Nitrite as Direct S-Nitrosylating Agent of Kir2.1 Channels

Nitrite, a physiological nitric oxide (NO) storage form and an alternative way for NO generation, affects numerous biological processes through NO-dependent and independent pathways, including the S-nitrosylation of thiol-containing proteins. Mechanisms underlying these phenomena are not fully understood. The purpose of this study was to analyse in the rat heart (as prototype of mammalian heart) whether nitrite affects S-nitrosylation of cardiac proteins and the potential targets for S-nitrosylation. Rat hearts, perfused according to Langendorff, were exposed to nitrite. By Biotin Switch Method, we showed that nitrite treatment increased the degree of S-nitrosylation of a broad range of membrane proteins. Further analysis, conducted on subfractioned proteins, allowed us to identify a high level of nitrosylation in a small range of plasmalemmal proteins characterized by using an anti-Kir2.1 rabbit polyclonal antibody. We also verified that this effect of nitrite is preserved in the presence of the NO scavenger PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide). Our results suggest, for the first time, that nitrite represents a direct S-nitrosylating agent in cardiac tissues and that inward-rectifier potassium ion channels (Kir2.1) 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 also a direct modulator of important functional cardiac proteins.