The effect of cloftlium, which is known to reduce the endocochlear potenziai (Mori a al., Eur. Arch. Otorhinolaryngol., 251, 186, 1993). was studied at the cytoneural junction of the intact frog labyrinth. MEPSP and spike rates were recorded from the posterior nerve at rest and during sinusoidal canal rotation (0.1 Hz, peak acceleration 12 deg/s2) in the absence or presence of 10-3 M clofilium. The recordings were analysed by means of signal processing techniques (Rossi et al., L Gen. Physiol. 94. 303, 1989; Rossi et al., J. Physiol., 421. 17, 1994). Frequency, amplitude and time intervals between successive mEPSPs were evaluated in control solution and in the presence of the drug. The amplitude distributions of mEPSPs were always continuous, unimodal and well fit by single lognormal distribution functions, and their time intervals were exponentially distributed. This suggests that transminer release retains its quantal and random nature in the presence of the drug. Clofilium decreased mEPSP amplitude (-24%) and rate (-30% at rest and -23% during stimulation), and abolished spike firing. Clofilium appears to operate at different sites in the sensory organ. A decrease in the hair cell transduction current could account for the observed moderate decrease in mEPSP rate. The disappearance of afferent action potentials (unexplained by the moderate decrease in transmitter release) and the reduction in mEPSP peak amplitude point to a postsynaptic action of the drug. Depolarization of the afferent fibre at rest (secondary to the K+ conductance decrease) might reduce mEPSP amplitude and partially inactivate Na+ channels, thus raising the firing threshold for the spike encoder.
THE EFFECT OF CLOFILIUM, A K-CHANNEL BLOCKER, ON THE AFFERENT DISCHARGE OF THE ISOLATED FROG LABYRINTH
ROSSI, Marialisa;MARTINI, Marta;PELUCCHI, Bruna
1996
Abstract
The effect of cloftlium, which is known to reduce the endocochlear potenziai (Mori a al., Eur. Arch. Otorhinolaryngol., 251, 186, 1993). was studied at the cytoneural junction of the intact frog labyrinth. MEPSP and spike rates were recorded from the posterior nerve at rest and during sinusoidal canal rotation (0.1 Hz, peak acceleration 12 deg/s2) in the absence or presence of 10-3 M clofilium. The recordings were analysed by means of signal processing techniques (Rossi et al., L Gen. Physiol. 94. 303, 1989; Rossi et al., J. Physiol., 421. 17, 1994). Frequency, amplitude and time intervals between successive mEPSPs were evaluated in control solution and in the presence of the drug. The amplitude distributions of mEPSPs were always continuous, unimodal and well fit by single lognormal distribution functions, and their time intervals were exponentially distributed. This suggests that transminer release retains its quantal and random nature in the presence of the drug. Clofilium decreased mEPSP amplitude (-24%) and rate (-30% at rest and -23% during stimulation), and abolished spike firing. Clofilium appears to operate at different sites in the sensory organ. A decrease in the hair cell transduction current could account for the observed moderate decrease in mEPSP rate. The disappearance of afferent action potentials (unexplained by the moderate decrease in transmitter release) and the reduction in mEPSP peak amplitude point to a postsynaptic action of the drug. Depolarization of the afferent fibre at rest (secondary to the K+ conductance decrease) might reduce mEPSP amplitude and partially inactivate Na+ channels, thus raising the firing threshold for the spike encoder.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
