No abstract

Significance The acute respiratory distress syndrome (ARDS) is a devasting clinical problem with high mortality, no drug therapy, and poorly understood pathogenesis. The hallmark of ARDS is persistent pulmonary edema, attributable in part to impaired Na + and fluid transport across the alveolo-capillary barrier, undertaken by the epithelial sodium channel (ENaC). We describe a unique signaling pathway driven by TGF-β, which acutely dysregulates ENaC trafficking, blocking alveolar Na + transport and edema resolution. This pathway represents a unique pathomechanism in ARDS, highlights potential “druggable” targets, and may represent a physiological means of acutely regulating ENaC in lungs and other organs.

Uncoupling of GJs prior to ischaemia either by PC or CBX preserves the electrical coupling of cells and results in an antiarrhythmic effect during a subsequent ischaemic insult, indicating that a partial closure of gap junctions may play a trigger role in the protection. In contrast, when CBX is administered in PC dogs the protection both against GJ uncoupling and arrhythmias is markedly attenuated, suggesting that the antiarrhythmic protection, at least in part, is mediated through GJs.

Our systematic analysis of anion channels and transporters in idiopathic pulmonary arterial hypertension (IPAH) showed marked upregulation of the Cl− channel TMEM16A gene. We hypothesised that TMEM16A overexpression might represent a novel vicious circle in the molecular pathways causing pulmonary arterial hypertension (PAH).We investigated healthy donor lungs (n=40) and recipient lungs with IPAH (n=38) for the expression of anion channel and transporter genes in small pulmonary arteries and pulmonary artery smooth muscle cells (PASMCs).In IPAH, TMEM16A was strongly upregulated and patch-clamp recordings confirmed an increased Cl− current in PASMCs (n=9–10). These cells were depolarised and could be repolarised by TMEM16A inhibitors or knock-down experiments (n=6–10). Inhibition/knock-down of TMEM16A reduced the proliferation of IPAH-PASMCs (n=6). Conversely, overexpression of TMEM16A in healthy donor PASMCs produced an IPAH-like phenotype. Chronic application of benzbromarone in two independent animal models significantly decreased right ventricular pressure and reversed remodelling of established pulmonary hypertension.Our findings suggest that increased TMEM16A expression and activity comprise an important pathologic mechanism underlying the vasoconstriction and remodelling of pulmonary arteries in PAH. Inhibition of TMEM16A represents a novel therapeutic approach to reverse remodelling in PAH.

Non-technical summary Women during their child-bearing years have longer QT intervals in their electrocardiograms than men and are more susceptible to lethal arrhythmias elicited by drugs that delay repolarization. Current theories posit that women have a reduced 'repolarization reserve' due to reduced potassium currents resulting in longer QT and greater repolarization delays. We proposed an alternative mechanism of higher calcium currents in women which would likewise prolong QT intervals, delay repolarization while increasing the force of contractions and intracellular calcium load. Here, we show that physiological concentrations of oestrogen increase the calcium current only in cells from the base of the heart, by increasing messenger RNA and proteins levels that encode for the calcium current. Moreover, oestrogen acts by interacting with oestrogen receptors (ER)α but not ERβ which may explain why hormone replacement therapy increases the risk of arrhythmia and offers a possible protective solution of using an oestrogen mimetic that selectively binds to ERβ.Abstract In type-2 long QT (LQT2), adult women and adolescent boys have a higher risk of lethal arrhythmias, called Torsades de pointes (TdP), compared to the opposite sex. In rabbit hearts, similar sex-and age-dependent TdP risks were attributed to higher expression levels of L-type Ca 2+ channels and Na + -Ca 2+ exchanger, at the base of the female epicardium. Here, the effects of oestrogen and progesterone are investigated to elucidate the mechanisms whereby I Ca,L density is upregulated in adult female rabbit hearts. I Ca,L density was measured by the whole-cell patch-clamp technique on days 0-3 in cardiomyocytes isolated from the base and apex of adult female epicardium. Peak I Ca,L was 28% higher at the base than apex (P < 0.01) and decreased gradually (days 0-3), becoming similar to apex myocytes, which had stable currents for 3 days. Incubation with oestrogen (E2, 0.1-1.0 nM) increased I Ca,L (∼2-fold) in female base but not endo-, apex or male myocytes. Progesterone (0.1-10 μM) had no effect at base myocytes. An agonist of the α-(PPT, 5 nM) but not the β-(DPN, 5 nM) subtype oestrogen receptor (ERα/ERβ) upregulated I Ca,L like E2. Western blots detected similar levels of ERα and ERβ in male and female hearts at the base and apex. E2 increased Cav1.2α (immunocytochemistry) and mRNA (RT-PCR) levels but did not change I Ca,L kinetics. I Ca,L upregulation by E2 was suppressed by the ER antagonist ICI 182,780 (10 μM) or by inhibition of transcription (actinomycin D, 4 μM) or protein biosynthesis (cycloheximide, 70 μM). Therefore, E2 upregulates I Ca,L by a regional genomic mechanism involving ERα which is a known determinant of sex differences in TdP risk in LQT2.X. Yang and G. Chen contributed equally to this work.

