Electrogenic sodium pump in frog crista ampullaris

The generator potential was recorded in the sensory organ of frog semicircular canals and some dynamic deviations from the Steinhausen's pendulum model due to adaptation were investigated. A suitable turntable enabled controlled ramps, steps and sinusoids of angular velocity to be applied to isolated labyrinths. Suction electrodes provided with sinterized Ag/AgCl tablets allowed stable DC recordings from distal stump of cut ampullary nerve. Substantial evidence is presented that an ion transport is activated in ampullary nerve fibres during excitation which is able of shifting the reference level, thus producing adaptation and related distortions. In fact the dynamics between the expected cupula position and time course in generator potential became remarkably reduced in the following conditions: a)- when Li was substituted for Na in the saline; b)- in the presence of Ouabain .02 mM/ml; c)- in solutions where K was lacking; d)- in the presence of DNP .2 mM/ml. An electroneutral pump shifting toward more negativity the K-equilibrium potential by an intense reabsorption of potassium, or, more probably, an electrogenic Na-pump which directly hyperpolarizes the membrane by driving a net positive charge outwards might produce the observed deviations from an overdamped behavior. Since the time course of the decline in the responses was maintained in the presence of TTX .1 microg/ml, any possible relation between the pump and the spikes arising at the encoder may be ruled out. The pump therefore should operate at the ultimate fibre endings where a consistent Na inward flux is expected during the activation of postsynaptic terminals.