Connexin expression and gap-junctional intercellular communication in ES cells and iPS cells

Pluripotent stem cells, i.e., embryonic stem (ES) and induced pluripotent stem (iPS) cells, can indefinitely proliferate without commitment and differentiate into all cell lineages. ES cells are derived from the inner cell mass of the preimplantation blastocyst, whereas iPS cells are generated from somatic cells by overexpression of a few transcription factors. Many studies have demonstrated that mouse and human iPS cells are highly similar but not identical to their respective ES cell counterparts. The potential to generate basically any differentiated cell types from these cells offers the possibility to establish new models of mammalian development and to create new sources of cells for regenerative medicine. ES cells and iPS cells also provide useful models to study connexin expression and gap-junctional intercellular communication (GJIC) during cell differentiation and reprogramming. In 1996, we reported connexin expression and GJIC in mouse ES cells. Because a substantial number of papers on these subjects have been published since our report, this Mini Review summarizes currently available data on connexin expression and GJIC in ES cells and iPS cells during undifferentiated state, differentiation, and reprogramming.

Observation of the (Λ)(7)He hypernucleus by the (e, e'K+) reaction

An experiment with a newly developed high-resolution kaon spectrometer and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab. The ground state of a neutron-rich hypernucleus, (Λ)(7)He, was observed for the first time with the (e, e'K+) reaction with an energy resolution of ~0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The (Λ)(7)He binding energy supplies the last missing information of the A = 7, T = 1 hypernuclear isotriplet, providing a new input for the charge symmetry breaking effect of the ΛN potential.

Regulation of connexin expression by transcription factors and epigenetic mechanisms

Gap junctions are specialized cell-cell junctions that directly link the cytoplasm of neighboring cells. They mediate the direct transfer of metabolites and ions from one cell to another. Discoveries of human genetic disorders due to mutations in gap junction protein (connexin [Cx]) genes and experimental data on connexin knockout mice provide direct evidence that gap junctional intercellular communication is essential for tissue functions and organ development, and that its dysfunction causes diseases. Connexin-related signaling also involves extracellular signaling (hemichannels) and non-channel intracellular signaling. Thus far, 21 human genes and 20 mouse genes for connexins have been identified. Each connexin shows tissue- or cell-type-specific expression, and most organs and many cell types express more than one connexin. Connexin expression can be regulated at many of the steps in the pathway from DNA to RNA to protein. In recent years, it has become clear that epigenetic processes are also essentially involved in connexin gene expression. In this review, we summarize recent knowledge on regulation of connexin expression by transcription factors and epigenetic mechanisms including histone modifications, DNA methylation, and microRNA. This article is part of a Special Issue entitled: The communicating junctions, roles and dysfunctions.

Connexin43 knockdown accelerates wound healing but inhibits mesenchymal transition after corneal endothelial injury in vivo

PURPOSE

To explore connexin43 (Cx43) knockdown as an efficient treatment for corneal endothelial injury in an in vivo rat corneal scrape injury model.

METHODS

Scrape injury was induced in the corneal endothelium, and immunolabeling (ZO-1, alpha-SMA, Cx43) was performed to analyze changes in Cx43 expression during wound healing. Single injection of Cx43 antisense oligodeoxynucleotide (AS-ODN), small interfering RNA (siRNA), or adenovirus (CMV-Cx43-mRFP1) was applied into the anterior chamber simultaneously with the injury, and wound closure was examined by immunolabeling (ZO-1, Cx43) and propidium iodide staining. Corneal endothelium proliferation on day 1 after injury was studied by Ki67-immunolabeling. Cx43-knockdown treatment was performed also without injury, and its effect on Cx43 expression and Ki67 immunolabeling was examined. The postinjury appearance of myofibroblasts in Cx43 AS-ODN- and sense-ODN-treated corneas was compared by alpha-SMA-immunolabeling.

RESULTS

Complete wound closures were observed in five of six corneas on day 3 after injury with either Cx43 AS-ODN or siRNA treatment, whereas no complete closure was observed on day 3 in the control corneas (S-ODN, zero of six; or nonsense siRNA, zero of six). Consistently, Cx43 overexpression using adenovirus delayed wound closure. Cx43 knockdown increased the number of Ki67-positive proliferating cells on day 1, whereas it decreased the number of alpha-SMA-positive myofibroblasts on day 5. Cx43 knockdown without injury decreased Cx43 expression and induced endothelial proliferation in vivo.

CONCLUSIONS

These results show that Cx43 knockdown induces corneal endothelium proliferation but inhibits endothelial-mesenchymal transition/transformation after injury, suggesting that Cx43 knockdown is a new therapeutic approach for acceleration of wound closure and for prevention of retrocorneal fibrous membrane formation.

Gap junctions mediate glucose transport between GLUT1-positive and -negative cells in the spiral limbus of the rat cochlea

To elucidate the role of the spiral limbus in glucose transport in the cochlea, we analyzed the expression and localization of GLUT1, connexin26, connexin30, and occludin in the spiral limbus of the rat cochlea. GLUT1 and occludin were detected in blood vessels. GLUT1, connexin26, connexin30, and occludin were also expressed in fibrocytes just basal to the supralimbal lining cells. Connexin26 and connexin30 were present among not only these GLUT1-positive fibrocytes but also GLUT1-negative fibrocytes. In vivo glucose imaging using 6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-6-deoxyglucose (6-NBDG, MW 342) together with Evans Blue Albumin (EBA, MW 68,000) showed that 6-NBDG was rapidly distributed throughout the spiral limbus, whereas EBA was localized only in the vessels. Moreover, the gap junctional uncoupler heptanol inhibited the distribution of 6-NBDG. These findings suggest that gap junctions play an important role in glucose transport in the spiral limbus, i.e., that gap junctions mediate glucose transport from GLUT1-positive fibrocytes to GLUT1-negative fibrocytes in the spiral limbus.

Different changes in the expression of multiple kinds of tight-junction proteins during ischemia-reperfusion injury of the rat ileum

Dysfunction of tight junctions (TJs), located at the most apical part of the intestinal epithelium, is believed to result in various complications in intestinal disease. However, the behaviors of multiple kinds of TJ proteins during ischemia-reperfusion injury are not understood in detail. To determine changes in expression and localization of TJ proteins during intestinal-barrier recovery, we induced intestinal ischemia-reperfusion injury in rats, measured mucosa-to-blood permeability of fluorescein isothiocyanate-dextran-4 kDa, and compared it with spatiotemporal changes of ZO-1, occludin, and claudin-1, -2, -3, -4, and -5 by immunoconfocal microscopy. At 1 hour post-reperfusion, villi were denuded and intestinal-barrier function was lost. From 6 to 24 hours post-reperfusion, villous epithelium was restored by cell migration, and barrier function together with reticular pattern expression of ZO-1, occludin, and claudin-1, -3, and -5, recovered time-dependently. To the contrary, after ischemia-reperfusion injury, the localized expression of claudin-2 and claudin-4 observed in the non-treated control was lost and replaced with broader expression from crypts to villi with increased basolateral claudin-4 expression in epithelial cells. These data demonstrated that recovery of intestinal barrier function is associated with expression of ZO-1, occludin, and claudin-1, -3, and -5, whereas claudin-2 and claudin-4 show unique changes in expression and localization.

