2014, Volume 30, Number 2, Page(s) 100-104
Morphological Aspects and Distribution of Interstitial Cells of Cajal in the Human Upper Urinary Tract
Radu-Alexandru PRIÞCĂ, Andrada LOGHIN, Horea-Gheorghe GOZAR, Cosmin MOLDOVAN, Tekla MOSÓ, Zoltán DERZSI, Angela BORDA
1Departments of Pediatric Surgery and Orthopedics, University of Medicine and Pharmacy Tirgu-Mures, TIRGU MURES, ROMANIA
2Departments of Histology, University of Medicine and Pharmacy Tirgu-Mures, TIRGU MURES, ROMANIA
3Departments of Pathology Laboratory, University of Medicine and Pharmacy Tirgu-Mures, TIRGU MURES, ROMANIA
Keywords: Interstitial cells of Cajal, Urinary tract, Immunohistochemistry, CD117 antigen
The mechanism by which the ureter propels urine towards
the bladder has a myogenic origin, through peristaltic contractions.
This pyeloureteral autorhythmicity is generated by specialized,
electrically active cells, the interstitial cells of Cajal, located in the
proximal regions of the upper urinary tract. The aim of this study was
to describe the exact location and the distribution of interstitial Cajal
cells in the human upper urinary tract and to analyze their normal
number and morphology. This is a preliminary study, which will
allow the study of these cells in different urinary tract pathologies.
Material and Method: Urinary tract fragments were sampled at
different levels, from 13 autopsy cases. Cases with clinical evidence
of renal disease, and with histological changes in the kidney or in the
urinary tract tissue samples, visible in hematoxylin-eosin staining,
were excluded. The interstitial Cajal cells were highlighted with
anti-CD117 antibody, immunohistochemically.
Results: Cajal cells were indirectly highlighted by the presence of a
finely granulated cytoplasm indicating immunoreactivity. These cells
were spindle-shaped or stellate, with cytoplasmic extensions at one or
both poles of the cell and large oval nucleus. We found that interstitial
Cajal cells were located at all upper urinary tract levels, with a higher
predominance in the calyces and pyelon. Interstitial Cajal cells were
observed mostly between the two layers of the muscularis, but also
between the muscle bundles. Most often, these cells were parallel to
the muscle fibers.
Conclusion: Our study describes the method of detection of
interstitial Cajal cells in normal human urinary tract. These results
can be used to analyze the number, morphology and the location of
these cells in different congenital pathologies, such as vesicoureteral
reflux, pyeloureteral junction obstruction or primary obstructive
The mechanisms by which the ureter propels urine towards
the bladder are generally accepted to have myogenic origin,
with peristaltic contractions propagating toward the bladder
without being influenced by nerve1-3
. As a consequence,
the presence of specialized electrically active cells in the
proximal regions of the upper urinary tract, which generate
pyeloureteral autorhythmicity, has been theorized. Initially,
the most likely candidates for these pacemaker cells were
considered “atypical” smooth muscle cells (SMC), in
which several morphological and electrical characteristics
similar to cardiac sino-atrial node cells were observed.
Consistent with the presence of a proximal pyelocalyceal
pacemaker, atypical smooth muscle cells were found to be
more numerous in the proximal regions of the pelvis, their
number decreasing with the distance from the renal fornix.
These cells were not highlighted in the ureter. However,
considerable evidence in humans and pigs show that, after
kidney transplantation or pyeloureteral/ureteral surgery,
the ureter, once disconnected from the renal pelvis, is
spontaneously active, and develops rudimentary peristaltic
waves. More recently, similarities were found between
“atypical” SMC and cells with similar morphological and
electrical features to the intestinal pacemaker cells4,5,
recognized as interstitial cells of Cajal (ICC). They have
been highlighted in the upper urinary tract in humans and
several mammals, and their important role in producing
and coordinating pyeloureteral peristalsis was settled6
Based on these observations, the aim of this study is to
describe the location of ICC cells and their morphology,
and quantitatively analyze their distribution along the
human upper urinary tract.
13 cases from autopsies performed at the Pathology
Department of the County Emergency Hospital Mureþ,
were included in this study. They were selected from patients
with ages varying between 7 months and 83 years, who had
no medical documentation of renal, urinary voiding system
The tissue samples were collected from several levels of the
upper urinary tract, as follows: 1st level: Kidney; 2nd level:
Calyces; 3rd level: Pyelon; 4th level: Pyeloureteral junction;
5th level: Proximal ureter; 6th level: Middle ureter; 7th level:
Distal ureter - intramural part.
