An analysis of the action of atropine and scopolamine on the end-plate current of frog sartorius muscle.

The effects of atropine sulfate and scopolamine hydrobromide were investigated on the end-plate current (EPC) of frog sartorius muscle by standard voltage-clamp techniques. Both atropine and scopolamine reduced the peak EPC amplitude although scopolamine was only one-third as potent as atropine. The reduction of amplitude became more pronounced with increasing membrane hyperpolarization resulting in nonlinear current-voltage characteristics. Atropine shortened the EPC duration and decreased the voltage-sensitivity of the falling phase; the latter, however, continued to remain a single exponential function of time as in the control. Scopolamine reduced the time to peak, and in addition, converted the falling phase to a double exponential function, consisting of a rapid initial phase followed by a slow terminal phase. Both phases of fall were altered by changes in drug concentration but only the terminal phase responded appreciably to changes in membrane potential. Atropine and scopolamine were without effect on the EPC reversal potential, indicating that the drugs do not exhibit a preference for the ionic species carrying the synaptic current.