Acute Aortic Dissection Presenting as a Neurologic Disorder

We present 3 patients who had dissections of the aorta that resulted in neurologic disorders. One patient had an altered mental state and developed cardiopulmonary arrest. Two patients had acute hemimotor findings. In 1 of these 2 cases, progression to cardiopulmonary arrest occurred. We discuss the possibility of neurologic disorder, especially acute ischemic stroke, caused by aortic dissection with reviewed reports, and emphasize that thrombolytic therapy may not be easily indicated for acute-stage stroke. We also mention the usefulness of noninvasive techniques, such as chest X-ray, transesophageal echocardiography, color coded Doppler echocardiography, and carotid ultrasound, for accurate diagnosis of the aortic dissection with neurologic deficit.

Regulation of connexin expression

Gap junctions contain cell-cell communicating channels that consist of multimeric proteins called connexins and mediate the exchange of low-molecular-weight metabolites and ions between contacting cells. Gap junctional communication has long been hypothesized to play a crucial role in the maintenance of homeostasis, morphogenesis, cell differentiation, and growth control in multicellular organisms. The recent discovery that human genetic disorders are associated with mutations in connexin genes and experimental data on connexin knockout mice have provided direct evidence that gap junctional communication is essential for tissue functions and organ development. Thus far, 21 human genes and 20 mouse genes for connexins have been identified. Each connexin shows tissue- or cell-type-specific expression, and most organs and many cell types express more than one connexin. Cell coupling via gap junctions is dependent on the specific pattern of connexin gene expression. This pattern of gene expression is altered during development and in several pathological conditions resulting in changes of cell coupling. Connexin expression can be regulated at many of the steps in the pathway from DNA to RNA to protein. However, transcriptional control is one of the most important points. In this review, we summarize recent knowledge on transcriptional regulation of connexin genes by describing the structure of connexin genes and transcriptional factors that regulate connexin expression.

In situ Ca2+ dynamics of Purkinje fibers and its interconnection with subjacent ventricular myocytes

Purkinje fibers play essential roles in impulse propagation to the ventricles, and their functional impairment can become arrhythmogenic. However, little is known about precise spatiotemporal pattern(s) of interconnection between Purkinje-fiber network and the underlying ventricular myocardium within the heart. To address this issue, we simultaneously visualized intracellular Ca(2+) dynamics at Purkinje fibers and subjacent ventricular myocytes in Langendorff-perfused rat hearts using multi-pinhole type, rapid-scanning confocal microscopy. Under recording of electrocardiogram at room temperature spatiotemporal changes in fluo3-fluorescence intensity were visualized on the subendocardial region of the right-ventricular septum. Staining of the heart with either fluo3, acetylthiocholine iodide (ATCHI), or di-4-ANEPPS revealed characteristic structures of Purkinje fibers. During sinus rhythm (about 60 bpm) or atrial pacing (up to 3 Hz) each Purkinje-fiber exhibited spatiotemporally synchronous Ca(2+) transients nearly simultaneously to ventricular excitation. Ca(2+) transients in individual fibers were still synchronized within the Purkinje-fiber network not only under high-K(+) (8 mM) perfusion-induced Purkinje-to-ventricular (P-V) conduction delay, but also under unidirectional, orthodromic P-V block produced by 10-mM K(+) perfusion. While spontaneous, asynchronous intracellular Ca(2+) waves were identified in injured fibers of Purkinje network locally, surrounding fibers still exhibited Ca(2+) transients synchronously to ventricular excitation. In summary, these results are the first demonstration of intracellular Ca(2+) dynamics in the Purkinje-fiber network in situ. The synchronous Ca(2+) transients, preserved even under P-V conduction disturbances or under emergence of Ca(2+) waves, imply a syncytial role of Purkinje fibers as a specialized conduction system, whereas unidirectional block at P-V junctions indicates a substrate for reentrant arrhythmias.

Multiphoton excitation-evoked chromophore-assisted laser inactivation using green fluorescent protein

Noninvasive, straightforward methods to inactivate selected proteins in living cells with high spatiotemporal resolution are needed. Chromophore-assisted laser inactivation (CALI) can be used to photochemically inactivate proteins, but it has several drawbacks, such as procedural complexity and nonspecific photodamage. Here we show that by application of multiphoton excitation to CALI, enhanced green fluorescent protein (EGFP) is an effective chromophore for inactivation of a protein's function without nonspecific photodamage in living mammalian cells.

Regional differences in blood-nerve barrier function and tight-junction protein expression within the rat dorsal root ganglion

To elucidate blood-nerve barrier function and tight-junction protein expression in the dorsal root ganglion (DRG), we analyzed the vascular permeability in the rat DRG by i.v. administration of fluorescent Evans-blue albumin (EBA) and compared it with the localization of claudin-1, claudin-5, and occludin by immunoconfocal microscopy. In the cell body-rich area within the DRG, extravascular leakage of EBA was noted and claudin-5 but neither claudin-1 nor occludin was detected. Conversely, in the nerve fiber-rich area within the DRG, no extravascular leakage of EBA was observed and both claudin-5 and occludin but no claudin-1 were detected in the blood vessel. These results demonstrate regional differences in the blood-nerve barrier function and tight-junction protein expression within the DRG.

Early stage-specific inhibitions of cardiomyocyte differentiation and expression of Csx/Nkx-2.5 and GATA-4 by phosphatidylinositol 3-kinase inhibitor LY294002

Inhibition of phosphatidylinositol 3-kinase (PI3-kinase) has been reported to block cardiomyocyte differentiation. However, at which stage PI3-kinase plays this important role and what its molecular targets are remain unknown. To answer these questions, we induced cardiomyocyte differentiation of P19CL6 mouse embryonal carcinoma cells and investigated the activation of PI3-kinase by analyzing phospho-Akt. We also treated P19CL6 cells with the PI3-kinase-specific inhibitor LY294002 either continuously or at various time points and monitored the expression of cardiac contractile proteins and transcription factors. Most cells differentiated into sarcomeric myosin heavy chain (MHC)-positive cardiomyocytes on day 16 after induction. An increase in phospho-Akt was observed after induction and was maintained throughout the differentiation. LY294002 treatment restricted to the phase from days 0 to 4 was sufficient to inhibit cardiomyocyte differentiation in a dose-dependent manner. In contrast, LY294002 treatment either from days 4 to 8 or from days 8 to 12 did not cause significant changes in sarcomeric MHC expression. LY294002 treatment from days 0 to 4 also suppressed Csx/Nkx-2.5 and GATA-4 expression. These results demonstrate that PI3-kinase becomes activated and plays a pivotal role at a very early stage of cardiomyocyte differentiation, possibly by modulating the expression of the cardiac transcription factors.

