The effects of high perilymphatic K and Rb concentrations (20 mM) on the posterior canal resting discharge have been examined in the isolated frog labyrinth. Both K and Rb usually increase the resting EPSP and spike frequencies recorded intra-axonally at the level of the posterior nerve. The afferent K-Rb facilitation is accompanied by a reduction in size and broadening of the spikes; no repetitive action potentials, however, occur in the fibre. Therefore, the higher resting receptor activity is exclusively related to the increase in the EPSP emission rate. The afferent discharge facilitation was inversely related to the fibre's initial resting activity. The K effect was larger than the Rb effect, and both K and Rb actions were more conspicuous in some units (high sensitive) than in others (low sensitive). High K and Rb media steadily depolarize the basolateral receptor membrane. The increase in EPSP rate observed under these conditions indicates that the reduction in hair celi membrane potential sustains an increased transmitter release at the junction. This presynaptic effect is most likely related to larger amounts of Ca entering the cell during maintained depolarization.
THE EFFECT OF HIGH POTASSIUM AND RUBIDIUM CONCENTRATIONS ON EPSP AND SPIKE DISCHARGES OF THE FROG LABYRINTH POSTERIOR CANAL
ROSSI, Marialisa;MARTINI, Marta
1989
Abstract
The effects of high perilymphatic K and Rb concentrations (20 mM) on the posterior canal resting discharge have been examined in the isolated frog labyrinth. Both K and Rb usually increase the resting EPSP and spike frequencies recorded intra-axonally at the level of the posterior nerve. The afferent K-Rb facilitation is accompanied by a reduction in size and broadening of the spikes; no repetitive action potentials, however, occur in the fibre. Therefore, the higher resting receptor activity is exclusively related to the increase in the EPSP emission rate. The afferent discharge facilitation was inversely related to the fibre's initial resting activity. The K effect was larger than the Rb effect, and both K and Rb actions were more conspicuous in some units (high sensitive) than in others (low sensitive). High K and Rb media steadily depolarize the basolateral receptor membrane. The increase in EPSP rate observed under these conditions indicates that the reduction in hair celi membrane potential sustains an increased transmitter release at the junction. This presynaptic effect is most likely related to larger amounts of Ca entering the cell during maintained depolarization.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
