Hydrogen sulfide inhibits human BK(Ca) channels

Area of Science:

• Physiology
• Molecular Biology
• Biochemistry

Background:

• Hydrogen sulfide (H2S) is an endogenous signaling molecule produced in mammalian cells.
• H2S has various molecular targets, including ion channels.
• The large conductance, calcium-sensitive potassium channel (BKCa) is crucial for carotid body glomus cell excitability and oxygen sensitivity.

Purpose of the Study:

• To investigate the effects of H2S on the BKCa channel.
• To compare the modulatory effects of H2S and carbon monoxide (CO) on BKCa channels.
• To determine if the carotid body has the endogenous capacity to produce H2S.

Main Methods:

• HEK 293 cells stably expressing the human BKCa channel alpha subunit were used.
• Patch-clamp electrophysiology in the inside-out configuration was employed.
• RT-PCR and immunohistochemistry were used to detect H2S-producing enzymes.

Main Results:

• H2S inhibited BKCa channels in a concentration-dependent manner (IC50 ≈ 670µM).
• H2S decreased BKCa channel open state probability and shifted activation voltage, opposing CO's effects.
• H2S and CO exhibited non-competitive inhibition, with KCN blocking CO but not H2S effects.
• mRNA for H2S-producing enzymes were found in HEK 293 cells and rat carotid bodies.
• Cystathionine-gamma-lyase was localized to glomus cells in the carotid body.

Conclusions:

• H2S and CO exert opposing effects on BKCa channels.
• These gases likely act through separate mechanisms and bind to different sites on the BKCa alpha subunit.
• The carotid body possesses the endogenous machinery to produce H2S, suggesting a role in modulating its activity.