Telocytes (TCs) have been described in various organs and species (www.telocytes.com) as cells with telopodes (Tps) – very long cellular extensions with an alternation of thin segments (podomers) and dilated portions (podoms). We examined TCs using electron microscopy (EM), immunohistochemistry (IHC), immunofluorescence (IF), time-lapse videomicroscopy and whole-cell patch voltage clamp. EM showed a three-dimensional network of dichotomous-branching Tps, a labyrinthine system with homocellular and heterocellular junctions. Tps release extracellular vesicles (mean diameter of 160.6±6.9 nm in non-pregnant myometrium and 171.6±4.6 nm in pregnant myometrium), sending macromolecular signals to neighbouring cells. Comparative measurements (non-pregnant and pregnant myometrium) of podomer thickness revealed values of 81.94±1.77 vs 75.53±1.81 nm, while the podoms' diameters were 268.6±8.27 vs 316.38±17.56 nm. IHC as well as IF revealed double c-kit and CD34 positive results. Time-lapse videomicroscopy of cell culture showed dynamic interactions between Tps and myocytes. In non-pregnant myometrium, patch-clamp recordings of TCs revealed a hyperpolarisation-activated chloride inward current with calcium dependence and the absence of L-type calcium channels. TCs seem to have no excitable properties similar to the surrounding smooth muscle cells (SMCs). In conclusion, this study shows the presence of TCs as a distinct cell type in human non-pregnant and pregnant myometrium and describes morphometric differences between the two physiological states. In addition, we provide a preliminary in vitro electrophysiological evaluation of the non-pregnant state, suggesting that TCs could influence timing of the contractile activity of SMCs.

We describe here ‐ presumably for the first time‐a Cajal‐like type of tubal interstitial cells (t‐ICC), resembling the archetypal enteric ICC. t‐ICC were demonstrated in situ and in vitro on fresh preparations (tissue cryosections and primary cell cultures) using methylene‐blue, crystal‐violet, Janus‐Green B or Mito Tracker‐Green FM Probe vital stainings. Also, t‐ICC were identified in fixed specimens by light microscopy (methylene‐blue, Giemsa, trichrome stainings, Gomori silver‐impregnation) or transmission electron microscopy (TEM). The positive diagnosis of t‐ICC was strengthened by immunohistochemistry (IHC; CD117/c‐kit+ and other 14 antigens) and immunofluorescence (IF; CD117/c‐kit+ and other 7 antigens). The spatial density of t‐ICC (ampullar‐segment cryosections) was 100–150 cells/mm2. Non‐conventional light microscopy (NCLM) of Epon semithin‐sections revealed a network‐like distribution of t‐ICC in lammina propria and smooth muscle meshwork. t‐ICC appeared located beneath of epithelium, in a 10–15μ thick ‘belt’, where 18±2% of cells were t‐ICC. In the whole lamina propria, t‐ICC were about 9%, and in muscularis ∼7%. In toto, t‐ICC represent ∼8% of subepithelial cells, as counted by NCLM. In vitro, t‐ICC were 9.9±0.9% of total cell population. TEM showed that the diagnostic ‘gold standard’ (Huizinga et al., 1997) is fulfilled by ‘our’ t‐ICC. However, we suggest a ‘platinum standard’, adding a new defining criterion ‐ characteristic cytoplasmic processes (number: 1–5; length: tens of μm; thickness: ±0.5μ; aspect: moniliform; braching: dichotomous; organization: network, labyrinthic‐system). Quantitatively, the ultrastructural architecture of t‐ICC is: nucleus, 23.6±3.2% of cell volume, with heterochromatin 49.1±3.8%; mitochondria, 4.8±1.7%; rough and smooth endoplasmic‐reticulum (1.1±0.6%, 1.0±0.2%, respectively); caveolae, 3.4±0.5%. We found more caveolae on the surface of cell processes versus cell body, as confirmed by IF for caveolins. Occasionally, the so‐called ‘Ca2+‐release units’ (subplasmalemmal close associations of caveolae+endoplasmic reticulum±mitochondria) were detected in the dilations of cell processes. Electrophysiological single unit recordings of t‐ICC in primary cultures indicated sustained spontaneous electrical activity (amplitude of field potentials: 57.26±6.56mV). Besides the CD117/c‐kit marker, t‐ICC expressed variously CD34, caveolins 1&2, α‐SMA, S‐100, vimentin, nestin, desmin, NK‐1. t‐ICC were negative for: CD68, CD1a, CD62P, NSE, GFAP, chromogranin‐A, PGP9.5, but IHC showed the possible existence of (neuro)endocrine cells in tubal interstitium. We call them ‘JF cells’. In conclusion, the identification of t‐ICC might open the door for understanding some tubal functions, e.g. pace‐making/peristaltism, secretion (auto‐, juxta‐ and/or paracrine), regulation of neurotransmission (nitrergic/purinergic) and intercellular signaling, via the very long processes. Furthermore, t‐ICC might even be uncommitted bipotential progenitor cells.

