Calcium-activated SK potassium channels are key modulators of the pacemaker frequency in locus coeruleus neurons

The physiological, intrinsic activity of noradrenergic locus coeruleus (LC) neurons is important for the control of sleep/wakefulness, cognition and autonomous body functions. Dysregulations of the LC-noradrenergic network contribute to the pathogenesis of psychiatric disorders and are key findings in early stages of neurodegenerative diseases. Therefore, identifying ion channels mediating the intrinsic pacemaking mechanism of LC neurons, which is in turn directly coupled to Ca²⁺ homeostasis and cell survival signaling pathways, can help to foster our understanding of the vulnerability of these neurons in neurodegenerative diseases. Small-conductance Ca²⁺-activated K⁺ (SK) channels regulate the intrinsic firing patterns in different central neurons and are essential regulators of the intracellular Ca²⁺ homeostasis. However, the role of SK channels for the intrinsic pacemaking of LC neurons in mice is still unclear. Therefore we performed qPCR expression analysis as well as patch clamp recordings of in vitro brainstem slices, for instance testing SK channel blockers and activators like apamin and NS309, respectively. Although we found a transcriptional expression of SK1, SK2 and SK3 channels, SK2 was the predominantly expressed subunit in mouse LC neurons. Using perforated-patch clamp experiments, we found that SK channels are essential regulators of the intrinsic pacemaking of LC neurons, mediating a large fraction of the afterhyperpolarization (AHP) in these cells. Consistent with a previous observation that a concerted action of L- and T-type Cav channels is essential for the pacemaking of LC neurons, we found that SK channel activation, and the respective AHP amplitude, is primarily coupled to Ca²⁺ influx via these types of Ca²⁺ channels. Our study identified SK2 channels as drug targets for the tuning of the pacemaker frequency in disorders involving a dysregulation of the LC.