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Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195-7290
The present study was designed to examine the role of ATP-sensitive potassium (KATP+) channels during exercise and to test the hypothesis that adenosine increases to compensate for the loss of KATP+ channel function and adenosine inhibition produced by glibenclamide. Graded treadmill exercise was used to increase myocardial O2 consumption in dogs before and during KATP+ channel blockade with glibenclamide (1 mg/kg iv), which also blocks adenosine mediated coronary vasodilation. Cardiac interstitial adenosine concentration was estimated from arterial and coronary venous values by using a previously tested mathematical model (Kroll K and Stepp DW. Am J Physiol Heart Circ Physiol 270: H1469-H1483, 1996). Coronary venous O2 tension was used as an index of the balance between O2 delivery and myocardial O2 consumption. During control exercise, myocardial O2 consumption increased ~4-fold, and coronary venous O2 tension fell from 19 to 14 Torr. After KATP+ channel blockade, coronary venous O2 tension was decreased below control vehicle values at rest and during exercise. However, during exercise with glibenclamide, the slope of the line of coronary venous O2 tension vs. myocardial O2 consumption was the same as during control exercise. Estimated interstitial adenosine concentration with glibenclamide was not different from control vehicle and was well below the level necessary to overcome the 10-fold shift in the adenosine dose-response curve due to glibenclamide. In conclusion, KATP+ channel blockade decreases the balance between resting coronary O2 delivery and myocardial O2 consumption, but KATP+ channels are not required for the increase in coronary blood flow during exercise. Furthermore, interstitial adenosine concentration does not increase to compensate for the loss of KATP+ channel function.
canine; glibenclamide; ATP-sensitive potassium channels
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