Voltage-independent autocrine modulation of L-type channels mediated by ATP, opioids and catecholamines in rat chromaffin cells.
The inhibition of L-type channels induced by either bath application of ATP, opioids and catecholamines or by endogenously released neurotransmitters was investigated in rat chromaffin cells with whole-cell recordings (5 mM Ba2+). In both cases, the L-type current, isolated pharmacologically using omega-toxin peptides and potentiated by Bay K 8644, was inhibited by approximately 50% with nearly no changes to the activation-inactivation kinetics. Inhibition was voltage independent at a wide range of potentials (-20 to +50 mV) and insensitive to depolarizing prepulses (+100 mV, 50 ms). Onset and offset of the inhibition were fast (time constants: tau(on) approximately 0.9 s, tau(off) approximately 3.6 s), indicating a rapid mechanism of channel modulation. Whether induced exogenously or from the released granules content in conditions of stopped cell superfusion, the neurotransmitter action was reversible and largely prevented by either intracellular GDP-beta-S, cell treatment with pertussis toxin or simultaneous application of P2y,2x delta/mu-opioidergic and alpha/beta-adrenergic antagonists. This suggests the existence of converging modulatory pathways by which autoreceptors-activated G-proteins reduce the activity of L-type channels through fast interactions. The autocrine inhibition of L-type currents, which was absent in superfused isolated cells, was effective on cell clusters, suggesting that L-type channels may be potently inhibited by cell exocytosis under physiological conditions resembling the intact adrenal glands.
Hernández-Guijo
J M
JM
Instituto de Farmacología Teófilo Hernando, Departamento de Farmacología, Universidad Autónoma de Madrid, Spain.
Carabelli
V
V
Gandía
L
L
García
A G
AG
Carbone
E
E
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000313:Adrenal Medulla / Q000166:cytology; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D019898:Autocrine Communication / Q000187:drug effects / Q000502:physiology; D001464:Barium / Q000493:pharmacokinetics; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology*; D004837:Epinephrine / Q000494:pharmacology*; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D051381:Rats; D017207:Rats, Sprague-Dawley; D011941:Receptors, Adrenergic / Q000502:physiology; D011983:Receptors, Purinergic / Q000502:physiology; D013566:Sympathomimetics / Q000494:pharmacology*; D013873:Thionucleotides / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000701:Analgesics, Opioid; D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D011941:Receptors, Adrenergic; D011983:Receptors, Purinergic; D013566:Sympathomimetics; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D006153:Guanosine Diphosphate; D001464:Barium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C023427:guanosine 5'-O-(2-thiodiphosphate); D020881:Enkephalin, D-Penicillamine (2,5)-; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D009543:Nifedipine; D009638:Norepinephrine; D004837:Epinephrine