The action of acetylcholine on background conductance in frog atrial trabeculae.

The action of acetylcholine (ACh) on membrane potential and currents in frog atrial muscle has been studied with a double sucrose gap technique. The results show the following. 1. ACh induces the development of an extra current, outward at the resting potential, which is dependent on the ACh concentration. 2. The preparation does not show any sign of desensitization. 3. The reversal potential of the current induced by ACh is between 0 and 20 mV more negative than the resting potential and behaves as a K electrode. 4. The mechanism of ACh-induced K conductance presents inward going rectification properties. 5. The delayed outward current is not affected by ACh. However the evolution of its tail current seems to indicate a process of K accumulation related to the ACh-induced current.