Effects of external calcium ions and strontium ions on interactions of isoprenaline and its competitive inhibitor with beta-adrenoceptors in the intestinal smooth muscle.

The effects were tested of Ca ions and Sr ions on interactions of isoprenaline and its competitive inhibitor with beta-adrenoceptors in the taenia caecum from the guinea pig. Ca ions were involved in the combination of isoprenaline with the beta-adrenoceptors but not involved in the combination of the competitive inhibitor with the beta-adrenoceptors. Sr ions could not substitute for Ca ions in the isoprenaline--receptor interaction.