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Regulation of a G protein‐gated inwardly rectifying K + channel by a Ca 2+ ‐independent protein kinase C
Author(s) -
Leaney Joanne L.,
Dekker Lodewijk V.,
Tinker Andrew
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.00367.x
Subject(s) - g protein , pertussis toxin , g protein coupled inwardly rectifying potassium channel , receptor , phospholipase c , protein kinase c , diacylglycerol kinase , stimulation , muscarinic acetylcholine receptor , gq alpha subunit , inhibitory postsynaptic potential , inward rectifier potassium ion channel , microbiology and biotechnology , ligand gated ion channel , biology , chemistry , signal transduction , ion channel , biochemistry , endocrinology
1 Members of the Kir3.0 family of inwardly rectifying K + channels are expressed in neuronal, atrial and endocrine tissues and play key roles in generating late inhibitory postsynaptic potentials (IPSPs), slowing heart rate and modulating hormone release. They are activated directly by G βγ subunits released in response to G i/o ‐coupled receptor stimulation. However, it is not clear to what extent this process can be dynamically regulated by other cellular signalling systems. In this study we have explored pathways activated by the G q/11 ‐coupled M 1 and M 3 muscarinic receptors and their role in the regulation of Kir3.1+3.2A neuronal‐type channels stably expressed in the human embryonic kidney cell line HEK293. 2 We describe a novel biphasic pattern of behaviour in which currents are initially stimulated but subsequently profoundly inhibited through activation of M 1 and M 3 receptors. This contrasts with the simple stimulation seen through activation of M 2 and M 4 receptors. 3 Channel stimulation via M 1 but not M 3 receptors was sensitive to pertussis toxin whereas channel inhibition through both M 1 and M 3 receptors was insensitive. In contrast over‐expression of the C‐terminus of phospholipase Cβ1 or a G q/11 ‐specific regulator of G protein signalling (RGS2) essentially abolished the inhibitory phase. 4 The inhibitory effects of M 1 and M 3 receptor stimulation were mimicked by phorbol esters and a synthetic analogue of diacylglycerol but not by the inactive phorbol ester 4αphorbol. Inhibition of the current by a synthetic analogue of diacylglycerol effectively occluded any further inhibition (but not activation) via the M 3 receptor. 5 The receptor‐mediated inhibitory phenomena occur with essentially equal magnitude at all intracellular calcium concentrations examined (range, 0‐669 n m ). 6 The expression of endogenous protein kinase C (PKC) isoforms in HEK293 cells was examined by immunoblotting, and their translocation in response to phorbol ester treatment by cellular extraction. The results indicated the expression and translocation of the novel PKC isoforms PKCδ and PKCε. 7 We also demonstrate that activation of such a pathway via both receptor‐mediated and receptor‐independent means profoundly attenuated subsequent channel stimulation by G i/o ‐coupled receptors. 8 Our data support a role for a Ca 2+ ‐independent PKC isoform in dynamic channel regulation, such that channel activity can be profoundly reduced by M 1 and M 3 muscarinic receptor stimulation.