[Modulating action of barium and other ions on the sensory activity of frog labyrinth].
The effect of Ba2+, TEA, 4-AP and CoCl2 on the EPSP and spike discharges recorded from single fibres of the posterior nerve in the isolated frog labyrinth has been investigated. In Ca-free solution Ba2+ preserved, at low concentration (0.3 mM), the resting activity and at higher levels (up to 6 mM) it resulted in a pronounced facilitation of the EPSP and spike discharges. Facilitation increased on increasing Ba2+ concentration up to 4-5 mM and it was more evident in those units exhibiting a low resting spike firing. The effect of Ba2+ (1 mM) was completely antagonized by 10 mM Ca2+ X CoCl2 (3 mM) suppressed the resting rate at the normal external Ca2+ concentration; the Co2+ block was partially relieved by 1.8 mM Ba2+ X TEA (20 mM) evoked a clear-cut increase in the EPSP and spike discharges which, however, was less consistent than that produced by Ba2+. By comparing the effect of TEA on the spike frequency with that obtained at different Ba2+ levels, the Ba2+ capacity to carry the Ca2+ current was dissected. Such an effect is dose-dependent and it is more evident in low-frequency units. Conversely, 4-AP did not affect the resting discharge frequency. These results indicate that either the Ca2+ or the Ba2+ current sustain the transmitter release at the cyto-neural junction. The effect of TEA suggests that the Ca2+-dependent K+ current may play an important role in supporting the neurosecretory process by controlling the membrane potential of the hair cells.
Rossi
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ML
Martini
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D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D001001:Anura; D001464:Barium / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D003035:Cobalt / Q000494:pharmacology; D007758:Ear, Inner / Q000187:drug effects* / Q000502:physiology; D004594:Electrophysiology; D011188:Potassium / Q000378:metabolism; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D000631:Aminopyridines; D013757:Tetraethylammonium Compounds; D001464:Barium; D003035:Cobalt; D015761:4-Aminopyridine; C018021:cobaltous chloride; D011188:Potassium; D002118:Calcium
Azione modulatrice del bario e di altri ioni sull'attività sensoriale del labirinto di rana.