Open Access, Peer-reviewed
pISSN 2233-7385
eISSN 2233-7393
    Chonnam Med J. 2009 Apr;45(1):38-46. Korean.
    Published online Apr 27, 2009.
    https://doi.org/10.4068/cmj.2009.45.1.38
    Copyright © 2009 Chonnam National University Medical School
    Original Article

    Effects of µ-Opioid Agonist on ATP-sensitive Potassium Channel Activity in Isolated Ventricular Cardiomyocytes

    Ling-Hua Piao, Meijin Wu and Jae-Ha Kim
      • Department of Pharmacology, Chonnam National University Medical School, Chonnam National University Research Institute of Medical Sciences, and The Brain Korea 21 Project, Center for Biomedical Human Resources at Chonnam National University, Gwangju, Korea.
    Accepted March 25, 2009.

    Abstract

    It is well known that opioid agonists are released from the myocardium during hypoxia or ischemia, and that ATP-sensitive potassium channels (KATP channels) exist in the cardiac cell membrane and function as a cardioprotector preventing the myocardium from ischemic damage. In the present study, therefore, to determine whether opioid agonists are involved in the regulation of ATP-sensitive potassium channel activities, effects of the µ-opioid agonist DAMGO were examined on KATP channel activities by using excised inside-out and cell-attached patch clamp techniques in enzymatically (collagenase and protease) isolated mouse ventricular cardiac myocytes. In the excised inside-out patches, DAMGO (1~300 µmol/L) inhibited KATP channel activities in a dose-dependent manner. KATP channel activity, which had been attenuated by the addition of ATP (100 µmol/L) to the internal solution, was not reactivated by DAMGO. The fashion of the single-channel inhibition by DAMGO was that both channel opening frequency and mean open-time were decreased, but the amplitudes of single channel currents and channel conductances were not altered. The half-maximal inhibition concentration (IC50) for DAMGO was 18 µmol/L. In the cell-attached patch configuration, however, DAMGO (1~300 µmol/L) increased dinitrophenol (50 µmol/L)-induced KATP channel activities. It was inferred that the µ-opioid agonist is involved in the regulation of ATP-sensitive potassium channel activity in cardiac myocardium, agonizing (through internal target) or antagonizing (through external target) the inhibitory action of ATP in a competitive manner, thereby attenuating or enhancing the channel openings.

    Keywords
    µ-Opioid agonist; KATP channels; Myocytes, Cardiac

    Figures

    Fig. 1
    Patch clamp configurations used in the present study. Excised inside-out (left) and cell-attached (right) configurations respectively.

    Fig. 2
    Representative recording of the typical KATP channel activity in the excised inside-out patch at -60 mV holding potential. The channel activity was appeared immediately after making inside-out patch, and 1 mM ATP almost completely inhibited the channel activity. The channel activity reappeared when the ATP was washed out from the bath solution, and then 50 µM glibenclamide inhibited the channel activity.

    Fig. 3
    I-V properties of the ATP-sensitive K+ channel (KATP) currents. Recordings were obtained in excised inside-out patch membrane of isolated rat ventricular myocytes at different clamp potentials ranging from -100 to +100 mV (right panel). The current-voltage relationship (left panel) was plotted with the single channel currents of the right panel.

    Fig. 4
    Effect of linoleic acid on the KATP channel activities. Recordings show that DAMGO (1~100 µmol/L) inhibited the channel activities at -60 mV holding potential in the excised inside-out patch.

    Fig. 5
    Dose-response curve of KATP channel inhibition by the DAMGO in the excised inside-out patch. Each points denote the mean of 3~4 experiments and the vertical bar is SEM.

    Fig. 6
    Influence of DAMGO (100 µM) on the current-voltage curves of the ATP-sensitive K+ channel (KATP). The current-voltage relationship was plotted with the single channel currents in the excised inside-out patch at different clamp potentials, and the channel conductance was not changed by the DAMGO.

    Fig. 7
    Effect of DAMGO (100 µM) on the attenuated KATP channel activity in the presence of internal 100 µM ATP in the inside-out patch at -60 mV holding potential. DAMGO did not increase the channel activity.

    Fig. 8
    A trace showing typical KATP channel activities in a cell-attached patch of an isolated mouse cardiac myocyte at -60 mV holding potential (HP). Dinitrophenol (DNP) induced channel activities and these activities were inhibited by glibenclamide.

    Fig. 9
    Effects of DAMGO (10 and 100 µmol/L) on the dinitrophenol (DNP)-induced KATP channel activities in the cell-attached patch at -60 mV holding potential (HP). DAMGO increased the DNP-induced channel activities in a dose-dependent manner.

    Fig. 10
    Effects of DAMGO on the dinitrophenol (DNP)-induced channel activities in the cell-attached patches. Relative activity at 1.0 represents the channel activities for 30 sec of DNP superfusion. Each columns and vertical bars represent mean ±SEM of 4 to 5 experiments. * and † indicate significant differences at p<0.05 (*) and p<0.01 (†) compared with the DNP-induced control activities, respectively.

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    MeSH Terms
    Adenosine Triphosphate
    Animals
    Anoxia
    Cell Membrane
    Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
    Felodipine
    Ischemia
    KATP Channels
    Mice
    Myocardium
    Myocytes, Cardiac
    Patch-Clamp Techniques
    Potassium
    Potassium Channels
    Metrics
    Share
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