Measurement by Quin2 of changes of the intracellular calcium concentration in strips of the rabbit ear artery and of the guinea-pig ileum.

Ca2+ transient and force development were investigated in smooth muscle strips of the rabbit ear artery and the longitudinal layer of the guinea-pig ileum by using the fluorescent indicator Quin2. Agonists only transiently increased the fluorescence intensity despite the enhanced contraction while excess potassium resulted in a maintained light signal. In Ca2+ free solutions the release by an agonist of Ca2+ from an intracellular store can be demonstrated. These observations illustrate the usefulness of the Ca2+ indicator Quin2 in the study of the excitation-contraction coupling in smooth muscle under various conditions.