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

1. The effects of intracellular pH (pH(i)) on the ATP-sensitive K+ cha nnel (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 t he 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, chann el activity did not recover to its original level. Subsequent applicat ion 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 b y a modified Hill equation with a Hill coefficient of 2.1, half-maxima l inhibition at pH(i) 6.48 and a maximum inhibition of 18.5%. 5. A dec rease in pH(i) reduced the extent of channel inhibition by ATP: K-i wa s 18 mu M at pH 7.2 and 33 mu M at pH 6.4. The Hill coefficient was al so reduced, being 1.65 at pH 7.2 and 1.7 at pH 6.4. 6. When channel ac tivity was plotted as a function of ATP(4-) (rather than total ATP) th ere 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 ext ernal pH had little effect on either single-channel or whole-cell K-AT P(+) currents. 8. The effects of pH(i) do not support a role for H+ in linking glucose metabolism to K-ATP(+) channel inhibition in pancreat ic beta-cells.