Nitrite, a physiological NO storage form and an alternative way for NO generation, affects numerous biological processes through NO-dependent and independent pathways (Bryan et al., 2005), including the S-nitrosylation of thiol-containing proteins (Foster et al., 2003). The purpose of this study was to analyse in the rat heart (as prototype of mammalian heart): i) whether S-nitrosylation is affected by nitrite; ii) the potential targets for protein S-nitrosylation.

Rat hearts, perfused according to Langendorff, were exposed to nitrite (10^­5M). By Biotin Switch Method, we showed that nitrite clearly increased the degree of S-nitrosylation of a broad range of membrane proteins. Further analysis, conducted on membrane fractions after protein subfractionation by linear concentration gradient of sucrose, showed a marked increase in S-nitrosylation after nitrite treatment in a small range of plasmalemmal proteins (45–50 kDa). The increment in S-nitrosylation at this location was identified using an anti-Kir2.1 rabbit polyclonal antibody. In addition, we verified that the effect of nitrite is preserved also in the presence of the NO scavenger P-TIO.

Our results suggest, for the first time, that nitrite represents a direct S-nitrosylating agent in cardiac tissues and, like NO, Kir2.1 channels are one of the targets. These observations are of relevance since they support the growing evidence that nitrite is not only a NO reserve but a direct cardiac modulator.