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Aims Damage of the blood–brain barrier (BBB) is a hallmark of brain injury during the early stages of ischemic stroke. The subsequent endothelial hyperpermeability drives the initial pathological changes and aggravates neuronal death. Transient receptor potential melastatin 2 (TRPM2) is a Ca2+-permeable nonselective cation channel activated by oxidative stress. However, whether TRPM2 is involved in BBB degradation during ischemic stroke remains unknown. We aimed to investigate the role of TRPM2 in BBB degradation during ischemic stroke and the underlying molecular mechanisms. Methods and results Specific deletion of Trpm2 in endothelial cells using Cdh5 Cre produces a potent protective effect against brain injury in mice subjected to middle cerebral artery occlusion (MCAO), which is characterized by reduced infarction size, mitigated plasma extravasation, suppressed immune cell invasion, and inhibited oxidative stress. In vitro experiments using cultured cerebral endothelial cells (CECs) demonstrated that either Trpm2 deletion or inhibition of TRPM2 activation attenuates oxidative stress, Ca2+ overload, and endothelial hyperpermeability induced by oxygen–glucose deprivation (OGD) and CD36 ligand thrombospondin-1 (TSP1). In transfected HEK293T cells, OGD and TSP1 activate TRPM2 in a CD36-dependent manner. Noticeably, in cultured CECs, deleting Trpm2 or inhibiting TRPM2 activation also suppresses the activation of CD36 and cellular dysfunction induced by OGD or TSP1. Conclusions In conclusion, our data reveal a novel molecular mechanism in which TRPM2 and CD36 promote the activation of each other, which exacerbates endothelial dysfunction during ischemic stroke. Our study suggests that TRPM2 in endothelial cells is a promising target for developing more effective and safer therapies for ischemic stroke. [ABSTRACT FROM AUTHOR]

Objective: A dog atrial ultra-rapid delayed rectifier current (IKur.d) is involved in canine atrial repolarization and shares similarities with the human atrial ultra-rapid delayed rectifier (IKur). Almost no information is available about the actions of antiarrhythmic drugs on IKur.d. This study evaluated effects of ambasilide, quinidine, flecainide and verapamil on IKur.d in isolated canine atrial myocytes. Methods: Standard whole-cell patch clamp techniques were used to study the effects of multiple concentrations of each drug. Results: All drugs produced reversible concentration-, voltage- and time-dependent IKur.d inhibition. Significant effects of quinidine, flecainide and ambasilide were noted at atrial-effective antiarrhythmic concentrations in the dog. Upon the onset of a depolarizing pulse, block developed exponentially in relation to time, with the blocking rate-constant increasing with drug concentration, consistent with open-channel blockade and permitting the calculation of forward and reverse rate-constants. For all drugs, the 50% blocking concentration (EC50) showed significant voltage-dependence, decreasing at more positive potentials. The magnitude of voltage-dependent block was directly related to the degree of drug-induced shift in the voltage dependence of activation (r=0.97), pointing to open-channel block as a mechanism for voltage-dependent action. An additional component of voltage-dependence suggested that blocking sites were subjected to 17–21% of the transmembrane voltage field. Conclusions: Ambasilide, quinidine, flecainide and verapamil inhibit IKur.d, with preferential action on the open state. IKur.d inhibition may play a role in antiarrhythmic effects in canine atrial arrhythmia models. Comparisons between the effects of these drugs on IKur.d and previously studied effects on IKur suggest potential opportunities for investigating the molecular structural determinants of drug-blocking action on atrial-specific ultrarapid delayed rectifiers. [ABSTRACT FROM PUBLISHER]

Background: We have shown that rapid atrial activation, as occurs during atrial fibrillation (AF), reduces L-type Ca2+ current (ICa) and that this is the principal mechanism of the action potential duration and refractoriness changes that characterize tachycardia-induced atrial remodeling. The present study was designed to determine whether atrial tachycardia alters biochemical indices of the number of L-type Ca2+ channels and/or of the number and binding affinity of β-adrenergic receptors. Methods: In canine atrial sarcolemmal preparations, the number and binding affinity of dihydropyridine receptors were determined with the use of 3H-nitrendipine and that of β-adrenergic receptors with 125I-iodocyanopindolol. Results were obtained with preparations from dogs paced at 400/min for 1 (P1, n=20), 7 (P7, n=9), and 42 (P42, n=9) days, and compared with observations in sham-operated controls (P0, n=14). Results: Pacing reduced the Bmax of dihydropyridine receptors, from 157±18 fmol/mg (P0) to 116±9 fmol/mg (P1, P <0.05), 100±14 fmol/mg (P7, P <0.05) and 94±9 fmol/mg (P42, P <0 .01). The affinity of dihydropyridine receptors was unchanged, with the Kd averaging 711±102 pM, 656±74 pM, 633±155 pM and 585±92 pM in P0, P1, P7 and P42 dogs. Neither Bmax nor Kd of β-adrenergic receptors was altered by rapid pacing. Values of Bmax of dihydropyridine receptors correlated with atrial ICa current density (r2=0.95) and ERP (r2=0.99). Conclusions: Rapid atrial activation results in downregulation in the number of dihydropyridine receptors without altering the number or affinity of β-adrenergic receptors. The reductions in ICa that play an important role in the atrial electrical remodeling by which ‘AF begets AF’ appear to be due at least in part to a decrease in the number of L-type Ca2+ channels in cardiac cell membranes. [ABSTRACT FROM PUBLISHER]