Abstract
Intracellular pH (pH(i)) is an important endogenous modulator of cardiac function. Inhibition of Na(+)/H(+) exchanger-1 (NHE-1) protects the heart by preventing Ca(2+) overload during ischemia/reperfusion. Hydrogen sulfide (H(2)S) has been reported to produce cardioprotection. The present study was designed to investigate the pH regulatory effect of H(2)S in rat cardiac myocytes and evaluate its contribution to cardioprotection. It was found that sodium hydrosulfide (NaHS), at a concentration range of 10 to 1000 μM, produced sustained decreases in pH(i) in the rat myocytes in a concentration-dependent manner. NaHS also abolished the intracellular alkalinization caused by trans-(±)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide methane-sulfonate hydrate (U50,488H), which activates NHEs. Moreover, when measured with an NHCl(4) prepulse method, NaHS was found to significantly suppress NHE-1 activity. Both NaHS and cariporide or [5-(2-methyl-5-fluorophenyl)furan-2-ylcarbonyl]guanidine (KR-32568), two NHE inhibitors, protected the myocytes against ischemia/reperfusion injury. However, coadministration of NaHS with KR-32568 did not produce any synergistic effect. Functional study showed that perfusion with NaHS significantly improved postischemic contractile function in isolated rat hearts subjected to ischemia/reperfusion. Blockade of phosphoinositide 3-kinase (PI3K) with 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), Akt with Akt VIII, or protein kinase G (PKG) with (9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-methoxy-2,9-dimethyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]]enzodiazocine-10-carboxylic acid, methyl ester (KT5823) significantly attenuated NaHS-suppressed NHE-1 activity and/or NaHS-induced cardioprotection. Although KT5823 failed to affect NaHS-induced Akt phosphorylation, Akt inhibitor did attenuate NaHS-stimulated PKG activity. In conclusion, this work demonstrated for the first time that H(2)S produced cardioprotection via the suppression of NHE-1 activity involving a PI3K/Akt/PKG-dependent mechanism.
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