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Heme is a carbon monoxide receptor for large-conductance Ca2+-activated K+ channels.

ABSTRACT: Carbon monoxide (CO) is an endogenous paracrine and autocrine gaseous messenger that regulates physiological functions in a wide variety of tissues. CO induces vasodilation by activating arterial smooth muscle large-conductance Ca2+-activated potassium (BK(Ca)) channels. However, the mechanism by which CO activates BK(Ca) channels remains unclear. Here, we tested the hypothesis that CO activates BK(Ca) channels by binding to channel-bound heme, a BK(Ca) channel inhibitor, and altering the interaction between heme and the conserved heme-binding domain (HBD) of the channel alpha subunit C terminus. Data obtained using thin-layer chromatography, spectrophotometry, mass spectrometry (MS), and MS-MS indicate that CO modifies the binding of reduced heme to the alpha subunit HBD. In contrast, CO does not alter the interaction between the HBD and oxidized heme (hemin), to which CO cannot bind. Consistent with these findings, electrophysiological measurements of native and cloned (cbv) cerebral artery smooth muscle BK(Ca) channels show that CO reverses BK(Ca) channel inhibition by heme but not by hemin. Site-directed mutagenesis of the cbv HBD from CKACH to CKASR abolished both heme-induced channel inhibition and CO-induced activation. Furthermore, on binding CO, heme switches from being a channel inhibitor to an activator. These findings indicate that reduced heme is a functional CO receptor for BK(Ca) channels, introduce a unique mechanism by which CO regulates the activity of a target protein, and reveal a novel process by which a gaseous messenger regulates ion channel activity.

SUBMITTER: Jaggar JH

PROVIDER: S-EPMC1415201 | biostudies-literature | 2005 Oct

REPOSITORIES: biostudies-literature

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Heme is a carbon monoxide receptor for large-conductance Ca2+-activated K+ channels.

Jaggar Jonathan H JH Li Anlong A Parfenova Helena H Liu Jianxi J Umstot Edward S ES Dopico Alejandro M AM Leffler Charles W CW

Circulation research 20050915 8

Carbon monoxide (CO) is an endogenous paracrine and autocrine gaseous messenger that regulates physiological functions in a wide variety of tissues. CO induces vasodilation by activating arterial smooth muscle large-conductance Ca2+-activated potassium (BK(Ca)) channels. However, the mechanism by which CO activates BK(Ca) channels remains unclear. Here, we tested the hypothesis that CO activates BK(Ca) channels by binding to channel-bound heme, a BK(Ca) channel inhibitor, and altering the intera ...[more]

PMID: 16166559

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Project description:The Ca2+-dependent gating mechanism of large-conductance calcium-activated K+ (BK) channels from cultured rat skeletal muscle was examined from low (4 microM) to high (1,024 microM) intracellular concentrations of calcium (Ca2+i) using single-channel recording. Open probability (Po) increased with increasing Ca2+i (K0. 5 11.2 +/- 0.3 microM at +30 mV, Hill coefficient of 3.5 +/- 0.3), reaching a maximum of approximately 0.97 for Ca2+i approximately 100 microM. Increasing Ca2+i further to 1,024 microM had little additional effect on either Po or the single-channel kinetics. The channels gated among at least three to four open and four to five closed states at high levels of Ca2+i (>100 microM), compared with three to four open and five to seven closed states at lower Ca2+i. The ability of kinetic schemes to account for the single-channel kinetics was examined with simultaneous maximum likelihood fitting of two-dimensional (2-D) dwell-time distributions obtained from low to high Ca2+i. Kinetic schemes drawn from the 10-state Monod-Wyman-Changeux model could not describe the dwell-time distributions from low to high Ca2+i. Kinetic schemes drawn from Eigen's general model for a ligand-activated tetrameric protein could approximate the dwell-time distributions but not the dependency (correlations) between adjacent intervals at high Ca2+i. However, models drawn from a general 50 state two-tiered scheme, in which there were 25 closed states on the upper tier and 25 open states on the lower tier, could approximate both the dwell-time distributions and the dependency from low to high Ca2+i. In the two-tiered model, the BK channel can open directly from each closed state, and a minimum of five open and five closed states are available for gating at any given Ca2+i. A model that assumed that the apparent Ca2+-binding steps can reach a maximum rate at high Ca2+i could also approximate the gating from low to high Ca2+i. The considered models can serve as working hypotheses for the gating of BK channels.

Dataset Information

Heme is a carbon monoxide receptor for large-conductance Ca2+-activated K+ channels.

Publications

Heme is a carbon monoxide receptor for large-conductance Ca2+-activated K+ channels.

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