Bumetanide Hyperpolarizes Madin–Darby Canine Kidney Cells and Enhances Cellular Gentamicin Uptake by Elevating Cytosolic Ca2+ Thus Facilitating Intermediate Conductance Ca2+-Activated Potassium Channels |
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Authors: | Tian Wang Yu-qin Yang Takatoshi Karasawa Qi Wang Amanda Phillips Bing-Cai Guan Ke-Tao Ma Meiyan Jiang Ding-Hua Xie Peter S Steyger Zhi-Gen Jiang |
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Institution: | 1. Oregon Hearing Research Center, NRC04, Department of Otolaryngology, Oregon Health & Science University, Portland, OR, 97239, USA 2. Institute of Otology, The Second Xiang-Ya Hospital, Central South University, 139 Renmin-Zhong Rd, Changsha, 410011, Hunan, People’s Republic of China 3. Department of Pharmacology, Hebei Medical University, 361 East Zhongshan Road, Shijiazhuang, 050017, People’s Republic of China 4. Department of Physiology, Shihezi University Medical College, Shihezi, 832002, People’s Republic of China
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Abstract: | Loop diuretics such as bumetanide and furosemide enhance aminoglycoside ototoxicity when co-administered to patients and animal models. The underlying mechanism(s) is poorly understood. We investigated the effect of these diuretics on cellular uptake of aminoglycosides, using Texas Red-tagged gentamicin (GTTR), and intracellular/whole-cell recordings of Madin–Darby canine kidney (MDCK) cells. We found that bumetanide and furosemide dose-dependently enhanced cytoplasmic GTTR fluorescence by ~60 %. This enhancement was suppressed by La3+, a non-selective cation channel (NSCC) blocker, and by K+ channel blockers Ba2+ and clotrimazole, but not by tetraethylammonium (TEA), 4-aminopyridine (4-AP) or glipizide, nor by Cl? channel blockers diphenylamine-2-carboxylic acid (DPC), niflumic acid (NFA), and CFTRinh-172. Bumetanide and furosemide hyperpolarized MDCK cells by ~14 mV, increased whole-cell I/V slope conductance; the bumetanide-induced net current I/V showed a reversal potential (V r) ~?80 mV. Bumetanide-induced hyperpolarization and I/V change was suppressed by Ba2+ or clotrimazole, and absent in elevated Ca2+]i, but was not affected by apamin, 4-AP, TEA, glipizide, DPC, NFA, or CFTRinh-172. Bumetanide and furosemide stimulated a surge of Fluo-4-indicated cytosolic Ca2+. Ba2+ and clotrimazole alone depolarized cells by ~18 mV and reduced I/V slope with a net current V r near ?85 mV, and reduced GTTR uptake by ~20 %. La3+ alone hyperpolarized the cells by ~?14 mV, reduced the I/V slope with a net current V r near ?10 mV, and inhibited GTTR uptake by ~50 %. In the presence of La3+, bumetanide-caused negligible change in potential or I/V. We conclude that NSCCs constitute a major cell entry pathway for cationic aminoglycosides; bumetanide enhances aminoglycoside uptake by hyperpolarizing cells that increases the cation influx driving force; and bumetanide-induced hyperpolarization is caused by elevating intracellular Ca2+ and thus facilitating activation of the intermediate conductance Ca2+-activated K+ channels. |
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