Smooth muscle cells and interstitial cells of blood vessels

Hydroxysafflor yellow A actives BKCa channels and inhibits L-type Ca channels to induce vascular relaxation

Hydroxy-safflor yellow A (HSYA) can exert a variety of effects upon the vascular system. However, the underlying mechanisms are not clear. The present study is to investigate its vasodilating effect and the mechanisms. Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were enrolled for studying effects of HSYA on blood pressure, vasodilation, intracellular Ca²⁺ transient and membrane ion channels. Vasodilation and intracellular Ca²⁺ transient were measured by using vasomotor assay and fluorescence imaging system, respectively. The effect of HSYA on the large conductance Ca²⁺ activated and voltage-gated potassium channel (BK_Ca channel) currents in rat mesentery artery and on L-type calcium channel (Ca-L) currents in HEK293cells expressed with Ca-L were investigated using patch clamp techniques. Blood pressure of SHR and WKY rats were concentration dependently reduced by HSYA with a larger effect of HSYA in SHR than that in WKY rats. The tension of mesenteric arteries induced by 3 μM phenylephrine was attenuated by HSYA (IC₅₀ = 90.8 μΜ). Patch clamp study showed that HSYA could activate BK_Ca channels and suppress Ca-L channels in a concentration dependent manner. The results of calcium signaling assays indicated that HSYA could reduce the intracellular free Ca²⁺ level. These findings demonstrate that HSYA could activate BK_Ca channels and inhibit Ca-L channels and reduce intracellular free Ca²⁺ level, which are probably important for its vasodilatory effect.

Telocytes express ANO-1-encoded chloride channels in canine ventricular myocardium

INTRODUCTION

It is unknown if ANO-1 is expressed in the heart, though the presence of a calcium-activated chloride current has been proposed to mediate some cardiac dysrhythmias. Furthermore, a specific cell type termed telocytes, morphologically mimicking Cajal cells which use ANO-1 to modulate their pacemaker activity in the gut, have been described in the heart. We therefore sought to determine whether this channel is expressed in the canine heart.

METHODS

Myocardium was sampled from the ventricles of five canines. Sections were labeled with anti-Kit and anti-ANO-1 antibodies. Slides were reviewed by four investigators looking at cell morphology, distribution, and co-localization. Identification of telocytes was based on criteria including morphology, Kit positivity (+), and ANO-1 positivity (+).

RESULTS

Clusters of cells meeting criteria for telocytes were seen in the epicardium, sub-epicardium, and mid-myocardium. A small subset of cells that were morphologically similar to myocytes was ANO-1 (+) but Kit (-). In total, three different cell classes were found: (i) Kit (+), ANO-1 (+) cells with the appearance of telocytes; (ii) Kit (+), ANO-1 (-) cells; and (iii) Kit (-), ANO-1 (+) cells with the morphologic appearance of cardiac myocytes.

CONCLUSIONS

Telocytes are present in the canine ventricle and express ANO-1. These data merit further study to elucidate the functional expression of these channels in the heart and whether they may be targets for cardiac arrhythmias.

Effects of ajmaline on contraction patterns of isolated rat gastric antrum and portal vein smooth muscle strips and on neurogenic relaxations of gastric fundus

Class-I-antiarrhythmics like ajmaline are known to alter smooth muscle function, which may cause alterations in gastrointestinal motility. The effects of ajmaline on isolated gastric and portal vein smooth muscle and the underlying mechanisms are unknown. We studied the effects of ajmaline on the contractile patterns of isolated preparations of gastric antrum and portal vein from Wistar rats. The organ bath technique was used to measure spontaneous or pharmacologically induced isometric contractions. Changes in force observed after application of ajmaline or under control conditions are reported as % of the amplitude of an initial K⁺-induced contraction. Electric field stimulation was used to study neurogenic relaxations of gastric fundus smooth muscle. Ajmaline increased the amplitude of spontaneous contractions of muscle strips (portal vein: control 31.1 ± 15.2%, with 100 μM ajmaline 76.6 ± 32.3%, n = 9, p < 0.01; gastric antrum: control 9.5 ± 1.6%, with 100 μM ajmaline 63.9 ± 9.96%, n = 14, p < 0.01). The frequency of spontaneous activity was reduced in portal vein, but not in gastric antrum strips. The effects of ajmaline were not blocked by tetrodotoxin, L-nitroarginine methyl ester, or atropine. Ajmaline abolished coordinated neurogenic relaxations triggered by electric field stimulation and partly reversed the inhibition of GA spontaneous activity caused by the gap junction blocker carbenoxolone. Ajmaline enhances the amplitude of spontaneous contractions in rat gastric and portal vein smooth muscle. This effect may be accompanied, but not caused by an inhibition of enteric neurotransmission. Enhanced syncytial coupling as indicated by its ability to antagonize the effects of carbenoxolone is likely to underlie the enhancement of contractility.

