Effects of sammarium on the contractile response of the isolated guinea pig ileum to acetylcholine, histamine, potassium and barium.

The effects of sammarium (Sm3+) on drug responsiveness of the isolated guinea pig ileum were studied. The lanthanid at the concentration of 2x10(-4) M reduced responsiveness to acetylcholine, histamine and submaximal concentrations of potassium. The maximum response to potassium and the responsiveness to barium remained unaffected. 2x10(-3) M Sm3+ reduced barium-induced contractions and smooth muscle response to potassium Ringer. Equipotent submaximal concentration of acetylcholine, histamine, potassium and barium were analysed in order to try to establish a Sm3+-induced differential reduction in smooth muscle responvisiveness. The lanthanid imparied tissue responsiveness to acetylcholine, histamine and potassium, but did not alter reponsiveness to barium. The results seem to be consistent with the hypothesis that in the guinea pig ileum responsivenesses to acetylcholine, histamine and potassium are, probably, supported by a calcium store(s) located at the cell membrane. The persistence of responsiveness to barium could indicated that this agonist acts upon a cellular calcium store(s) insensitive to Sm3+.