NO-cGMP pathway increases the hyperpolarisation-activated current, I(f), and heart rate during adrenergic stimulation.
OBJECTIVE
The role of the nitric oxide (NO)-cGMP pathway in the autonomic modulation of cardiac pacemaking is controversial and may involve an interplay between the L-type calcium current, I(CaL), and the hyperpolarisation activated current, I(f). We tested the hypothesis that following adrenergic stimulation, the NO-cGMP pathway stimulates phosphodiesterase 2 (PDE2) to reduce cAMP dependent stimulation of I(f) and heart rate (HR).


METHODS
In the presence of norepinephrine (NE, 1 microM), the effects of the NO donor sodium nitroprusside (SNP) were evaluated in sinoatrial node (SAN)/atria preparations and isolated SAN cells from adult guinea pigs.


RESULTS
Contrary to our hypothesis, SNP (10 and 100 microM, n=5) or the membrane permeable cGMP analogue, 8Br-cGMP (0.5 mM, n=6) transiently increased HR by 5+/-1, 12+/-1 and 12+/-2 beats/min, respectively. The guanylyl cyclase inhibitor 1H-(1,2,4)-oxadiazolo-(4,3-a)-quinoxalin-1-one (ODQ, 10 microM, n=5) abolished the increase in HR to SNP (100 microM) as did the I(f) blockers caesium chloride (2 mM, n=7) and 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino)-pyrimidinium chloride (ZD7288, 1 microM, n=7). Addition of SNP (10 microM) also transiently increased I(f) in SAN cells (n=5). After inhibition of PDE2 with erythro-9-(2-hydroxy-3-nonyl)-adenine (EHNA, 10 microM, n=5), the increase in HR to SNP in the presence of NE was significantly augmented and maintained. RT-PCR analysis confirmed the presence of PDE2 in addition to cGMP inhibited PDE3 mRNA in central SAN tissue.


CONCLUSIONS
These results suggest that during adrenergic stimulation, activation of the NO-cGMP pathway does not decrease HR, but has a transient stimulatory effect that is I(f) dependent, and is limited in magnitude and duration by stimulation of PDE2.
Herring
N
N
University Laboratory of Physiology, University of Oxford, Parks Road, OX1 3PT, Oxford, UK.
Rigg
L
L
Terrar
D A
DA
Paterson
D J
DJ
D015105:3',5'-Cyclic-AMP Phosphodiesterases; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002586:Cesium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D006152:Cyclic GMP / Q000378:metabolism; D054678:Cyclic Nucleotide Phosphodiesterases, Type 2; D005260:Female; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects*; D007473:Ion Channels / Q000187:drug effects*; D009569:Nitric Oxide / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012849:Sinoatrial Node / Q000187:drug effects* / Q000378:metabolism; D013268:Stimulation, Chemical
D002121:Calcium Channel Blockers; D002712:Chlorides; D007473:Ion Channels; D020030:Nitric Oxide Donors; D010726:Phosphodiesterase Inhibitors; D011743:Pyrimidines; D012333:RNA, Messenger; C082246:ICI D2788; D009599:Nitroprusside; D002586:Cesium; D015124:8-Bromo Cyclic Adenosine Monophosphate; D009569:Nitric Oxide; C010192:9-(2-hydroxy-3-nonyl)adenine; D010727:Phosphoric Diester Hydrolases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054678:Cyclic Nucleotide Phosphodiesterases, Type 2; D006162:Guanylate Cyclase; C028019:cesium chloride; D006152:Cyclic GMP; D000225:Adenine; D009638:Norepinephrine