Vascular Interstitial Cells in Retinal Arteriolar Annuli Are Altered During Hypertension

Purpose

It has been suggested that arteriolar annuli localized in retinal arterioles regulate retinal blood flow acting as sphincters. Here, the morphology and protein expression profile of arteriolar annuli have been analyzed under physiologic conditions in the retina of wild-type, β-actin-Egfp, and Nestin-gfp transgenic mice. Additionally, to study the effect of hypertension, the KAP transgenic mouse has been used.

Methods

Cellular architecture has been studied using digested whole mount retinas and transmission electron microscopy. The profile of protein expression has been analyzed on paraffin sections and whole mount retinas by immunofluorescence and histochemistry.

Results

The ultrastructural analysis of arteriolar annuli showed a different cell population found between endothelial and muscle cells that matched most of the morphologic criteria established to define interstitial Cajal cells. The profile of protein expression of these vascular interstitial cells (VICs) was similar to that of interstitial Cajal cells and different from the endothelial and smooth muscle cells, because they expressed β-actin, nestin, and CD44, but they did not express CD31 and α-SMA or scarcely express F-actin. Furthermore, VICs share with pericytes the expression of NG2 and platelet-derived growth factor receptor beta (PDGFR-β). The high expression of Ano1 and high activity of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase observed in VICs was diminished during hypertensive retinopathy suggesting that these cells might play a role on the motility of arteriolar annuli and that this function is altered during hypertension.

Conclusions

A novel type of VICs has been described in the arteriolar annuli of mouse retina. Remarkably, these cells undergo important molecular modifications during hypertensive retinopathy and might thus be a therapeutic target against this disease.

Venous Vasomotion

Veins exhibit spontaneous contractile activity, a phenomenon generally termed vasomotion. This is mediated by spontaneous rhythmical contractions of mural cells (i.e. smooth muscle cells (SMCs) or pericytes) in the wall of the vessel. Vasomotion occurs through interconnected oscillators within and between mural cells, entraining their cycles. Pharmacological studies indicate that a key oscillator underlying vasomotion is the rhythmical calcium ion (Ca²⁺) release-refill cycle of Ca²⁺ stores. This occurs through opening of inositol 1,4,5-trisphosphate receptor (IP₃R)- and/or ryanodine receptor (RyR)-operated Ca²⁺ release channels in the sarcoplasmic/endoplasmic (SR/ER) reticulum and refilling by the SR/ER reticulum Ca²⁺ATPase (SERCA). Released Ca²⁺ from stores near the plasma membrane diffuse through the cytosol to open Ca²⁺-activated chloride (Cl^-) channels, this generating inward current through an efflux of Cl^-. The resultant depolarisation leads to the opening of voltage-dependent Ca²⁺ channels and possibly increased production of IP₃, which through Ca²⁺-induced Ca²⁺ release (CICR) of IP₃Rs and/or RyRs and IP₃R-mediated Ca²⁺ release provide a means by which store oscillators entrain their activity. Intercellular entrainment normally involves current flow through gap junctions that interconnect mural cells and in many cases this is aided by additional connectivity through the endothelium. Once entrainment has occurred the substantial Ca²⁺ entry that results from the near-synchronous depolarisations leads to rhythmical contractions of the mural cells, this often leading to vessel constriction. The basis for venous/venular vasomotion has yet to be fully delineated but could improve both venous drainage and capillary/venular absorption of blood plasma-associated fluids.

Calcium movement in smooth muscle and evaluation of graded functional intercellular coupling

Spontaneous activity of vascular smooth muscle is present in small arteries and some venous tissues like the hepatic portal vein. Whereas the ability to generate rhythmic membrane potential changes is expressed in a high number of primary oscillators, the generation of physiological tone and phasic activity requires synchronization of specialized pacemaker activity (Interstitial Cajal-like cells) by intercellular propagation and regeneration of excitation or a strong coupling mechanism of smooth muscle cells. The aim of this study was to deduce oscillator coupling by analyzing the spatiotemporal homogeneity of calcium oscillations within a native tissue preparation. Portal vein tissue was loaded with a calcium-sensitive dye (Fluo-3). By combining confocal microscopy and computation of spatial auto- and cross-correlation of the calcium signals, temporal and spatial coupling between cells was characterized. Spontaneous oscillations of calcium signals were measured at different predefined regions of interest. Cross-correlation analysis of these signals revealed that their damping was very similar in all directions of the investigated z-plane. In single experiments, improved cell-to-cell coupling was seen when noradrenaline (1-10 μM) was added to the bath-solution. With the chosen parameters of frame refresh, the velocity of signal propagation was faster than the maximum detectable velocity, but it could be estimated to exceed 0.1 mm/s. Correlative Network Analysis is a new and very useful tool to determine the functional coupling parameters of quasi-homogenous biological networks and their temporal changes. The action and significance of pharmacological modulators can be well studied on cellular and functional aspects with this newly introduced technique in biological sciences.

