Korbmacher C, Helbig H, Förster C, Wiederholt M
Institut für Klinische Physiologie, Freie Universität Berlin, FRG.
Curr Eye Res. 1988 Jun;7(6):619-26. doi: 10.3109/02713688809031819.
Two methods were used to investigate cellular ion transport processes in confluent monolayers of cultured bovine corneal epithelial cells: measurements of membrane voltage (V) using conventional microelectrodes, and intracellular pH (pHi) measurements using the pH sensitive absorbance of intracellularly trapped 5 (and 6)-carboxy-4', 5'dimethyl-fluorescein. (1) V averaged -39.2 +/- 0.9 mV (mean +/- SEM, n = 71) with a range of -30 to -59 mV. Increasing extracellular potassium depolarized the cell membrane with a K+-slope of 43.3 mV/decade [K+] (for [K+] between 20 and 80 mM). Intracellular as well as extracellular acidification reversibly depolarized the cell membrane. Depolarization induced by 40 mM K+-pulses was smaller at extracellular pH (pHo) of 6.9 as compared to pHo = 7.9. These findings are compatible with a pH-sensitive K+ conductance. (2) During steady state pHi was 6.96 +/- 0.05 (mean +/- SEM, n = 7). After intracellular acidification, induced by NH4Cl-prepulse technique, pHi was regulated back towards normal steady state pHi. Application of 1 mM amiloride reversibly inhibited pHi recovery. Furthermore, pHi backregulation was inhibited by removing sodium from the extracellular solution. The effect was reversible after readdition of sodium. These findings suggest that a Na+/H+ exchange is present in corneal epithelial cells and participates in pHi backregulation after an intracellular acid load.
