[Tonic mechanisms of efferent inhibition in the frog labyrinth].
Activation of the efferent system of the isolated group labyrinth inhibits the afferent EPSP and spike discharge by releasing ACh, which opens the Cl- channel of the hair cells membrane. Experiments in which increasing amounts of Cl- in the bath are replaced by equivalent amounts of Br-, NO2-, NO3-, CH3 CO2-, SO4(2-), CH3CH2CO2-, CH3(CH2)2CO2-, CH3(CH2)3CO2- benzoate, indicate that all these anions are able to penetrate the postsynaptic membrane, since full inhibition was invariably elicited. On the other hand, when citrate or isethionate are substituted for Cl- inhibition disappeared. In the presence of anions which are known to chelate calcium, its bath concentration was adequately increased. The presence of inhibition of Ringer-benzoate (benzoate ion size 6.5 A) and its disappearance in Ringer-citrate (8 A) or in Ringer-isethionate (greater than 10 A), suggests that the Cl- channel is at least 7 A in diameter, a size significantly larger than at other inhibitory synapses. Since metabolic inhibitors (DNP 0.1 mM and NaN3 1 mM) or acetazolamide (5 mM) and ammonium acetate (10 mM), which are known to block active Cl- pumping in other systems, do not affect the efferent synapse it appears difficult to interfere with the mechanisms which maintain the Cl- concentration gradient across the hair cell membrane.
D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D001966:Bromine / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D002951:Citrates / Q000494:pharmacology; D007758:Ear, Inner / Q000187:drug effects*; D007513:Isethionic Acid / Q000494:pharmacology; D009411:Nerve Endings / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects; D011898:Ranidae; D000159:Vestibulocochlear Nerve / Q000187:drug effects*
D001565:Benzoates; D002712:Chlorides; D002951:Citrates; D007513:Isethionic Acid; D001966:Bromine
Meccanismi ionici dell'inibizione efferente nel labirinto di rana.