Atypical Action of Barium Chloride on Rabbit Colon.

During experiments on excised smooth muscle organs, approximately one hundred segments of rabbit colon have been subjected to the action of barium chloride in concentrations of from 1:100,000 to 1:20,000. The segments were suspended in Tyrode solution according to the method of Magnus. Colon segments as a rule were stimulated immediately by the introduction of barium chloride into the bath, resulting in an increase in tonus or in amplitude of rhythmic contractions and often in an increase in rate of contractions. In the case of seven segments, however, the stimulation due to barium chloride was slight, and was preceded by a period of depression, lasting from 15 to 250 seconds and manifested by a fall in tonus and decrease in amplitude. Rate was little affected. The accompanying figure shows two examples of this atypical response to barium. Roth has described primary and persistent depression of rings of the lower intestine of the frog by barium; the writer previously reported barium depression of rabbit uterus suspended in potassium-free Tyrode solution. These depressions agree with the atypical response of rabbit colon. The similarity suggests that barium affects smooth muscle according to the functional state determined by the physical and chemical conditions of its environment.