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

ABSTRACT: 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-µM 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_V1.5 is potently inhibited by extracellular hemin (IC ₅₀ ≈ 80 nM), while heme, dimethylhemin, and protoporphyrin IX are ineffective. Hemin is selective for hNa_V1.5 channels: hNa_V1.2, hNa_V1.4, hNa_V1.7, and hNa_V1.8 are insensitive to 1 µM hemin. Using domain chimeras of hNa_V1.5 and rat rNa_V1.2, 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_V1.5 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.

SUBMITTER: Gessner G

PROVIDER: S-EPMC9661527 | biostudies-literature | 2022 Nov

REPOSITORIES: biostudies-literature

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

Gessner Guido G Jamili Mahdi M Tomczyk Pascal P Menche Dirk D Schönherr Roland R Hoshi Toshinori T Heinemann Stefan H SH

Biological chemistry 20220829 11-12

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-µM 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 car ...[more]

PMID: 36038266

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Project description:Propofol is widely used in the clinic for the induction and maintenance of general anesthesia. As with most general anesthetics, however, our understanding of its mechanism of action remains incomplete. Local and general anesthetics largely inhibit voltage-gated Na+ channels (Navs) by inducing an apparent stabilization of the inactivated state, associated in some instances with pore block. To determine the biophysical and molecular basis of propofol action in Navs, we investigated NaChBac and NavMs, two prokaryotic Navs with distinct voltage dependencies and gating kinetics, by whole-cell patch clamp electrophysiology in the absence and presence of propofol at clinically relevant concentrations (2-10 µM). In both Navs, propofol induced a hyperpolarizing shift of the pre-pulse inactivation curve without any significant effects on recovery from inactivation at strongly hyperpolarized voltages, demonstrating that propofol does not stabilize the inactivated state. Moreover, there was no evidence of fast or slow pore block by propofol in a non-inactivating NaChBac mutant (T220A). Propofol also induced hyperpolarizing shifts of the conductance-voltage relationships with negligible effects on the time constants of deactivation at hyperpolarized voltages, indicating that propofol does not stabilize the open state. Instead, propofol decreases the time constants of macroscopic activation and inactivation. Adopting a kinetic scheme of Nav gating that assumes preferential closed-state recovery from inactivation, a 1.7-fold acceleration of the rate constant of activation and a 1.4-fold acceleration of the rate constant of inactivation were sufficient to reproduce experimental observations with computer simulations. In addition, molecular dynamics simulations and molecular docking suggest that propofol binding involves interactions with gating machinery in the S4-S5 linker and external pore regions. Our findings show that propofol is primarily a positive gating modulator of prokaryotic Navs, which ultimately inhibits the channels by promoting activation-coupled inactivation.

Dataset Information

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

Publications

Extracellular hemin is a reverse use-dependent gating modifier of cardiac voltage-gated Na<sup>+</sup> channels.

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