Functional Compartmentalization of ATP Is Involved in Angiotensin II–Mediated Closure of Cardiac ATP-Sensitive K + Channels

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°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 IC 50 value of 3.2±0.5 pmol/L (Hill coefficient=1.3±0.3). CV11974 (100 nmol/L), an angiotensin 1 (AT 1 ) receptor-selective antagonist, blocked the inhibitory action of Ang II. Preincubation of myocytes with pertussis toxin (5 μg/mL for >120 min at 37°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 AT 1 receptors/PTX-sensitive G proteins.