In the kidney a sagittal section was performed, and the
samples containing both cortical and medullar regions
were collected. Patients with histological changes of the kidney, highlighted in hematoxylin-eosin (H&E) staining
were excluded from study.
From all the levels of the upper urinary tract, the samples
were collected by cross sections through their long axis,
performed at 3-5 mm. In the ureter, prior sectioning, to
prevent the collapse during processing, a catheterization
with a suitable silicone tube was performed. The samples
were fixed in 10% formaldehyde solution. Paraffin
embedding was performed according to the standard
protocol. The best samples, containing a morphologically
intact tissue, were selected by microscopic examination in
For immunohistochemistry (IHC), the DAKO protocol was
used. After incubation at 56°C, the samples were dewaxed and
rehydrated. Antigen unmasking was done with EDTA buffer
in 1:10 concentration, moist heat (98-99°C) and cooling to
room temperature. To block endogenous peroxidase, Large
Volume Hydrogen Peroxide Block was used. Blocking nonspecific
reactions was made with the Large Volume Ultra V
Block. CD117 primary antibody was used at a concentration
of 1:600. After visualizing by 3,3-diaminobenzidine (DAB), a
hematoxylin counterstain was performed. All samples were
processed in the same time and normal breast epithelium
was used as external positive control. An optical microscope
Olympus BX 46 (Olympus America, Center Valley, PA, USA)
with a digital camera was used to analyze the specimens, at
different magnifications. Randomized high-power fields
of each level were analyzed at a magnification of 400x by
three distinct examiners. Three different fields per level were
analyzed by each examiner. ICCs were morphologically
studied and counted. Data obtained from counting being
ordinal variables, the median and the range were calculated.
C-kit positive cells were indirectly highlighted by the
presence of a finely granulated cytoplasm, which indicates
a strong immunoreactivity to CD117 (Figure 1
). These cells
were observed at the junction between the internal and
external smooth muscle layers, and also between muscle
bundles (Figure 2
). Most often, the arrangement of the cells
was parallel to the muscle fibers. Differentiation from other
CD117 positive cells, such as mast cells or macrophages, was
based on morphological features, as ICC are spindle-shaped
or stellate, with cytoplasmic extensions at one or both cell
poles and a large oval nucleus, whilst mast cells are round
with round nucleus, and no dendritic processes (Figure
). Another differentiation criterion was the location of
the cells, ICCs, unlike mast cells and macrophages, are not
found in the lamina propria or submucosa.
Click Here to Zoom
|Figure 1: Interstitial cells of Cajal (ICC) and a mast cell in
renal calyces (black arrow: ICC, red arrow: mast cell). The ICC
presents a finely granulated cytoplasm, which indicates a strong
immunoreactivity to CD 117. ICC is spindle-shaped, with
cytoplasmic extensions at both cell poles and a large oval nucleus.
Click Here to Zoom
|Figure 2: Interstitial cells of Cajal (ICC) and mast cells in upper
urinary tract muscle layers (black arrow: ICC, red arrow: mast
cell). Spindle shaped ICC (black arrow) highlighted by CD117
immunoreactivity, parallel to the smooth muscle fibers. The
round cell (red arrow) is a mast cell.
The ICCs were present at all upper urinary tract levels
(levels 2-7), being more numerous in the calyces and pyelon
(Figure 3). Only scattered cells were present in the middle
and distal ureter. The ICCs count showed a decrease from
the proximal to distal part of the upper urinary tract. This
can be seen from the data obtained by each examiner. The
resulting median and range are highlighted in Table I.
Click Here to Zoom
|Table I: Processed data indicating the reduction in number of
interstitial cells of Cajal from proximal toward the distal part of
the urinary tract
No correlation between patients’ age, sex and the number of
interstitial cells of Cajal was found.
Interstitial cells of Cajal (ICC) were first described by
Ramon y Cajal as a characteristic interstitial cell network7,8
. In 1982, Thuneberg proposed the hypothesis that ICC
could act as pacemaker cells and as a conductor of impulses
in muscle layers of the intestine, generating the peristaltism
in an analogue manner with the cardiac pacemaker cells.
Since then, many researchers, in physiological and morphological
studies, have provided evidence, strengthening
Thuneberg’s hypothesis and concluding that ICC are distinct
mesenchymal cells9 with pacemaker or neuromediator
function in the muscle layer of the gastrointestinal
In the digestive tract, ICC were found around the muscle
layer of the esophagus, stomach, small and large intestine.