No abstract

Class III antiarrhythmic agents exhibit reverse rate-dependent lengthening of the action potential duration (APD). In spite of the several theories developed so far to explain this reverse rate-dependency (RRD), its mechanism has not yet been clarified. The aim of the present work was to further elucidate the mechanisms responsible for RRD in mammalian ventricular myocardium. Action potentials were recorded using conventional sharp microelectrodes from human, canine, rabbit and guinea pig ventricular myocardium in a rate-dependent manner varying the cycle length (CL) between 0.3 and 5 s. Rate-dependent drug effects were studied using agents known to lengthen or shorten action potentials, and these drug-induced changes in APD were correlated with baseline APD values. Both drug-induced lengthening (by dofetilide, sotalol, E-4031, BaCl(2), veratrine, BAY K 8644) and shortening (by mexiletine, tetrodotoxin, lemakalim) of action potentials displayed RRD, i.e., changes in APD were greater at longer than at shorter CLs. In rabbit, where APD is a biphasic function of CL, the drug-induced APD changes were proportional to baseline APD values but not to CL. Similar results were obtained when repolarization was modified by injection of inward or outward current pulses in isolated canine cardiomyocytes. In each case the change in APD was proportional to baseline APD (i.e., that measured before the superfusion of drug or injection of current). Also, the net membrane current (I (net)), determined from the action potential waveform at the middle of the plateau, was inversely proportional to APD and consequently with to CL. The results indicate that RRD is a common characteristic of all the drugs tested regardless of the modified ion current species. Thus, drug-induced RRD can be considered as an intrinsic property of cardiac membranes based on the inverse relationship between I (net) and APD.

Background and purpose: Nitric oxide (NO) donors provide a preconditioning-like anti-arrhythmic protection in the anaesthetized dog. As NO may modulate gap junction (GJ) function, the present study investigated whether this anti-arrhythmic effect is due to a modification of GJs by NO, derived from the NO donor sodium nitroprusside (SNP). Experimental approach: In chloralose-urethane-anaesthetized, open-chest dogs, either saline (controls; n = 11) or SNP (0.2 mg·kg -1 ·min -1 ; n = 10) was infused at a rate of 0.5 mL·min -1 by the intracoronary route. The infusions were started 20 min prior to and maintained throughout the entire 60 min occlusion period of the left anterior descending coronary artery. The severity of ischaemia and of arrhythmias, tissue electrical impedance and permeability, as well as the phosphorylation of connexin43, were assessed. Key results: Compared with the controls, SNP infusion markedly suppressed the total number of ventricular premature beats (666 Ϯ 202 vs. 49 Ϯ 18; P < 0.05), and the number of ventricular tachycardiac episodes (8.1 Ϯ 2.3 vs. 0.2 Ϯ 0.1; P < 0.05) without significantly modifying the incidence of ventricular tachycardia or ventricular fibrillation. The severity of ischaemia (epicardial ST-segment changes, inhomogeneity of electrical activation) and tissue electrical impedance changes were significantly less in the SNP-treated dogs. SNP improved GJ permeability and preserved the phosphorylated form of connexin43. Conclusion and implications:The anti-arrhythmic protection resulting from SNP infusion in the anaesthethized dog may, in part, be associated with the modulation of gap junctional function by NO.