A comparison of two different indicators: quin 2 and aequorin in isolated single cells and intact strips of ferret portal vein.

A comparison between the fluorescent indicator quin 2 and the bioluminescent indicator aequorin was performed in the same smooth muscle cell type. Aequorin was loaded into intact strips and quin was loaded into enzymatically isolated single cells from ferret portal vein. Both indicators gave qualitatively the same calcium profiles when the tissue was challenged with agonists. Quin loading caused a dramatic shift to the right in dose response curves to potassium and phenylephrine. The ED50 values for quin loaded cells were significantly different from those for control cells for both agonists. Intracellular calcium levels at rest were not significantly different with quin and aequorin. Cells stimulated with potassium gave significantly different intracellular calcium values with the two indicators suggesting a change in the stimulated steady state level due to the introduction of an additional calcium buffer (quin2) into the cell.