Inhibition of Ca2+ channels via alpha 2-adrenergic and muscarinic receptors in pheochromocytoma (PC-12) cells.
Biochemical studies have suggested a voltage-dependent dihydropyridine-sensitive catecholamine release in adrenal chromaffin cells. This release is inhibited by activation of alpha 2-adrenergic and muscarinic receptors; the underlying molecular mechanism is not known. We used undifferentiated PC-12 cells to study the effect of epinephrine and carbachol on transmembranous currents. Applying the patch-clamp technique in the whole cell configuration and using Ba2+ as charge carrier, we identified a high voltage-activated Ca2+ channel current. Both epinephrine (10 microM, in the presence of 1 microM propranolol) and carbachol (10 microM) reversibly inhibited the Ca2+ channel current by 30-40%. Yohimbine abolished and clonidine mimicked the effect of epinephrine. Phenylephrine failed to inhibit the Ca2+ channel current. The effect of carbachol was abolished by atropine. Epinephrine and carbachol did not affect the Ca2+ channel current reduced by the dihydropyridine, PN 200-110 (1 microM), suggesting a selective inhibition of dihydropyridine-sensitive Ca2+ channels. The Ca2+ channel current and its inhibition by receptor agonists were not influenced by intracellularly applied adenosine 3',5'-cyclic monophosphate (cAMP; 100 microM). Pretreatment of cells with pertussis toxin or intracellular infusion of the GDP analogue guanosine-5'-O-(2-thiodiphosphate) was without effects on the control Ca2+ channel current but abolished its hormonal inhibition. Four pertussis toxin-sensitive G proteins were identified in membranes of PC-12 cells: two members of the Gi family, Gi1 and Gi2, and two members of the Go family, Go2 and another Go subtype (possibly Go1). The present data indicate that activated alpha 2-adrenergic and muscarinic receptors inhibit dihydropyridine-sensitive Ca2+ channels via pertussis toxin-sensitive G proteins without the involvement of a cAMP-dependent intermediate step.
Gollasch
M
M
Institut für Physiologie, Humboldt-Universität zu Berlin, Germany.
Hescheler
J
J
Spicher
K
K
Klinz
F J
FJ
Schultz
G
G
Rosenthal
W
W
D000310:Adrenal Gland Neoplasms; D000595:Amino Acid Sequence; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology*; D005071:Evoked Potentials / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000276:immunology / Q000502:physiology; D007106:Immune Sera; D017275:Isradipine; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D010069:Oxadiazoles / Q000494:pharmacology; D010455:Peptides / Q000138:chemical synthesis; D010456:Peptides, Cyclic / Q000494:pharmacology; D037342:Pertussis Toxin; D010673:Pheochromocytoma; D011433:Propranolol / Q000494:pharmacology*; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007106:Immune Sera; D010069:Oxadiazoles; D010455:Peptides; D010456:Peptides, Cyclic; D011943:Receptors, Adrenergic, beta; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D020960:omega-Conotoxins; C053423:Conus magus toxin; D001464:Barium; D015016:Yohimbine; D016308:Enkephalin, Leucine-2-Alanine; D001285:Atropine; D002217:Carbachol; D011433:Propranolol; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D004837:Epinephrine; D017275:Isradipine