Progesterone activation of β₁-containing BK channels involves two binding sites

Area of Science:

• Neuroscience
• Molecular Biology
• Pharmacology

Background:

• Progesterone (≥1 µM) aids cerebral ischemia recovery, potentially via cerebrovascular dilation.
• The specific molecular targets of progesterone's cerebrovascular effects remain unidentified.
• Cerebrovascular smooth muscle cells express large-conductance calcium-activated potassium (BK) channels.

Purpose of the Study:

• To identify the molecular targets of progesterone action in cerebrovascular myocytes.
• To elucidate the mechanism by which progesterone activates BK channels.
• To investigate the role of BK channel regulatory subunits in progesterone-mediated cerebrovascular effects.

Main Methods:

• Electrophysiological recordings (e.g., patch-clamp) of mouse cerebrovascular myocytes and heterologous expression systems.
• Site-directed mutagenesis of BK channel α and β1/β4 regulatory subunits.
• In vivo and in vitro studies assessing cerebrovascular responses to progesterone and alcohol.

Main Results:

• Micromolar progesterone activates BK channels in mouse cerebrovascular myocytes, dependent on β1 and β4 subunits.
• Progesterone binds to conserved steroid binding sites on β1/β4 subunits, with distinct high-affinity and low-affinity sites.
• Mutations in key residues (Trp87, Tyr32, Trp163) of the β1 subunit abolish progesterone-induced channel activation and cerebrovascular dilation.

Conclusions:

• Progesterone activates cerebrovascular BK channels through a mechanism involving both high- and low-affinity binding sites on β1/β4 regulatory subunits.
• This activation is crucial for progesterone-mediated cerebrovascular dilation and recovery from cerebral ischemia.
• Progesterone counteracts alcohol-induced cerebrovascular constriction, suggesting therapeutic potential.