EFFECTS OF EXTRACELLULARY APPLIED ATP AND RELATED COMPOUNDS ON ELECTRICAL AND MECHANICAL ACTIVITY OF SMOOTH MUSCLE TAENIA COLI FROM GUINEA-PIG

The effect of external ATP and related compounds on the electrical and mechanical activity of isolated pieces of taenia coli has been studied. ATP, AMP and adenosine caused a decrease in the spontaneous tone, a decrease in the frequency of spike discharge, and hyperpolarization. ATP was up to 100 times as potent an inhibitor of spontaneous activity as AMP or adenosine. GMP, guanosine and inosine had no effect. High K+ contractures were relaxed by the same compounds and adenine, which was the most potent. Here again GMP, guanosine and inosine had no effect. ATP, AMP and adenosine prevented or shortened the initial depolarization produced by acetylcholine and carbachol. Inorganic phosphate was liberated from ATP and AMP applied to the bathing solution. The hydrolysis was not significantly decreased by g‐strophanthin. p‐Hydroxy‐mercuribenzoate caused an initial excitation as well as g‐strophanthin but neither inhibited the relaxing effect of ATP. The effects of extracellularly applied ATP are consistent with the view that they are exerted through changes in membrane permeabilities and that some of these effects are brought about by the adenosine part of the molecule. © 1969 Scandinavian Physiological Society