They form two- and three-dimensional networks and
bundles of cells that provide close contacts between them
or with nerve plexus and smooth muscle cells10-12.
In the urinary tract, these cells were described in various
manners, sometimes leading to contradictory results. Lang
et al. have published in 1999 the first paper describing a
population of electrically active cells in the upper urinary
tract of guinea pigs13. In electron microscopy, these
cells appeared stellate, with an oval nucleus, numerous
mitochondria occupying 4% of the section area of the cell,
a well developed Golgi apparatus, but without contractile
filaments or immunoreactivity to α smooth muscle actin.
Plasma membrane showed a discontinuous basal lamina.
These interstitial cells had tight and adherent junctions
between each other (80%) or between them and smooth
muscle fibers13. Further studies were extended to rats14.
Another study, carried out by Metzger et al. on the human
upper urinary tract described a population of c-kit positive
spindle cells in the internal and external smooth muscle
layers and also in the lamina propria15. In a later study
on different species of mammals, it was concluded that
these cells had the same distribution in several species16.
In addition, Solari et al. have described c-kit positive cells in
the human pyeloureteral junction as spindle cells, with two
specific dendrites17, while Pezzone et al., who studied the
upper urinary tract in mice, described Cajal cells as having
a stellate form18. These cells were described as forming
networks, located adjacent to the internal muscle layer and
between the internal and external layers of SMC18.
Our study reports the presence and describes the
morphological characteristics of the ICCs in the upper
urinary tract. We found spindle-shaped or stellate ICCs, with cytoplasmic extensions at one or both cell poles
and a large oval nucleus, morphological features already
described in other studies15-17. The location of these
cells at the junction between the internal and external
smooth muscle layers, and also between muscle bundles
has been emphasized also by other authors6,10,15,19.
Unlike Metzger et al15 we did not found ICCs in the
lamina propria. Regarding the shape of these cells, in our
study, ICCs were more often spindle-shaped while other
authors describe them as stellate cells18. They formed
a histologically well-defined network placed in the muscle
layer of the urinary voiding system. Showing the same
morphology, ultrastucture and immunophenotype as the
ICCs of the gastrointestinal tract, ICCs of the urinary tract
are thought to have similar functions: pacemaker cells,
inducing smooth muscle contraction18. They also seem
to act as intermediaries in transmitting nerve signals to
smooth muscle fibers20,21. When evaluating the number
of ICCs, we noticed that it gradually decreases from the
proximal toward the distal urinary tract system. This result
would lead us to conclude that in the upper urinary tract,
the large number of cells could be related to the initiation of
the peristaltic wave. Once initiated, a lower number of cells
is necessary for its propagation.
To properly identify ICCs in IHC, they should be
differentiated from mast cells, macrophages and other
hematopoietic cells, which also express CD117.
Out of ICCs, our study has revealed the ubiquity of mast
cells in the muscle layer and lamina propria of the human
upper urinary system. The presence of these cells may
suggest important functional properties16,22. There is a
clear evidence that mast cells contribute to smooth muscle
stimulation and neuronal activity by releasing a variety
of cytokines with pro-and anti-inflammatory properties
that modulate function, lifespan and proliferation of
other cells22,23. Structural and functional relationships
between ICCs and mast cells have been documented in
the gastrointestinal tract too, where intramuscular ICCs
are surrounded mostly by mast cells24. This evidence
deserve further research which can clarify the functionality
of this cellular complex.
An increasing number of pathologies related to ureteral
peristalsis, and the abnormal urine flow are reported in the
recent literature. ICCs could be involved in these pathologies,
and hence the importance of the studding them in normal
and pathological conditions. Koleda et al. described an ICC
increased number in pyeloureteral junction obstructive
disease, and explained the phenomenon as a compensatory
mechanism to the loss of the ability to conduct the urine from the pyelon toward the ureter25. Kang incriminates
the low number of ICCs in the ureter along with smooth
muscle apoptosis19 as a possible mechanism in the
development of congenital vesicoureteral reflux and
These studies can be a starting point for further
investigations, on human surgical samples or on animal
models that can provide more information about the
involvement of ICCs in different pathological conditions
and the modulation of their function.
In conclusion; The information provided by our study
demonstrates the ubiquitary distribution of interstitial cells
of Cajal in the upper urinary tract. The ultra-specialized
behavior of these cells can be better understood through
morphological and functional studies in pathological
conditions of the urinary tract. Understanding ICC
abnormalities in the urinary tract can provide many
explanations concerning congenital pathological conditions
such as vesicoureteral reflux, pyeloureteral junction
obstruction or primary obstructive megaureter.
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