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Gi- and Gs-coupled receptors up-regulate the cAMP cascade to modulate HCN2, but not HCN1 pacemaker channels

C Ulens1, J Tytgat

  • 1Laboratory of Toxicology, University of Leuven, Belgium.

Pflugers Archiv : European Journal of Physiology
|October 30, 2001
PubMed

Insights

Neurotransmitters modulate pacemaker channels via cAMP. Researchers found that activating G protein-coupled receptors enhanced HCN2 channels, but not HCN1, by increasing current amplitude and altering activation kinetics.

Area of Science:

  • Neuroscience
  • Molecular Biology
  • Cardiology

Background:

  • Pacemaker channels (HCN) are crucial for heart rhythm.
  • Their function is regulated by neurotransmitters and hormones via cyclic AMP (cAMP).

Purpose of the Study:

  • To investigate how G protein-coupled receptors (GPCRs) modulate cloned HCN1 and HCN2 pacemaker channels.
  • To elucidate the signaling pathways involved in this modulation.

Main Methods:

  • Heterologous expression of HCN1 and HCN2 channels and GPCRs (μ-opioid and 5-HT4(a)) in Xenopus oocytes.
  • Two-electrode voltage-clamp recordings to measure ionic currents.
  • Pharmacological inhibition using SQ22536 (adenylyl cyclase inhibitor).

Main Results:

  • Activation of both μ-opioid and 5-HT4(a) receptors enhanced HCN2 currents, but not HCN1 currents.
  • Receptor activation increased HCN2 current amplitude, accelerated activation, slowed deactivation, and increased maximal conductance.
  • These effects were mediated by cAMP, independent of protein kinases A and C, and involved Gβγ/adenylyl cyclase and Gαs pathways.

Conclusions:

  • GPCRs differentially modulate HCN channel subtypes.
  • The findings reveal a novel cAMP-dependent mechanism for HCN2 channel regulation by specific GPCRs.
  • This modulation may contribute to functional heterogeneity of pacemaker currents in neurons co-expressing HCN2 and 5-HT4(a) receptors.

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