BK Channel Gating-Ring Voltage Dependence Motions

Abstract

The open probability of Large Conductance Voltage and Calcium dependent potassium (BK) channels is regulated allosterically by change in the transmembrane voltage and intracellular concentration of divalent ions (Ca2+ and Mg2+). BK channels are formed as tetramers of alpha subunits. The “divalent sensor” resides within the gating-ring, a large tetrameric structure formed by eight Regulator of Conductance of Potassium (RCK) domains, two from each subunit. Each RCK domain (RCK1 and RCK2) contains a high affinity- Ca2+binding site. Using Patch-clamp fluorometry, we have shown large changes in FRET signals within the gating-ring in response to Ca2+ and voltage. Here we investigate the origins of the voltage dependent motions. We tested manipulations that mostly change the BK channels’ relative probability of opening and in all cases the voltage dependence of the FRET signals remained within the voltage range of wild-type. However, mutations in the voltage sensor that are known to shift the charge displacement currents have a parallel shift of the gating ring's motions. These result suggest that the conformational changes of the gating ring are coupled to the voltage sensor, and could be relevant in the allosteric modulation of the BK channels.