min in a lysis buffer, containing 2.5 M
NaCl; 100 mM Na2EDTA; 10 mM Tris; 1% lauryl sar-
cosin; 1% Triton X-100; 10% DMSO; pH 10. Subsequ-
ently, the cover slips were placed in a horizontal gel ele-
ctrophoresis chamber, filled with an electrophoresis bu-
ffer for the alkaline comet assay (1 mM Na2EDTA; 300
mM NaOH; pH 13). After 40 min of adaptation to
the buffer, electrophoresis was performed (25 V; 300 mA;
4ºC; 20 min). For neutralisation, the slides were washed
three times with Tris-buffer (400 mM Tris; pH 7.5) and


S. Schlie et al. / J. Biomedical Science and Engineering 3 (2010) 884-891
887
dried at room temperature. Comets were visualised by
ethidium bromide staining (20 µg/ml) and examined at
200-fold magnification with a fluorescence microscope
(Zeiss, Oberkochen Germany), using a xenon lamp and
ethidium bromide filter set (excitation at λ = 520 nm).
The images were recorded with a CCD Camera. For a
quantitative analysis of the DNA breaking, the tailmo-
ment is an indication of DNA strand breaking, and it was
evaluated using comet scoring software (http://www.aut-
ocomet.com/home.php). The results are given as the
mean of tailmoment ± SEM (n = 4). At least 1000 cells/
treatment were evaluated.
3. RESULTS
To analyse gap junctions during different phases of the
cell cycle, granulosa cells were synchronised as describ-
ed above. We found that mitotic cells harvested by mi-
totic-shake-off completed mitosis within 3 h and contin-
ued to undergo synchronised division for at least two ge-
nerations every 16 h (Figure 1). Gap junction coupling
of the mitotic cells was analysed using a double whole
cell patch-clamp beginning 2 h before the division and
ending 1 h after the division. Correspondingly, the gap
junction coupling of GFSHR-17 granulosa cells in inte-
rphase was studied 4-14 h after the division. It was
found that the macroscopic gap junction conductance (Gj)
in cells in mitotic phase was significantly reduced com-
pared to the conductance of gap junctions in cells in the
interphase (Figure 2(a)). At the molecular level, western
blotting revealed two forms of Cx43 (Figure 2(b)). A
01.534.514.5 16 17.5 19 20.5 40
0
200
400
600
800
1000
Time [h]
Proliferation [%]
Figure 1. Synchronisation of GFSHR-17 granulosa
cells by the mitotis shake off method. It is shown that
after selection, the mitotic cells finished mitosis wit-
hin 3 h. Thereafter, they continued to divide in a syn-
chronous manner for at least two generations. The re-
sults were normalised to the population at the seeding
time (105 cells) and are given as average  SEM for at
least 10 experiments for each treatment.
0
5
10
15
20
25 Interphase
Gj [nS]
Mitosis
(a)
42 kDa
52 kDa
32 kDa
Mitosis Interphase
(b)
Figure 2. (a) Absolute amplitudes of the
gap junction conductance in cells in inter-
phase, in comparison with cells in mitotic
phase. The amplitudes are significantly
different (p < 0.01 student’s t-test); (b)
Western blot analysis showing expression
of Cx43, a representative of three indepe-
ndent experiments. Two bands at 41-42
kDa and 44-46 kDa can be distinguished
in both mitotic cells and in cells in interp-
hase. The bands probably correlate to non-
phosphorylated and phosphorylated Cx43,
respectively. It is noteworthy that the non-
phosphoprylated ba- nd is more intense in
cells in interphase as compared to mitotic
cells.
band at 41-42 kDa and a band to 44-46 kDa (Figure 2
(b), arrows). The Western blotting blot result showed in
Figure 2(b) is a representative of three independent ex-
periments. For each of these experiments the preparatory
work and the blotting of interphase and mitotic cells
were performed in parallel. Furthermore special care was
taken to use the same quantity of the cells and of protein.
Both bands were observed in mitotic cells as well as in
cells in interphase. While no difference in intensity of
the band at 44-46 kDa was observed, a careful analysis
shows a recognisable intensity reduction of the band at
41-42 kDa for for the mitotic cells compared to cells in
interphase (Figure 2(b)).

S. Schlie et al. / J. Biomedical Science and Engineering 3 (2010) 884-891
888
Recently, it was shown that inhibition of gap junction
coupling correlated with induction of apoptotic process-
ses such as chromatin condensation or DNA strand br-
eaks [10]. Therefore, we hypothesised that the sensitivity
to gap junction inhibition-dependent stimulation of the
apoptotic process would be increased in mitotic cells,
which present low gap junction coupling (Figure 2(a)).
