Comparative Studies of Furosemide Effects on Membrane Potential and Intracellular Chloride Activity in Human and Rabbit Ciliary Epithelium

Abstract

Furosemide (1 m M), 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 PDI of isolated human CE. In rabbit CE, furosemide consistently depolarized PDi byChloride transport 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 hyper polarization 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-sul-fopropyl) quinolinium (SPQ) in hypotonic solution (145 mosm) for 4 min at 37°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 Ch-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.