Previous reports describing Cajal‐like interstitial cells in human uterus are contradictory in terms of c‐kit immunoreactivity: either negative (but vimentin‐positive) in pregnant myometrium, or positive, presumably in the endometrium. The aim of this study was to verify the existence of human myometrial Cajal‐like interstitial cells (m‐CLIC). Six different, complementary approaches were used: 1) methylene‐blue supravital staining of tissue samples (cryosections), 2) methylene blue and Janus green B vital staining (m‐CLIC and mitochondrial markers, respectively), and 3) extracellular single‐unit electrophysiological recordings in cell cultures, 4) non‐conventional light microscopy on glutaraldehyde/osmium fixed, Epon‐embedded semi‐thin sections (less than 1μm) stained with toluidine blue (TSM), 5) transmission electron microscopy (TEM), and 6) immunofluorescence (IF). We found m‐CLIC in myometrial cryosections and in cell cultures. In vitro, m‐CLIC represented ∼7% of the total cell number. m‐CLIC had 2–3 characteristic processes which were very long (∼ 60 μm), very thin (±0.5μm) and moniliform. The dilated portions of processes usually accomodated mitochondria. In vitro, m‐CLIC exhibited spontaneous electrical activity (62.4 ± 7.22 mV field potentials, short duration: 1.197 ± 0.04ms). Moreover, m‐CLIC fulfilled the usual TEM criteria, the so‐called ‘gold’ or ‘platinum’ standards (e.g. the presence of discontinuos basal lamina, caveolae, endoplasmic reticulum, and close contacts between each other, with myocytes, nerve fibers and/or capillaries etc.). IF showed that m‐CLIC express CD117/c‐kit, sometimes associated with CD34 and with vimentin along their processes. In conclusion, we describe myometrial Cajal‐like interstitial cells that have affinity for methylene blue and Janus green B vital dyes, fulfill (all) TEM criteria, express CD117/c‐kit and have spontaneous electric activity.

Recently, parallels have been drawn between enteric interstitial cells of Cajal (ICC) and similar cells outside the gut-interstitial Cajal-like cells (ICLC). This article reviews our laboratory findings on ICLC in the female reproductive tract. Since the morphology and function of ICLC are still a subject of debate, our purpose was to investigate whether ICLC are present in the fallopian tube and/or uterus, and if they share ultrastructural and immunohistochemical (IHC) features and/or functional roles. We studied ICLC presence in the human fallopian tube and myometrium primarily by light microscopy, and then by transmission electron microscopy (TEM), in tissue samples and at a single cell level. Taking advantage of our ICLC studies of several organs (pancreas, mammary gland, myocardium), we assembled a set of criteria, derived from ultrastructural features of ICLC, called "platinum standard." Besides the putative pacemaker function, ICLC might have other physiological roles, depending on tissue type (e.g., intercellular signaling, immune surveillance, steroid sensors). Consequently, there is a great urge for a conceptual framework that could allow a better understanding, from a functional point of view, and more so, as the ICLC processes are the longest cellular prolongations (except neurons).

We show here (presumably for the first time) a special type of cell in the human and rat exocrine pancreas. These cells have phenotypic characteristics of the enteric interstitial cells of Cajal (ICC). To identify pancreatic interstitial cells of Cajal (pICC) we used routine light microscopy, non‐conventional light microscopy (less than 1 μm semi‐thin sections of Epon‐embedded specimens cut by ultramicrotomy and stained with Toluidine blue), transmission electron microscopy (TEM), and immunocytochemistry. The results showed that pICC can be recognized easily by light microscopy, particularly on semi‐thin sections, as well as by TEM. Two‐dimensional reconstructions from serial photos suggest a network‐like spatial distribution of pICC. pICC represent 3.3±0.5% of all pancreatic cells, and seem to establish close spatial relationships with: capillaries (43%), acini (40%), stellate cells (14%), nerve fibres (3%). Most of pICC (88%) have 2 or 3 long processes (tens of μm) emerging from the cell body. TEM data show that pICC meet the criteria for positive diagnosis as ICC (e.g. numerous mitochondria, 8.7±0.8% of cytoplasm). Immunocytochemistry revealed that pICC are CD117/c‐kit and CD34 positive. We found pICC positive (40–50%) for smooth muscle α‐actin or S‐100, and, occasionally, for CD68, NK1 neurokinin receptor and vimentin. The reactions for desmin and chromogranin A were negative in pICC. At present, only hypotheses and speculations can be formulated on the possible role of the pICC (e.g., juxtacrine and/or paracrine roles). In conclusion, the quite‐established dogma: “ICC only in cavitary organs” is overpassed.

