Regulation of Adenosine-activated GIRK Channels by Gq-coupled Receptors in Mouse Atrial Myocytes

Hana Cho

doi:10.4196/kjpp.2010.14.3.145

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Cho: Regulation of Adenosine-activated GIRK Channels by Gq-coupled Receptors in Mouse Atrial Myocytes

Original Article

Korean J Physiol Pharmacol 2010;14(3):145-150.

Published online: 18 February 2010

DOI: https://doi.org/10.4196/kjpp.2010.14.3.145

Regulation of Adenosine-activated GIRK Channels by Gq-coupled Receptors in Mouse Atrial Myocytes

Hana Cho

Department of Physiology, Sungkyunkwan University School of Medicine, Suwon 440-746, Korea

Corresponding to: Hana Cho, Department of Physiology, Sungkyunkwan University School of Medicine, 300, Cheoncheon-dong, Jangan-gu, Suwon 440-746, Korea. (Tel) 82-31-299-6104, (Fax) 82-31-299-6129, (E-mail) hanacho@med.skku.ac.kr

Received 28 April 2010 Revised 11 May 2010 Accepted 19 May 2010

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Adenosine (Ado) is an important mediator of the endogenous defense against ischemia-induced injury in the heart. The action of Ado is mediated by activation of G protein-gated inwardly rectifying K⁺ (GIRK) channels. In turn, GIRK channels are inhibited by reducing phosphatidylinositol 4,5-bisphosphate (PIP₂) through Gq protein-coupled receptors (GqPCRs). We previously found that GIRK channels activated by acetylcholine, a muscarinic M2 acetylcholine receptor agonist, are inhibited by GqPCRs in a receptor-specific manner. However, it is not known whether GIRK channels activated by Ado signaling are also regulated by GqPCRs. Presently, this was investigated in mouse atrial myocytes using the patch clamp technique. GIRK channels were activated by 100 μM Ado. When Ado was repetitively applied at intervals of 5 ∼ 6 min, the amplitude of second Ado-activated GIRK currents (I_K(Ado)) was 88.3±3.7% of the first I_K(Ado) in the control. Pretreatment of atrial myocytes with phenylephrine, endothelin-1, or bradykinin prior to a second application of Ado reduced the amplitude of the second I_K(Ado) to 25.5±11.6%, 30.5±5.6%, and 96.0±2.7%, respectively. The potency of I_K(Ado) inhibition by GqPCRs was different with that observed in acetylcholine-activated GIRK currents (I_K(ACh)) (endothelin-1 > phenylephrine > bradykinin). I_K(Ado) was almost completely inhibited by 500 μM of the PIP₂ scavenger neomycin, suggesting low PIP₂ affinity of I_K(Ado). Taken together, these results suggest that the crosstalk between GqPCRs and the Ado-induced signaling pathway is receptor-specific. The differential change in PIP₂ affinity of GIRK channels activated by Ado and ACh may underlie, at least in part, their differential responses to GqPCR agonists.

Keywords: GIRK channel, Adenosine, Acetylcholine, PIP₂, Gq protein-coupled receptors

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Fig. 1.

Differential activation of atrial GIRK currents by ACh and Ado. (A) Outward current activated by rapid exposure to Ado and ACh. The rapid deflections in this figure represent changes in membrane current due to ramp pulse from –120 to +60 mV, which were applied to obtain I-V curves of I_K(Ado) and I_K(ACh). Inset, the I-V curves for net I_K(Ado) (black) I_K(ACh) (gray). Data were calculated from data in left. The reversal potential was –70 mV. (B) Ado (100 μM) and ACh (100 μM) were applied for 2 min sequentially at a 6 min interval, as indicated by the horizontal lines above the trace. Inset, response to 100 μM Ado (black) and onset of response to 100 μM ACh (gray) on an expanded time scale. The response to 100 μM Ado was scaled up to match the amplitude of the response to 100 μM ACh. The arrow indicates the beginning of agonist exposure. (C) Summarized data for normalized peak amplitude of I_K(Ado) to that of I_K(ACh).

Fig. 2.

Differential regulation of I_K(Ado) by different GqPCRs. (A) Ado (100 μM) was applied for 2 min twice at a 6 min interval, as indicated by the horizontal lines above the trace. (B∼D) Phenylephrine (PE, 100 μM), endothelin-1 (ET-1, 30 nM), or bradykinin (BK, 10 μM) was applied prior to the application of Ado as indicated by the horizontal lines above the trace. (E) Summarized data for potency of I_K(Ado) inhibition. The numbers in parentheses indicate numbers of cells. ^∗p<0.01. Error bars indicate S.E.M.

Fig. 3.

PDBu has little effect on I_K(Ado) in mouse atrial myocytes. (A) PDBu (100 nM), a PKC activator, was applied as a pretreatment before the activation of I₂. (B) the I₂, _peak in the absence and presence of PDBu was 88.3±3.7% (n=4) and 97.5±0.5% (n=5) of I_1,peak, respectively. The numbers in parentheses indicate numbers of cells. Error bars indicate S.E.M.

Fig. 4.

Neomycin inhibition of I_K(Ado). (A, B) Neomycin at concentrations of 500 μM (A) or 100 μM (B) was applied prior to the application of Ado as indicated by the horizontal lines above the trace. (C) Summarized data for the neomycin inhibition of I_K(Ado). The numbers in parentheses indicate numbers of cells. ^∗p<0.01. Error bars indicate S.E.M.

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