Expression of gap junction protein connexin43 in the adult rat cochlea: comparison with connexin26

To elucidate whether the two different gap junction proteins connexin43 (Cx43) and connexin26 (Cx26) are expressed and localized in a similar manner in the adult rat cochlea, we performed three-dimensional confocal microscopy using cryosections and surface preparations. In the cochlear lateral wall, Cx43-positive spots were localized mainly in the stria vascularis and only a few spots were present in the spiral ligament, whereas Cx26-positive spots were detected in both the stria vascularis and the spiral ligament. In the spiral limbus, Cx43 was widely distributed, whereas Cx26 was more concentrated on the side facing the scala vestibuli and in the basal portion. In the organ of Corti, Cx43-positive spots were present between the supporting cells but they were fewer and much smaller than those of Cx26. These data demonstrated distinct differences between Cx43 and Cx26 in expression and localization in the cochlea. In addition, the area of overlap of zonula occludens-1 (ZO-1) immunolabeling with Cx43-positive spots was small, whereas it was fairly large with Cx26-positive spots in the cochlear lateral wall, suggesting that the differences are not associated with the structural difference between carboxyl terminals, i.e., those of Cx43 possess sequences for binding to ZO-1, whereas those of Cx26 lack these binding sequences.

In situ visualization of the intracellular Ca2+ dynamics at the border of the acute myocardial infarct

Ischemic insult to the heart produces myocyte Ca2+ ([Ca2+]i) overload. However, little is known about spatiotemporal changes in [Ca2+]i within the ischemic heart in situ at the cellular level. Using real-time confocal microscopy, we successfully visualized [Ca2+]i dynamics at the border zone on the subepicardial myocardium of the heart 2 h after coronary ligations followed by loading with fluo 3/AM. Three distinct regions were identified in the acute infarcted heart. In intact regions, the myocytes showed spatially uniform Ca2+ transients synchronously to QRS complex in the electrocardiogram. The myocytes at the infarcted regions showed no fluorescence intensity (FI). At the border zones between the intact and infarcted regions, Ca2+ waves emerged sporadically and randomly, instead of Ca2+ transients, at a mean frequency of 11.5 +/- 8.5 min/cell with a propagation velocity of 151.0 +/- 35.7 microm/sec along the longitudinal axis of the individual myocytes. In addition, some myocytes within the border zone exhibited homogeneously high static FI, indicating severe Ca2+ overload. In summary, we provided the first direct evidence of abnormal [Ca2+]i dynamics in acute infarcted hearts at the cellular level. The observed diversity in spatiotemporal [Ca2+]i dynamics at the border zone may contribute to the arrhythmias or contractile failure in acute myocardial infarction.

Loss and recovery of the blood-nerve barrier in the rat sciatic nerve after crush injury are associated with expression of intercellular junctional proteins

The blood-nerve barrier in peripheral nerves is important for maintaining the environment for axons. Breakdown of the barrier by nerve injury causes various pathologies. We hypothesized that the breakdown and recovery of the blood-nerve barrier after injury are associated with the changes in the expression of intercellular junctional proteins. To test this hypothesis, we induced crush injuries in the rat sciatic nerve by ligation and analyzed spatiotemporal changes of claudin-1, claudin-5, occludin, VE-cadherin, and connexin43 by immunoconfocal microscopy and morphometry and compared them with changes in the permeability of the blood-nerve barrier by intravenous and local administration of Evans blue-albumin (EBA). On day 1 after removal of the ligature EBA leaked into the connective tissue in the endoneurium and then the leakage gradually decreased and disappeared on day 7. On day 1 claudin-1, claudin-5, occludin, VE-cadherin, and connexin43 had totally disappeared from the perineurium and endoneurium. Thereafter, claudin-1, claudin-5, occludin, and VE-cadherin recovered from day 2, whereas connexin43 was redetected on day 5. These results indicate that the breakdown and following recovery of the blood-nerve barrier are closely associated with changes in the expression of claudins, occludin, VE-cadherin, and connexin43 and that the recovery time course is similar but nonidentical.

Abnormalities in gap junctions and Ca2+ dynamics in cardiomyocytes at the border zone of myocardial infarcts

Abnormalities in gap junction function and Ca2+ dynamics are believed to be important factors in arrhythmogenesis after myocardial infarction. To elucidate the relationship between changes in Ca2+ dynamics and gap junctions, we analyzed by real-time in situ Ca2+ imaging of fluo-3 loaded whole hearts the spatiotemporal occurrence of Ca2+ waves and the localization of connexin43 (Cx43) at the border zone of myocardial infarcts induced in the rat by coronary ligation. At early time points (2-4 hours postligation), different regions of the left ventricle showed distinct changes in cytosolic free Ca2+ concentrations [Ca2+]i. While some cardiomyocytes of infarcted regions exhibited high levels of resting fluo-3 fluorescence, at border zones frequent Ca2+ waves were observed. Some of the waves were abolished by spontaneous Ca2+ transients and others were not. Intact myocardium apart from infarcted regions exhibited homogenous Ca2+ transients. Confocal imaging of Cx43 and actin filaments in the rat heart fixed 2 hours after coronary ligation revealed that Cx43 was markedly decreased in the area of myocyte necrosis with contraction bands and in the neighboring myocardium. These results suggest that abnormal expression and function of gap junctions could be associated with Ca2+ waves at the border zone of myocardial infarcts, possibly through Ca2+ overload.

