Closed state-coupled C-type inactivation in BK channels

Area of Science:

• Molecular biology
• Ion channel physiology
• Biophysics

Background:

• Potassium (K+) channels are crucial for regulating ion flow via pore gates.
• BK channels, unlike other K+ channels, lack a typical intracellular activation gate and C-type inactivation.
• This study investigates the gating mechanisms of BK channels.

Purpose of the Study:

• To test the hypothesis that BK channel activation and C-type inactivation gates overlap.
• To explore the relationship between BK channel activation/deactivation and C-type inactivation/recovery.
• To elucidate the gating properties of BK channels under specific conditions.

Main Methods:

• Induced C-type inactivation in BK channels using low extracellular K+ and specific mutations (Y294E/K/Q/S or Y279F).
• Studied BK channel gating dynamics, including activation, deactivation, inactivation, and recovery.
• Investigated the role of membrane potential, intracellular calcium ([Ca(2+)]i), and constitutively open mutations.

Main Results:

• Prominent slow C-type inactivation and recovery were observed in BK channels under specific conditions.
• BK channel C-type inactivation occurred during hyperpolarization or low [Ca(2+)]i and recovered with depolarization or high [Ca(2+)]i.
• Constitutively open mutations prevented C-type inactivation, indicating closed-state dependence.

Conclusions:

• BK channel C-type inactivation is closed-state dependent and inversely correlates with channel open probability.
• BK channel closing may represent an early conformational stage of C-type inactivation.
• The gating mechanism of BK channels differs significantly from canonical K+ channels.