Hypertension Induced Morphological and Physiological Changes in Cells of the Arterial Wall

Morphological and physiological changes in the vasculature have been described in the evolution and maintenance of hypertension. Hypertension-induced vascular dysfunction may present itself as a contributing, or consequential factor, to vascular remodeling caused by chronically elevated systemic arterial blood pressure. Changes in all vessel layers, from the endothelium to the perivascular adipose tissue (PVAT), have been described. This mini-review focuses on the current knowledge of the structure and function of the vessel layers, specifically muscular arteries: intima, media, adventitia, PVAT, and the cell types harbored within each vessel layer. The contributions of each cell type to vessel homeostasis and pathophysiological development of hypertension will be highlighted.

Extragastrointestinal stromal tumor of the inferior vena cava: a case report

Here, we present a case report of a 60-year-old female with a 5-cm tumor in the inferior vena cava (IVC) that was positive for c-kit and CD34 expression. Thus, we considered this to be an extragastrointestinal c-kit-positive stromal tumor (EGIST). To the best of our knowledge, no primary EGISTs of the IVC have been described thus far. The potential occurrence of EGISTs outside the tubular gastrointestinal tract should be recognized in the differential diagnosis of tumors of the great vessels. Thus, we concluded that primary c-kit-positive stromal tumors of the IVC do indeed occur.

Calcium Signaling in Interstitial Cells: Focus on Telocytes

In this review, we describe the current knowledge on calcium signaling pathways in interstitial cells with a special focus on interstitial cells of Cajal (ICCs), interstitial Cajal-like cells (ICLCs), and telocytes. In detail, we present the generation of Ca²⁺ oscillations, the inositol triphosphate (IP₃)/Ca²⁺ signaling pathway and modulation exerted by cytokines and vasoactive agents on calcium signaling in interstitial cells. We discuss the physiology and alterations of calcium signaling in interstitial cells, and in particular in telocytes. We describe the physiological contribution of calcium signaling in interstitial cells to the pacemaking activity (e.g., intestinal, urinary, uterine or vascular pacemaking activity) and to the reproductive function. We also present the pathological contribution of calcium signaling in interstitial cells to the aortic valve calcification or intestinal inflammation. Moreover, we summarize the current knowledge of the role played by calcium signaling in telocytes in the uterine, cardiac and urinary physiology, and also in various pathologies, including immune response, uterine and cardiac pathologies.

Mitochondrial Ca²⁺ handling is crucial for generation of rhythmical Ca²⁺ waves in vascular interstitial cells from rabbit portal vein

Vasomotion is the rhythmical changes in vascular tone of various blood vessels. It was proposed that in rabbit portal vein (RPV) the spontaneous contractile activity is driven by vascular interstitial cells (VICs), since RPV VICs generate rhythmical changes in intracellular Ca(2+) concentration ([Ca(2+)]i) associated with membrane depolarisation in these cells. In this work, using confocal imaging in Fluo-3 loaded RPV VICs we studied if generation of rhythmical [Ca(2+)]i changes is affected when Ca(2+) handling by mitochondria is compromised. We also visualised mitochondria in VICs using Mito Tracker Green fluorescent dye. Our results showed that freshly dispersed RPV VICs generated rhythmical [Ca(2+)]i oscillations with a frequency of 0.2-0.01 Hz. Imaging of VICs stained with Mito Tracker Green revealed abundant mitochondria in these cells with a higher density of the organelles in sub-plasmalemmar region compared to the central region of the cell. Oligomycin, an ATP synthase inhibitor, did not affect the amplitude and frequency of rhythmical [Ca(2+)]i oscillations. In contrast, two uncoupling agents, carbonylcyanide-3-chlorophenylhydrazone (CCCP) and carbonylcyanide-4-trifluoromethoxyphenylhydrazone (FCCP) effectively abolished rhythmical [Ca(2+)]i changes with simultaneous increase in basal [Ca(2+)]i in RPV VICs. These data suggest that in RPV VICs mitochondrial Ca(2+) handling is important for the generation of rhythmical [Ca(2+)]i changes which underlie the spontaneous rhythmical contractile activity in this vessel.

