The objective of the present study was to characterize the role of adenosine in regulation of ATP-sensitive K<sup>+</sup> channel (K<sub>ATP</sub> channel) activity in isolated rabbit ventricular myocytes using the patch clamp technique. Internal adenosine had little effects on KaTr channel activity. In an outside-out patch with intrapipette GTP and ATP, external adenosine stimulated K<sub>ATP</sub> channel activity. In an inside-out Patch with intrapipette adenosine, ATP reduced K<sub>ATP</sub> channel activity, and GTP stimulated K<sub>ATP</sub> channel activity. Adenosine receptor activation shifted the half-maximal inhibition Of K<sub>ATP</sub> channel from 70 to 241 μm. These results Suggest that activation of adenosine receptors stimulates K<sub>ATP</sub> channels in rabbit ventricular myocytes by reducing the apparent affinity of the channel for ATP. The effect may be important for activating K<sub>ATP</sub> channels during early phase of myocardial ischemia.
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