Interstitial cells of Cajal (ICC), located in the musculature of the gastrointestinal tract, are well characterized (as much as possible nowadays) from the ultrastructural, cytochemical and functional points of view (recent reviews: [1][2][3][4][5][6][7][8]). Moreover, ICC J. Cell. Mol. Med. Vol 9, No 3, 2005 pp. 714-730 The connective connection: Challenging glimpse AbstractWe present transmission electron microscope (TEM) evidence that ICC and ICC-like cells frequently establish close contacts (synapses) with several types of immunoreactive cells (IRC): lymphocytes, plasma cells, eosinophils, basophils, macrophages and mast cells. Such synapses were found in various organs: human mammary gland and myometrium, as well as rat stomach, gut, bladder and uterus. Specimens were observed by conventional TEM on ultrathin sections. Based on morphometric analyses and computer-aided 3-D reconstructions from serial sections, we propose an operational definition of ICC-IRC synapses: cell-to-cell close contacts where the two cells are separated by only ~15nm, equivalent to twice the plasmalemmal thickness. Two types of such synapses were found: (i) uniform ('plain') synapses (PS) − close contact extending for >200 nm, and (ii) multicontact ('kiss and run') synapses (MS) − with multiple, focal, close-contact points alternating with regions of wider intermembrane distance. For instance, a typical PS between a rat bladder ICC-like cell and an eosinophil was 2.48 μm long and 11±4nm wide. By contrast, a MS synapse in rat myometrium (between an ICC-like cell and an eosinophil) was 8.64 μm long and had 13 contact points. The synaptic cleft measured 15±8nm at contact points and ~100nm or more in wider areas. These synapses are different from gap junctions usually seen between ICC and between ICC and smooth muscle cells.We previously proposed that ICC-like cells might represent stromal progenitor cells, participate in juxtacrine/paracrine signaling and play a role in immune surveillance. The nanoscopic distances between the two contiguous membranes suggest a juxtacrine cell-to-cell signaling (chemical synapse), via juxtacrinins, a specific case of phenomenins. However, the (micro)vesicles found in the synaptic cleft may correspond to an exosome-based mechanism.

At present, the so-called interstitial cells of Cajal (ICC) are quite well described ultrastructurally and immunocytochemically [1][2][3][4][5][6]. Moreover, these ICC are implicated in rhythmicity and neural control of gastrointestinal smooth muscle [7,8]. However, cells similar to ICC could be present outside the musculature of the gastrointestinal tract [9] and we called them interstitial AbstractWe have previously described interstitial Cajal-like cells (ICLC) in human atrial myocardium. Several complementary approaches were used to verify the existence of ICLC in the interstitium of rat or human ventricular myocardium: primary cell cultures, vital stainings (e.g.: methylene blue), traditional stainings (including silver impregnation), phase contrast and non-conventional light microscopy (Epon-embedded semithin sections), transmission electron microscopy (TEM) (serial ultrathin sections), stereology, immunohistochemistry (IHC) and immunofluorescence (IF) with molecular probes. Cardiomyocytes occupy about 75% of rat ventricular myocardium volume. ICLC represent ~32% of the number of interstitial cells and the ratio cardiomyocytes/ICLC is about 70/1. In the interstitium, ICLC establish close contacts with nerve fibers, myocytes, blood capillaries and with immunoreactive cells (stromal synapses). ICLC show characteristic cytoplasmic processes, frequently two or three, which are very long (tens up to hundreds of μm), very thin (0.1-0.5μm thick), with uneven caliber, having dilations, resulting in a moniliform aspect. Gap junctions between such processes can be found. Usually, the dilations are occupied by mitochondria (as revealed by Janus green B and MitoTracker Green FM) and elements of endoplasmic reticulum. Characteristically, some prolongations are flat, with a veil-like appearance, forming a labyrinthic system. ICLC display caveolae (about 1 caveola/1μm cell membrane length, or 2-4% of the relative cytoplasmic volume). Mitochondria and endoplasmic reticulum (rough and smooth) occupy 5-10% and 1-2% of cytoplasmic volume, respectively. IHC revealed positive staining for CD34, EGFR and vimentin and, only in a few cases for CD117. IHC was negative for: desmin, CD57, tau, chymase, tryptase and CD13. IF showed that ventricular ICLC expressed connexin 43. We may speculate that possible ICLC roles might be: intercellular signaling (neurons, myocytes, capillaries etc.) and/or chemomechanical sensors. For pathology, it seems attractive to think that ICLC might participate in the process of cardiac repair/remodeling, arrhythmogenesis and, eventually, sudden death.

ARFI elastography had very good accuracy for the assessment of liver fibrosis and was superior to other noninvasive methods (APRI Index, FibroMax) for staging liver fibrosis.