Effects of tetrodotoxin on the slowly adapting stretch receptor neurone of lobster

Abstract

1. A study has been made of the effects of tetrodotoxin on the impulse activity, resting membrane potential, input resistance, and the generator potential and its after‐hyperpolarization of the slowly adapting stretch receptor neurone of the lobster. 2. Tetrodotoxin was able to abolish completely within about 2 min the impulse activity in most cells, when given in a dose of 2 × 10−8 g/ml., but in all cells, when administered in a dose of 4 × 10−8 g/ml. After blockage by the toxin in concentrations as high as 4 × 10−6 g/ml. for periods of up to 30 min the action potential was restored by washing the preparation in physiological solution for 1 hr. 3. In a concentration of 4 × 10−8 g/ml. tetrodotoxin produced within 1–2 min an average increase of 4·8 mV of the resting membrane potential and a simultaneous 47% reduction of the resting input resistance. These effects were reversed by washing the preparation in physiological solution for 1 hr. 4. Tetrodotoxin administered in doses as high as 4 × 10−6 g/ml. for periods of up to 30 min had no effect on the amplitude of the steady phase of the generator potential. 5. In a concentration of 4 × 10−8 g/ml. tetrodotoxin produced within 5 min a 65% reduction of the amplitude of the hyperpolarization following the generator potential. This effect was reversed by washing the preparation in physiological solution for 1 hr. 6. The simultaneous increase in resting membrane potential and decrease in membrane resistance is suggested to be due to an elevated potassium permeability besides a reduced sodium conductance. The constancy in height of the generator potential in the presence of a decreased membrane resistance makes necessary the assumption of an augmented generator current. The decrease in amplitude of the hyperpolarization following the generator potential may be the result of an increase in potassium conductance and/or a reduction in acceleration of an electrogenic pump in consequence of a diminished sodium influx during the generator potential.

Responses in the Sensory Nerve Terminal of Leaf-Like Receptors in the Frog Sartorius Muscle

“…When the slow potential deflects to negative at the sensory terminal in reference to the proximal portion of the axon, it may be considered a generator potential. The behavior of the slow potential that was not significantly influenced by tetrodotoxin and procaine is similar to the response of spindle potentials in the frog muscle spindle (ALBUQUERQUE et al, 1969) and in the crustacean slowly adapting stretch receptor neuron (ALBUQUERQUE and GRAMPP, 1968 ;LOWENSTEIN et al, 1963) to application of the drugs. However, the slow potential may not be a generator potential for the following reasons.…”

TTX sensitive plateau potentials in the crayfish slowly adapting stretch receptor neuron

“…Spikes were also eventually suppressed leaving only a small rebound (B3). TTX did not evoke the hyperpolarization reported in the lobster stretch receptor, an effect which was identified with an increased K + permeability as well as a reduced Na + conductance (Albuquerque and Grampp 1968), because the K + current was blocked by TEA in our experiments.…”

Depolarization of sensory nerve endings and impulse initiation in common carotid baroreceptors

“…The slow potential was not blocked by tetrodotoxin which blocks the initiation of the spike potential. In other mechanosensitive structures such as the muscle spindle, the stretch receptor and the Pacinian corpuscle, tetrodotoxin blocks nerve conduction without depressing appreciably the receptor potential (Ito, 1971;Albuquerque & Grampp, 1968), if the concentration of the drug is not high (Nishi & Sato, 1966). S.MATSUURA 54 GENERATOR POTENTIAL OF BARORECEPTOR FIBRES 55 Results obtained in this study show that the slow potential recorded from a point close to the sensory terminals of the baroreceptor fibres has the typical characteristics of a generator potential, as reported for other mechanoreceptors. In the baroreceptor, the sensory terminals of the fibre have been proposed to be the receptor site from electron microscopic studies, and afferent synapses have not been found around the terminal region (Rees, 1967).…”

“…In other mechanosensitive structures such as the muscle spindle, the stretch receptor and the Pacinian corpuscle, tetrodotoxin blocks nerve conduction without depressing appreciably the receptor potential (Ito, 1971;Albuquerque & Grampp, 1968), if the concentration of the drug is not high (Nishi & Sato, 1966 …”