Increased sensitivity to damaging effects of hypoxia and anoxia of isolated hearts from rats after prolonged exposure to ethanol: apparent protection by nitrendipine

Acute ethanol induces apoptosis by stimulating TRPC6 via elevation of superoxide in oxygenated podocytes

Our recent studies indicate that hydrogen peroxide (H2O2) only at high concentrations can cause oxidative stress in renal epithelial cells and induce apoptosis of podocytes. Consistently, the present study shows that H2O2, even at 1 mM, failed to induce intracellular oxidative stress and apoptosis of the podocytes due to efficient activity of catalase, an enzyme which degrades H2O2 to produce water and oxygen (O2). However, H2O2 acted as a source of O2 to allow acute ethanol to induce superoxide production and cause apoptosis of the podocytes. In contrast, acute ethanol alone did not elevate intracellular superoxide, even though it stimulates expression and translocation of p47phox to the plasma membrane. Inhibition of catalase abolished not only O2 production from H2O2 degradation, but also NOX2-dependent superoxide production in the podocytes challenged by both H2O2 and acute ethanol. In parallel, acute ethanol in the presence of H2O2, but neither ethanol nor H2O2 alone, stimulated transient receptor potential canonical 6 (TRPC6) channels and caused TRPC6-dependent elevation of intracellular Ca2+. These data suggest that exogenous H2O2 does not induce oxidative stress due to rapid degradation to produce O2 in the podocytes, but the oxygenated podocytes become sensitive to acute ethanol challenge and undergo apoptosis via a TRPC6-dependent elevation of intracellular Ca2+. Since cultured podocytes are considered in hypoxic conditions, H2O2 may be used as a source of O2 to establish an ischemia-reperfusion model in some type of cultured cells in which H2O2 does not directly induce intracellular oxidative stress.

Mechanisms of myocardial protection produced by chronic ethanol consumption

Recent evidence suggests that chronic ingestion of small quantities of ethanol may protect myocardium from ischemic injury by activating many of the endogenous signal transduction elements that have been implicated during other forms of preconditioning. Studies conducted in a variety of animal models in vitro and in vivo have indicated that chronic ethanol consumption improves functional recovery after global ischemia, reduces biochemical markers of ischemic injury, and decreases myocardial infarct size. Many of these beneficial actions appear to occur independent of alterations in systemic and coronary hemodynamics and transmural myocardial perfusion. To date, adenosine type 1 (A(1)) receptors, alpha(1)-adrenoceptors, the epsilon isoform of protein kinase C (PKC), and adenosine triphosphate-dependent potassium (K(ATP)) channels have been shown to mediate cardioprotection associated with chronic ethanol ingestion. These data suggest another mechanism by which chronic, intermittent consumption of ethanol may reduce overall cardiovascular mortality, decrease the incidence of coronary artery disease, and improve survival after myocardial infarction in humans. In this brief review, we discuss current evidence supporting a role for endogenous signaling in chronic ethanol-induced myocardial protection against ischemic injury.

Damaging effects of the calcium paradox are reduced in isolated hearts from ethanol-dependent rats: paradoxic effects of dihydropyridine drugs

Previous experiments showed that isolated hearts from ethanol-exposed rats show a marked increase in sensitivity to anoxic myocardial damage, and we suggested that this may be due to excess calcium entry through L-type voltage-operated calcium channels (L-VOCCs). To challenge this hypothesis, we investigated the effect of ethanol treatment ex vivo on a damaging stimulus, the "calcium paradox," which is associated with removal of calcium from the perfusate. Adult male Sprague-Dawley rats were exposed to intoxicating concentrations of ethanol for 6-10 days by inhalation. Isolated hearts from these animals were perfused with Krebs-Henseleit buffer by using a modified Langendorff technique, and the calcium paradox induced by a 10-min period of perfusion with calcium-free buffer, followed by reperfusion with calcium-containing buffer. Compared with controls, hearts from ethanol-exposed rats were significantly protected against myocardial damage, as shown by a marked reduction in release of intracellular proteins (lactate dehydrogenase, creatine phosphokinase, and myoglobin) during the reperfusion phase. These indices of myocardial damage were modified by the presence of the dihydropyridine (DHP) calcium channel antagonist nitrendipine (10(-6) M) and the DHP L-VOCC activator Bay K 8644 (10(-7) M) in the perfusate during the calcium paradox. Paradoxically, both drugs appeared to increase the damaging effects of calcium-free perfusion, with this effect being generally greater in the preparations from ethanol-exposed rats. As a result, the difference between these hearts and those from control rats was reduced, although a significant degree of protection against the calcium paradox remained. The results support the hypothesis that long-term exposure to ethanol in vivo produces marked alterations in the toxic effects of changes in myocardial calcium concentration. The increased sensitivity to DHP drugs of isolated hearts from ethanol-treated rats is consistent with previous experiments showing increased DHP radioligand-binding sites in these tissues.