No abstract

The effect of hydrogen peroxide (H2O2) on the sheep cardiac sarcoplasmic reticulum (SR) Ca(2+)-release channel has been investigated under voltage-clamp conditions after incorporation of native membrane vesicles into planar phospholipid bilayers. In the presence of micromolar activating calcium concentrations on the cytosolic side of the membrane, H2O2 (3-5 mM) increased open probability of the channels. H2O2 did not affect the conductance of the channel or the response to activating compounds, such as ATP and caffeine. H2O2 did not alter the inhibitory response to magnesium or the modification of channels by ryanodine. At subactivating calcium concentrations (approximately 45 pM) on the cytosolic side of the membrane, 5 mM H2O2 was still able to open the channel. Analysis of single-channel open and closed lifetimes suggested that H2O2 had a direct effect on the gating mechanism of the channel. Open probability of the SR Ca(2+)-release channel is reduced by millimolar concentrations of dithiothreitol, a sulfhydryl-protecting compound, in a concentration-dependent manner. In conclusion, it is probable that H2O2 activates the SR Ca(2+)-release channel via an oxidation of cysteine thiol groups in the channel protein.

under severe low-flow ischemia, myocardial NADPH levels can decrease despite the accumulation of NADH. The reduced myocardial capacity to maintain NADPH/NADP redox potential can result in thiol redox state changes. These abnormalities may have important consequences on cellular function and viability.

Our data show that the anti-oxidant activity of carvedilol is relevant for the maintenance of myocardium viability.

Adenosine protects myocardium from ischemia and reperfusion damage; however, the mechanism of action is still under discussion. We investigated whether (a) adenosine protects isolated crystalloid-perfused rabbit heart from ischemia/ reperfusion injury; (b) this action is receptor mediated and what receptor subtypes are involved, and (c) this action is dependent on an enhanced nitric oxide production. Our results showed a cardioprotective effect of adenosine (10(-4) M), of nonselective adenosine-receptor agonist 5'-N-ethyl-carboxamidoadenosine (NECA; 5 x 10(-6) M), and of A2A agonists CGS 21680 (10(-8) and 10(-6) M), 2-hexynylNECA (10(-7) M). On the contrary, A1 agonist CCPA (10(-8) and 10(-6) M) does not provide any protection. The effect has been achieved in terms of significant reduction in contracture development during reperfusion [diastolic pressure was 46.8 +/- 7.1 mm Hg (p < 0.01); 46.1 +/- 7.8 mm Hg (p < 0.01); 46.9 +/- 5.5 mm Hg (p < 0.01); and 59.3 +/- 6.7 mm Hg (p < 0.05) with 10(-4) M adenosine, 5 x 10(-6) M NECA, 10(-6) M CGS 21680, and 10(-7) M 2-hexynylNECA, respectively, versus 77.6 +/- 5.0 mm Hg in control]; reduced creatine phosphokinase release (13.5 +/- 1.6, 22.2 +/- 7.9, 14.2 +/- 3.3, and 14.1 +/- 4.5 U/gww in treated hearts vs. 34.6 +/- 7.2 U/gww in controls; p < 0.05); improved energy metabolism [adenosine triphosphate (ATP) content is 9.9 +/- 0.5, 10.4 +/- 0.6, 9.8 +/- 0.5, and 10.5 +/- 0.5 micromol/gdw in treated hearts vs. 7.6 +/- 0.2 micromol/gdw; p < 0.05]. Moreover, our data indirectly show a functional presence of A2A receptors on cardiomyocytes as the protection is A2A mediated and exerted only during reperfusion, although in the absence of blood and coronary flow changes. These activities appear independent of nitric oxide pathways, as adenosine and 2-hexynylNECA effects are not affected by the presence of a nitric oxide-synthase inhibitor (10(-4) M L-NNA).