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Departments of Medicine and Radiology, University of Minnesota, Minneapolis, Minnesota 55455
Opening of mitochondrial
ATP-sensitive potassium (KATP) channels has been postulated
to prevent inhibition of respiration resulting from matrix contraction
during high rates of ATP synthesis. Glibenclamide, which blocks
KATP channels on the sarcolemma of vascular smooth muscle
cells and myocardial myocytes as well as on the inner mitochondrial
membrane, results in a decrease of myocardial oxygen consumption
(M
O2) both at rest and during exercise.
This study examined whether this represents a primary effect of
blockade of mitochondrial KATP channels or occurs secondary to coronary resistance vessel constriction with a decrease of coronary
blood flow (CBF) and myocardial oxygen availability. M
O2 was measured at rest and during
treadmill exercise in 10 dogs during control conditions, after
selective mitochondrial KATP channel blockade with
5-hydroxydecanoate (5-HD), and after nonselective KATP
channel blockade with glibenclamide. During control conditions,
exercise resulted in progressive increases of CBF and
M
O2. Glibenclamide (50 µg · kg
1 · min
1 ic)
resulted in a 17 ± 6% decrease of resting CBF with a downward shift of CBF during exercise and a decrease of coronary venous PO2, indicating increased myocardial oxygen
extraction. In contrast with the effects of glibenclamide, 5-HD (0.7 mg · kg
1 · min
1 ic) had no
effect on CBF, M
O2, or myocardial oxygen
extraction. These findings suggest that glibenclamide decreased
M
O2 by causing resistance vessel
constriction with a decrease of CBF and oxygen available to the
myocardium rather than to a primary reduction of mitochondrial respiration.
glibenclamide; 5-hydroxydecanoate; exercise; coronary blood flow
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