Ca2+-activated KCa3.1 potassium channels contribute to the slow afterhyperpolarization in L5 neocortical pyramidal neurons

Abstract

Layer 5 neocortical pyramidal neurons are known to display slow Ca 2+ -dependent afterhyperpolarization (sAHP) after bursts of spikes, which is similar to the sAHP in CA1 hippocampal cells. However, the mechanisms of sAHP in the neocortex remain poorly understood. Here, we identified the Ca 2+ -gated potassium KCa3.1 channels as contributors to sAHP in ER81-positive neocortical pyramidal neurons. Moreover, our experiments strongly suggest that the relationship between sAHP and KCa3.1 channels in a feedback mechanism underlies the adaptation of the spiking frequency of layer 5 pyramidal neurons. We demonstrated the relationship between KCa3.1 channels and sAHP using several parallel methods: electrophysiology, pharmacology, immunohistochemistry, and photoactivatable probes. Our experiments demonstrated that ER81 immunofluorescence in layer 5 co-localized with KCa3.1 immunofluorescence in the soma. Targeted Ca 2+ uncaging confirmed two major features of KCa3.1 channels: preferential somatodendritic localization and Ca 2+ -driven gating. In addition, both the sAHP and the slow Ca 2+ -induced hyperpolarizing current were sensitive to TRAM-34, a selective blocker of KCa3.1 channels.

The Molecular Basis for the Calcium-Dependent Slow Afterhyperpolarization in CA1 Hippocampal Pyramidal Neurons

“…The latter findings are also emphasized by differences between CA1 pyramidal and cerebellar Purkinje cells, in that bath application of even 100 nM TRAM-34 rapidly blocked an IK-mediated sAHP in Purkinje cells (Engbers et al, 2012) compared to a relatively slower block of the CA1 cell sAHP by bath applied 1 µM TRAM-34 (King et al, 2015). Importantly, a block of the sAHP by TRAM-34 has now been repeated in CA1 pyramidal cells and neocortical pyramidal cells (Sahu et al, 2017(Sahu et al, , 2019Tiwari et al, 2018Tiwari et al, , 2019Roshchin et al, 2020), lending support for the effects of TRAM-34. A specific role for IK channels in pilocarpine-induced epileptic discharge was also reported (Tiwari et al, 2019).…”

Diversity and Functional Features of Calcium-Dependent Potassium Channels as Determinants of Their Role in the Plasticity of Cerebral Neurons

“…1, b) are es in the intensity of adaptation of spike discharges in these neurons [Groh et al, 2010;Guan et al, 2015]. It is interesting that neurons in neocortex layer 5 expressing IK channels/Kv2.2 channels and having a slow afterhyperpolarization phase [Bishop et al, 2015;Roshchin et al, 2020] differ in terms of the sign of their plasticity from non-expressing neurons in this same layer: in IK + /Kv2.2 + mice, neurons show depression associated with removal of the whiskers and do not demonstrate potentiation [Jacob et al, 2012].…”

“…SK and IK channels can be activated by increased intracellular calcium independently of membrane depolarization and action potentials, which distinguishes these channels from voltage-activated channels in experimental conditions [Roshchin et al, 2020]. Specifi c blockers can be used for physiological characterization of these channels in neurons (Fig.…”

“…1, c). However, production of action potentials in normal conditions is always accompanied by transient increases in calcium, so one of the most notable properties of SKand IK-type channels is their involvement in prolonged afterhyperpolarization, which follows the rapid afterhyperpolarization induced by voltage-dependent channels [King et al, 2015;Roshchin et al, 2020].…”

“…Recent studies have shown that the important property of adaptation in neocortex layer 5 pyramidal neurons depends on the afterhyperpolarization mediated by IK (KCa3.1) channels [Roshchin et al, 2020]. The existence of slow afterhyperpolarization correlates strictly with increas-the mechanisms of plasticity was supported by the Russian Science Foundation .…”