G-proteins and G-protein subunits mediating cholinergic inhibition of N-type calcium currents in sympathetic neurons.
One postsynaptic action of the transmitter acetylcholine in sympathetic ganglia is to inhibit somatic N-type Ca2+ currents: this reduces Ca2+-activated K+ currents and facilitates high-frequency spiking. Previous experiments on rat superior cervical ganglion neurons have revealed two distinct pathways for this inhibitory action: a rapid, voltage-dependent inhibition through activation of M4 muscarinic acetylcholine receptors (mAChRs), and a slower, voltage-independent inhibition via M1 mAChRs [Hille (1994) Trends in Neurosci., 17, 531-536]. We have analysed the mechanistic basis for this divergence at the level of the individual G-proteins and their alpha and betagamma subunits, using a combination of site-directed antibody injection, plasmid-driven antisense RNA expression, overexpression of selected constitutively active subunits, and antagonism of endogenously liberated betagamma subunits by over-expression of Dy-binding P-adrenergic receptor kinase 1 (PARK1) peptide. The results indicate that: (i) M4 mAChR-induced inhibition is mediated by GoA; (ii) a and Py subunits released from the activated GoA heterotrimer produce separate voltage-insensitive and voltage-sensitive components of inhibition, respectively; and (iii) voltage-insensitive M1 mAChR-induced inhibition is likely to be mediated by the alpha subunit of Gq. Hence, Ca2+ current inhibition results from the concerted, but independent actions of three different G-protein subunits.
Delmas
P
P
Wellcome Laboratory for Molecular Pharmacology, Department of Pharmacology, University College London, UK. ucklpds@ucl.ac.uk
Abogadie
F C
FC
Dayrell
M
M
Haley
J E
JE
Milligan
G
G
Caulfield
M P
MP
Brown
D A
DA
Buckley
N J
NJ
D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000166:cytology / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015220:Calcium Channels; D010446:Peptide Fragments; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D019204:GTP-Binding Proteins