ANALYSIS OF ACTION OF ATROPINE AND SCOPOLAMINE ON ENDPLATE CURRENT OF FROG SARTORIUS MUSCLE

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  • 1 January 1976
    • journal article
    • research article
    • Vol. 196  (2) , 360-372
Abstract
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 1/3 as potent as atropine. The reduction of amplitude was 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 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. Atropine and scopolamine may modify the EPC by acting at sites distinct from the combination of acetylcholine with receptors. The drugs probably act on a regulatory component of the end-plate channel, termed the ionic conductance modulator, to alter the kinetics and voltage sensitivity of ion translocation. This effect may be exerted by direct action on the ionic conductance modulator or indirectly through alterations of the end-plate membrane.