kt-5720 and trequinsin

Nitric oxide (NO) donors increase heart rate (HR) through a guanylyl cyclase-dependent stimulation of the pacemaker current I(f), without affecting basal I(Ca-L). The activity of I(f)is known to be enhanced by cyclic nucleotides and by an increase in cytosolic Ca(2+). We examined the role of cGMP-dependent signaling pathways and intracellular Ca(2+)stores in mediating the positive chronotropic effect of NO donors. In isolated guinea pig atria, the increase in HR in response to 1-100 micromol/l 3-morpholino-sydnonimine (SIN-1; with superoxide dismutase, n=6) or diethylamine-NO (DEA-NO, n=8) was significantly attenuated by blockers of the cGMP-inhibited phosphodiesterase (PDE3; trequinsin, milrinone or Ro-13-6438, n=22). In addition, the rate response to DEA-NO or sodium nitroprusside (SNP) was significantly reduced following inhibition of PKA (KT5720 or H-89, n=15) but not PKG (KT5728 or Rp-8-pCPT-cGMPs, n=16). Suppression of sarcoplasmic (SR) Ca(2+)release by pretreatment of isolated atria with ryanodine or cyclopiazonic acid (2 micromol/l and 60 micromol/l, n=16) significantly reduced the chronotropic response to 1-100 micromol/l SIN-1 or DEA-NO. Moreover, in isolated guinea pig sinoatrial node cells 5 micromol/l SNP significantly increased diastolic and peak Ca(2+)fluorescence (+13+/-1% and +28+/-1%, n=6, P<0.05). Our findings are consistent with a functionally significant role of cAMP/PKA signaling (via cGMP inhibition of PDE3) and SR Ca(2+)in mediating the positive chronotropic effect of NO donors.

Topics: Animals; Calcium; Carbazoles; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Dose-Response Relationship, Drug; Enzyme Inhibitors; Guinea Pigs; Heart Atria; Heart Rate; Hydrazines; Indoles; Isoquinolines; Male; Milrinone; Models, Biological; Molsidomine; Nitric Oxide Donors; Nitrogen Oxides; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases; Platelet Aggregation Inhibitors; Pyrroles; Quinazolines; Ryanodine; Sarcoplasmic Reticulum; Signal Transduction; Spectrometry, Fluorescence; Sulfonamides; Superoxide Dismutase; Tetrahydroisoquinolines; Thionucleotides; Time Factors; Vasodilator Agents