title: Acute effects of gentamicin on the ionic currents of semicircular canal hair cells in the frog.
abstract: The effects of acute gentamicin application on hair cells isolated from the frog semicircular canals have been tested by using the patch-clamp technique in the whole-cell configuration. Extracellular gentamicin (1 mM) mostly affected the Ca(2+) macrocurrent, I(Ca), and the Ca-dependent K(+) current, I(KCa). The drug, applied to the hair cell basolateral membrane through a fast perfusion system, produced a rapid and relevant decrease (∼34%) of I(Ca) amplitude, without apparently affecting its activation-deactivation kinetics. The I(KCa) component of the delayed I(KD) was similarly affected: peak and steady-state mean amplitudes were significantly reduced, by about 47 and 54%, respectively, whereas the time constant of the mono-exponential current rising phase did not change. The Ca(2+) independent fraction of I(KD), I(KV), and the fast IA current were unaffected. Transduction channels (permeable to and blocked by gentamicin) are not available in the isolated hair cell, so the effect of intracellular gentamicin was tested by applying the drug through the patch pipette (1 mM in the pipette): again, it significantly reduced both I(Ca) and I(KD) amplitude, without affecting currents kinetics. IA properties were also unaffected. The drug did not affect the onset and removal of I(KD) inactivation, although the changes were scaled to the reduced I(KD) amplitude. From these observations, it is expected that hair cells exposed to gentamicin 'in vivo' become unresponsive to physiological stimulation (block of the transduction channels) and transmitter release at the cytoneural junction be drastically depressed due to reduced Ca(2+) inflow. In particular, functional impairment ensues much earlier than biochemical events that lead to hair cell apoptosis.
authors: Dipartimento di Biologia ed Evoluzione, Sezione di Fisiologia e Biofisica, Università di Ferrara, Via Borsari 46, I-44121 Ferrara, Italy. mrm@unife.it
authors: Marta
authors: M
authors: Martini
authors: Rita
authors: R
authors: Canella
authors: Ivo
authors: I
authors: Prigioni
authors: Giancarlo
authors: G
authors: Russo
authors: Elisa
authors: E
authors: Tavazzani
authors: Riccardo
authors: R
authors: Fesce
authors: Maria Lisa
authors: ML
authors: Rossi
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000633:toxicity*; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005839:Gentamicins / Q000633:toxicity*; D006198:Hair Cells, Auditory / Q000187:drug effects* / Q000378:metabolism; D017136:Ion Transport; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects* / Q000378:metabolism; D011893:Rana esculenta; D012665:Semicircular Canals / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D015220:Calcium Channels; D005839:Gentamicins; D024681:Potassium Channels, Calcium-Activated