pH in principal cells of frog skin (Rana pipiens): effects of amiloride and potential

Intracellular pH (pHi) and apical cell membrane potential (Va) were determined in principal cells of frog skin (Rana pipiens) with double-barrel micro-electrodes. In the Northern and Southern varieties, respectively, pHi is 0.38 and 0.26 pH units below bath pH. Amiloride, applied apically, causes reversible intracellular acidification at concentrations of 10(-5) M or higher. Voltage clamp-induced hyperpolarization and depolarization of Va result in intracellular acidification and alkalinization, respectively. This response of pHi is inhibited or abolished when the apical side is treated with 10(-3) M 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). Amiloride-induced intracellular acidification is not exclusively due to the hyperpolarization of Va that accompanies amiloride treatment since 1) amiloride causes greater acidification than equivalent voltage clamp-induced hyperpolarization of Va, 2) amiloride-induced acidification persists in DIDS-treated tissues, and 3) there is no correlation between hyperpolarization of Va and intracellular acidification occurring after amiloride. We conclude that pHi is below the extracellular pH. Amiloride causes intracellular acidification that may be in part connected with hyperpolarization of Va. However, a major component of amiloride-induced acidification is due to other factors, possibly inhibition of apical Na+-H+ exchange. The inhibitory effect of apically applied DIDS suggests that the voltage dependent changes in pHi are related to movement of HCO3 (or OH) ions across the apical cell membrane.