COMPARATIVE-STUDIES OF FUROSEMIDE EFFECTS ON MEMBRANE-POTENTIAL AND INTRACELLULAR CHLORIDE ACTIVITY IN HUMAN AND RABBIT CILIARY EPITHELIUM

Furosemide (1 mM), a potent loop diuretic, caused a 10-mV (n = 14) depolarization of the intracellular potential difference (PD(I)) of isolated rabbit ciliary epithelium (CE), but produced a 9-mV (n = 5) hyperpolarization of PD(I) of isolated human CE. In rabbit CE, furosemide consistently depolarized PD(I) by 13, 7 and 8 mV in HCO3--free Ringer, Na+-free Ringer and after BaCl2 treatment, respectively. The depolarization of PD(I) was reduced to 2 mV (n = 11) in Cl--free conditions. A hyperpolarization of PD(I) caused by furosemide that was quantitatively similar to that seen in normal Ringer also occurred in human CE during immersion in HCO3--free Ringer, Na+-free Ringer and after BaCl2 treatment. There was a small hyperpolarization (3 mV) of PD(I) in Cl--free conditions. Human or rabbit tissue-cultured nonpigmented ciliary epithelial cells were loaded with the Cl--sensitive fluorophore 6-methoxy-N-(3-sulfopropyl) quinolinium (SPQ) in hypotonic solution (145 mosm) for 4 min at 37-degrees-C. Furosemide decreased intracellular Cl- fluorescence activity of both human and rabbit ciliary epithelial cells by 30 +/- 5 (n = 8) and 25 +/- 7% (n = 13), respectively, when the cells were immersed in Cl--rich solution. It is suggested that a furosemide-sensitive Cl- movement exists in both rabbit and human CE, although the mode of Cl- movement to the aqueous across CE may differ between these species.