Excitation-dependent intracellular Ca2+ waves at the border zone of the cryo-injured rat heart revealed by real-time confocal microscopy

Intracellular Ca2+ waves, which develop under Ca2+-overloaded conditions of the injured myocardium, are regarded as an important substrate for triggered arrhythmias. However, little is known about whether Ca2+ waves arise or become proarrhythmic in the injured heart in situ. On the hypothesis that injured myocardium manifests frequent Ca2+ waves and produce an oscillatory [Ca2+]i rise leading to triggered activity, we applied cryo-injury to the epicardial surface of fluo 3-AM-loaded perfused rat hearts and analyzed spatiotemporal [Ca2+]i changes at border zones of the injured myocardium using real-time confocal microscopy. In intact regions Ca2+ waves barely emerged, whereas the border zone myocardium exhibited frequent Ca2+ waves, propagating randomly within the individual cells. Two different types of Ca2+ waves were identified: highly frequent waves (159.6+/-86.5 waves/min/cell, n=266) adjacent to the cryo-ablated regions, and less frequent waves (79.0+/-50.1 waves/min/cell, n=160) slightly farther (>2 cells) away from the ablated regions (vicinities). The former Ca2+ waves emerged asynchronously to Ca2+ transients. Contrariwise, the latter depended on ventricular excitation: they vanished instantaneously on Ca2+ transients, but emerged more frequently and propagated more swiftly after cessation of higher-frequency pacing. Immediately after 3-Hz pacing, some cryo-injured hearts exhibited oscillatory [Ca2+]i rises; an instantaneous and synchronous elevation of [Ca2+]i followed by burst occurrence of Ca2+ waves with a gradual decrease in incidence and propagation velocity in a considerable number of cells. These observations indicate that myocardial injury induces Ca2+ waves in the heart, and that their synchronous occurrence could become a substrate for triggered arrhythmias.

Dominant-negative connexin43-EGFP inhibits calcium-transient synchronization of primary neonatal rat cardiomyocytes

Recent studies using mice with genetically engineered gap junction protein connexin (Cx) genes have provided evidence that reduced gap-junctional coupling in ventricular cardiomyocytes predisposes to ventricular arrhythmia. However, the pathological processes of arrhythmogenesis due to abnormalities in gap junctions are poorly understood. We have postulated a hypothesis that dysfunction of gap junctions at the single-cell level may affect synchronization of calcium transients among cardiomyocytes. To examine this hypothesis, we developed a novel system in which gap-junctional intercellular communication in primary neonatal rat cardiomyocytes was inhibited by a mutated (Delta130-137) Cx43 fused with enhanced green fluorescent protein (Cx43-EGFP), and calcium transients were imaged in real time while the mutated Cx43-EGFP-expressing cardiomyocytes were identified. The mutated Cx43-EGFP inhibited dye coupling not only in the liver epithelial cell line IAR 20 but also in primary neonatal rat cardiomyocytes in a dominant-negative manner, whereas wild-type Cx43-EGFP made functional gap junctions in otherwise communication-deficient HeLa cells. The mutated Cx43-EGFP induced desynchronization of calcium transients among cardiomyocytes with significantly higher frequency than wild-type Cx43-EGFP. These results suggest that dysfunction of gap-junctional intercellular communication at the single-cell level could hamper synchronous beating among cardiomyocytes as a result of desynchronization of calcium transients.

Different regulation of connexin26 and ZO-1 in cochleas of developing rats and of guinea pigs with endolymphatic hydrops

Using confocal microscopy and morphometry, we analyzed the expression of connexin26 (Cx26) and ZO-1 in rat cochlea during the postnatal period to elucidate spatiotemporal changes in gap junctions and tight junctions during auditory development. We also studied changes in these junctions in experimental endolymphatic hydrops in the guinea pig. In the adult rat cochlear lateral wall, Cx26 was detected in fibrocytes in the spiral ligament and in the basal cell layer of the stria vascularis, whereas ZO-1 was detected in the apical surfaces of marginal cells and in the basal cell layer. During postnatal development, Cx26 expression increased mainly in the spiral ligament, whereas ZO-1 expression increased in the basal cell layer. The morphometry of Cx26 showed a sigmoid time course with a rapid increase on postnatal day (PND) 14, whereas that of ZO-1 showed a marked increase on PND 7. In experimental endolymphatic hydrops, the expression of Cx26 significantly decreased, whereas there were no obvious changes in the expression of ZO-1. These results indicate that gap junctions and tight junctions in the cochlea increase in a different spatiotemporal manner during the development of auditory function and that gap junctions and tight junctions in the cochlea are differentially regulated in experimental endolymphatic hydrops. (J Histochem Cytochem 49:573-586, 2001)

Observation of coherent cerenkov radiation from a solid dielectric with short bunches of electrons

Short bunches of 150-MeV electrons of a linear accelerator passed along the surface of a crystal quartz or a teflon and coherent Cerenkov radiation from the solid dielectrics has been observed in the wavelength range from 0.5 to 4 mm. Properties of the radiation have been experimentally investigated. The angular distribution of the observed radiation showed a maximum peak in the direction of the Cerenkov angle with several satellite peaks. The intensity increased linearly with increasing the length of the medium and was proportional to the square of the number of electrons in the bunch. The spectral intensity was enhanced by almost five orders of magnitude in comparison with the theoretical calculation of incoherent radiation.

Three distinct types of Ca(2+) waves in Langendorff-perfused rat heart revealed by real-time confocal microscopy

Although Ca(2+) waves in cardiac myocytes are regarded as arrhythmogenic substrates, their properties in the heart in situ are poorly understood. On the hypothesis that Ca(2+) waves in the heart behave diversely and some of them influence the cardiac function, we analyzed their incidence, propagation velocity, and intercellular propagation at the subepicardial myocardium of fluo 3-loaded rat whole hearts using real-time laser scanning confocal microscopy. We classified Ca(2+) waves into 3 types. In intact regions showing homogeneous Ca(2+) transients under sinus rhythm (2 mmol/L [Ca(2+)](o)), Ca(2+) waves did not occur. Under quiescence, the waves occurred sporadically (3.8 waves. min(-1) x cell(-1)), with a velocity of 84 microm/s, a decline half-time (t(1/2)) of 0.16 seconds, and rare intercellular propagation (propagation ratio <0.06) (sporadic wave). In contrast, in presumably Ca(2+)-overloaded regions showing higher fluorescent intensity (113% versus the intact regions), Ca(2+) waves occurred at 28 waves x min(-1) x cell(-1) under quiescence with a higher velocity (116 microm/s), longer decline time (t(1/2) = 0.41 second), and occasional intercellular propagation (propagation ratio = 0.23) (Ca(2+)-overloaded wave). In regions with much higher fluorescent intensity (124% versus the intact region), Ca(2+) waves occurred with a high incidence (133 waves x min(-1) x cell(-1)) and little intercellular propagation (agonal wave). We conclude that the spatiotemporal properties of Ca(2+) waves in the heart are diverse and modulated by the Ca(2+)-loading state. The sporadic waves would not affect cardiac function, but prevalent Ca(2+)-overloaded and agonal waves may induce contractile failure and arrhythmias.