After applying the guanylyl cyclase inhibitor ODQ,
which has been previously shown to suppress gap junc-
tion coupling [10], the following results were obtained. 1)
In agreement with our previous results, ODQ inhibits
gap junction coupling as shown by dye transfer experi-
ment (Figure 3). Quantitative analysis showed that, 10
min after the establishment of a whole-cell configuration
on one cell within a monolayer (Figure 3), Lucifer yel-
low diffused in only 5.7  1.5 ODQ treated cells (n = 6
experiments), whereas under control conditions, 19.5 
4.2 cells (n = 6 experiments) were achieved. In inter-
phase cells a dye coupling and an ODQ-related reduction
of coupling comparable to that observed in non synchro-
nised cells (Figure 3) was found. In mitotic cells the dye
coupling was strongly reduced and ODQ treatment could
not reinforce the reduction of coupling (results not sho-
wn). 2) Analysis of chromatin structure and comet ass-
50 μm 50 μm
(a)
20 μm 20 μm
(b)
Figure 3. ODQ reduced gap junction coupling in GFSHR-17
granulosa cells. (a) Control experiment with cells not treated or
treated (b) with 20µM ODQ for 6 h. The images were taken 10
min after establishment of the whole-cell patch-clamp conf-
iguration on one cell in a monolayer with a pipette filling solu-
tion containing 0.5% Lucifer yellow. Quantitative evaluation
showed that, in a monolayer, Lucifer yellow could diffuse into
19.5  4.2 cells (n = 6 experiments) under control conditions,
whereas the treatment with ODQ reduced the coupled cells to
5.7  1.5 (n = 6 experiments).
ays respectively revealed that the ODQ-dependent indu-
ction of apoptotic reactions such as chromatin condensa-
tion or DNA strand breaks was significantly increased in
cells in mitotic phase, compared to cells in interphase
(Figure 4 and Figure 5). ODQ dependent induction of
apoptotic reactions was only observed in cells which no-
rmally express gap junction such as GFSHR-17 granul-
osa cells. Cells which never relay on gap junctions such
as HeLa cells were not affected (Figure 4(b) and Figure
5(b)).
4. DISCUSSION
The present report shows that gap junction coupling in
the GFSHR-17 granulosa cells, the in vitro model for gr-
anulosa cell in the maturing ovular follicle [12], is regu-
lated in a cell cycle-dependent manner. We observed that
cells in mitotic phase had a reduced gap junction condu-
ctance (Gj) compared to cells in interphase (Figure 1,
Figure 2(a)). Gap junction communication serves as a
pathway for synchronisation of cells in tissues, allowing
the formation of physiological units within an organ. Ho-
wever, the cells must be able to evade the community of
the cells for individual division. It is therefore hypothe-
sised that mitotic cells reduce their gap junction coupling
with neighbouring cells in order to undergo individual
division. This hypothesis is in agreement with the obse-
rvation that cellular division in tissues such as the ovular
0
2
4
6
8
10
12
14
HeLa cells
Mitosis
Tailmoment
control
0.5% DMSO
20礛 ODQ
Interphase
GFSHR-17 granulosa cells
μ
m
Figure 4. Induction of chromatin condensation by ODQ. (a)
The chromatin condensation observed under control conditions
(left) and after incubation with ODQ for 6 h (right). The im-
ages are micrographs of cells stained with DAPI and observed
under a fluorescence microscope. (b) The portion of cells
showing chromatin condensation after treatment with ODQ
was significantly (p < 0.01; student’s t-test) increased in cells
in mitotic phase compared to cells in interphase. The results
represent the average  SEM for n = 5 experiments for each
treatment. At least 1,000 cells were counted for each treatment.
It is noteworthy that 0.5% DMSO did not affect the chromatin.

S. Schlie et al. / J. Biomedical Science and Engineering 3 (2010) 884-891
889
(a)
0
10
20
30
40 Interphase
HeLa cells
Cells with condensed chromatin [%]
control
0.5% DMSO
20礛 ODQ
GFSHR-17 granulosa cells
Mitosis
μm
(b)
Figure 5. Induction of DNA strand breaking in GFSHR-17 gra-
llicle is not concomitant [22]. The closure of gap junc-
nction
co
ulated that gap junction coupling
re
ations presented in this report
nulosa cells by ODQ. (a) An example of non-affected cells (left)
and affected cells (right) as revealed by comet assay experim-
ents; (b) The tailmoment as a marker of DNA damage induced
by treatment with ODQ is increased in cells in mitotic phase
than in cells in interphase (p < 0.01 student’s t-test). The results
represent the average  SEM for n = 4 experiments. At least
1,000 cells were counted for each treatment.
fo
tion stops the exchange of metabolites such as second
messengers between the cells [23] and thereby allows in-
dividual mitotic division. Two forms of Cx43 were fou-
nd in the GFSHR-17 granulosa cells by western blot an-
alysis. These proteins had apparent molecular weights of
41-42 kDa and 44-46 kDa (Figure 2(b)). According to
Musil et al. [24], the revealed proteins correspond to the
non-phosphorylated and phosphorylated forms of Cx43.
