Inhibition of ouabain-induced arrhythmias of ouabain-sensitive myocardial cells (quail) by contact with ouabain-resistant cells (mouse) and its mechanism

Mapping the genomic diaspora of gastric cancer

Gastric cancer (GC) is a leading contributor to global cancer incidence and mortality. Pioneering genomic studies, focusing largely on primary GCs, revealed driver alterations in genes such as ERBB2, FGFR2, TP53 and ARID1A as well as multiple molecular subtypes. However, clinical efforts targeting these alterations have produced variable results, hampered by complex co-alteration patterns in molecular profiles and intra-patient genomic heterogeneity. In this Review, we highlight foundational and translational advances in dissecting the genomic cartography of GC, including non-coding variants, epigenomic aberrations and transcriptomic alterations, and describe how these alterations interplay with environmental influences, germline factors and the tumour microenvironment. Mapping of these alterations over the GC life cycle in normal gastric tissues, metaplasia, primary carcinoma and distant metastasis will improve our understanding of biological mechanisms driving GC development and promoting cancer hallmarks. On the translational front, integrative genomic approaches are identifying diverse mechanisms of GC therapy resistance and emerging preclinical targets, enabled by technologies such as single-cell sequencing and liquid biopsies. Validating these insights will require specifically designed GC cohorts, converging multi-modal genomic data with longitudinal data on therapeutic challenges and patient outcomes. Genomic findings from these studies will facilitate 'next-generation' clinical initiatives in GC precision oncology and prevention.

Manipulation of cellular excitability by cell fusion: effects of rapid introduction of transient outward K+ current on the guinea pig action potential

To investigate the still-undetermined role of the Ca2+-independent transient outward current (Ito1) on repolarization of the cardiac action potential, we used cell fusion to introduce Ito1 into guinea pig cardiomyocytes, which normally lack this current. This technique enables the rapid delivery of premade functional ion channels to cardiomyocytes within hours of isolation, thus eliminating the action potential alterations that complicate prolonged cell culture. Chinese hamster ovary (CHO) cells stably expressing Kv4.3 (CHO-Kv4. 3) were loaded with a fluorescent dye and fused to guinea pig cardiomyocytes using polyethylene glycol. As controls, nontransfected CHO cells were fused using the same protocol. Myocytes fused with CHO-Kv4.3 cells exhibited a robust Ito1 (16. 5+/-2.6 pA/pF at +40 mV; 37 degrees C; n=19), whereas controls had none. Ito1 accelerated the early repolarization velocity (r=-0.68; 3 ms after the overshoot) and progressively suppressed the voltage of the plateau phase (r=-0.90) with increasing Ito1 density. Reduction of the action potential duration to 50% repolarization (r=-0.76) and to 90% repolarization (r=-0.65) also correlated well with Ito1 density. Thus, Ito1 exerted a significant effect on the early repolarization phase and abbreviated action potential duration. Cell fusion is a valuable and generalizable technique to introduce preformed membrane proteins into native cells.

Protective effect of gamma-glutamylcysteinylethyl ester on dysfunction of the selenium-deficient rat heart

We investigated the protective effect of intracellular GSH against cardiac dysfunction in selenium (Se)-deficient neonatal rats and cultured fetal rat myocytes. A Se-deficient diet with or without daily subcutaneous injections of gamma-glutamylcysteinylethyl ester (gammay-GCE) (a membrane-permeating GSH precursor) was given to rats from gestation day 4 via the dam to postnatal day 14. Se deficiency induced a 62% incidence of electrocardiographic abnormalities such as sinus arrhythmias or extrasystole, a 63% reduction in dP/dt in the left ventricle, and an increase in thiobarbituric acid reacting substances (TBARS), but no ultrastructural cardiac lesions were observed. Administration of gamma-GCE increased the intracellular GSH concentration ([GSH]i) of both neonatal rat hearts and cultured fetal rat cardiac myocytes. gamma-GCE-like sodium selenite prevented the cardiac dysfunction and the TBARS increment. gamma-GCE also prevented H2O2 toxicity in the cultured myocytes. The Vmax, but not the Km, for GSH of Se-dependent GSH peroxidase (Se-Gpx) activity in Se-deficient rat heart homogenates was one-third that of normal rat heart homogenates. Although gamma-GCE did not affect the Se-Gpx Vmax and Km for GSH, it did induce a substantial and significant increase in [GSH]i, which was postulated to increase the velocity of H2O2 decomposition by Se-Gpx activity 1.6-fold. These data suggest that the increase in [GSH]i may have played a role in preventing the TBARS increase and cardiac dysfunction in Se-deficient rats.

