Nav1.3 KO cells exhibit either of two forms of spontaneous electrical activity . (A) Spontaneous firing is illustrated for a WT CC recording by using the perforated patch method. Right trace shows faster time base examples of individual APs. (B) From the cell in A, the indicated voltage protocol was used to activate BK current, highlighting the inactivating nature of the current following a 50-ms depolarization to 0 mV to elevated cytosolic Ca²⁺ (Solaro et al., 1995). On the right, a faster time base example of the transient inward current immediately following depolarization to 0 mV is shown. (C) Spontaneous firing in an Nav1.3 KO cell at two different time bases. Peak AP amplitude is markedly reduced compared with WT cells, which is consistent with the role of voltage-dependent Cav channels in APs during blockade of Nav current (Vandael et al., 2015). (D) For the Nav1.3 KO cell in C, the Ca-loading protocol resulting in the activation of inactivating BK current, but no indication of any fast inactivating inward current (right trace). (E) Spontaneous slow wave burst firing in another Nav1.3 KO cell. (F) The Ca-loading protocol for the cell in E results in the activation of noninactivating BK current. Little or no inward current was observed during the initial step to 0 mV. The tendency of cells lacking inactivating BK channels to exhibit spontaneous slow wave bursts has been previously noted (Martinez-Espinosa et al., 2014).