Effect of pH on the ATP-sensitive K+ channel in aortic smooth muscle cells from rats

ABSTRACT

The effects of pH on K+ currents were investigated in single smooth muscle cells isolated from the thoracic aorta of Wistar-Kyoto rats. Whole-cell K+ currents were recorded in the conventional configuration of the voltage-clamp technique. Pinacidil (10muM) activated the whole-cell current and the pinacidil-activated current was completely inhibited by glibenclamide (10muM), an inhibitor of ATP-sensitive K+ channel (KATP channel). Pinacidil-activated current was reversed at near the K+ equilibrium potential. This current was time- and voltage-independent and reduced by elevating intracellular ATP. Pinacidil-activated current was reduced by lowering the external pH. However, alteration of internal pH has controversial effects on pinacidil-activated current. When the single cell was dialyzed with 0.1 mM ATP, alteration of internal pH had no effect on pinacidil-activated K+ current. In the contrast, when the single cell was dialyzed with 3 mM ATP, pinacidil-activated current was increased by lowering internal pH. Our results suggest that K+ channel activated by pinacidil may be KATP channel and internal H+ may reduce the inhibitory effect of ATP on KATP channel.