Extracellular hemin is a reverse use-dependent gating modifier of cardiac voltage-gated Na+ channels

Heme (Fe2+-protoporphyrin IX) is a well-known protein prosthetic group; however, heme and hemin (Fe3+-protoporphyrin IX) are also increasingly viewed as signaling molecules. Among the signaling targets are numerous ion channels, with intracellular-facing heme-binding sites modulated by heme and hemin in the sub-mu M range. Much less is known about extracellular hemin, which is expected to be more abundant, in particular after hemolytic insults. Here we show that the human cardiac voltage-gated sodium channel hNa(V)1.5 is potently inhibited by extracellular hemin (IC (50) approximate to 80 nM), while heme, dimethylhemin, and protoporphyrin IX are ineffective. Hemin is selective for hNa(V)1.5 channels: hNa(V)1.2, hNa(V)1.4, hNa(V)1.7, and hNa(V)1.8 are insensitive to 1 mu M hemin. Using domain chimeras of hNa(V)1.5 and rat rNa(V)1.2, domain II was identified as the critical determinant. Mutation N803G in the domain II S3/S4 linker largely diminished the impact of hemin on the cardiac channel. This profile is reminiscent of the interaction of some peptide voltage-sensor toxins with Na-V channels. In line with a mechanism of select gating modifiers, the impact of hemin on Na(V)1.5 channels is reversely use dependent, compatible with an interaction of hemin and the voltage sensor of domain II. Extracellular hemin thus has potential to modulate the cardiac function.

Automated summary

Hemin can potently inhibit the human cardiac voltage-gated sodium channel hNa(V)1.5, while being ineffective on other sodium channels. Its impact on hNa(V)1.5 channels is reversely use dependent, potentially modulating cardiac function by interacting with the voltage sensor of domain II.