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 Kchannels (K-ATP) were investigated in ventricular myocytes enzymatical ly isolated from adult guinea pig heart. Methods and Results In the wh ole-cell and cell-attached configurations (including open-cell-attache d mode) elf the patch-clamp technique, K-ATP currents (I-KATP) were ac tivated through metabolic poisoning by the use of inhibitors of both g lycolytic and oxidative ATP productions at 37 degrees C. In the whole- cell mode, I-KATP were reversibly suppressed by increasing extracellul ar glucose and Ang II (1 nmol/L). In the cell-attached mode, Ang II co ncentration-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 (AT(1)) receptor-selective antagonist, block ed the inhibitory action of Ang II. Preincubation of myocytes with per tussis toxin (5 mu g/mL for >120 min at 37 degrees C) virtually preven ted subsequent Ang II action. The inhibitory effect of Ang II was also abolished in the open-cell-attached mode (achieved by a prior perfusi on of streptolysin-O, 0.08 U/mL). In this mode, through tiny membrane holes, the intracellular ATP concentration can be controlled by bathin g extracellular solutions containing a known ATP concentration. Conclu sions The inhibitory actions of Ang II on K-ATP appear to be mediated by an increase in the subsarcolemmal ATF concentration that results fr om the inhibition of adenylate cyclase activities via AT(1) receptors/ PTX-sensitive G proteins.