Emerging roles for native Orai Ca2+ channels in cardiovascular disease

Orai proteins form highly calcium (Ca(2+))-selective channels located in the plasma membrane of both nonexcitable and excitable cells, where they make important contributions to many cellular processes. The well-characterized Ca(2+) release-activated Ca(2+) current is mediated by Orai1 multimers and is activated, upon depletion of inositol 1,4,5-trisphosphate-sensitive stores, by direct interaction of Orai1 with the endoplasmic reticulum Ca(2+) sensor, stromal interaction molecule 1 (STIM1). This pathway is known as capacitative Ca(2+) entry or store-operated Ca(2+) entry. While most investigations have focused on STIM1 and Orai1 in their store-dependent mode, emerging evidence suggests that Orai1 and Orai3 heteromultimeric channels can form store-independent Ca(2+)-selective channels. The role of store-dependent and store-independent channels in excitation-transcription coupling and the pathological remodeling of the cardiovascular system are beginning to come forth. Recent evidence suggests that STIM/Orai-generated Ca(2+) signaling couples to gene transcription and subsequent phenotypic changes associated with the processes of cardiac and vascular remodeling. This short review will explore the contributions of native Orai channels to heart and vessel physiology and their role in cardiovascular diseases.

The primary cilium of telocytes in the vasculature: electron microscope imaging

Blood vessels are highly organized and complex structure, which are far more than simple tubes conducting the blood to almost any tissue of the body. The fine structure of the wall of blood vessels has been studied previously using the electron microscope, but the presence the telocytes associated with vasculature, a specific new cellular entity, has not been studied in depth. Interestingly, telocytes have been recently found in the epicardium, myocardium, endocardium, human term placenta, duodenal lamina propria and pleura. We show the presence of telocytes located on the extracellular matrix of blood vessels (arterioles, venules and capillaries) by immunohistochemistry and transmission electron microscopy. Also, we demonstrated the first evidence of a primary cilium in telocytes. Several functions have been proposed for these cells. Here, the telocyte-blood vessels cell proximity, the relationship between telocytes, exosomes and nervous trunks may have a special significance.

Extrahepatic and intrahepatic human portal interstitial Cajal cells

Portal interstitial cells of Cajal (PICCs), acting as vascular pacemakers, were previously only identified in nonhumans. Moreover, there is no evidence available about the presence of such cells within the liver. The objective of the study is to evaluate whether or not PICCs are identifiable in humans and, if they are, whether or not they are following the scaffold of portal vein (PV) branches within the liver. We obtained extrahepatic PVs and liver samples from six adult human cadavers, negative for liver disease, in accordance with ethical rules. They were stained with hematoxylin-eosin (HE) and Giemsa, and then we performed immunohistochemistry on formalin-fixed paraffin-embedded specimens for CD117/c-kit, a marker of the Cajal's cells. Immune labeling was also performed for S-100 protein, desmin, glial fibrillary acidic protein (GFAP), neurofilaments, α-smooth muscle actin (α-SMA), and CD34. c-kit-Positive PICCs were identified within the extrahepatic PV, in portal spaces, and septa. On adjacent sections, these PICCs were negative for all the other antibodies used. In conclusion, our study confirms the presence of extrahepatic PICCs on humans, which may act as a possible intrinsic pacemaker in the human PV. However, the intrahepatic PICCs, which were evidenced here for the first time, are in need for further experimental studies to evaluate their functional role. A promising further direction of the study is the PICCs role in the idiopathic portal hypertension.

Seeing is believing! Imaging Ca2+-signalling events in living cells

Ever since it was shown that maintenance of muscle contraction required the presence of extracellular Ca(2+), evidence has accumulated that Ca(2+) plays a crucial role in excitation-contraction coupling. This culminated in the use of the photoprotein aequorin to demonstrate that [Ca(2+)](i) increased after depolarization but before contraction in barnacle muscle. Green fluorescent protein was extracted from the same jellyfish as aequorin, so this work also has important historical links to the use of fluorescent proteins as markers in living cells. The subsequent development of cell-permeant Ca(2+) indicators resulted in a dramatic increase in related research, revealing Ca(2+) to be a ubiquitous cell signal. High-speed, confocal Ca(2+) imaging has now revealed subcellular detail not previously apparent, with the identification of Ca(2+) sparks. These act as building blocks for larger transients during excitation-contraction coupling in cardiac muscle, but their function in smooth muscle appears more diverse, with evidence suggesting both 'excitatory' and 'inhibitory' roles. Sparks can activate Ca(2+)-sensitive Cl() and K(+) currents, which exert positive and negative feedback, respectively, on global Ca(2+) signalling, through changes in membrane potential and activation of voltage-operated Ca(2+) channels. Calcium imaging has also demonstrated that agonists that appear to evoke relatively tonic increases in average [Ca(2+)](i) at the whole tissue level often stimulate much higher frequency phasic Ca(2+) oscillations at the cellular level. These findings may require re-evaluation of some of our models of Ca(2+) signalling to account for newly revealed cellular and subcellular detail. Future research in the field is likely to make increasing use of genetically coded Ca(2+) indicators expressed in an organelle- or tissue-specific manner.

