Inhibition of Ca2+ channels via alpha 2-adrenergic and muscarinic receptors in pheochromocytoma (PC-12) cells

Item Type:	Article
Title:	Inhibition of Ca2+ channels via alpha 2-adrenergic and muscarinic receptors in pheochromocytoma (PC-12) cells
Creators Name:	Gollasch, M. and Hescheler, J. and Spicher, K. and Klinz, F.J. and Schultz, G. and Rosenthal, W.
Abstract:	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.
Keywords:	Adrenal Gland Neoplasms, Amino Acid Sequence, Atropine, Barium, Calcium Channel Blockers, Calcium Channels, Carbachol, Cell Line, Cell Membrane, Leucine-2-Alanine Enkephalin, Epinephrine, Evoked Potentials, GTP-Binding Proteins, Immune Sera, Isradipine, Membrane Potentials, Molecular Sequence Data, Oxadiazoles, Peptides, Cyclic Peptides, Pertussis Toxin, Pheochromocytoma, Propranolol, Adrenergic beta Receptors, Muscarinic Receptors, Bordetella Virulence Factors, Yohimbine, Omega-Conotoxins, Animals, Rats
Source:	American Journal of Physiology
ISSN:	0002-9513
Publisher:	American Physiological Society
Volume:	260
Number:	6 Pt 1
Page Range:	C1282-C1289
Date:	June 1991
Official Publication:	http://ajpcell.physiology.org/cgi/content/abstract/260/6/C1282
PubMed:	View item in PubMed

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