Abstract
Although many G-protein-coupled neurotransmitter receptors are potentially capable of modulating both voltage-dependent Ca(2+) channels (I(Ca)) and G-protein-gated K(+) channels (I(GIRK)), there is a substantial degree of selectivity in the coupling to one or other of these channels in neurons. Thus, in rat superior cervical ganglion (SCG) neurons, M(2) muscarinic acetylcholine receptors (mAChRs) selectively activate I(GIRK) whereas M(4) mAChRs selectively inhibit I(Ca). One source of selectivity might be that the two receptors couple preferentially to different G-proteins. Using antisense depletion methods, we found that M(2) mAChR-induced activation of I(GIRK) is mediated by G(i) whereas M(4) mAChR-induced inhibition of I(Ca) is mediated by G(oA). Experiments with the beta gamma-sequestering peptides alpha-transducin and beta ARK1(C-ter) indicate that, although both effects are mediated by G-protein beta gamma subunits, the endogenous subunits involved in I(GIRK) inhibition differ from those involved in I(Ca) inhibition. However, this pathway divergence does not result from any fundamental selectivity in receptor-G-protein-channel coupling because both I(GIRK) and I(Ca) modulation can be rescued by heterologously expressed G(i) or G(o) proteins after the endogenously coupled alpha-subunits have been inactivated with Pertussis toxin (PTX). We suggest instead that the divergence in the pathways activated by the endogenous mAChRs results from a differential topographical arrangement of receptor, G-protein and ion channel.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Calcium Channels / drug effects
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Calcium Channels / metabolism
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Carbachol / pharmacology
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Cells, Cultured
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Cyclic AMP-Dependent Protein Kinases / genetics
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G Protein-Coupled Inwardly-Rectifying Potassium Channels
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GTP-Binding Protein alpha Subunits, Gi-Go / drug effects
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GTP-Binding Protein alpha Subunits, Gi-Go / genetics
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GTP-Binding Protein alpha Subunits, Gi-Go / metabolism*
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GTP-Binding Proteins / drug effects
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GTP-Binding Proteins / genetics
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GTP-Binding Proteins / metabolism*
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Ganglia, Sympathetic / cytology
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Ganglia, Sympathetic / drug effects
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Ganglia, Sympathetic / metabolism*
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Immunohistochemistry
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Male
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Membrane Potentials / drug effects
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Membrane Potentials / physiology
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Mutation / drug effects
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Mutation / physiology
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Neurons / cytology
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Neurons / drug effects
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Neurons / metabolism*
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Norepinephrine / pharmacology
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Pertussis Toxin*
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Potassium Channels / agonists
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Potassium Channels / drug effects
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Potassium Channels / genetics
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Potassium Channels / metabolism*
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Potassium Channels, Inwardly Rectifying*
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RNA, Antisense / pharmacology
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Rats
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Rats, Sprague-Dawley
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Receptor, Muscarinic M2
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Receptor, Muscarinic M4
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Receptors, Adrenergic, alpha-2 / drug effects
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Receptors, Adrenergic, alpha-2 / metabolism
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Receptors, Muscarinic / drug effects
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Receptors, Muscarinic / metabolism
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Transducin / genetics
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Virulence Factors, Bordetella / pharmacology*
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beta-Adrenergic Receptor Kinases
Substances
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Calcium Channels
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G Protein-Coupled Inwardly-Rectifying Potassium Channels
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Potassium Channels
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Potassium Channels, Inwardly Rectifying
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RNA, Antisense
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Receptor, Muscarinic M2
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Receptor, Muscarinic M4
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Receptors, Adrenergic, alpha-2
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Receptors, Muscarinic
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Virulence Factors, Bordetella
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Carbachol
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Pertussis Toxin
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Cyclic AMP-Dependent Protein Kinases
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beta-Adrenergic Receptor Kinases
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GTP-Binding Proteins
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GTP-Binding Protein alpha Subunits, Gi-Go
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Transducin
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Norepinephrine