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Involvement of Ca2+ in Signaling Mechanisms Mediating Muscarinic Inhibition of M Currents in Sympathetic Neurons
Journal article   Open access   Peer reviewed

Involvement of Ca2+ in Signaling Mechanisms Mediating Muscarinic Inhibition of M Currents in Sympathetic Neurons

Jin-Young Yoon and Won-Kyung Ho
Cellular and molecular neurobiology, Vol.43(5), pp.2257-2271
07/2023
DOI: 10.1007/s10571-022-01303-7
PMCID: PMC10287826
PMID: 36369494
url
https://doi.org/10.1007/s10571-022-01303-7View
Published (Version of record) Open Access

Abstract

Acetylcholine can excite neurons by suppressing M-type (KCNQ) potassium channels. This effect is mediated by M-1 muscarinic receptors coupled to the G(q) protein. Although PIP2 depletion and PKC activation have been strongly suggested to contribute to muscarinic inhibition of M currents (I-M), direct evidence is lacking. We investigated the mechanism involved in muscarinic inhibition of I-M with Ca2+ measurement and electrophysiological studies in both neuronal (rat sympathetic neurons) and heterologous (HEK cells expressing KCNQ2/KCNQ3) preparations. We found that muscarinic inhibition of I-M was not blocked either by PIP2 or by calphostin C, a PKC inhibitor. We then examined whether muscarinic inhibition of I-M uses multiple signaling pathways by blocking both PIP2 depletion and PKC activation. This maneuver, however, did not block muscarinic inhibition of I-M. Additionally, muscarinic inhibition of I-M was not prevented either by sequestering of G-protein beta gamma subunits from G(alpha)-transducin or anti-G(beta gamma) antibody or by preventing intracellular trafficking of channel proteins with blebbistatin, a class-II myosin inhibitor. Finally, we re-examined the role of Ca2+ signals in muscarinic inhibition of I-M. Ca2+ measurements showed that muscarinic stimulation increased intracellular Ca2+ and was comparable to the Ca2+ mobilizing effect of bradykinin. Accordingly, 20-mM of BAPTA significantly suppressed muscarinic inhibition of I-M. In contrast, muscarinic inhibition of I-M was completely insensitive to 20-mM EGTA. Taken together, these data suggest a role of Ca2+ signaling in muscarinic modulation of I-M. The differential effects of EGTA and BAPTA imply that Ca2+ microdomains or spatially local Ca2+ signals contribute to inhibition of I-M.
 Cell Biology Life Sciences & Biomedicine Neurosciences Neurosciences & Neurology Science & Technology

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