Relationship of gap junction formation to phosphorylation of connexin43 in mouse preimplantation embryos

To clarify the relationship of gap junction formation to phosphorylation of connexin43 (Cx43) in mouse preimplantation embryos, immunofluorescence and Western blot analysis were conducted. Immunofluorescence showed Cx43 positive spots first at the mid-eight-cell stage (6 hr postdivision to the eight-cell stage). The number of spots increased from 6 to 15 hr postdivision to the eight-cell stage. Western blot analysis suggested Cx43 to possibly be present in the nonphosphorylated form at the mid-four-cell stage (6 hr postdivision to the four-cell stage), and phosphorylated Cx43 to increase from the mid-eight-cell stage (6 hr post-division to the eight-cell stage) onward. Dibutyryl cAMP (dbcAMP), a protein kinase A (PKA) activator, added to the culture medium increased the phosphorylation of Cx43 and Cx43 positive spots. The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C (PKC) activator, increased the phosphorylation of Cx43, but decreased Cx43 positive spots. These results suggest that the phosphorylation of Cx43, induced by different protein kinase, leads to a different effect on gap junction formation in mouse preimplantation embryos.

Remodeling of cell-cell and cell-extracellular matrix interactions at the border zone of rat myocardial infarcts

At the border zone of myocardial infarcts, surviving cardiomyocytes achieve drastic remodeling of cell-cell and cell-extracellular matrix interactions. Spatiotemporal changes in these interactions are likely related to each other and possibly have significant impact on cardiac function. To elucidate the changes, we conducted experimental infarction in rats and performed 3-dimensional analysis of the localization of gap junctions (connexin43), desmosomes (desmoplakin), adherens junctions (cadherin), and integrins (beta(1)-integrin) by immunoconfocal microscopy. After myocardial infarction, changes in the distribution of gap junctions, desmosomes, and adherens junctions showed a similar but nonidentical tendency. In the early phase, gap junctions almost disappeared at stumps (longitudinal edges of cardiomyocytes facing the infarct), and, although desmosomes and adherens junctions decreased, they still remained. In the healing phase, at stumps, connexin43, desmoplakin, and cadherin were closely associated between multiple cell processes originating from a single cardiomyocyte. Electron microscopy confirmed the presence of junctional complexes between the cell processes. beta(1)-Integrin at the cell process increased during the formation of papillary myotendinous junction-like structures. Abnormal localization of connexin43 was often accompanied by desmoplakin and cadherin on lateral surfaces of surviving cardiomyocytes. These findings suggested that remodeling of gap junction distribution was closely linked to changes in desmosomes and adherens junctions and that temporary formation of intracellular junctional complexes was an element of the remodeling of cell-cell and cell-extracellular matrix interactions after myocardial infarction. Moreover, the remodeling of the intercalated disk region at the myocardial interface with area of scar tissues was associated with the acquisition of extracellular matrix and beta(1)-integrin.

Formation of cell junctions between grafted and host cardiomyocytes at the border zone of rat myocardial infarction

BACKGROUND

Cardiomyocyte transplantation is an innovative strategy for the treatment of heart failure after myocardial infarction. Cell junctions show diverse temporal polarization toward intercalated disks during postnatal development and exhibit altered distribution in diseased hearts. To elucidate the formation of cell junctions between grafted and host cardiomyocytes at the border zone of myocardial infarction, the 3D distribution of cell junctions was examined using immunohistochemistry and confocal microscopy.

METHODS AND RESULTS

Neonatal cardiomyocytes obtained from 3-day-old rats by collagenase digestion and Percoll density centrifugation were injected into the border zones of infarction sites 10 days after coronary ligation in adult rats. At 4 to 14 days after transplantation, hearts were harvested and processed by immunohistochemistry. Antibodies against connexin43, desmoplakin, and cadherin were used to analyze the distribution of gap junctions, desmosomes, and adherens junctions, respectively. Grafted cardiomyocytes were identified by immunohistochemistry for alpha-smooth muscle actin. Grafted cardiomyocytes tended to align parallel to the host cardiomyocytes. Connexin43, desmoplakin, and cadherin were localized between grafted cardiomyocytes themselves and between grafted and host cardiomyocytes. Semiquantitative analysis revealed that all junctions showed increasing polarization to longitudinal cell termini, especially at the border of grafted and host cardiomyocytes, as time advanced from 4 to 7 days after transplantation.

CONCLUSIONS

These findings indicate that grafted cardiomyocytes foster electrical pathways with host counterparts through the gap junction and suggest that the environment in infarcted hearts could influence the localization of gap junctions, desmosomes, and adherens junctions.

Reduction in interleukin-2-producing cells but not Th1 to Th2 shift in moderate and advanced stages of human immunodeficiency virus type-1-infection: direct analysis of intracellular cytokine concentrations in CD4+ CD8- T cells

Previous studies have suggested that CD4+ T lymphocytes shift from the Th1 type to the Th2 type during disease progression in patients with the human immunodeficiency virus type-1 (HIV-1). In the present study, we used a modified method that allowed a direct measurement of intracellular cytokines in CD4+ CD8- T cells. A total of 48 HIV-1-infected (HIV+) and 16 HIV-1-uninfected (HIV-) individuals were studied. The percentages of CD4+ CD8- T cells producing interleukin-2 (IL-2), interferon-gamma (IFN-gamma), interleukin-4 (IL-4), or interleukin-5 (IL-5) in HIV+ and HIV- subjects were 23.6% versus 34.9% (P < 0.01), 13.7% versus 13.2%, 1.3% versus 1.0%, and 1. 2% versus 0.9%, respectively. The population of IL-2-producing cells decreased proportionately with reductions in CD4 counts (< 200/mm3, 200-500/mm3, and > 500/mm3 to 18.0%, 23.5%, and 30.5%, P < 0.05, respectively). There was an inverse correlation between the percentage of IL-2-producing cells and plasma viral load (r = - 0. 446, P < 0.05). However, the percentages of CD4+ CD8- T cells producing other cytokines were not different between HIV+ and HIV-. Our cross-sectional study demonstrated a decrease in IL-2-producing cells but not the Th1 to the Th2 shift in the CD4+ CD8- T cell population in the moderate and advanced stages of HIV-1-infection.

