title: cAMP signaling inhibits dihydropyridine-sensitive Ca2+ influx in vascular smooth muscle cells.
abstract: This study examines the role of the cAMP signaling pathway in the regulation of 45Ca influx in cultured vascular smooth muscle cells from the rat aorta. K+o-induced depolarization of smooth muscle cells increased the rate of 45Ca uptake by twofold to threefold. This effect was completely abolished by the dihydropyridine derivatives nifedipine and nicardipine, with a Ki of 3 and 10 nmol/L, respectively. Activators of cAMP signaling (isoproterenol, forskolin, cholera toxin) increased cAMP content by 50- to 100-fold and decreased voltage-dependent 45Ca uptake by 50% to 70%. Neither the dihydropyridines nor the cAMP activators affected basal 45Ca influx. Direct addition of the protein kinase inhibitor H-89 to the incubation medium in the 1- to 10-micromol/L range did not alter basal 45Ca uptake but completely abolished voltage-dependent Ca2+ transport. Preincubation of cells for 1 hour with 10 micromol/L H-89 did not modify basal and depolarization-induced 45Ca uptake in H-89-free medium but prevented forskolin-induced inhibition of voltage-dependent Ca2+ influx. The addition of cytoskeleton-active compounds reduced voltage-dependent Ca2+ transport and completely abolished its regulation by cAMP. Activation of cAMP signaling decreased the volume of smooth muscle cells by 12% to 15%. The same cell volume diminution in hyperosmotic medium did not alter voltage-dependent 45Ca uptake. Thus, data obtained in this study show that in contrast to cardiac and skeletal myocytes, in vascular smooth muscle cells, 45Ca influx, putatively due to L-type channels, is inhibited by cAMP. This regulatory pathway appears to be mediated via protein kinase A activation and cytoskeleton reorganization.
authors.affiliation: Centre de Recherche Hôtel-Dieu de Montréal, Université de Montréal,Québec, Canada.
authors.forename: S N
authors.initials: SN
authors.lastname: Orlov
authors.forename: J
authors.initials: J
authors.lastname: Tremblay
authors.forename: P
authors.initials: P
authors.lastname: Hamet
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D048429:Cell Size / Q000502:physiology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D007546:Isoquinolines / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D051381:Rats; D011914:Rats, Inbred BN; D015398:Signal Transduction; D013449:Sulfonamides
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004095:Dihydropyridines; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D013449:Sulfonamides; C038806:1,4-dihydropyridine; D000242:Cyclic AMP; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D002118:Calcium