6-(bromomethylene)tetrahydro-3-(1-naphthaleneyl)-2h-pyran-2-one and Myocardial-Ischemia

Thrombin plays a role in mediating ischemic injury and cardiac arrhythmias, but the mechanisms involved are poorly understood. Because voltage-gated sodium channels (VGSCs) have not previously been considered, putative effects of thrombin on VGSC function were investigated in human isolated cardiomyocytes.. Sodium current (I(Na)) was recorded by the whole-cell patch-clamp method. Thrombin increased peak I(Na) amplitude in an activity-dependent manner, from 1 to 100 U/mL, with an apparent EC50 of 91+/-16 U/mL. When tested at 32 U/mL, thrombin-increased I(Na) was abolished by tetrodotoxin (50 micromol/L). Thrombin effects on I(Na) were reversible and repeatable, and 100 U/mL doubled peak I(Na) amplitude. Thrombin (32 U/mL) shifted I(Na) activation to hyperpolarized potentials without affecting steady-state inactivation, producing unusually large increases in window current. Hirudin (320 U/mL) or haloenol lactone suicide substrate (10 micromol/L) failed to significantly affect these effects of thrombin. In current-clamped cardiomyocytes, thrombin (32 U/mL) depolarized resting membrane potential by 10 mV.. Facilitation of VGSC activation causing large increases in window current is a major mechanism by which thrombin may promote ischemic sodium loading and injury.

Topics: Action Potentials; Aged; Cells, Cultured; Dose-Response Relationship, Drug; Heart; Hirudins; Humans; Ion Channel Gating; Ion Transport; Membrane Potentials; Middle Aged; Myocardial Ischemia; Myocardium; Naphthalenes; Patch-Clamp Techniques; Pyrones; Sodium; Sodium Channels; Thrombin

In isolated, perfused adult rat hearts, global ischemia increased the phosphorylation of cAMP response element-binding protein (CREB) relative to control levels, and this phosphorylation was reversed with reperfusion. CREB phosphorylation elicited by 5 min of global ischemia was sensitive to treatments with the calcium-independent phospholipase A(2) (iPLA(2)) inhibitor bromoenol lactone (BEL) and occurred in the absence of increases in myocardial cAMP content. In contrast, CREB phosphorylation elicited by 15 min of global ischemia was likely mediated by elevated cAMP levels. The expression of c-fos, in response to brief myocardial ischemia, was also sensitive to BEL treatment. The induction of iPLA(2)-mediated CREB phosphorylation was further substantiated by the observations that lysoplasmenylcholine increased both the phosphorylation of CREB and the induction of c-fos expression in the absence and presence of BEL. CREB phosphorylation in both ischemic hearts and lysoplasmenylcholine-perfused hearts was inhibited by pretreatment of hearts with the specific cAMP-dependent protein kinase (PKA) inhibitor H-89. Taken together, these data demonstrate that iPLA(2) mediates CREB phosphorylation through a PKA-dependent pathway during brief periods of myocardial ischemia, possibly through the formation of lysophospholipids.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Biological Transport; Calcium; Cyclic AMP Response Element-Binding Protein; Lysophospholipids; Male; Myocardial Ischemia; Naphthalenes; Phospholipases A; Phosphorylation; Proto-Oncogene Proteins c-fos; Pyrones; Rats; Rats, Sprague-Dawley; RNA, Messenger

The aim of this study was to investigate whether cardiodepressant mediators are released after myocardial ischaemia during reperfusion.. Using a double heart model, the effect of the reoxygenated coronary effluent of an isolated guinea pig heart on a sequentially perfused second heart was studied under control conditions and after 10 min ischaemia of the first heart. Investigation of the modulating role of known autacoids took place by using free radical scavengers, an NO synthase inhibitor and adenosine receptor antagonists. In order to identify the chemical nature of cardiac metabolites, the coronary effluent was also subjected to different chemical treatment modes.. No haemodynamic changes were observed during sequential perfusion under control conditions. After 10 min of global ischaemia in heart I, a marked decrease in LVP (-22%), LVdP/dtmax (-43%), LVdP/dtmin (-41%) and coronary perfusion pressure (-25%) was measured in heart II during sequential perfusion. The negative inotropic effect was rapid in onset and reversible within 5 min; free radicals, nitric oxide and adenosine were not involved. Storage of the coronary effluent of the first heart up to 24 h, heating, or protease treatment did not modify its cardiodepressant effects on the second sequentially perfused heart.. These results suggest the release--from an isolated heart after ischaemia during reperfusion--of a cardiodepressant mediator which induces a potent reversible negative inotropic effect on a sequentially perfused heart. The mediator is stable and in all probability not a protein.

Topics: Adenosine Deaminase; Adrenergic beta-Antagonists; Animals; Autacoids; Catalase; Depression, Chemical; Female; Free Radical Scavengers; Guinea Pigs; Male; Metoprolol; Myocardial Contraction; Myocardial Ischemia; Myocardial Reperfusion; Myocardium; Naphthalenes; Nitric Oxide Synthase; Nitroarginine; Perfusion; Phospholipases A; Purinergic P1 Receptor Antagonists; Purinergic P2 Receptor Antagonists; Pyrones; Superoxide Dismutase; Theobromine; Xanthines

A myocardial calcium-independent PLA2 has been described that is activated during myocardial ischemia and this enzyme may modulate ATP-sensitive potassium channels (KATP). The aim of this study was to determine the effect of an inhibitor of this enzyme, a bromoenol lactone, in isolated globally ischemic rat hearts.. Isolated rat hearts were treated for 10 min with 0.3-6 microM bromoenol lactone and then subjected to 25 min ischemia and 30 min reperfusion.. The bromoenol lactone significantly increased coronary flow in nonischemic myocardium, and slightly reduced cardiac function at 6 microM. During global ischemia, time to contracture was significantly increased from vehicle group values in the presence of the bromoenol lactone (EC50 = 1.2 microM). During reperfusion, a concentration-dependent increase in function and a reduction in LDH release were observed for the PLA2 inhibitor. The concentrations of the PLA2 inhibitor which were significantly cardioprotective, inhibited this enzyme in membrane fractions of rat myocardium (IC50 = 0.87 microM). The KATP blocker sodium 5-hydroxydecanoate (5-HD) inhibited the increase in time to contracture observed for the bromoenol lactone. During reperfusion, 5-HD abolished the protective effects of the bromoenol lactone on cardiac function and LDH release. Glyburide had similar effects on the cardioprotective activity of the bromoenol lactone, although it only partially abolished the LDH reducing effect of this agent.. The bromoenol lactone protects ischemic myocardium at concentrations which also inhibit calcium-independent PLA2. This cardioprotection can be attenuated by blockers of KATP, suggesting a potential mechanism for modulation of myocardial KATP.

Topics: Animals; Anti-Arrhythmia Agents; Calcium; Coronary Circulation; Decanoic Acids; Dose-Response Relationship, Drug; Glyburide; Heart; Hydroxy Acids; In Vitro Techniques; L-Lactate Dehydrogenase; Male; Myocardial Contraction; Myocardial Ischemia; Myocardial Reperfusion Injury; Naphthalenes; Phospholipases A; Phospholipases A2; Pyrones; Rats; Rats, Sprague-Dawley; Sodium-Potassium-Exchanging ATPase