Sarcoplasmic reticulum function in smooth muscle

The sarcoplasmic reticulum (SR) of smooth muscles presents many intriguing facets and questions concerning its roles, especially as these change with development, disease, and modulation of physiological activity. The SR's function was originally perceived to be synthetic and then that of a Ca store for the contractile proteins, acting as a Ca amplification mechanism as it does in striated muscles. Gradually, as investigators have struggled to find a convincing role for Ca-induced Ca release in many smooth muscles, a role in controlling excitability has emerged. This is the Ca spark/spontaneous transient outward current coupling mechanism which reduces excitability and limits contraction. Release of SR Ca occurs in response to inositol 1,4,5-trisphosphate, Ca, and nicotinic acid adenine dinucleotide phosphate, and depletion of SR Ca can initiate Ca entry, the mechanism of which is being investigated but seems to involve Stim and Orai as found in nonexcitable cells. The contribution of the elemental Ca signals from the SR, sparks and puffs, to global Ca signals, i.e., Ca waves and oscillations, is becoming clearer but is far from established. The dynamics of SR Ca release and uptake mechanisms are reviewed along with the control of luminal Ca. We review the growing list of the SR's functions that still includes Ca storage, contraction, and relaxation but has been expanded to encompass Ca homeostasis, generating local and global Ca signals, and contributing to cellular microdomains and signaling in other organelles, including mitochondria, lysosomes, and the nucleus. For an integrated approach, a review of aspects of the SR in health and disease and during development and aging are also included. While the sheer versatility of smooth muscle makes it foolish to have a "one model fits all" approach to this subject, we have tried to synthesize conclusions wherever possible.

Inherent rhythmicity and interstitial cells of Cajal in a frog vein

Interstitial cells of Cajal are responsible for rhythmic contractions of the musculature of the gastrointestinal tract and blood vessels.The existence of these cells and spontaneous rhythmicity were noticed in amphibian vein and the findings are reported in this paper.The postcaval vein was identified in the frog, Rana tigrina and was perfused with amphibian Ringer solution after isolation.Contractile activity was recorded through a tension transducer connected to a polygraph.The isolated postcaval vein showed spontaneous rhythmic activity. Addition of cold Ringer solution decreased, while warm Ringer increased, the rate of contraction. Adrenaline caused inhibition of rhythmic activity at a dosage that increased the rate of isolated sinus venosus.Sections of the postcaval vein,when stained supravitally with methylene blue, showed the presence of interstitial cells of Cajal. Photic stimulation of the vein in the presence of methylene blue led to a significant decrease in the rate of spontaneous beating of the vein.These findings indicate that the postcaval vein of frog is capable of inherent rhythmcity, which is dependent on the interstitial cells of Cajal but is independent of the sinus venosus.

Interstitial cells from rat middle cerebral artery belong to smooth muscle cell type

It is now established that non-contractile cells with thin filopodia, also called vascular interstitial cells (VICs), are constitutively present in the media of many, if not all, blood vessels. The aim of this study was to determine the type of cell lineage to which arterial VICs belong using immunocytochemical, and real-time and reverse transcription PCR (RT-PCR). Using RT-PCR, we compared gene expression profiles of single VICs and smooth muscle cells (SMCs) freshly dispersed from rat middle cerebral artery. Both VICs and SMCs expressed the SMC marker, smooth muscle myosin heavy chain (SM-MHC), but did not express fibroblast, pericyte, neuronal, mast cell, endothelial or stem cell markers. Freshly isolated VICs also did not express c-kit, which is the marker for interstitial cells of Cajal in the gastrointestinal tract. Immunocytochemical labelling of contractile proteins showed that VICs and SMCs expressed SM-MHC similarly to the same degree, but VICs in contrast to SMCs had decreased expression of alpha-SM-actin and very low or no expression of calponin. Real-time RT-PCR was consistent with immunocytochemical experiments and showed that VICs had four times lower gene expression of calponin comparing to SMCs, which may explain VICs' inability to contract. VICs had greater expression than SMCs of structural proteins such as non-muscular beta-actin and desmin. The results obtained suggest that VICs represent a subtype of SMCs and may originate from the same precursor as SMCs, but later develop filopodia and a non-contractile cell phenotype.

Effect of adenosine on membrane potential and Ca2+ in juxtaglomerular cells. Comparison with angiotensin II

BACKGROUND

Renin is mainly secreted from the juxtaglomerular cells (JGC) in the kidney situated in the afferent arteriole close to the vessel pole. Angiotensin II (ANG II) and adenosine inhibit renin secretion and synergistically constrict the afferent arteriole. ANG II depolarises JGC and increases the cytoplasmic free Ca2+ concentration [Ca2+]i. The responses of JGC to adenosine are less known.

