Species-Specific PKC Activation of IK S Channels

Abstract

Calcium activated potassium channels (IKs) is a slow activating potassium channel that is one of the main channels controlling cardiac repolarization. The IKs channel is formed by a pore subunit, KCNQ1 and an auxiliary subunit, KCNE1. These can be modulated by two different secondary messenger kinase proteins, PKA and PKC. Previous reports have suggested that activation of PKC decreases the IKs current in mice, while in humans, PKC activation increases the IKs current. However the detailed mechanism underlying this species-different regulation of IKs by PKC is not known. Here, we expressed the channel in Xenopus oocytes by injecting them with RNA encoding for the rat and human KCNQ1 and KCNE1 subunits. In addition, the muscarinic receptor (M1), a Gq-protein coupled receptor which downstream signaling activates PKC, was also expressed. We used two-electrode voltage clamp techniques to measure channel current. We measured the effect of PKC on both channel ability to conduct current and voltage to activate the channel by measuring the maximal channel conductance (Gmax) and the voltage that activates half of the maximal current (V1/2), respectively. Our results shows that upon short acetylcholine stimulation, human IKs channels show an increase in Gmax and a shift in V1/2 whereas rat channels exhibit a shift in V1/2 without Gmax changes. Finally, prolonged acetylcholine stimulation abolished Gmax increase on human channels whereas decreases it on rat channels. Thus, understanding of the PKC regulation of human IKs current as compared with other species, may allow the development of specific drugs to control cardiac rhythm pathologies.