CALCIUM SENSITIVITY OF BK-TYPE K-CA CHANNELS DETERMINED BY A SEPARABLE DOMAIN

High conductance, Ca2+-activated (BK-type) K+ channels from mouse (mSl o) and Drosophila (dSlo) differ in their functional properties but sha re a conserved core resembling voltage-gated K+ channels and a tail ap pended to the core by a nonconserved linker. We have found that the ch annel subunit is physically divisible into these two conserved domains and that the core determines such properties as channel open time, co nductance, and, probably, voltage dependence, whereas the tail determi nes apparent Ca2+ sensitivity. Both domains are required for function. We demonstrated the different roles of the core and tail by taking ad vantage of the functional differences between mSlo and dSlo. Heterolog ous pairing of cores and tails from mSlo and dSlo showed that single-c hannel properties were always characteristic of the core species, but that apparent Ca2+ sensitivity was adjusted up or down depending on th e species of the tail. Thus, the tail is implicated in the Ca2+ sensin g role of BK channels.