METHODS

Effects of adenosine on membrane potential and [Ca2+]i were studied in afferent arterioles from NaCl-depleted rats and mice.

RESULT

Stimulation of A1 adenosine receptors (A1AR) by adenosine (10 microM) or cyclohexyladenosine (1 microM) increased the spiking frequency of JGC, slightly depolarised the cells and, in < or =50% of the cases, increased [Ca2+]i. These effects were much smaller than those of ANG II (3 nM). Simultaneous application of cyclohexyladenosine and ANG II gave only additive effects on [Ca2+]i; in addition, responses to ANG II in JGC from A1AR knockout mice were similar to those from control mice.

CONCLUSION

The small changes in membrane potential and [Ca2+]i in response to A1AR stimulation as compared to those of ANG II may suggest that these 2 tissue hormones use different signal transduction mechanisms to affect JGC function, including the inhibition of renin release.

Stochastic resonance on excitable small-world networks via a pacemaker

We show that the correlation between the frequency of subthreshold pacemaker activity and the response of an excitable array is resonantly dependent on the intensity of additive spatiotemporal noise. Thereby, the effect of the underlying network, defining the interactions among excitable units, largely depends on the coupling strength. Only for intermediate coupling strengths is the small world property able to enhance the stochastic resonance, whereas for smaller and larger couplings the impact of the transition from diffusive to random networks is less profound. Thus, the optimal interplay between a localized source of weak rhythmic activity and the response of the whole array demands a delicate balance between the strength of excitation transfer and the effectiveness of the network structure to support it.

Heterogeneity of hypoxia-mediated decrease in I(K(V)) and increase in [Ca2+](cyt) in pulmonary artery smooth muscle cells

Hypoxic pulmonary vasoconstriction is caused by a rise in cytosolic Ca(2+) ([Ca(2+)](cyt)) in pulmonary artery smooth muscle cells (PASMC) via multiple mechanisms. PASMC consist of heterogeneous phenotypes defined by contractility, proliferation, and apoptosis as well as by differences in expression and function of various genes. In rat PASMC, hypoxia-mediated decrease in voltage-gated K(+) (Kv) currents (I(K(V))) and increase in [Ca(2+)](cyt) were not uniformly distributed in all PASMC tested. Acute hypoxia decreased I(K(V)) and increased [Ca(2+)](cyt) in approximately 46% and approximately 53% of PASMC, respectively. Using combined techniques of single-cell RT-PCR and patch clamp, we show here that mRNA expression level of Kv1.5 in hypoxia-sensitive PASMC (in which hypoxia reduced I(K(V))) was much greater than in hypoxia-insensitive cells (in which hypoxia negligibly affected I(K(V))). These results demonstrate that 1) different PASMC express different Kv channel alpha- and beta-subunits, and 2) the sensitivity of a PASMC to acute hypoxia partially depends on the expression level of Kv1.5 channels; hypoxia reduces whole-cell I(K(V)) only in PASMC that express high level of Kv1.5. In addition, the acute hypoxia-mediated changes in [Ca(2+)](cyt) also vary in different PASMC. Hypoxia increases [Ca(2+)](cyt) only in 34% of cells tested, and the different sensitivity of [Ca(2+)](cyt) to hypoxia was not related to the resting [Ca(2+)](cyt). An intrinsic mechanism within each individual cell may be involved in the heterogeneity of hypoxia-mediated effect on [Ca(2+)](cyt) in PASMC. These data suggest that the heterogeneity of PASMC may partially be related to different expression levels and functional sensitivity of Kv channels to hypoxia and to differences in intrinsic mechanisms involved in regulating [Ca(2+)](cyt).

Role of intracellular stores in the regulation of rhythmical [Ca2+]i changes in interstitial cells of Cajal from rabbit portal vein

Interstitial cells of Cajal (ICCs) freshly isolated from rabbit portal vein and loaded with the Ca(2+)-sensitive indicator fluo-3 revealed rhythmical [Ca(2+)](i) changes occurring at 0.02-0.1 Hz. Each increase in [Ca(2+)](i) originated from a discrete central region of the ICC and propagated as a [Ca(2+)](i) wave towards the cell periphery, but usually became attenuated before reaching the ends of the cell. In about 40% of ICCs each rhythmical change in [Ca(2+)](i) consisted of an initial [Ca(2+)](i) increase (phase 1) followed by a faster rise in [Ca(2+)](i) (phase 2) and then a decrease in [Ca(2+)](i) (phase 3); the frequency correlated with the rate of rise of [Ca(2+)](i) during phase 1, but not with the peak amplitude. Rhythmical [Ca(2+)](i) changes persisted in nicardipine, but were abolished in Ca(2+)-free solution as well as by SK&F96365, cyclopiazonic acid, thapsigargin, 2-APB, xestospongin C or ryanodine. Intracellular Ca(2+) stores visualised with the low-affinity Ca(2+) indicator fluo-3FF were found to be enriched with ryanodine receptors (RyRs) detected with BODIPY TR-X ryanodine. Rhythmical [Ca(2+)](i) changes originated from a perinuclear S/ER element showing the highest RyR density. Immunostaining with anti-TRPC3,6,7 antibodies revealed the expression of these channel proteins in the ICC plasmalemma. This suggests that these rhythmical [Ca(2+)](i) changes, a key element of ICC pacemaking activity, result from S/ER Ca(2+) release which is mediated via RyRs and IP(3) receptors and is modulated by the activity of S/ER-Ca(2+)-ATPase and TRP channels but not by L-type Ca(2+) channels.

