Dual effect of nitric oxide on the hyperpolarization-activated inward current (I(f)) in sino-atrial node cells of the rabbit

Shin Yoo, Suk Ho Lee, Bok Hee Choi, Jae Bum Yeom, Won Kyung Ho*, Yung E. Earm

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


Using the whole-cell voltage-clamp technique, we have investigated the effect of nitric oxide (NO) donor (sodium nitroprusside, SNP) on hyperpolarization-activated inward current, I(f), in isolated rabbit sinoatrial node (SAN) cells. I(f) in the basal state increased when NO was applied but decreased when I(f) was pre-stimulated by isoproterenol (ISO) or by adding cAMP to the pipette solution. Both the stimulatory and the inhibitory effects of NO were abolished by guanylyl cyclase inhibitor, methylene blue (MB), suggesting that the effect of NO is mediated by cGMP. The inhibitory effect of NO was abolished when I(f) was pre-stimulated by 3-isobutyl-1-methylxanthine (IBMX), which is a phosphodiesterase (PDE) inhibitor, or by adding 8Br-cAMP (which is resistant to PDE) to the pipette solution. An analogue of cGMP, 8Br-cGMP, which is a potent stimulator of cGMP-dependent protein kinase (PKG) but has little effect on PDE, did not inhibit I(f) when I(f) was pre-stimulated by ISO. In its basal state, I(f) was still increased by 8Br-cGMP, and this effect was not prevented by the pretreatment with H-7, PKG inhibitor. The effect of acetylcholine (ACh) was not identical to that of NO; I(f) decreased when pre-stimulated not only by ISO, but also by IBMX. The above results suggest that via cGMP, NO exerts a dual effect on I(f): the inhibitory effect is mediated by cGMP-stimulated PDE, and the stimulatory effect may be attributable to direct binding of cGMP to I(f) channels.

Original languageEnglish (US)
Pages (from-to)2729-2738
Number of pages10
JournalJournal of Molecular and Cellular Cardiology
Issue number12
StatePublished - Dec 1998


  • Hyperpolarization-activated inward current (I(f))
  • NO
  • Sino-atrial node
  • cAMP
  • cGMP

ASJC Scopus subject areas

  • Molecular Biology
  • Cardiology and Cardiovascular Medicine


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