Activation of the efferent system in the isolated frog labyrinth inhibits the afferent EPSP and spike discharge by releasing ACh, which opens the Cl- channel of the hair cell membrane. Experiments in which increasing amounts of Cl- in the bath are replaced by equivalent amounts of Br- , NO2-, NO3- , CH3CO2-, SO4--, CH3 CH2CO2-; CH3(CH2)2CO2-, CH3(CH2)3 CO2-, benzoate, indicate that all these anions are able to penetrate the post¬synaptic 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 in Ringer-benzoate (benzoate ion size 6.5 A°) and its disappearance in Ringer-citrate (8 A°) or in Ringer-isethionate (>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.

Meccanismi ionici dell'inibizione efferente nel labirinto di rana

ROSSI, Marialisa
1981

Abstract

Activation of the efferent system in the isolated frog labyrinth inhibits the afferent EPSP and spike discharge by releasing ACh, which opens the Cl- channel of the hair cell membrane. Experiments in which increasing amounts of Cl- in the bath are replaced by equivalent amounts of Br- , NO2-, NO3- , CH3CO2-, SO4--, CH3 CH2CO2-; CH3(CH2)2CO2-, CH3(CH2)3 CO2-, benzoate, indicate that all these anions are able to penetrate the post¬synaptic 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 in Ringer-benzoate (benzoate ion size 6.5 A°) and its disappearance in Ringer-citrate (8 A°) or in Ringer-isethionate (>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.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/1478116
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