Smooth muscle research: from Edith Bülbring onwards

The properties of smooth muscle are currently being studied extensively. Indeed, the small size of myocytes and the huge range of behaviours they exhibit make them an attractive focus for current research. However, this was not always the case. These properties initially made smooth muscles more difficult to study than the larger specialized striated muscles that were the focus of attention of leading researchers. In the UK, research into the physiology of smooth muscles began in the Pharmacology Department at Oxford, led by Edith Bülbring; her early results attracted much attention and resulted in the formation of an active international smooth muscle research group. Although several areas of current interest in the field of smooth muscle were not tackled by the Oxford group, progression of much of the field has clear links to Bülbring and her group.

Excitation-transcription coupling in smooth muscle

Calcium (Ca2+) signals affect virtually every biological process, including both contraction and gene transcription in smooth muscle. Ca2+-regulated gene transcription is known to be important for both physiological and pathological responses in smooth muscle. The aim of this review is to discuss the current understanding of gene transcription regulated by excitation through Ca2+ signalling using a comparison of the two most characterized Ca2+-regulated transcription factors in smooth muscle, Ca2+-cyclic AMP response element binding protein (CREB) and nuclear factor of activated T-cells (NFAT). Recent studies have shown commonalities and differences in the regulation of CREB and NFAT through both voltage- and non-voltage-gated Ca2+ channels that lead to expression of smooth muscle cell specific differentiation markers as well as markers of proliferation. New insights into the regulation of specific genes through companion elements on the promoters of Ca2+-regulated genes have led to new models for transcriptional regulation by Ca2+ that are defined both by the source and duration of the Ca2+ signal and the composition of enhancer elements found within the regulatory regions of specific genes. Thus the combination of signalling pathways elicited by particular Ca2+ signals affect selective promoter elements that are key to the ultimate pattern of gene transcription.

Interstitial cells in the vasculature

Interstitial cells of Cajal are believed to play an important role in gastrointestinal tissues by generating and propagating electrical slow waves to gastrointestinal muscles and/or mediating signals from the enteric nervous system. Recently cells with similar morphological characteristics have been found in the wall of blood vessels such as rabbit portal vein and guinea pig mesenteric artery. These non-contractile cells are characterised by the presence of numerous processes and were easily detected in the wall of the rabbit portal vein by staining with methylene blue or by antibodies to the marker of Interstitial Cells of Cajal c-kit. These vascular cells have been termed "interstitial cells" by analogy with interstitial cells found in the gastrointestinal tract. Freshly dispersed interstitial cells from rabbit portal vein and guinea pig mesenteric artery displayed various Ca2+-release events from endo/sarcoplasmic reticulum including fast localised Ca2+ transients (Ca2+ sparks) and longer and slower Ca2+ events. Single interstitial cells from the rabbit portal vein, which is a spontaneously active vessel, also demonstrated rhythmical Ca2+ oscillations associated with membrane depolarisations, which suggests that in this vessel interstitial cells may act as pacemakers for smooth muscle cells. The function of interstitial cells from the mesenteric arteries is yet unknown. This article reviews some of the recent findings regarding interstitial cells from blood vessels obtained by our laboratory using electron microscopy, immunohistochemistry, tight-seal patch-clamp recording, and fluorescence confocal imaging techniques.

Rhythmicity in arterial smooth muscle

Many arteries and arterioles exhibit rhythmical contractions which are synchronous over considerable distances. This vasomotion is likely to assist in tissue perfusion especially during periods of altered metabolism or perfusion pressure. While the mechanism underlying vascular rhythmicity has been investigated for many years, it has only been recently, with the advent of imaging techniques for visualizing intracellular calcium release, that significant advances have been made. These methods, when combined with mechanical and electrophysiological recordings, have demonstrated that the rhythm depends critically on calcium released from intracellular stores within the smooth muscle cells and on cell coupling via gap junctions to synchronize oscillations in calcium release amongst adjacent cells. While these factors are common to all vessels studied to date, the contribution of voltage-dependent channels and the endothelium varies amongst different vessels. The basic mechanism for rhythmical activity in arteries thus differs from its counterpart in non-vascular smooth muscle, where specific networks of pacemaker cells generate electrical potentials which drive activity within the otherwise quiescent muscle cells.

