Zn2+ Activates Human Large-Conductance Ca2+-Activated K+ Channel

Abstract

Zinc plays a crucial role as an integral structural and catalytic factor in many transcription factors and enzymes and this metal ion (Zn2+) is also increasingly recognized as a potential intracellular signaling molecule. However, the direct Zn2+ sensors especially those membrane localized are not fully established. Using inside-out patch clamp recording, we observed that heterologously expressed human large-conductance and voltage-and Ca2+-activated K+ (BKCa, Slo1 BK, or KCa1.1) channels were quickly and reversibly activated by intracellular Zn2+. Zn2+ did not affect the unitary conductance but significantly increased the channel open probability. Macroscopic current measurements showed that Zn2+-mediated activation of the channel was accompanied by a leftward shift of the conductance-voltage (G-V) curve by up to 75 mV. The effect of Zn2+ was antagonized by high concentrations of intracellular H+ or Ca2+, indicating the three factors activate BK channels via a common mechanism. Mutagenesis experiments showed that mutation of H365 to arginine, a critical residue for the channel activation by H+ and Ca2+, fully abolished the effect of Zn2+. In addition, mutation of two other nearby acidic residues D367 or E399 to alanine also partially impaired the effect of Zn2+. Collectively, our results suggest that a novel multifunctional structure located in the regulator of conductnace for K+ (RCK)1 domain is involved in Zn2+ coordination and activation of the Slo1 BK channel and indicate a potential role of Slo1 BK channel in Zn2+ signaling in both physiological condition and hypoxic/ischemic diseases in which [Zn2+]i is significantly increased. (Supported in part by NIH)