The membrane properties of the rat anococcygeus muscle, during rest and activity, were investigated with micro-electrodes and partition stimulation. 2. Intercellular current spread occurred within the muscle and the mean length constant was 2-7 mm. The membrane showed rectification to depolarizing pulses. 3. The mean resting potential was --62-1 mV and the input resistance was 23-0 MOMEGA. Stimulation of intramural nerves produced depolarization to --21 mV and a 10% reduction in input resistance. Displacement of the membrane potential indicated that the transmembrane potential at the peak of the response was independent of the membrane potential. 4. Noradrenaline also produced depolarization and this was accompanied by a decrease in membrane resistance as indicated by a reduction in amplitude of the electrotonic potential. 5. It was concluded that the muscle possesses cable properties and that the action of the transmitter, noradrenaline, is to increase membrane permeability so that the membrane potential moves towards an equilibrium potential.
