Nitric oxide regulates cardiac Ca2+ current. Involvement of cGMP-inhibited and cGMP-stimulated phosphodiesterases through guanylyl cyclase activation.
The effects of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) on the L-type Ca2+ current (ICa) were examined in frog ventricular myocytes under basal and phosphorylated conditions. SIN-1 was found to exert insignificant effects on basal ICa but to induce a biphasic action on stimulated ICa. Indeed, in the nanomolar range of concentrations (0.1-10 nM), SIN-1 induced a pronounced (approximately 40%) stimulation of ICa elevated by a non-maximal concentration of forskolin (0.3 microM). However, the stimulatory effects of SIN-1 on ICa were not additive with those of maximal concentrations (10 microM) of forskolin or intracellular cAMP. In contrast, at higher concentrations (100 nM to 1 mM), SIN-1 strongly reduced ICa (by up to 85%) which had been previously stimulated by cAMP, forskolin, or isoprenaline. All the effects of SIN-1 appeared to be mediated by the liberation of NO since they were suppressed by methylene blue and LY83583 and were not mimicked by SIN-1C, a metabolite of SIN-1. The stimulatory or inhibitory effects of SIN-1 were absent, respectively, in the presence of milrinone (10 microM) or when the hydrolysis-resistant cAMP analog 8-bromo-cAMP was used instead of cAMP to stimulate ICa. In addition to its effects on ICa, SIN-1 induced a dose-dependent stimulation of guanylyl cyclase activity in the cytosolic and membrane fractions of frog ventricle. The membrane form of guanylyl cyclase displayed a higher sensitivity to SIN-1 than the cytosolic form, which correlated with SIN-1 sensitivity of ICa. Our data suggest that the activatory and inhibitory effects of NO donors on ICa result from an inhibition of the cGMP-inhibited cAMP-phosphodiesterase and an activation of the cGMP-stimulated cAMP-phosphodiesterase, respectively, both linked to the activation of guanylyl cyclase, possibly a membrane form of the enzyme.
Méry
P F
PF
Laboratoire de Cardiologie Cellulaire et Moléculaire, Institut National de la Santé et de la Recherche Médicale CJF 92-11, Université de Paris-Sud, Faculté de Pharmacie, Châtenay-Malabry, France.
Pavoine
C
C
Belhassen
L
L
Pecker
F
F
Fischmeister
R
R
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D006152:Cyclic GMP / Q000494:pharmacology; D004789:Enzyme Activation; D006162:Guanylate Cyclase / Q000378:metabolism; D006352:Heart Ventricles / Q000187:drug effects* / Q000201:enzymology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008981:Molsidomine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism / Q000494:pharmacology*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D011893:Rana esculenta
D015220:Calcium Channels; D005576:Colforsin; D009569:Nitric Oxide; C002385:linsidomine; D008981:Molsidomine; D010727:Phosphoric Diester Hydrolases; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D007545:Isoproterenol