Activation of the efferent system in the isolated frog labyrinth inhibits the afferent EPSP and spike discharge by releasing ACh. When Na-isethionate is substituted for external Cl-, inhibition disappears, thus indicating that ACh opens the Cl channel. Experiments in which increasing amounts of Cl- in the bath are replaced by equivalent amounts of Br-, NO2-, NO3-, CH3CO2-, SO4-- indicate that all these anions are able to penetrate the postsynaptic membrane, since full inhibition can invariably be evoked. At present it is possible to set a lover limit (4.52 A°) to the size of the inhibitory channel. It appears that Cl- is passively distributed across the hair cell membrane since long lasting treatments with metabolic inhibitors such as DNP (0.1mM) or NaN3 (up to 10-3 M) do not affect inhibition at all. In the presence of ammonium acetate (10mM), which is known to block active Cl-pumping in other systems, inhibition was similarly unaffected.
Ionic mechanisms sustaining inhibition in the frog labyrinth
ROSSI, Marialisa
1980
Abstract
Activation of the efferent system in the isolated frog labyrinth inhibits the afferent EPSP and spike discharge by releasing ACh. When Na-isethionate is substituted for external Cl-, inhibition disappears, thus indicating that ACh opens the Cl channel. Experiments in which increasing amounts of Cl- in the bath are replaced by equivalent amounts of Br-, NO2-, NO3-, CH3CO2-, SO4-- indicate that all these anions are able to penetrate the postsynaptic membrane, since full inhibition can invariably be evoked. At present it is possible to set a lover limit (4.52 A°) to the size of the inhibitory channel. It appears that Cl- is passively distributed across the hair cell membrane since long lasting treatments with metabolic inhibitors such as DNP (0.1mM) or NaN3 (up to 10-3 M) do not affect inhibition at all. In the presence of ammonium acetate (10mM), which is known to block active Cl-pumping in other systems, inhibition was similarly unaffected.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
