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Phosphorylation‐ and voltage‐dependent inhibition of neuronal calcium currents by activation of human D 2(short) dopamine receptors
Author(s) -
Brown Nicola A.,
Seabrook Guy R.
Publication year - 1995
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1995.tb16355.x
Subject(s) - chemistry , okadaic acid , quinpirole , pertussis toxin , endocrinology , medicine , g protein , calcium , biophysics , receptor , dopamine receptor d2 , biochemistry , phosphatase , phosphorylation , biology , organic chemistry
1 Activation of human D 2(8) dopamine receptors with quinpirole (10 n M ) inhibits ω‐conotoxin GVIa‐sensitive, high‐threshold calcium currents when expressed in differentiated NG108‐15 cells (55% inhibition at +10 mV). This inhibition was made irreversible following intracellular dialysis with the non‐hydrolysable guanosine triphosphate analogue GTP‐γ‐S (100 μ M ), and was prevented by pretreatment with pertussis toxin (1 μg ml −1 for 24 h). 2 Stimulation of protein kinase C with the diacylglycerol analogue, 1‐oleoyl‐2‐acetyl‐sn‐glycerol (100 μ M ), also attenuated the inhibition of the sustained calcium current but did not affect the receptor‐mediated decrease in rate of current activation. Similarly, okadaic acid (100 n M ), a protein phosphatase 1/2A inhibitor, selectively occluded the inhibition of the sustained current. 3 The depression of calcium currents by quinpirole (10 n M ) was enhanced following intracellular dialysis with 100 μ M cyclic adenosine monophosphate (cyclic AMP, 72.8 ±9.8% depression), but was not mimicked by the membrane permeant cyclic GMP analogue, Sp‐8‐bromoguanosine‐3′, 5′:cyclic monophosphorothioate (100 μ M ). 4 Inhibition of calcium currents was only partly attenuated by 100 ms depolarizing prepulses to +100 mV immediately preceding the test pulse. However, following occlusion of the sustained depression with okadaic acid (100 n M ) the residual kinetic slowing was reversed in a voltage‐dependent manner ( P <0.05). 5 Thus pertussis toxin‐sensitive G‐proteins liberated upon activation of human D 2(short) dopamine receptors inhibited high‐threshold calcium currents in two distinct ways. The decrease in rate of calcium current activation involved a voltage‐dependent pathway, whereas the sustained inhibition of calcium current involved, in part, the voltage‐resistant phosphorylation by cyclic AMP‐dependent protein kinases and subsequent dephosphorylation by protein phosphatases 1/2A.