The Journal of Neuroscience, May 15, 1999, 19(10):3739-3751
Roles of G-Protein 
, Arachidonic Acid, and Phosphorylation
in Convergent Activation of an S-Like Potassium Conductance by
Dopamine, Ala-Pro-Gly-Trp-NH2, and
Phe-Met-Arg-Phe-NH2
Hind
van Tol-Steye1, 2,
Johannes C.
Lodder1,
Huibert D.
Mansvelder1,
Rudi J.
Planta2,
Harm
van Heerikhuizen2, and
Karel S.
Kits1
Departments of 1 Neurophysiology, Research Institute
Neurosciences, and 2 Biochemistry and Molecular Biology,
Faculty of Chemistry, Vrije Universiteit, 1081 HV Amsterdam, The
Netherlands
Dopamine and the neuropeptides Ala-Pro-Gly-Trp-NH2
(APGWamide or APGWa) and Phe-Met-Arg-Phe-NH2 (FMRFamide or
FMRFa) all activate an S-like potassium channel in the light
green cells of the mollusc Lymnaea stagnalis,
neuroendocrine cells that release insulin-related peptides. We studied
the signaling pathways underlying the responses, the role of the
G-protein 
subunit, and the interference by phosphorylation
pathways. All responses are blocked by an inhibitor of arachidonic acid
(AA) release, 4-bromophenacylbromide, and by inhibitors of
lipoxygenases (nordihydroguaiaretic acid and AA-861) but not by
indomethacin, a cyclooxygenase inhibitor. AA and phospholipase
A2 (PLA2) induced currents with similar
I-V characteristics and potassium selectivity as
dopamine, APGWa, and FMRFa. PLA2 occluded the response to
FMRFa. We conclude that convergence of the actions of dopamine, APGWa,
and FMRFa onto the S-like channel occurs at or upstream of the level of
AA and that formation of lipoxygenase metabolites of AA is necessary to
activate the channel. Injection of a synthetic peptide, which interferes with G-protein subunits, inhibited the
agonist-induced potassium current. This suggests that subunits
mediate the response, possibly by directly coupling to a phospholipase.
Finally, the responses to dopamine, APGWa, and FMRFa were inhibited by activation of PKA and PKC, suggesting that the responses are
counteracted by PKA- and PKC-dependent phosphorylation. The
PLA2-activated potassium current was inhibited by
8-chlorophenylthio-cAMP but not by 12-O-tetradecanoylphorbol 13-acetate
(TPA). However, TPA did inhibit the potassium current induced by
irreversible activation of the G-protein using GTP--S. Thus, it
appears that PKA targets a site downstream of AA formation, e.g., the
potassium channel, whereas PKC acts at the active G-protein or the phospholipase.
Key words:
FMRFamide; dopamine; neuropeptide; K+-current; S-current; molluscs; arachidonic acid; G-protein subunits; neuron; signal transduction; convergence
Copyright © 1999 Society for Neuroscience 0270-6474/99/19103739-13$05.00/0
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