β2 subunit modulation of BK channels has opposing effects on excitability during constant current injection and spontaneous firing. BK/β2 channels support greater tonic firing during constant current injection (top left), whereas the β2 KO cells fire less frequently (not depicted) or fail to maintain spiking (bottom left). Spontaneous firing chromaffin neurons (top right) undergo burst firing after KO of β2 (bottom right). Traces are modified from Martinez-Espinosa et al. (2014).