Presynaptic calcium currents in squid giant synapse

A voltage clamp study has been performed in the presynaptic terminal of the squid stellate ganglion. After blockage of the voltage-dependent sodium and potassium conductances, an inward calcium current is demonstrated. Given a step-depolarization pulse, this voltage- and time-dependent conductance has an S-shaped onset. At the "break" of the voltage step, a rapid tail current is observed. From these results a kinetic model is generated which accounts for the experimental results and predicts for the time course and amplitude a possible calcium entry during presynaptic action potentials.

Relationship between presynaptic calcium current and postsynaptic potential in squid giant synapse

The relationship between calcium current and transmitter release was studied in squid giant synapse. It was found that the voltage-dependent calcium current triggers the release of synaptic transmitter in direct proportion to its magnitude and duration. Transmitter release occurs with a delay of approximately 200 mus after the influx of calcium. A model is presented which describes these relations formally.

Transmission in the squid giant synapse: a model based on voltage clamp studies

1. Voltage clamp studies were performed in squid giant synapse after blockage of the voltage-dependent sodium and potassium conductances. 2. Presynaptic depolarization under these conditions demonstrates the presence of voltage-dependent calcium conductance change for the duration of the voltage step, and a tail current at the break of the pulse. 2. This calcium current triggers a postsynaptic response which can be measured directly at the postsynaptic fiber. 4. These voltage clamp experiments have allowed the development of a mathematical model that describes the kinetics of the calcium current and the relationship between calcium current and transmitter release.

Presynaptic calcium currents and their relation to synaptic transmission: voltage clamp study in squid giant synapse and theoretical model for the calcium gate

A voltage clamp study of the presynaptic terminal in squid stellate ganglion has given quantitative results relating inward Ca2+ current to presynaptic membrane potential and postsynaptic response to inward Ca2+ current. The results indicate an S-shaped curve for the relationship between presynaptic potential and Ca2+ current and a linear relationship between Ca2+ current and postsynaptic potential. A similar S-shaped curve was found for the time-dependent properties of the Ca2+ conductance. Based on these results a mathematical model was developed which accounts for the experimental results in this and previously published papers by other authors. The model suggests that five subunits are involved in the Ca2+ gate and that the subunits change noncooperatively from an inactive to an active form upon membrane depolarization.

Inferior olive: its role in motor learing

Specific chemical lesion of the rat inferior olive by intraperitoneal administration of 3-acetylpyridine prevents recuperation from motor abnormalities generated by unilateral labyrinthine lesion. Moreover, in animals that have recuperated from the balyrinthine lesion, 3-acetylpyridine produces a reversal of the symptoms within 2 hours of administration. These results indicate that the integrity of the olivo-cerebellar system is necessary for the acquisition and retention of this form of motor learning, but that the cerebellum itself is not the seat of such learning.