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Functional compartmentalization of ATP is involved in angiotensin II-mediated closure of cardiac ATP-sensitive K+
K Tsuchiya1, M Horie, M Watanuki
1Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Japan.
Background:
The effects of angiotensin II (Ang II) on ATP-sensitive K+ channels (K(ATP)) were investigated in ventricular myocytes enzymatically isolated from adult guinea pig heart.
Methods And Results:
In the whole-cell and cell-attached configurations (including open-cell-attached mode) of the patch-clamp technique, K(ATP) currents (I(KATP)) were activated through metabolic poisoning by the use of inhibitors of both glycolytic and oxidative ATP productions at 37 degrees C. In the whole-cell mode, I(KATP) were reversibly suppressed by increasing extracellular glucose and Ang II (1 nmol/L). In the cell-attached mode, Ang II concentration-dependently inhibited single K(ATP) activities with an IC50 value of 3.2+/-0.5 pmol/L (Hill coefficient=1.3+/-0.3). CV11974 (100 nmol/L), an angiotensin 1 (AT1) receptor-selective antagonist, blocked the inhibitory action of Ang II. Preincubation of myocytes with pertussis toxin (5 microg/mL for > 120 min at 37 degrees C) virtually prevented subsequent Ang II action. The inhibitory effect of Ang II was also abolished in the open-cell-attached mode (achieved by a prior perfusion of streptolysin-O, 0.08 U/mL). In this mode, through tiny membrane holes, the intracellular ATP concentration can be controlled by bathing extracellular solutions containing a known ATP concentration.
Conclusions:
The inhibitory actions of Ang II on K(ATP) appear to be mediated by an increase in the subsarcolemmal ATP concentration that results from the inhibition of adenylate cyclase activities via AT1 receptors/PTX-sensitive G proteins.