The Na+-dependent regulation of the internal pH in chick skeletal muscle cells. The role of the Na+/H+ exchange system and its dependence on internal pH.

The internal pH (pHi) of chick muscle cells is determined by the transmembrane Na+ gradient. Li+, but not K+, Rb+ or Cs+, can substitute for Na+ for regulating the internal pH of chick muscle cells. Pharmacological evidence using amiloride and amiloride analogs has shown that the Na+/H+ exchange system is the membrane mechanism that couples the pHi to the transmembrane Na+ gradient. The pHi dependence of the amiloride-sensitive Na+/H+ exchange mechanism was defined. Internal H+ interacts cooperatively with the Na+/H+ exchange system, in contrast with external H+, thus indicating an asymmetrical behaviour of this exchanger. The half-maximum effect for the activation by the internal H+ of the Na+ transporting activity of the amiloride-sensitive Na+/H+ exchange was observed at pH 7.4. The Hill coefficient of the H+ concentration dependence is higher than 3. Insulin was shown to have no effect on the pHi of chick muscle cells.