A mitosis-dependent reduction of expression of connex-
ins such as Cx43 was observed in different cell systems
such as murine neocortical precursors [25]. However,
our western blot analysis does not show a significant re-
duction of the expression of Cx43, it only revealed that
cells a dislevel of the non-phosphorylated form of Cx43
compared to cells in interphase (Figure 2(b)). We hy-
pothesise, therefore, that the observed reduction of the
conductance of gap junction coupling is related to post-
translational modifications such as phosphorylation. This
hypothesis is in agreement with experiments that have
shown that phosphorylation reduced gap junction cou-
pling [26] and that the phosphorylation of Cx- 43 was
increased during the G2/M phase transition [11].
Recently, we showed that inhibition of gap ju
upling in GFSHR-17 granulasa cells correlated with
hallmarks of apoptosis, including induction of chromatin
condensation, DNA strand breaks, and formation of ble-
bs [10]. Since we observed that the cells in mitotic phase
present a reduced Gj compared to cells in interphase and
non-synchronised cells (Figure 2(a)), we postulated that
the cells in mitotic phase should be more sensitive to the
induction of apoptosis by ODQ, which inhibits gap junc-
tion coupling [10] (Figure 3). This hypothesis was con-
firmed by the observation that ODQ induced an increase
in the portion of cells with condensed chromatin (Figure
4), as well as an increased tailmoment in cells in mitotic
phase, compared to cells in interphase and non-synchr-
onised cells (Figure 5). The importance of the gap junc-
tion coupling in the system is also shown by the experi-
ments with HeLa cells which do not express gap juncti-
ons. In the HeLa cells which do not relay on gap junc-
tions the ODQ which acts by reducing gap junction did
not induce the apoptotic reactions (Figure 4 and Figure
5). Furthermore the results with HeLa cells show that the
activation of apoptotic reactions is not a non specific
effect of ODQ
Evidence has accum
gulates highly complex cellular functions. It was sho-
wn that a reduction of gap junction coupling reduced the
differentiation of cultured chick leg bud mesenchymal
cells [27], the proliferation and fusion of the myoblast [6,
7] and the differentiation of progenitor cells of the retina
[28,29]. Additionally, it was observed that inhibition of
gap junction coupling was involved in stimulation of ap-
optosis in granulosa cells [10,20]. Diverse molecular
mechanisms that could link gap junction coupling to the
cellular functions have been described. It was shown that
gap junction coupling was involved in regulation of
DNA synthesis [5] and in the expression and activation
of cyclin-dependent kinase inhibitors (CDK-inhibitors)
such as p21waf1/Cip1 and p27kip1 [8,9]. Furthermore, it is
known that expression and activation of p21waf1/Cip1 and
p27kip1 is involved in regulation of the cell cycle and
apoptosis in granulosa cells [17,30].
5. CONCLUSIONS
Taken together, the observ
suggest that the non-phosphorylated form of Cx43 is re-
duced during the mitotic phase of GFSHR-17 granulosa
cells. This yields a reduction of gap junction conductance
and could result in elevated activity of the CDK-inhibi-
tors and render mitotic granulosa cells more sensitive to
apoptosis compared to cells in interphase. We therefore

S. Schlie et al. / J. Biomedical Science and Engineering 3 (2010) 884-891
890
LEDGEMENTS
excel-
y supported by the project NANOTOME and
th
uropean Graduate College; I
fer
1) Emerging issues of connexin chan-
2003) Astrocytic
, Dang, X., Ping, P., Fandrich, R.R., Nickel,
, Becker, D.L., Dux, L., Stelkovics, E., Kren-
, J E. and Becker, D.L
a, I., Ikeda. M., Ma, K.W. and Mu-
eng,
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204, 137-144.
in43 phosphorylation at S368 is acute
Establishment of steroidegenic granulosa cell li-
43
(2001) Intercellular communication via
3 gap junction messenger ribonucleic acid and
and differential express-
one receptor and the cell cycle modulate apoptosis
ular
tion.
onal coupling, ion fluxes and cell
ytosolic phosph-
l Oncology, 21(6),
004) Complex changes in cellular inositol
tion
cortical
propose that connexins phosphorylation-dependent mod-
ulation of gap junction coupling is a relevant mechanism
to regulate apoptosis of granulosa cells during the folic-
ular maturation.
6. ACKNOW
The authors thank Hans-Georg Hannibal and Frank Koepke for
lent technical support.
The project was partl
e DFG project Transregio 37/Q1.
Sabrina Schlie was supported by Enter-
and connexin 45 but absence of connexin 40 in granulosa
cell gap junctions of rat ovary. Journal Reprod Fertil,
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