Abstract
Our recent study demonstrated that by activating CCK-A receptors, CCK-8 excites substantia nigra (SN) dopaminergic (DA) neurons via increasing a non-selective cationic conductance. In the present study, we further studied the molecular mechanism by which CCK-8 induces cationic currents in SN DA neurons. CCK-8-evoked inward currents were inhibited by the intracellular perfusion of GDP-beta-S (1 mM). In DA neurons internally perfused with GTP-gamma-S (0.5 mM), the inward currents produced by CCK-8 became irreversible. Pretreating DA neurons with 500 ng/ml pertussis toxin (PTX) did not significantly affect the ability of CCK-8 to induce cationic currents. Intracellular application of heparin (2 mg/ml), an inositol 1,4,5-trisphosphate (InsP3) receptor antagonist, and buffering intracellular calcium with the Ca(2+)-chelator BAPTA (10 mM) suppressed CCK-8-evoked cationic currents. Dialyzing DA neurons with protein kinase C (PKC) inhibitors, staurosporine and PKC(19-31), failed to prevent CCK-8 from generating cationic currents. It is concluded that PTX-insensitive G-proteins mediate CCK-8-induced enhancement of cationic conductance of SN DA neurons. The coupling mechanism via G-proteins is likely to involve the generation of InsP3, and subsequent InsP3-evoked Ca2+ release from the intracellular store results in activating the non-selective cationic conductance.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Alkaloids / pharmacology
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Animals
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Calcium / metabolism*
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Calcium Channels / drug effects
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Dopamine / metabolism*
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Egtazic Acid / analogs & derivatives
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Egtazic Acid / pharmacology
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Evoked Potentials / drug effects
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Guanosine 5'-O-(3-Thiotriphosphate) / pharmacology
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Guanosine Diphosphate / analogs & derivatives
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Guanosine Diphosphate / pharmacology
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Heparin / pharmacology
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In Vitro Techniques
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Inositol 1,4,5-Trisphosphate / physiology*
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Inositol 1,4,5-Trisphosphate Receptors
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Ion Channels / drug effects
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Ion Channels / physiology*
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Neurons / drug effects
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Neurons / physiology*
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Peptide Fragments / pharmacology
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Pertussis Toxin
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Protein Kinase C / antagonists & inhibitors
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Rats
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Rats, Sprague-Dawley
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Receptors, Cytoplasmic and Nuclear / drug effects
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Sincalide / pharmacology*
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Staurosporine
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Substantia Nigra / physiology*
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Thionucleotides / pharmacology
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Time Factors
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Virulence Factors, Bordetella / pharmacology
Substances
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Alkaloids
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Calcium Channels
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Inositol 1,4,5-Trisphosphate Receptors
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Ion Channels
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Peptide Fragments
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Receptors, Cytoplasmic and Nuclear
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Thionucleotides
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Virulence Factors, Bordetella
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Guanosine Diphosphate
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Guanosine 5'-O-(3-Thiotriphosphate)
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Egtazic Acid
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guanosine 5'-O-(2-thiodiphosphate)
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Inositol 1,4,5-Trisphosphate
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Heparin
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Pertussis Toxin
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Protein Kinase C
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Staurosporine
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1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
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Sincalide
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Calcium
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Dopamine