The synaptic effect of the blockade of the hair cell Ca- and K-currents has been examined in the isolated frog labyrinth to investigate whether in the presence of Ba (1 mM), TEA (20 mM) or 4-AP (20 mM), the resting receptor discharge frequency could be still modulated by mechanical stimulation (0.1-0.3 Hz; acceleratory peaks of 12.5 and 63.4°/sec2, respectively) and to define the possible link between the resting rate and response to rotation in different units. In normal saline a linear relationship was found between the mean resting discharge and the respective excitatory peak response during sinusoidal stimulation. Consistent evoked responses were also obtained under Ba and TEA treatment which proved to depend linearly on the new mean resting discharge of the units. Conversely, a reduced evoked response was invariably observed in all the fibres tested in the presence of 4-AP. The analysis of the linear equations fitting the experimental data suggests that, when moderate accelerations are used and similar resting rates are considered in normal solution and under Ba or TEA treatment, Ba is more effective than Ca in sustaining the evoked transmitter release. On the other hand, the TEA response was always less consistent than the corresponding one in control solution. The results suggest that the resting discharge provides the different units with the possibility of coding different information in the presence of the same mechanical input. It appears also evident that the safety factor for synaptic transmission should be high. In fact in the presence of Ba or TEA, despite a considerable fraction of the available transmitter pool being spent to sustain the new resting discharge level, the evoked response still increases consistently.
Ruolo delle correnti Ca and K nella trasmissione sinaptica afferente del labirinto isolato di rana
ROSSI, Marialisa;MARTINI, Marta
1987
Abstract
The synaptic effect of the blockade of the hair cell Ca- and K-currents has been examined in the isolated frog labyrinth to investigate whether in the presence of Ba (1 mM), TEA (20 mM) or 4-AP (20 mM), the resting receptor discharge frequency could be still modulated by mechanical stimulation (0.1-0.3 Hz; acceleratory peaks of 12.5 and 63.4°/sec2, respectively) and to define the possible link between the resting rate and response to rotation in different units. In normal saline a linear relationship was found between the mean resting discharge and the respective excitatory peak response during sinusoidal stimulation. Consistent evoked responses were also obtained under Ba and TEA treatment which proved to depend linearly on the new mean resting discharge of the units. Conversely, a reduced evoked response was invariably observed in all the fibres tested in the presence of 4-AP. The analysis of the linear equations fitting the experimental data suggests that, when moderate accelerations are used and similar resting rates are considered in normal solution and under Ba or TEA treatment, Ba is more effective than Ca in sustaining the evoked transmitter release. On the other hand, the TEA response was always less consistent than the corresponding one in control solution. The results suggest that the resting discharge provides the different units with the possibility of coding different information in the presence of the same mechanical input. It appears also evident that the safety factor for synaptic transmission should be high. In fact in the presence of Ba or TEA, despite a considerable fraction of the available transmitter pool being spent to sustain the new resting discharge level, the evoked response still increases consistently.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
