Characterization of the effects of amphotericin B on ion channels in MDCK cells using the patch-clamp technique.
Cultured Madin-Darby Canine Kidney cells were used as a model to study the mechanism of nephrotoxicity of amphotericin B using the patch-clamp technique. At the whole-cell level, amphotericin B altered potassium conductances in two types of these cells categorized on the basis of whole-cell potassium currents. The first cell type, classified as Type I, exhibited no significant whole-cell potassium currents. The second type, Type II, exhibited depolarization-induced outward potassium currents that rundown over time. In both of these subpopulations, exposure to amphotericin B at a concentration of 68 nM for a prolonged period of time (approximately 30-45 min) led to an increased whole-cell potassium conductance. In Type I cells, it increased by a factor of 16 and in Type II cells, by a factor of 3.5. Furthermore, the potassium currents observed in Type I cells following amphotericin B treatment bore no resemblance to currents through pores formed by amphotericin B in artificial membranes. At the single-channel level, incubation with amphotericin B led to a significantly higher potassium channel activity in both inside-out and outside-out patches. Kinetic studies in inside-out patches revealed that the increases in channel activity were associated with a decrease in the mean closed time and an overall increase in the mean open time. In summary, our data suggest that the direct toxicity of amphotericin B is primarily related to its ability to disturb normal ion channel functioning rather than to formation of pores in cell membranes.
Hsu
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School of Pharmacy, University of Wisconsin-Madison, 53706, USA. shsu4@facstaff.wisc.edu
Burnette
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D000666:Amphotericin B / Q000494:pharmacology* / Q000633:toxicity; D000818:Animals; D002460:Cell Line; D004285:Dogs; D004553:Electric Conductivity; D007686:Kidney Tubules, Distal / Q000187:drug effects* / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism
D015221:Potassium Channels; D000666:Amphotericin B; D011188:Potassium