Metabolic coupling of glutathione between mouse and quail cardiac myocytes and its protective role against oxidative stress

Cultured quail myocytes were much more resistant to H2O2 toxicity than cultured mouse myocytes. The intracellular concentration of glutathione ([GSH]i) and the activity of gamma-glutamylcysteine synthetase (gamma-GCS) in quail heart cells were about five and three times higher, respectively, than in mouse heart cells, although catalase and glutathione peroxidase (GSHpx) activity was similar in both. Preloading of gamma-glutamylcysteine monoethyl ester (gamma-GCE), a membrane-permeating GSH precursor, increased the H2O2 resistance of cultured mouse myocytes. These observations suggest that the high [GSH]i and the high activity of gamma-GCS in quail myocytes are responsible for their high resistance to H2O2. Both H2O2 sensitivity and [GSH]i of mosaic sheets composed of equal amounts of mouse and quail myocytes approximated those of sheets composed entirely of quail myocytes. From these observations, it is hypothesized that GSH was transferred from quail myocytes to mouse myocytes, probably through gap junctions between them, and that quail myocytes resynthesized GSH by a feedback mechanism, thus maintaining their intracellular GSH levels. When the fluorescent dye lucifer yellow was injected into a beating quail myocyte in a mosaic sheet, it spread to neighboring mouse myocytes but not to neighboring L cells (a cell line derived from mouse connective tissue). These observations indicate that existence of gap junctions in the region of cell contact between mouse and quail myocytes but not between quail myocytes and L cells. When quail myocytes preloaded with [3H]gamma-GCE were cocultured with mouse myocytes and L cells, the radioactivity was transmitted to neighboring mouse myocytes but not L cells. These observations show that GSH and/or its precursors can be transmitted from quail myocytes to mouse myocytes through gap junctions and that this can protect mouse myocytes from H2O2 toxicity. Mouse myocyte sheets composed of 10(4) cells or more showed higher resistance to H2O2 toxicity than single isolated mouse myocytes. Metabolic coupling of GSH between myocytes may contribute at least in part to this high resistance of the cell sheets.

Deleterious effects of digitalis on reperfusion-induced arrhythmias and myocardial injury in ischemic rat hearts: possible involvements of myocardial Na+ and Ca2+ imbalance

Isolated rat hearts were made ischemic for 25 min after an initial recirculating perfusion, followed by 30 min of reperfusion. In some hearts, interventions including administration of ouabain and/or high [K+] in the buffer were performed during the first 10 min of reperfusion. During ischemia, intracellular Na+ (Nai) increased from 15 to 64 mumol/g dry weight (dwt). During reperfusion, Nai declined rapidly (at 10 min of reperfusion: 48 mumol/g dwt, at 30 min: 25 mumol/g dwt) and regular rhythm was recovered within 10 min in hearts without any intervention during reperfusion. 45Ca2+ uptake increased from 0.8 to 7.5 mumol/g dwt after 30 min of reperfusion. Ventricular function recovered by 45%. A 10-min perfusion with 10 or 50 microM of ouabain increased Nai (17 to 21 or 27 mumol/g dwt) with increased left-ventricular (LV) contractile function, but these effects were reversed by combination of high perfusate [K+] (20 mM) in non-ischemic hearts. A 10-min reperfusion with ouabain retarded or stopped the decline in Nai (at 10 min of reperfusion: 54 or 63 mumol/g dwt, at 30 min: 32 or 40 mumol/g dwt). These amounts of ouabain also increased the incidence of ventricular tachyarrhythmias during reperfusion to 30% or 50%, and increased the duration of ventricular fibrillation from 6.5 to 11.5 or 18.0 min. 45Ca2+ uptake reached to 8.8 or 10.0 mumol/g dwt, and function recovered only 35% or 28%. When high perfusate [K+] was combined with ouabain during reperfusion, the retarded decline in Nai, augmented 45Ca2+ uptake, and reduced recovery of function caused by ouabain alone were attenuated. These results suggest that digitalis has toxic effects on reperfused ischemic hearts by inhibition of rapid active outward transport of previously elevated Nai and potentiation of Ca2+ overload.

