Membrane stretch and cytoplasmic Ca2+ independently modulate stretch-activated BK channel activity

Area of Science:

• Biophysics
• Molecular Biology
• Cardiovascular Physiology

Background:

• Large conductance Ca(2+)-activated K(+) (BK) channels are crucial for cellular signaling, responding to Ca(2+), Mg(2+), and membrane potential changes.
• Previous studies identified a chick heart BK channel (SAKCaC) activated by membrane stretch.
• SAKCaC activity is allosterically regulated by both membrane stretch and intracellular Ca(2+) via the gating ring complex linker.

Purpose of the Study:

• To investigate the interaction between membrane stretch and intracellular Ca(2+) in regulating SAKCaC channel activity.
• To elucidate the independent contributions of mechanosensitivity and Ca(2+) sensitivity to SAKCaC function.

Main Methods:

• Molecular cloning and functional characterization of the SAKCaC channel.
• Site-directed mutagenesis to disrupt Ca(2+) binding (Ca(2+) bowl) and mechanosensing (STREX) domains.
• Electrophysiological recordings to assess channel activity under varying stretch and Ca(2+) conditions.

Main Results:

• SAKCaC channels were activated by stretch force even without cytoplasmic Ca(2+).
• Disruption of the Ca(2+) bowl reduced Ca(2+)-dependent activation but preserved mechanosensitivity.
• Abolition of the STREX domain eliminated mechanosensitivity while maintaining Ca(2+) sensitivity.

Conclusions:

• Membrane stretch and intracellular Ca(2+) act as independent modulators of SAKCaC channel activity.
• Distinct structural elements mediate Ca(2+) and stretch activation, suggesting separate gating principles.
• SAKCaC exhibits a dual gating mechanism allowing for independent regulation by mechanical and chemical signals.