Figure 1.

Biophysical properties conferred by BK β2 subunits and their effect on the adrenal chromaffin AP. (A) Example of β2-mediated inactivation of BK currents in adrenal chromaffin cells (blue trace). Noninactivating BK currents (orange trace) are shown for comparison. (B) Chromaffin cells with inactivating BK currents (β2-expressing cells) have G-V relations that are shifted to negative membrane potentials (blue trace) relative to β2 KO chromaffin cells (orange trace). (C) Theoretical effect of β2 on BK currents (blue trace) during a short time period (before inactivation occurs) as compared with BK channels lacking β subunits (orange trace). β2 “slow activation” reduces early BK channel recruitment. However, the negative shift of the G-V relations (“gating shift”) promotes a larger current activation than BK channels lacking β2. In addition, the β2 “slow deactivation” sustains BK current after repolarization more than BK channels lacking β2. (D) Comparison of adrenal chromaffin APs from an inactivating wild-type (blue trace) and β2 KO (orange trace) cell evoked by short current injection (150 pA, 5 ms). Theoretically, β2 slow activation allows a larger AP peak, whereas the gating shift and slow deactivation promote a faster repolarization and larger AHP. Example data from A, B, and D are taken from Martinez-Espinosa et al. (2014). C is a schematic based on data from Brenner et al. (2000).