Korean J Physiol Pharmacol.  2010 Jun;14(3):145-150. 10.4196/kjpp.2010.14.3.145.

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

• Cho H

• KMID: 2285395
• DOI: http://doi.org/10.4196/kjpp.2010.14.3.145

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 micrometer 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 micrometer 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.

Keyword

GIRK channel; Adenosine; Acetylcholine; PIP2; Gq protein-coupled receptors

MeSH Terms

Acetylcholine
Adenosine
Animals
Bradykinin
Carotenoids
Endothelin-1
Heart
Mice
Muscle Cells
Neomycin
Oxygenases
Phenylephrine
Phosphatidylinositols
Acetylcholine
Adenosine
Bradykinin
Carotenoids
Endothelin-1
Neomycin
Oxygenases
Phenylephrine
Phosphatidylinositols

Figure

• 

  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 IK(Ado) and IK(ACh). Inset, the I-V curves for net IK(Ado) (black) IK(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 IK(Ado) to that of IK(ACh).

• 

  Fig. 2. Differential regulation of IK(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 IK(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 IK(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 I1,peak, respectively. The numbers in parentheses indicate numbers of cells. Error bars indicate S.E.M.

• 

  Fig. 4. Neomycin inhibition of IK(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 IK(Ado). The numbers in parentheses indicate numbers of cells. ∗p<0.01. Error bars indicate S.E.M.

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