The mechanisms of action of cyanide on the rabbit aorta

Pretreatment of strips of rabbit aorta with 10(-3) M sodium cyanide reduced contractions to 10(-8) through 10(-4) M norepinephrine (NE) added cumulatively. This antagonism by cyanide was not altered by 4 X 10(-6) M ouabain or verapamil, suggesting a lack of involvement of Na+, K+ ATPase or of calcium influx in the antagonism. Cyanide potentiated contractions caused by 3 X 10(-2) M potassium, but reduced contractions induced by higher potassium concentrations. Because the antagonism of higher concentrations of potassium and NE were similar, it seems that selective actions on different calcium pools are possibly not involved in the antagonism of agonist-induced contractions. 10(-2) M cyanide contracted rabbit aorta with a mean contraction 16% of that induced by 10(-4) M NE. These contractions were potentiated by pretreatment with 4 X 10(-6) M ouabain and 4 X 10(-6) M verapamil but were unaffected by the serotonin antagonist 2-bromo lysergic acid diethylamide, 10(-4) M (2-BrLSD), the alpha adrenergic antagonist phentolamine, 4 X 10(-5) M, the H1 antihistaminic pyrilamine, 10(-5) M, or the antimuscarinic atropine, 10(-6) M. The contractions were reduced by 10(-4) M 4,4'-di-isothiocyano-2,2'-stilbene disulfonic acid (DIDS) or chlorpromazine. The reduction may be due to a blockade of anionic channel mechanisms facilitating entry of cyanide into the vascular smooth muscle cell, as both of these agents can block anionic channels in other tissues.

Effects of Na+ gradient on the intracellular Ca2+ oscillation in the sympathetic ganglion cell: Na-Ca exchange in the neurone cell soma?

The effects of the removal of extracellular Na+ and the increase in the intracellular Na+ on the slow rhythmic membrane hyperpolarizations (rmhs) were studied in bullfrog sympathetic ganglion cells. The interval of rmhs, reflecting a relative change in the basal intracellular Ca2+, was lengthened by either treatment, disfavouring the possible involvement of the Na-Ca exchange mechanism in the Ca2+-buffering in the ganglion cell soma.

Beating activity of heterokaryons between myocardial and non-myocardial cells in culture

Cultured mouse myocardial cells grown as monolayers fused upon treatment with HVJ (Sendai virus). The myocardial cells also fused with quail myocardial cells, neuroblastoma cells and non-excitable cells, such as KB cells. The beating activity of these heterokaryons was studied in the present work. Heterokaryons composed of myocardial cells from different species maintained spontaneous beating activity for 2 days or more. Those of one myocardial and one neuroblastoma cell maintained the activity for 22-26 h, while those of one myocardial and one non-excitable cell, such as KB cell, lost the activity within 2-4 h after addition of HVJ. Heterokaryons that had stopped spontaneous beating did not contract on application of electrical-field stimulation. The ration of non-myocardial cells in the heterokaryons increased in inverse proportion to the decrease in beating activity of the heterokaryons. Study of the rapid disappearance of beating activity in heterokaryons composed of one myocardial and one KB cell showed that both excitability of the cell membrane and myofibril organization were rapidly lost.