Differential expression of gap junction proteins connexin26, 32, and 43 in normal and crush-injured rat sciatic nerves. Close relationship between connexin43 and occludin in the perineurium

We immunohistochemically and morphometrically examined the expression of gap junction protein connexin (Cx) in normal and crush-injured rat sciatic nerves using confocal laser scanning microscopy. Cx26 was localized in the perineurium and Cx43 was present in the perineurium and the epineurium, whereas Cx32 was confined to the paranodal regions of the nodes of Ranvier. Double labeling for connexins and laminin revealed that Cx43 was localized in multiple layers of the perineurium, whereas Cx26 was confined to the innermost layer. Double labeling for connexins and a tight junction protein, occludin, showed that occludin frequently coexisted with Cx43 but existed separately from Cx26 in the perineurium. After crush injury, the pattern of normal Cx32 expression was initially lost but recovered, whereas Cx43 rapidly appeared in the endoneurium and its expression was subsequently attenuated. Although crush injury produced no apparent alteration in Cx43 and occludin in the perineurium, a rapid increase and a subsequent decrease in the frequency of Cx26-positive spots during nerve regeneration were shown by morphometric analysis. These results indicate that Cx26, Cx32, and Cx43 are expressed differently in various types of cells in peripheral nerves and that their expressions are differentially regulated after injury. The expression of connexins and occludin in the perineurium suggests that perineurial cells are not uniform in type and that the regulation of gap junctions and tight junctions is closely related in the perineurium.

Real-time imaging of two-photon-induced fluorescence with a microlens-array scanner and a regenerative amplifier

A real-time two-photon fluorescence microscope with a microlens-array scanner using a regenerative amplifier is presented. The regenerative amplifier generates pulsed laser lights with extremely high peak power and produces brighter two-photon-induced fluorescence compared with that produced without the amplifier. Experimental results obtained from the observation of some biological samples with the proposed microscope are given.

Regulation of cytosol-nucleus pH gradients by K+/H+ exchange mechanism in the nuclear envelope of neonatal rat astrocytes

In order to study the subcellular heterogeneity of intracellular H+ concentration in reactive astrocytes, the pH in the nucleus and cytosol of cultured astrocytes was measured using a confocal laser scanning microscope (CLSM) and pH indicator dye, 5'(and 6')-carboxyseminaphthofluorescein (carboxy SNAFL-1). The change in intracellular pH was indexed by the fluorescence ratio (F535/F610) at an excitation wavelength of 514.5 nm. The in vitro fluorescence ratio increased as pH decreased. This ratio in the nucleus was significantly lower than that in the cytosol of astrocytes when perfused by HEPES-buffered Hanks' balanced salt solution (HHBSS) at pH 7.4. Acid stimulations of cells (pH 5.0) raised the fluorescence ratio in both nucleus and cytosol. However, the increase in the fluorescence ratio of the nucleus was less than that of cytosol. Treatment with a K+/H+ ionophore, nigericin (20 microM), reversibly nullified this cytosol-nucleus pH gradient. These findings suggest that a buffering mechanism(s) for maintaining of intracellular pH exists between the nucleus and cytosol, and a K+/H+ exchanger may act on the nuclear envelope to eventuate intranuclear pH maintenance in the living cells.

Design study of a free-electron laser on a storage ring at Tohoku University

A free-electron laser (FEL) based on the proposed Tohoku Light Source storage ring is discussed. In the first stage the FEL is made to operate in the visible region with a relative low beam energy to avoid the complication of mirrors. Then, with a higher beam energy, the FEL can produce radiation of wavelengths in the UV or VUV region. Some simulation results of the storage-ring FEL with wavelengths of approximately 200 nm are presented.

Co-ordinated expression of connexins 26 and 32 in human endometrial glandular epithelium during the reproductive cycle and the influence of hormone replacement therapy

Hormones are involved in the regulation of intercellular communication, and gap junction intercellular communication may play an important role in the prevention of endometrial cancer. We have investigated changes in the expression of the gap junction proteins connexin 26 (Cx26) and Cx32 in human endometrial glandular epithelium during the reproductive cycle as well as the influence of hormone replacement therapy. Frozen sections from 71 endometrial tissue samples (53 taken from women who had undergone hysterectomy during the menstrual cycle, 3 early pregnancy deciduae and 15 from menopausal women, some of whom were receiving estrogen alone or estrogen plus progesterone) were analyzed by immunofluorescence and confocal laser scanning microscopy. Cx26 and Cx32 were expressed weakly in the proliferative phase, markedly during ovulation and most strongly in the mid-secretory phase; by the late secretory phase, they decreased drastically. Cx26 and Cx32 also were expressed in early pregnancy. Women who had received estrogen and progesterone expressed the Cxs, but those who had received estrogen only or no therapy did not. These results were confirmed by Western blot analysis. They indicate that expression of Cx26 and Cx32 is correlated with cell differentiation and with the glandular function of the endometrial epithelium and suggest that expression of Cxs is controlled by serum progesterone.

Changes in the expression of gap junction proteins (connexins) in hamster tongue epithelium during wound healing and carcinogenesis

We examined changes in the expression and localization of connexin proteins and transcripts by means of immunofluorescence and in situ hybridization in normal conditions, wound healing and carcinogenesis using hamster tongue epithelium, in which differentiation, migration and growth of keratinocytes takes place physiologically and pathologically. In normal hamster tongue epithelium, immunofluorescent staining showed that Cx26 and Cx43 proteins were localized differently during differentiation of keratinocytes, but in in situ hybridization, the localization of Cx26 and Cx43 transcripts overlapped considerably, suggesting that the different localization of Cx26 and Cx43 proteins in squamous epithelium is largely regulated at post-transcriptional levels. During wound healing, the expression and localization of connexin proteins and transcripts were changed drastically. Shortly (6 h) after injury the expression of Cx26 and Cx43 proteins decreased at wound edges, but by 1-3 days after injury the expression of both proteins increased and both proteins co-localized to the same spots in the epithelium near wound edges. During carcinogenesis, the increased expression of Cx26 and Cx43 proteins and their transcripts and co-localization of both proteins occurred in papillomas, and the expression of Cx26 was reduced as cancer cells became morphologically less differentiated. We also found, that during wound healing in papillomas, squamous cell carcinomas and keratinocytes, Cx26 and Cx43 proteins were localized aberrantly in the cytoplasm, especially around nuclei, rather than on plasma membranes. These results indicate that quantitative and qualitative changes in connexin expression are associated with differentiation, migration and proliferation of keratinocytes in squamous epithelium.

