EFFECTS OF INTRACELLULAR PH ON ATP-SENSITIVE K+ CHANNELS IN MOUSE PANCREATIC BETA-CELLS

1. The effects of intracellular pH (pH(i)) on the ATP-sensitive K+ channel (K-ATP(+) channel) from mouse pancreatic beta-cells were examined in inside-out patches exposed to symmetrical 140 mM K+ solutions. 2. The relationship between channel activity and pH(1) was described by the Hill equation with half-maximal inhibition (K-i) at pH(i) 6.25 and a Hill coefficient of 3.7. 3. Following exposure to pH(i) < 6.8, channel activity did not recover to its original level. Subsequent application of trypsin to the intracellular membrane surface restored channel activity to its initial level or above. 4. At -60 mV the relationship between pH(i) and the single-channel current amplitude was described by a modified Hill equation with a Hill coefficient of 2.1, half-maximal inhibition at pH(i) 6.48 and a maximum inhibition of 18.5%. 5. A decrease in pH(i) reduced the extent of channel inhibition by ATP: K-i was 18 mu M at pH 7.2 and 33 mu M at pH 6.4. The Hill coefficient was also reduced, being 1.65 at pH 7.2 and 1.7 at pH 6.4. 6. When channel activity was plotted as a function of ATP(4-) (rather than total ATP) there was no effect of pH(i) on the relationship. This suggests that ATP(4-) is the inhibitory ion species and that the effects of reducing pH(i) are due to the lowered concentration of ATP(4-). 7. Changes in external pH had little effect on either single-channel or whole-cell K-ATP(+) currents. 8. The effects of pH(i) do not support a role for H+ in linking glucose metabolism to K-ATP(+) channel inhibition in pancreatic beta-cells.