Calcium-activated channels open in response to

Calcium-activated channels open in response to

• A. Decreased intracellular Ca++
• B. Increased intracellular Ca++
• C. Decreased Na+
• D. Voltage-dependent gating only

Answer: (B)

Calcium-activated channels open when intracellular calcium rises. Calcium ions bind to the channel or its regulatory subunits and cause a conformational change that shifts the channel from closed to open, allowing ion flow. This direct Ca2+ binding links intracellular Ca2+ signals to changes in membrane conductance, which is why the trigger is an increase in intracellular Ca2+. A decrease in Ca2+ would not promote opening, and choices invoking Na+ changes or gating driven only by voltage describe different mechanisms (though some channels can be both voltage- and Ca2+-dependent, the Ca2+-trigger is the defining feature here).

Calcium-activated channels open when intracellular calcium rises. Calcium ions bind to the channel or its regulatory subunits and cause a conformational change that shifts the channel from closed to open, allowing ion flow. This direct Ca2+ binding links intracellular Ca2+ signals to changes in membrane conductance, which is why the trigger is an increase in intracellular Ca2+. A decrease in Ca2+ would not promote opening, and choices invoking Na+ changes or gating driven only by voltage describe different mechanisms (though some channels can be both voltage- and Ca2+-dependent, the Ca2+-trigger is the defining feature here).