Differential regulation of gap junction protein (connexin) genes during cardiomyocytic differentiation of mouse embryonic stem cells in vitro

Using an in vitro system for differentiation of embryonic stem (ES) cells into cardiac myocytes, we analyzed the expression of connexin (Cx) genes by RT-PCR to learn what changes in the expression of multiple connexin genes occur during the early stage of heart development. We also examined gap junctional intercellular communication by using Lucifer Yellow dye microinjection transfer, studied intracellular Ca2+ transients by confocal laser image analysis using fluo 3, and determined localization of Cx43 by immunofluorescence during in vitro differentiation of ES cells into cardiac myocytes. The transcripts for Cx43 and Cx45 were detected in undifferentiated ES cells and in embryoid bodies before and after the appearance of beating cardiomyocytes. In contrast, Cx40 transcripts were not observed in undifferentiated ES cells and were barely detectable in 3- and 5-day-old embryoid bodies. Cx40 transcripts significantly increased with the appearance of beating cells similar to those of cardiac-specific genes. Dye coupling was present among undifferentiated ES cells, prebeating cells of embryoid body outgrowth and ES cell-derived beating cardiomyocytes. When dye was injected into a beating cell, dye spread was restricted to neighboring beating cells. Immunofluorescence demonstrated that Cx43 protein was localized not only in beating cells but also in surrounding nonbeating cells, whereas myosin heavy chain alpha/beta was exclusively positive in the beating cells. These data suggest that the expression of multiple connexins is differentially regulated during the cardiomyocytic differentiation of ES cells in vitro and that Cx40 expression may be linked to early stages in cardiomyocytic differentiation.

Reversible inhibition of gap junctional intercellular communication, synchronous contraction, and synchronism of intracellular Ca2+ fluctuation in cultured neonatal rat cardiac myocytes by heptanol

We analyzed by Fotonic Sensor, a fiber-optic displacement measurement instrument, the effects of heptanol on synchronized contraction of primary neonatal rat cardiac myocytes cultured at confluent density. We also examined the effect of heptanol on the changes in gap junctional intercellular communication by using the microinjection dye transfer method, and on intercellular Ca2+ fluctuation by confocal laser scanning microscopy of myocytes loaded with the fluorescent Ca2+ indicator fluo 3. In addition, we studied expression, phosphorylation, and localization of the major cardiac gap junction protein connexin 43 (Cx43) using immunofluorescence and Western blotting. At Day 6 of culture, numerous myocytes exhibited spontaneous, synchronous contractions, excellent dye coupling, and synchronized intracellular Ca2+ fluctuations. We treated the cells with 1.5, 2.0, 2.5, and 3.0 mmol/liter heptanol. With 1.5 mmol/liter heptanol, we could not observe significant effects on spontaneous contraction of myocytes. At 3.0 mmol/liter, the highest concentration used in the current experiment, heptanol inhibited synchronous contractions and even after washing out of heptanol, synchronous contraction was not rapidly recovered. On the other hand, at the intermediate concentrations of 2.0 and 2.5 mmol/liter, heptanol reversely inhibited synchronized contraction, gap junctional intercellular communication, and synchronization of intracellular Ca2+ fluctuations in the myocytes without preventing contraction and changes of intracellular Ca2+ in individual cells. Brief exposure (5-20 min) to heptanol (2.0 mmol/liter) did not cause detectable changes in the expression, phosphorylation, or localization of Cx43, despite strong inhibition of gap junctional intercellular communication. These results suggest that gap junctional intercellular communication plays an important role in synchronous intracellular Ca2+ fluctuations, which facilitate synchronized contraction of cardiac myocytes.

Aberrant expression of gap junction proteins (connexins) is associated with tumor progression during multistage mouse skin carcinogenesis in vivo

To elucidate what changes in the expression of gap junction proteins (connexins) occur at what stages during multistage mouse skin carcinogenesis in vivo, we immunohistochemically and morphometrically analyzed the expression of connexin 26 (Cx26) and connexin 43 (Cx43) in papillomas, well-, moderately- and poorly-differentiated squamous cell carcinomas, as well as in squamous cell carcinomas at invasion sites and those metastasized into lymph nodes in female CD-1 mice as a result of treatment with dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate. In papillomas, no clear reduction of the two connexins was observed; however, Cx26 and Cx43 were frequently co-localized in the same gap junction plaques, whereas the two kinds of Cxs were differentially expressed in normal and surrounding non-tumorous epidermis. In squamous cell carcinomas, the expression of both Cx26 and Cx43 significantly decreased compared with surrounding non-tumorous epidermis and papillomas. The Western blot analysis confirmed that both Cx26 and Cx43 proteins were reduced in squamous cell carcinomas compared with papillomas. Furthermore, the expression of Cx26 was reduced as cancer cells became morphologically less differentiated, while that of Cx43 did not change. Squamous cell carcinomas at invasive sites showed clear reduction of Cx26 and Cx43. In squamous cell carcinomas metastasized into lymph nodes, Cx26 was expressed, but few carcinoma cells expressed Cx43. The localization of E-cadherin on the plasma membrane between cancer cells was maintained even at invasive and metastatic sites. Our data suggest that quantitative and qualitative changes in connexin expression are associated with tumor progression, including the loss of differentiation, and invasion and metastasis, during multistage mouse skin carcinogenesis.

Rapid appearance of connexin 26-positive gap junctions in centrilobular hepatocytes without induction of mRNA and protein synthesis in isolated perfused liver of female rat

In the adult rat liver, the gap junction protein connexin 32 (Cx32) is evenly distributed in hepatocytes within the liver lobules, while connexin 26 (Cx26) is preferentially localized in hepatocytes in periportal zones. We report here that Cx26-positive gap junctions rapidly appear in the centrilobular hepatocytes of adult female rat livers during a 30 minute perfusion of the liver through the hepatic portal vein with a 1:1 mixture of Dulbecco's modified Eagle's medium (DMEM) and oxygen transport FC-43 fluid at a physiological flow rate without any changes in the distribution of Cx32. The change in the localization of Cx26 was closely related to that of E-cadherin, and there was no significant increase in the amounts of Cx26 protein and mRNA. The appearance of Cx26 in the centrilobular hepatocytes was inhibited by treatment with cytoskeleton disruptors such as colchicine and cytochalasin B, and intracytoplasmic transport inhibitors such as brefeldin A. The liver perfusion induced the appearance of Cx26 in the centrilobular hepatocytes only in female rats. Estrogen treatment of ovariectomized rats caused the appearance of both Cx26 and E-cadherin in centrilobular hepatocytes not only in the perfused liver but also in the non-perfused liver. Our results indicate that in the rat liver: (a) the localization of Cx26 can be modulated by a post-translational mechanism; (b) E-cadherin may play an important role in the formation of gap junctions composed of Cx26; and (c) the formation of gap junctions is regulated by female steroid hormones.

