Akt/eNOS signaling and PLN S-sulfhydration are involved in H2S-dependent cardiac effects in frog and rat

Hydrogen sulfide (H2S) has recently emerged as an important mediator of mammalian cardiovascular homeostasis. In nonmammalian vertebrates, little is known about the cardiac effects of H2S. This study aimed to evaluate, in the avascular heart of the frog, Rana esculenta, whether and to what extent H2S affects the cardiac performance, and what is the mechanism of action responsible for the observed effects. Results were analyzed in relation to those obtained in the rat heart, used as the mammalian model. Isolated and perfused (working and Langendorff) hearts, Western blot analysis, and modified biotin switch (S-sulfhydration) assay were used. In the frog heart, NaHS (used as H2S donor, 10(-12)/10(-7) M) dose-dependently decreased inotropism. This effect was reduced by glibenclamide (K-ATP channels blocker), N-G-monomethyl-L-arginine (NOS inhibitor), 1H-[1,2,4] oxadiazolo-[4,3-a]quinoxalin-1-one (guanylyl cyclase inhibitor), KT5823 (PKG inhibitor), and it was blocked by Akt1/2 (Akt inhibitor) and by detergent Triton X-100. In the rat, in addition to the classic negative inotropic effect, NaHS (10(-12)/10(-7) M) exhibited negative lusitropism. In both frog and rat hearts, NaHS treatment induced Akt and eNOS phosphorylation and an increased cardiac protein S-sulfhydration that, in the rat heart, includes phospholamban. Our data suggest that H2S represents a phylogenetically conserved cardioactive molecule. Results obtained on the rat heart extend the role of H2S also to cardiac relaxation. H2S effects involve K-ATP channels, the Akt/NOS-cGMP/PKG pathway, and S-sulfhydration of cardiac proteins.