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βγ dimers derived from G o and G i proteins contribute different components of adrenergic inhibition of Ca 2+ channels in rat sympathetic neurones
Author(s) -
Delmas Patrick,
Abogadie Fe C.,
Milligan Graeme,
Buckley Noel J.,
Brown David A.
Publication year - 1999
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.1469-7793.1999.0023r.x
Subject(s) - pertussis toxin , depolarization , g protein , endocrinology , medicine , gi alpha subunit , biophysics , protein kinase a , biology , microbiology and biotechnology , chemistry , signal transduction , phosphorylation
1 Using perforated‐patch recordings, we have examined the part played by endogenous G‐protein subunits in the α 2 ‐adrenoceptor‐mediated inhibition of N‐type Ca 2+ currents in sympathetic neurones. 2 Two components of I Ca inhibition by noradrenaline were recorded: a prominent, high affinity and voltage‐dependent pertussis toxin (PTX)‐sensitive pathway and a minor, low affinity and mostly voltage‐insensitive PTX‐resistant pathway. 3 PTX‐sensitive inhibition was reduced by microinjection of antibodies against either Gα oA,B or Gα i1,2 . The voltage‐dependent fraction of inhibition was reduced by anti‐Gα o but not by anti‐Gα i antibody. 4 Antisense depletion of Gα oA led to a marked reduction of noradrenaline‐induced inhibition and voltage dependence. By contrast, Gα i depletion attenuated noradrenergic modulation without affecting the voltage dependence. 5 Expression of the βγ‐binding agents β‐adrenergic receptor kinase 1 (C‐terminus, βARK1 C‐ter ) or Gα i1 with a Cys3 to Ser mutation partially prevented noradrenergic inhibition while α‐transducin abolished it. Residual inhibition was mostly voltage independent in cells expressing βARK1 C‐ter but was strongly reversed by depolarization in Gα i1 Cys3Ser‐expressing cells. 6 Expression of the PTX‐resistant Gα i1 Cys351Ile mutant in cells treated with PTX restored α 2 ‐adrenoceptor inhibition. This restored inhibition was weakly reversed by depolarization. Both the degree and voltage dependence of inhibition were correlated with the level of expression of the Gα i1 Cys351Ile subunit. 7 Our findings identify βγ dimers associated with Gα oA and Gα i as mediators of the PTX‐sensitive α 2 ‐adrenoceptor‐mediated inhibition of N‐type Ca 2+ channels. Different βγ combinations may account for the differential voltage‐dependent effects of G o and G i on I Ca .