Inhibition of voltage-dependent Ca2+ channels via alpha 2-adrenergic and opioid receptors in cultured bovine adrenal chromaffin cells.
Adrenal chromaffin cells secrete catecholamines and opioids. The effects of these agents on whole-cell Ca2+ channel currents were studied, using bovine adrenal chromaffin cells kept in short term culture. Ca2+ channel currents recorded during voltage-clamp pulses from a holding potential of -80 mV to 0 mV were reversibly reduced by 10 microM epinephrine (in the presence of 1 microM propranolol) or 5 microM of the synthetic opioid, d-Ala2-d-Leu5-enkephalin (DADLE) by approximately 35% and 25%, respectively. The inhibitory action of epinephrine was mimicked by clonidine, reduced by yohimbine but not affected by prazosin. The DADLE-induced reduction of the Ca2+ channel current was antagonized by naloxone. The dihydropyridine (+)PN 200-110 (5 microM) reduced the Ca2+ channel current by approximately 40%; the Ca2+ channel current inhibited by (+)PN 200-110 was not further reduced by epinephrine. Intracellular infusion of guanosine-5'-O-(2-thiodiphosphate) and pretreatment of cells with pertussis toxin abolished the inhibitory effect of both epinephrine and DADLE. In membranes of adrenal chromaffin cells, four pertussis-toxin-sensitive G-proteins were identified, including Gi1, Gi2, Go1 and another Go subtype, possibly Go2. The data show that activation of alpha 2-adrenergic and opioid receptors causes an inhibition of dihydropyridine-sensitive Ca2+ channels in adrenal chromaffin cells. These inhibitory modulations are mediated by pertussis-toxin-sensitive G-proteins and may represent a mechanism for a negative feedback signal by agents released from the adrenal medulla.
Kleppisch
T
T
Institut für Physiologie, Humboldt-Universität zu Berlin, Federal Republic of Germany.
Ahnert-Hilger
G
G
Gollasch
M
M
Spicher
K
K
Hescheler
J
J
Schultz
G
G
Rosenthal
W
W
D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002417:Cattle; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D004594:Electrophysiology; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D015151:Immunoblotting; D009270:Naloxone / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D037342:Pertussis Toxin; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D011957:Receptors, Opioid / Q000187:drug effects*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D010456:Peptides, Cyclic; D011942:Receptors, Adrenergic, alpha; D011957:Receptors, Opioid; D010566:Virulence Factors, Bordetella; D020960:omega-Conotoxins; C053423:Conus magus toxin; D009270:Naloxone; D016308:Enkephalin, Leucine-2-Alanine; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D004837:Epinephrine