Ultrastructural features of smooth muscle and endothelial cells of isolated isobaric human placental and maternal arteries

The ability of a blood vessel to develop tone is dependent upon morphological parameters of the smooth muscle cells (SMC), including density, relationship with the endothelium and subcellular distribution of myofilaments and intracellular organelles. Consequently, wall ultrastructure of isolated human placental chorionic plate arteries (n=12), fixed when pressurised to mimic their in vivo geometry, was examined qualitatively using electron microscopy, and compared with maternal arteries (omental, n=10, myometrial, n=6). Arteries from women with uncomplicated pregnancy were tested for contractile viability before fixing, with some vessels post-fixed in osmium-ferricyanide for sarcoplasmic reticulum (SR) identification. In contrast to maternal arteries, placental arteries had no internal elastic lamina but exhibited considerable extracellular matrix separating circularly orientated SMC. Human SMC contained tightly packed arrays of myofilaments running parallel to the plasma membrane, enveloping cellular organelles. Synthetic SMC, with few myofilaments and much rough SR, were observed in placental arteries only. SR in SMC from maternal arteries was located centrally, often encircling mitochondria, and also near the plasma membrane associated with caveolae. Positive SR staining was rarely observed in SMC of placental arteries. This study highlights ultrastructural differences between placental and maternal arteries that may underlie specialised mechanisms of regulating vascular tone in the placenta.

Interstitial cell of Cajal-like cells in the upper urinary tract

Autorhythmicity in the upper urinary tract (UUT) has long been considered to arise in specialized atypical smooth muscle cells (SMC) predominately situated in the most proximal regions of the pyeloureteric system. These atypical SMC pacemakers have been thought to trigger adjacent electrically-quiescent typical SMC to fire action potentials which allow an influx of Ca2+ and the generation of muscle contraction. More recently, the presence of cells with many of the morphological, electrical and immunohistochemical characteristics of interstitial cells of Cajal (ICC), the pacemaker cells of the gastrointestinal tract, have been located in many regions of both the upper and lower urinary tract. This article reviews the evidence from the literature and from our laboratory supporting a role of both atypical SMC and ICC-like cells in the initiation and propagation of pyeloureteric peristalsis in the UUT. We propose a new model in which there are 2 populations of pacemaker cells, high frequency atypical SMC and lower frequency ICC-like cells, both of which can drive electrically-quiescent typical SMC. The relative presence of these 2 populations of pacemaker cells and the relatively-long refractoriness of typical SMC determines the decreasing frequency of contraction with distance from the renal fornix. In the absence of the proximal pacemaker drive from atypical SMC after pyeloureteral/ureteral obstruction or surgery, ICC-like cell pacemaking provides a compensatory mechanism allowing the ureter to maintain rudimentary peristaltic waves and movement of urine from the pyelon towards the bladder.

Subset of cells immunopositive for neurokinin-1 receptor identified as arterial interstitial cells of Cajal in human large arteries

In the adventitia of large arteries, dendritic cells are located between nerve fibers, some of which contain substance P. The aim of the present study was to examine whether neurokinin 1 receptor (NK-1R) was expressed by dendritic cells in the arterial wall. Parallel sections of aortic and carotid artery segments were immunostained with anti-NK-1R and cell-type-specific antibodies. Dendritic cells in the arterial wall expressed NK-1R, albeit at a low level. Other cells, which intensely expressed NK-1R, were located along the border between the media and adventitia. They did not co-express any dendritic cell markers, including fascin, CD1a, S100, or Lag-antigen, and were negative for CD68, CD3, and mast cell tryptase. These NK-1R(+) cells were laser-capture microdissected and studied by means of electron-microscopic analysis. The microdissected cells were in direct contact with nerve endings, and their ultrastructure was typical of the interstitial cells of Cajal present in the gastrointestinal tract. Further systematic electron-microscopic analysis revealed that the cells displaying the features typical of interstitial cells of Cajal were a basic element of the human arterial wall architectonics. Arterial interstitial cells of Cajal were negative for c-kit but they expressed vasoactive intestinal peptide receptor 1 (VIPR1). Destructive alterations of contacts between arterial interstitial cells of Cajal and nerve endings were observed in arterial segments with atherosclerotic lesions. The functional significance of the arterial interstitial cells of Cajal and their possible involvement in atherosclerosis and other vascular diseases need clarification.

Interstitial cells of Cajal in pancreas

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 mum 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 mum) 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 alpha-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.