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.