Studies of the electrical excitability of aorta smooth muscle of rabbit.

1. Electrical records were made from the smooth muscle of rabbit aorta in normal solution and after excitation by noradrenaline, by the partitioned chamber method.2. Noradrenaline (3 x 10(-7) g/ml.) produced depolarization and periodic slow potentials, the amplitudes of which were decreased by depolarizing currents and increased by small hyperpolarizing currents. Application of strong hyperpolarizing current stopped production of the slow potentials.3. After application of small amounts of noradrenaline, electrical stimulation produced slow potentials.4. Membrane resistance at the top of the slow potential induced by noradrenaline (3 x 10(-7) g/ml.) was decreased to a few percent of the stable potential level during application of noradrenaline.5. The voltage-current relationship of smooth muscle cells in the aorta showed marked cathodal rectification both in standard solution and upon the application of noradrenaline.6. High K (24 mM) elicited periodic slow potentials, the electrical properties of which were very similar to those induced by noradrenaline. Phentolamine (5 x 10(-5) g/ml.) and guanithidine (10(-5) g/ml.), however, blocked the production of these slow potentials.7. The conditions required for the production of slow potentials are discussed.8. Evoked slow potentials by current flow during application of noradrenaline (3 x 10(-7) g/ml.) was recorded at 5 mm from the stimulating partition. Thus it is concluded that the slow potential can be conducted.