title: Nitric oxide signaling mediates stimulation of L-type Ca2+ current elicited by withdrawal of acetylcholine in cat atrial myocytes.
abstract: A perforated-patch whole-cell recording method was used to determine whether nitric oxide signaling participates in acetylcholine (ACh)-induced regulation of basal L-type Ca2+ current (ICa,L) in cat atrial myocytes. Exposure to 1 microM ACh for 2 min inhibited basal ICa,L (-21 +/- 3%), and withdrawal of ACh elicited rebound stimulation of ICa,L above control (80 +/- 13%) (n = 23). Stimulation of ICa,L elicited by withdrawal of ACh (but not ACh-induced inhibition of ICa,L) was blocked by either 50 microM hemoglobin; 30 microM ODQ or 10 microM methylene blue, inhibitors of soluble guanylate cyclase; 10 microM W-7, a calmodulin inhibitor; or 10 microM L-NIO, an inhibitor of constitutive NO synthase (NOS). In cells incubated in 5 mM L-arginine, ACh-induced rebound stimulation of ICa,L was enhanced compared with control responses. Histochemical assay (NADPH diaphorase) indicated that atrial myocytes express constitutive NOS. NO-donor, spermine/NO (SP/NO), >1 microM stimulated basal ICa,L. SP/NO-induced stimulation of ICa,L was inhibited by 50 microM hemoglobin, 30 microM ODQ, or 5 microM H-89, an inhibitor of PKA, and was unchanged by 50 microM MnTBAP, a peroxynitrite scavenger. When ICa,L was prestimulated by 10 microM milrinone, an inhibitor of cGMP-inhibited phosphodiesterase (type III) activity, SP/NO failed to further increase ICa,L. In cells incubated in pertussis toxin (3.4 microg/ml for 6 h; 36 degrees C), ACh failed to affect ICa,L, but 100 microM SP/NO or 10 microM milrinone still increased basal ICa,L. These results indicate that in cat atrial myocytes NO signaling mediates stimulation of ICa,L elicited by withdrawal of ACh but not ACh-induced inhibition of basal ICa,L. NO activates cGMP-induced inhibition of phosphodiesterase (type III) activity. Upon withdrawal of ACh, this mechanism allows cAMP to recover to levels above control, thereby stimulating ICa,L. Pertussis toxin-sensitive G-proteins couple M2 muscarinic receptors to NO signaling. NO-mediated stimulation of ICa, L elicited by withdrawal of ACh may be an important mechanism that rapidly restores cardiac pacemaker and contractile functions after cholinergic suppression of atrial activity.
authors.affiliation: Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois 60153, USA.
authors.forename: Y G
authors.initials: YG
authors.lastname: Wang
authors.forename: C E
authors.initials: CE
authors.lastname: Rechenmacher
authors.forename: S L
authors.initials: SL
authors.lastname: Lipsius
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism; D002415:Cats; D000242:Cyclic AMP / Q000819:agonists / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004594:Electrophysiology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006162:Guanylate Cyclase / Q000378:metabolism; D006325:Heart Atria / Q000166:cytology; D006454:Hemoglobins / Q000494:pharmacology; D006651:Histocytochemistry; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000201:enzymology; D009206:Myocardium / Q000166:cytology*; D009569:Nitric Oxide / Q000378:metabolism*; D037342:Pertussis Toxin; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013096:Spermine / Q000494:pharmacology; D013449:Sulfonamides; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D002147:Calmodulin; D004791:Enzyme Inhibitors; D006454:Hemoglobins; D007546:Isoquinolines; D010726:Phosphodiesterase Inhibitors; D013449:Sulfonamides; D010566:Virulence Factors, Bordetella; D013096:Spermine; D009569:Nitric Oxide; D001120:Arginine; D000242:Cyclic AMP; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; D010727:Phosphoric Diester Hydrolases; D006162:Guanylate Cyclase; D006152:Cyclic GMP; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D000109:Acetylcholine