The effect of atropine and curarine on the time course of the end-plate potential in frog sartorius muscle

Abstract

The effect of atropine and curarine on the time course of the end-plate potential was studied in the presence and absence of anticholinesterases.

Methods consisted of measuring the voltage-current relation of the muscle membrane, using microelectrophoretic application of acetylcholine to the end-plate region, and measuring end-plate current with a voltage-clamp technique.

Atropine (10⁻⁴Eq/1) decreased the amplitude and shortened the time course of the end-plate potential in curarized muscle. The underlying end-plate current was decreased on the average by about 20%, and its time course was shortened by 30–40%. These effects of atropine became more pronounced during treatment of the muscle with anticholinesterases prostigmine (3 × 10⁻⁶M), diisopropylfluorophosphate (10⁻⁴ M) and tetraethylpyrophosphate (10⁻⁴ M).

Curarine decreased the amplitude but did not affect the time course of the end-plate potential and end-plate current. During treatment of the muscle with prostigmine (3 × 10⁻⁶M) ,however, a similar increase in the concentration of curarine shortened the time course on the average by 5–10%.

It is possible that in presence of atropine and curarine a late component of transmitter action (e.g. on more distant receptors) is suppressed.