Sequential changes in intercellular junctions between hepatocytes during the course of acute liver injury and restoration after thioacetamide treatment

Sequential changes of gap junctions (GJs), tight junctions (TJs) and desmosomes (DSs) between hepatocytes during restorative proliferation were studied in rats after a single intraperitoneal administration of 200 mg/kg thioacetamide (TAA). Antibody against connexin 32 was used to demonstrate GJs; simultaneously the changes in TJs and DSs were studied using antibodies against 7H6 protein and desmoplakins. Propidium iodide and bromodeoxyuridine were used to recognize necrotic and proliferative cells. GJs were evenly distributed in early necrotic hepatocytes at 16 h after TAA treatment, then disappeared from necrotic and surrounding cells at 24 h. At 48 h, GJs had disappeared completely from hepatocytes in whole liver lobules, while many hepatocytes were heavily labelled with BrdU. At 72 h, GJs reappeared, firstly in perinecrotic areas. At 96 h after treatment, when the injured areas had disappeared and restorative proliferation ceased, GJs were distributed evenly throughout the lobules. Immunohistochemical observation of GJs in centrilobular, perinecrotic and periportal areas after TAA-induced hepatic necrosis was confirmed by counting the number of connexin-32-positive spots in the respective areas. TJs and DSs disappeared from necrotic cells at 24 h, but then increased between 24 and 48 h in perinecrotic areas, though the increased intensity of these junctions was more evident at 48 h. At 72 h, localization of TJs and DSs returned to normal. These results suggest that during the course of acute hepatic injury, GJs (cell-cell communication) behave differently from other intercellular junctions.

Localization of the 7H6 antigen at tight junctions correlates with the paracellular barrier function of MDCK cells

An important function of the tight junction is to act as a selective barrier to ions and small molecules, although no molecule responsible for the barrier function has been identified. Here we report evidence that the localization of the 7H6 tight junction-associated antigen identified in our laboratory at tight junctions correlates with the barrier function of MDCK cells. MDCK cells in a confluent monolayer possessed a polarized morphology, having an apical plasma membrane and a basolateral membrane, which is separated from the former by tight junctions. MDCK cells expressed both ZO-1 and 7H6 antigen at tight junctions, which maintain a tight barrier as determined by resistance to lanthanum permeation and high transepithelial electrical resistance (TER, 1500 ohm-cm2). The 7H6 antigen disappeared as tight junctions became permeable to lanthanum with a decrease in TER (below 100 ohm-cm2) due to treatment with metabolic inhibitors (10 microns antimycin A and 10 mM 2-deoxyglucose) for 30 min, while leaving ZO-1 at the cell border. The 7H6 antigen appeared at tight junctions again as TER recovered to a high level (1500 ohm-cm2) within 3 h after withdrawal of metabolic inhibitors. In addition, we found that 7H6 antigen is a phosphorylated protein and that phosphorylation is closely related to the localization of 7H6 antigen in the area of tight junctions.

Hormonal regulation of connexin 43 expression and gap junctional communication in human osteoblastic cells

We have recently shown that connexin 43 (Cx43), a major gap junction protein in osteoblasts, is expressed with an increase in cell density (CHIBA, H. et al. (1993). Cell Struc. Funct., 18: 419-426). In the present study, we examined what kinds of hormones and cytokines regulate the gap junction protein in osteoblastic cells, using a human osteoblastic cell line (SV-HFO) after reaching a confluent density to avoid influence of cell proliferation. Either retinoic acid (RA) or transforming growth factor-beta 1 (TGF-beta 1) induced the Cx43 expression of SV-HFO cells, as revealed by Northern blot analysis and immunocytochemistry. These modulators also increased gap junctional intercellular communication, in terms of the extent of dye transfer. On the other hand, 1 alpha, 25-dihydroxyvitamin D3 did not influence the Cx43 expression and gap junctional intercellular communication of the cells. These results suggest that RA and TGF-beta might maintain bone tissue as an organized tissue in vivo by increasing intercellular communication of osteoblastic cells.

The expression, phosphorylation, and localization of connexin 43 and gap-junctional intercellular communication during the establishment of a synchronized contraction of cultured neonatal rat cardiac myocytes

We analyzed the expression, phosphorylation, and localization of the major cardiac gap-junction protein connexin 43 (Cx43) during the establishment of a synchronized contraction in confluent monolayers of primary cultured neonatal rat cardiac myocytes, combined with a functional assay of gap junctions by the microinjection-dye transfer method. Monitoring of the beating rate and synchronization by Fotonic Sensor showed that at Day 1 of culture cardiac myocytes contracted spontaneously but irregularly, that the contractile rate increased with culture time, and that a synchronized contraction was gradually formed. At Day 7, the confluent cells exhibited synchronous contraction with a relatively constant rate (125 +/- 20 beats/min). Cardiac myocytes expressed a large amount of Cx43 mRNA even at Day 1 and maintained the expression until at least Day 7. Immunofluorescence of Cx43 showed that the localization of Cx43-positive spots was mostly restricted to cell-cell contacts between myocytes and that few Cx43-positive spots were present between myocytes and fibroblasts or between fibroblasts. The amount of Cx43 protein, the proportion of phosphorylated forms to the nonphosphorylated one, and the number and total area of Cx43-positive spots increased with culture time. Gap-junctional intercellular communication measured by dye transfer assay was also increased with culture time and correlated well with the number and total area of Cx43-positive spots. Our systematic study suggests that a concerted action of the expression, phosphorylation, and localization of Cx43 and gap-junctional intercellular communication plays a major role in the reestablishment of synchronous beating of cultured neonatal rat cardiac myocytes.

Effect of DDT on hepatic gap junctional intercellular communication in rats

The effects of in vivo exposure to DDT on hepatic gap junctional intercellular communication (GJIC) and connexin gene/protein expression in Sprague-Dawley rats were examined by in vivo/in vitro dye-transfer assay, immunohistochemical staining, and by Western and Northern blot analyses. In the dose-response study, three dose levels of DDT (5, 25 and 50 mg/kg/day) were administered orally to rats once a day for 2 weeks. The average size of the dye spread after injection of Lucifer Yellow and the area of Cx32 spots per hepatocyte decreased in a dose-dependent manner, but there was no effect on the number of Cx32 spots per hepatocyte. In the time-course study, DDT (50 mg/kg/day) was administered orally once a day for up to 6 weeks. Hepatic GJIC decreased at week 1 but recovered at week 6. The average area of Cx32 spots per hepatocyte gradually decreased at weeks 2 and 4, and remained at the same level at week 6, correlating with the decreased Cx32 protein level in plasma membranes. The average area of Cx26 spots per hepatocyte in the peripheral zones clearly decreased at week 1, but quickly recovered at week 2 and increased at week 6; however, no clear change of the Cx26 protein level in plasma membranes was observed. No changes of Cx32 and Cx26 mRNA levels were observed in DDT groups. These results suggest that DDT, a liver tumor-promoting agent, inhibits hepatic GJIC in vivo dose-dependently in rats and that aberrant Cx32 and Cx26 protein expression and/or localization may be responsible for this effect.